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[build] dual 281 boards
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author [build] dual 281 boards
lessavyfav
nanners It's motherfucking bacon yo It's peanut butter jelly time! It's motherfucking bacon yo

Tobbobrillo said it was ok for me to open this thread!

First thing is... Thanks Rowman for your BOM. Sorry if it is lame to quote you here aesthetically but it is a great kickoff...

rowman wrote:
Ok take 2:

Revised 281 BOM

Now the only things not on the BOM are the L7810, MPF-102, pots and switches.

Edit: I put in polypropylene caps for .1uF, would c0g mlcc be better? The ones consumed listed are double the price of the polyprops though.

Also updated BOM, polypropylene caps had too large lead spacing.


I am hoping to build the quad euro version and plan to stuff the boards in advance! (Famous last words)


arrow EDIT: 11/12/12-
Cribbing shamelessly off Rowman, I went with these high voltage super caps mentioned here:
rowman wrote:

Also in my personal spreadsheet I've changed my 47nF film caps to these polypropylene ones instead of polyester
They have a bigger footprint then the board want's to accomodate. I just kinda left mine sitting over the neighboring resistors, hopefully that isn't a problem.

The .1uf caps in the BOM had the same chubby case size. I checked some other caps I had and 2.5mm wide x 7.2 long x 6.5 high seem like the expected case size. FWIW, Mouser part: 80-R82EC3100DQ70J look like the right size for the .1uF and, for the .047uF, Mouser part:
80-R82EC2470DQ60J looks like the right size. You need 2 of each per board.

alternately, for the .1uF caps Consumed suggested the following:
consumed wrote:

here's another "high quality" .1uF cap. this is not polypropylene or polystyrene, but c0g mlcc
double check the lead spacing on the board if this is a concern (i dont have mine in front of me)

Mouser part: 810-FK26C0G1H104J
rowman
No problem, I'll quote emmaker here too for the regulator:
emmaker wrote:

Probably a LM7810 since it's in a TO220 package. Check the pinout and pick your poison.

http://www.mouser.com/Semiconductors/Power-Management-ICs/Linear-Regul ators-Standard/_/N-5cg9gZscv7?P=1z0z73rZ1z0y1znZ1z0y48cZ1z0xn56&Keywor d=7810&FS=True


Also in my personal spreadsheet I've changed my 47nF film caps to these polypropylene ones instead of polyester, and my electros to these and these. It only costs a couple dollars more per build to get better quality caps so I figure why not. I know the electros are for power filtering but I'm thinking the ones with a higher voltage rating and temperature range will last longer before the module has to get recapped.

But I'm learning all this stuff as I go so take it all with a grain of salt.
bsmith
The 1k* resistors that say in the bom "r7,r8 for 12v operation use 1.2/1.5 here'.... Is this just 'choose one value for both' or is it 1.2 for r7 1.5 for r8...or.....?
consumed
dual 281 pdf says 1.2k for those two resistors.

edit
ive built five of the single v3 boards, and i may have used 1.2k on one and 1.5k on the other. ill have to go look now
d'oh!
bsmith
Thanks for response, sorry for question that was answered right there on the wiring PDF. Took the box of components, my boards, and the bom sheet from the single boards with me to stuff and tick parts off the list while watching a movie with the family - had that bit about the 1.2k/1.5k on there and it gave me pause....
So, stuffed and ready to go, will take a crack at wiring in the next day or so, at least try slapping some temporary panel together to have something to play with while the panel and daughter cards get finished. Gonna take it slow on the wiring, a bit more going on with this one than on previous projects, wiring-wise (and I'm doing the twf as well, which wow, a lot going on with it doing the pots and jacks as well).
bsmith
allright - so have one board half up on my euro 12v supply - the A side is working like i want to see - the b side however is no diggity - i'm measuring a little over 11v coming from the B out at all times on it - but i can't for the life of me see where i've gone wrong, probably something with the wiring on that B+, but i'm not spotting it. replaced all ic's, double checked electro cap polaritys, regulator is outputting 10v from that pad, diodes facing the correct direction. transistors are in the right place (however what does the 's' part of 3906s silkscreen mean? Using 2n3906 there).... gone over all the connections on the wiring diagrams and it all seems correct.. Puzzled. Obviously can't tell if the quadrature is working correctly, but I can tell that 'peak' out is working just because as I pull the pot up that 11v from the B overtakes the A side cycling or whatever.
It's fun playing with the A side though!
Any ideas?
bsmith
so after ripping that first board completely apart like three times and always getting the constant voltage deal on the b side i built up my second board and hooray right out the gate both sides are working, quadrature is happening, this thing is badass! really this is super fun. Hooray!
Did have one question about cycle mode - I understand after browsing through the build thread at e-m that the cycle mode needs a kick in the but from a trigger to get going - is there some method anyone experienced with building these is aware of where 'flip the switch, it starts cycling' is possible?
Unrelated, with the trims cranked all the way over I'm getting around 450hz in cycle mode with no cv applied and a/d all the way down - have been reading that these are typically trimmed to 1khz. Not a big deal - fast enough for me, but would be cool to be able to get higher into audio range. I'm running this on 12v btw...
toppobrillo
hey great you got it workin. there is a mod, a sort of 'start capacitor' that Roman noticed on the Easel pulser circuit that can be added here to initiate cycling when the switch is closed. ill put it up on my site. I still don't know for sure for sure but I've always assumed the 'standard' operation of the old 281 was as-is. the 281e may self-start not sure.

the range is pretty close, 1mS rise and fall times [as indicated on the panel as min time] would give u 500Hz when self-cycling. what value resistors did you use for R7 and 8? on 12V they should both be 1.5K.
bsmith
Thanks Josh.
d'oh! rise and fall - was thinking twice as fast as I should have been.... no this is fine. Had a fun audio rate freakfest here a short while ago and was just fine with the range I was getting.
But - I'm glad you asked that: on the dual board, is there some pcb drawing somewhere that correlates the resistor numbers with the values (and other components)? - like I was maybe going to play with the cycle modes, but am not sure what is what on the dual board when component numbers are referred to.
I used 1.2k for the locations I think you're referring to, the ones that say 1k on the screen - not that I'm unhappy with anything about how this thing is acting, but should I maybe change those to 1.5k?
That's cool on the roman self start thing, would be in to checking that out.
toppobrillo
right the 1K* spots- 1.2 to 1.5K is OK, I went 1.5 on my newest boards, just increases the control range to about what It whould be,, the actual ideal value would be around 1.35K i think- you should be able to trim it for 1mS at min and around 10S slope at max [w no CV in] I dont thnk I ever posted a ref. designator picture of the board, as it really doesnt have any perse, but the ones w the asterisks are the ones..
lessavyfav
bSmith - I'm stuffing boards this week. Thanks for blazing the trail. and to toppo for the feedback.

Also, doing a dual power supply kit so I can stop crossing my fingers while testing + debugging plugged directly into on my 9u FUUUCCKKKK!!!
lessavyfav
Hey Yall, I realized that I don't have the mpf102. I looked online and found someone recommending bf245 Bs or Cs but that the pinout in inverted so they must go in "backwards" apparently "bf245 B or C will bias near the mpf102"

I am gonna try the "B" I guess, unless someone knows better (technically almost anyone knows better)
http://www.mouser.com/Search/ProductDetail.aspx?R=BF245Bvirtualkey5121 0000virtualkey512-BF245B

reference to the quote:
http://www.diystompboxes.com/smfforum/index.php?topic=48333.0
bsmith
got my mpf102's at ratshack, looks like it's generally stocked in their stores..
textual
lessavyfav wrote:
Hey Yall, I realized that I don't have the mpf102. I looked online and found someone recommending bf245 Bs or Cs but that the pinout in inverted so they must go in "backwards" apparently "bf245 B or C will bias near the mpf102"


I've got an MPF102 I can give you if you want. I'm in NYC as well. AND pretty sure If you have any relation to the band that is your handle, we played together roughly 10 years ago.. anyhoo let me know if you would like the 102, or I imagine its easy enough to find one via order.
demian
What diodes must be used? I cannot find it except for the two 5240 zenerdiodes..

And what about "A" and "B" ?
bsmith
demian wrote:
What diodes must be used? I cannot find it except for the two 5240 zenerdiodes..

And what about "A" and "B" ?


1N914 or 1N418 for the non-zener's - A and B you must mean the trimmers? 50k trim is what I have on mine I just did. I referred mostly to http://www.sdiy.org/toppobrillo/DOWNLOADS/2814_V3/2812%20BOM%20V3.pdf which was for the previous itereation of single channel boards with a few little changes...
demian
Thanks!
falafelbiels
demian wrote:
What diodes must be used? I cannot find it except for the two 5240 zenerdiodes..

And what about "A" and "B" ?


Are you actually building something Demian?
lessavyfav
Textual- yes that is me. I will pm you for details about our history together!
demian
falafelbiels wrote:
demian wrote:
What diodes must be used? I cannot find it except for the two 5240 zenerdiodes..

And what about "A" and "B" ?


Are you actually building something Demian?


Ofcourse not, you know me..! Mr. Green

I am making a list of components to order so i can start building when i am ready for it.. hihi
falafelbiels
Don't back out! Not even during the complicated and tedious wiring job that this module will present you! The module when finished is quite the reward.

Remember MASK has your back...
hpsounds
Is the BOM at the top of this topic for 1 or 2 PCBs ?

hmmm.....

Hédi K.
bsmith
def looking like dual bom to me - ie for 1 dual channel board (I see 10 x 49.9k resistors, 1 x LM13700, etc...).
rowman
Yeah you need to double it to build a quad module.
hpsounds
Thanks. That's what I was thinking too, but I've counted 32 47K resistors for each PCB and there is 40 x 47K in the BOM. hmmm.....

Hédi K.
bsmith
There are another 4 x 47k off board, 1 each for the attack and decay pots x 2 - another 4 more for good 47k morale perhaps?
http://www.sdiy.org/toppobrillo/DOWNLOADS/2812_DUAL/Dual%20281%20PDF.p df
rowman
I just doubled the quantities from the single 281 board BOM.
hpsounds
bsmith wrote:
There are another 4 x 47k off board, 1 each for the attack and decay pots x 2 - another 4 more for good 47k morale perhaps?
http://www.sdiy.org/toppobrillo/DOWNLOADS/2812_DUAL/Dual%20281%20PDF.p df

I've counted also them. Doesn't matter, a few more resistors can always be useful. hihi

Other question : this MOUSER reference (581-08055C104M) is a SMD/SMT component ? hmmm..... seriously, i just don't get it

Sorry for my "newbee" questions ... oops

Hédi K.
rowman
There's a few smd 100nF caps for power decoupling to the ICs, you don't have to put them on if you don't want to, from memory.
lessavyfav
The 47ks get lonely. I stuffed and soldered the board resistors and diodes. Got a +-12v power supply board from MFOS to use for my new testing set up. The board is well organized between the A half and the B half- nice Toppobrillo. I put 20ks in place of the 100k* resistors - the notes suggest 22k for "smoother" LED response. I love smooth. I hope to finish stuffing on Monday. Then debate hand wiring the whole thing on a card stock panel or waiting for the panel/daughterboard to happen.

BSmith- do you dare post images of your progress?
marvkaye
Got my dual 281 PCBs just about completely populated, only missing the 7810 regulators... it's always something...

There are 2 circles with 3 pads in them just above the "A" and "B" at the end of the board...



They look like placement marks for something in a TO-5 package but there's no legend or mention of them on the schematic or wiring diagram... anyone know what they're for? hmmm..... hmmm.....

<marv>
lessavyfav
Marvkay- I think those might be 20-50k trim pots. I just now looked at the old v.3 single board documentation for clues. Could be wrong though, I am not there yet.
bsmith
lessavyfav wrote:

BSmith- do you dare post images of your progress?


*gulp*



embarrased to post this one, much tidying needed!....



I think I used 33k on that led resistor and it's fine - didn't compare to other values though. Used 50k's on those A and B trims. I did end up doing a couple resistors in series to get 1.35k there where he says to use 1.2k - 1.5k in place of the 1k* for 12v operation - I like the range here.
One thing that was a booger for me that I was bonking on initially due to newbishness, and the daughter board will be helpful for this especially, was those resistors that go between the lugs and the B+ for the A and D pots. Have my other board standing by, so when the panel and board happen I'll rip this dude apart gladly - that panel george did up is amazing how much it packs into that space, in what looks like a pretty damn ergonomic manner!
lessavyfav
"Plex" appeal.
lessavyfav
I just finished populating my board and found that in the Rowman's BOM linked above that the 2 .1uF "high quality" caps per board mentioned above were missing. I'm not sure how to update Rowman's BOM but in the board order thread Consumed mentioned the below which I'm gonna order....

consumed wrote:

here's another "high quality" .1uF cap. this is not polypropylene or polystyrene, but c0g mlcc
double check the lead spacing on the board if this is a concern (i dont have mine in front of me)

Mouser part: 810-FK26C0G1H104J


Also, cribbing shamelessly off Rowman, I went with these high voltage super caps mentioned here:
rowman wrote:

Also in my personal spreadsheet I've changed my 47nF film caps to these polypropylene ones instead of polyester


Unfortunately they have a bigger footprint then the board want's to accomodate. I just kinda left mine sitting over the neighboring resistors, hopefully that isn't a problem. There is a 250v version which seems like it would fit normally. Anyone know if that would be a better choice?

CHUBBY CAPS
rowman
lessavyfav wrote:
Unfortunately they have a bigger footprint then the board want's to accomodate. I just kinda left mine sitting over the neighboring resistors, hopefully that isn't a problem. There is a 250v version which seems like it would fit normally. Anyone know if that would be a better choice?


Sorry about that, I didn't realize they could be too wide!
The ones you've linked are 470pF with a 7.5mm lead spacing, these are 47nF and might be a bit narrower, though it says they won't be in stock for 5 days.

Also for the .1uF high quality caps, try these, slightly cheaper then the C0G caps. They are in the BOM though, just after the electrolytics.

And good on you for keeping the first post up to date, it will help a lot of people myself included.
lessavyfav
Thanks for the info Rowman. Those .1 caps were there after all. Got tired at the end of the day. I'll correct the opening post. Notably those are also wide fellas. I checked some other caps I had and 2.5mm wide x 7.2 long x 6.5 high seem like the proper case size FWIW. On Mouser different products seem to assign LWH to different sizes but these look like the right size for the .1uF and then
for the .047uF this seems like the right size

do these seem good? Why some cost .33 and some cost .25 is a mystery to me. I usually go with the one with the highest stock for these ida parts assuming herd mentality. Unless someone knows better I'll update the first message comments... I'll also order so for my second board to make sure they work...
bsmith
hey just chiming in - I did try some c0g ones there on my other board and it worked fine.
negativspace
lessavyfav wrote:
Marvkay- I think those might be 20-50k trim pots. I just now looked at the old v.3 single board documentation for clues. Could be wrong though, I am not there yet.


Nope, you're correct. thumbs up
marvkaye
Thanks, guys... I see them now. I even managed to have some 20Ks in my parts bin that fit.... how cool is that? thumbs up

<marv>
rowman
lessavyfav wrote:
Thanks for the info Rowman. Those .1 caps were there after all. Got tired at the end of the day. I'll correct the opening post. Notably those are also wide fellas. I checked some other caps I had and 2.5mm wide x 7.2 long x 6.5 high seem like the proper case size FWIW. On Mouser different products seem to assign LWH to different sizes but these look like the right size for the .1uF and then
for the .047uF this seems like the right size

do these seem good? Why some cost .33 and some cost .25 is a mystery to me. I usually go with the one with the highest stock for these ida parts assuming herd mentality. Unless someone knows better I'll update the first message comments... I'll also order so for my second board to make sure they work...


Those will fit much better, but for the 0.1uF 'high quality' caps, toppo recommended using polypropylene which is apparently better spec the polyester. I had the idea to just use polypropylene everywhere since it only adds up to a few extra dollars per build, but they don't fit! It's probably the best to just use c0g 0.1uF caps.

Here's a BOM with C0G caps instead of the chubby polyprops:
https://au.mouser.com/ProjectManager/ProjectDetail.aspx?State=EDIT%20& ProjectGUID=e675c4f7-0083-490b-92ac-c4c7098677f5

edit: and I've attached the spreadsheet I've been working from, in case anyone wants to make their own changes and import it to Mouser, it's pretty easy.
camelneck
I just started building my Buchla 281 clone. Unfortunately, I couldn't find any of the Dual 281 PCBs so I'm using two version 2 and two version 3 Single 281 PCBs.

So far I have finished installing FG #1 and it appears to be running just fine. In order to get the 281 to cycle (or behave as an LFO), I have to apply a pulse to the trigger input jack in order to "jump start" the FG.

I heard that if the FG's mode switch is in the cycle (or loop) position when the 281 module is powered up, the FG will begin cycling automatically. (When I say "automatically", I mean no trigger pulse is needed to "jump start" the cycling.).

QUESTIONS (in order of importance):
1) If the FGs are in cycle mode when the module is powered up, are trigger pulses still needed to jump start the FGs so they will begin to cycle (like an LFO)?

2) I've heard that there is a modification for this looping problem. Does anybody have any info or details that they can share regarding this modification?

3) Could someone tell me how to adjust the trim pot? (I have a scope in case one is required.)

4) In the dual 281, it appears like Topps has changed the value of one of the 100K resistors in the 2N3904 (LED) circuit to a value of 22K. Could someone take a meter to this 22K resistor and tell me if one end of the resistor is connected to ground. (Once I have this information, I'll be able to determine which resistor this is in the rev3 schematic--R30 or $31--since only one of these is connected to ground.)

Thanks.
lessavyfav
So, I'm finally gonna do this! Hardware in the mail from Mouser! and I finally stopped hoping for the euro panel! I quote myself from the panel thread:


lessavyfav wrote:
Since you've been gone. We are never ever ever getting back together. I can get another man like you in a minute. Etc.

I am over you thread! SlayerBadger! No more late night stalking love , no more shameless begging we're not worthy , no more faux casual "how you doin' thread?" meh , and best of all no more pitiful bumps cry ! [Mordor] no more! [Mort d'amour] no more!






....unless you guys are about to have the Daughterboard done Dead Banana

I got a pack of water-slide decals coming from Amazon with this lil puppy's name written all over it!



It's motherfucking bacon yo nanners It's motherfucking bacon yo nanners It's motherfucking bacon yo nanners It's motherfucking bacon yo nanners
hank
Hi folks,
I'm having some trouble with my 281 (2010 dual board) build. I can get it to go from 0v -- 10v, but I can't change the attack and decay times.

As it stands, I can get it to act as a LFO or one-shot function generator but the cycle time is around 1 minute, somewhat limiting it's usefulness smile

This affects both sides of the circuit, which leads me to believe that I've messed up the panel wiring somehow.

Does this ring a bell?

Also if anyone happens to have a picture of their panel wiring I would love to take a peek.

Thanks!
hank
For future reference and for my own humiliation, I had mistakenly used a CD4001 instead of a CD4016(!). d'oh! d'oh! d'oh! d'oh! d'oh!
toppobrillo
Quote:
I just started building my Buchla 281 clone. Unfortunately, I couldn't find any of the Dual 281 PCBs so I'm using two version 2 and two version 3 Single 281 PCBs.

So far I have finished installing FG #1 and it appears to be running just fine. In order to get the 281 to cycle (or behave as an LFO), I have to apply a pulse to the trigger input jack in order to "jump start" the FG.

I heard that if the FG's mode switch is in the cycle (or loop) position when the 281 module is powered up, the FG will begin cycling automatically. (When I say "automatically", I mean no trigger pulse is needed to "jump start" the cycling.).

QUESTIONS (in order of importance):
1) If the FGs are in cycle mode when the module is powered up, are trigger pulses still needed to jump start the FGs so they will begin to cycle (like an LFO)?

2) I've heard that there is a modification for this looping problem. Does anybody have any info or details that they can share regarding this modification?

3) Could someone tell me how to adjust the trim pot? (I have a scope in case one is required.)

4) In the dual 281, it appears like Topps has changed the value of one of the 100K resistors in the 2N3904 (LED) circuit to a value of 22K. Could someone take a meter to this 22K resistor and tell me if one end of the resistor is connected to ground. (Once I have this information, I'll be able to determine which resistor this is in the rev3 schematic--R30 or $31--since only one of these is connected to ground.)

Thanks.



this is old, so apologies, but I feel like I already answered it in the main thread? perhaps not so I will again-

1) yes they do, tho often mine power up cycling if the switches are in cycle mode. I never knew and still don't whether the original 281 had any additional mods or peripheral circuitry to 'fix' this. I kind of like having to send a trigger to initialize cycling, but YMMV.. which brings me to
2) I posted about this for sure. Roman has designed a 281 board for his series of 200 clones. he messaged me a while back about a mod he grifted from the 208's pulser schematic, this involves a "start capacitor" of sorts but I still haven't tested it and it doesn't seem like it would work very well or reliably.. ? duno I posted the drawing he sent me in the other thread..
3) the trim is to trim to the Buchla spec for panel control range, ie 1mS to 10S per slope over the travel of the knob, or as close as u want to get to it..
4)I cant recall the part number but 1 end is connected to ground yes
fluxmonkey
the buchla-format (RSFC) panel has 2 LEDs per set of function generators... but the topobrillo board only has a single? what a folks feeding to the second LED?
toppobrillo
Quote:
the buchla-format (RSFC) panel has 2 LEDs per set of function generators... but the topobrillo board only has a single? what a folks feeding to the second LED?


that 2nd LED is the quadrature indicator- as I understand it on the original, when A and B are in quad, both LEDs will light at A and B. you could of course only install one LED and use the other hole to mount a standoff..
fluxmonkey
for the attack/decay pots, does 10v go to the full-clockwise end of the pot? or the anti-clockwise end.

why, yes, 2 years later i am just getting around to building these.
djs
toppobrillo wrote:
Quote:
the buchla-format (RSFC) panel has 2 LEDs per set of function generators... but the topobrillo board only has a single? what a folks feeding to the second LED?


that 2nd LED is the quadrature indicator- as I understand it on the original, when A and B are in quad, both LEDs will light at A and B. you could of course only install one LED and use the other hole to mount a standoff..


any idea how to wire this? I could see doing something with the quadrature switch, but i don't know if the led current draw would mess that circuit up somehow?
djs
also- is there a schematic available? I see there's ones for the older boards, but I don't know if that is valid or not for the newer dual board?
logicgate
Can someone please post a very simple sketch of the wiring? I mean, for noobs Mr. Green

I find it easier when there´s the rear view of the pots



Thank you
logicgate
Another question:

Can someone please confirm if this ferrite bead is ok for this project?

http://www.newark.com/panasonic/exc-elsa35/ferrite-bead-0-01ohm-7a-axi al-leaded/dp/55T6191?in_merch=Popular%20Products


Cheers!
djs
logicgate wrote:
Another question:

Can someone please confirm if this ferrite bead is ok


Looks ok to me. I wouldn't be too picky about the ferrites, other than if they physically fit.
valis
Greetings all,

I'm building a 281 into a buchla style 281 panel and have two questions:

1. In the "Peak" section (which is sometime called the "Or" section), what do the two knobs do? Do they just attenuate the Peak output from 0v to the peak output?

2. My second question has been asked before and involves how one wires the second LED/quadrature indicator. Would this work best running a buffered LED indicator from the quadrature switch or can I run an LED straight from the switch? Am I missing something?

djs wrote:
toppobrillo wrote:
Quote:
the buchla-format (RSFC) panel has 2 LEDs per set of function generators... but the topobrillo board only has a single? what a folks feeding to the second LED?


that 2nd LED is the quadrature indicator- as I understand it on the original, when A and B are in quad, both LEDs will light at A and B. you could of course only install one LED and use the other hole to mount a standoff..


any idea how to wire this? I could see doing something with the quadrature switch, but i don't know if the led current draw would mess that circuit up somehow?


Thanks for your time!

David
Ginko
Nearly done:

pre55ure
Lookin good!

I just finished the first of mine a few days ago.

Wiring the Led's is what actually prompted my soldering wire to wire thread. hihi

davidschwan1
Hope to start building mine soon.
Ginko
Annoyingly, I just bought like 50 knobs to fit spiked shafts, then realised that every potentiometer I have bought recently has a round shaft angry
Ginko
Alright, finished! Seems to be working great as well grin

Two questions:

The pulse out, when does the pulse happen in the cycle? Is it at the start or at the end of the attack?

WTF does B Level do? hihi

Ok three questions, does the envelope behave differently in response to gate and pulse signals?

EDIT: ok I found answers to question one and three, the pulse happens at the end of the cycle and yeah gate / transient mode makes sense now.

I still don't get what B Level is for???
FetidEye
i have a question:

I'm populating the (new) board. In the BOM it says 15 x 4.7k resistors (3 x external). I can only find 10 on the PCB. > see attachment
Am i blind?
eolianmollisol
this could be a stupid idea...but, perhaps, some of the 4.7M is supposed to be 4.7K, and it is a typo, considering they are so close on the computer keyboard. Could be a possibility seriously, i just don't get it
Ginko
I would be very interested to know if this is the case!! I also found that I was short of 2 47ks or 4.7ks from the bom (can't remember which, maybe both). I used two 4.7M on the board for those two at the top...
keninverse
Any off board resistors?
FetidEye
yeah 3 , that's what i meant by externals.. so i'm missing two 4.7k places.
Ginko
With mine built according to the PCB though, I'm not sure there is anything wrong. I was a bit surprised by the attack / decay time though, I thought you would be able to make them a lot longer, the attack and decay seems to go to about 2 seconds or so when the knob is at 95% but then jumps to something a lot longer (possibly locks) if turned to 100% - not sure if this is normal or not.

I still can't figure out what BLevel does by the way hihi
Ginko
toppobrillo wrote:
right the 1K* spots- 1.2 to 1.5K is OK, I went 1.5 on my newest boards, just increases the control range to about what It whould be,, the actual ideal value would be around 1.35K i think- you should be able to trim it for 1mS at min and around 10S slope at max [w no CV in] I dont thnk I ever posted a ref. designator picture of the board, as it really doesnt have any perse, but the ones w the asterisks are the ones..


Ah, just got this from page one of the thread, I tweaked the envelope to around 2ms at fully CCW, but although I may get 10S at fully CW, I don't get a smooth transition between those times - I wonder if I got the wrong value parallel resistors on the pots?
regenbot
Ginko wrote:


I still can't figure out what BLevel does by the way hihi


I think it's the amount of B out of peak out thumbs up
Ginko
regenbot wrote:
Ginko wrote:


I still can't figure out what BLevel does by the way hihi


I think it's the amount of B out of peak out thumbs up


Ok cool. That is probably the one thing I didn't try! thumbs up

I had a little wiggle this morning and yeah, in the attack/decay time I get about 8-9 seconds at a full turn, but millimeters before on the turn I am on like 3 seconds!! The curve is a bit sucky. Is it like this for anyone else? Any idea what might cure that?
pre55ure
My curves seems to feel pretty good hihi

Maybe you inadvertently used log pots instead of linear? hmmm.....

Do you have the wiring diagram that shows the 4.7k resistors across the pot input and wiper?
Ginko
Yeah I have the diagram and installed the resistors, I don't think I installed log pots instead of lins but I have a bad feeling I may have used 47k instead of 4.7k for the parallel resistors...
Ginko
Having looked at the wiring diagram, it shows that 47k resistors should be used across the pots - am I looking at the same thing as you? I am going to double check them with a multimeter and check the pots are linear!
Ginko
Riiiiight OK, I double checked and the build documentation that I have for the dual board shows a 47K resistor being used as the parallel across each pot. I measured across the resistors I had soldered to the pots and I was getting a reading of around 4.33k with the pot fully CCW- I thought that was odd as I was expecting something around 22 - 24k - at first I presumed that I had used 4.7K resistors by mistake and began desoldering them, but then realised that the 47K resistors I was pulling out the draw had exactly the same colour bands...

So, on a hunch I tried soldering a 4.7K resistor across the pot terminals and upon testing - it works much much better!!

So... I apologise for confusion and misinformation added to this thread, but there definitely is an error in some versions of the build documentation

Use 4.7K resistors across the pot terminals!! thumbs up

EDIT: I would also say, in response to the earlier question, just solder up all the resistors you can see, you will have a few left over from the BOM - this is almost certainly an error, your 281 will work fine thumbs up
pre55ure
Ok well now I'm totally confused. I actually did use 47k resistors across the pot terminals as stated on the wiring diagram. So my apologies for making this potentially more confusing for others to follow along with. Dead Banana

Anyway, even with the 47k resistors across my pots I still don't find the curves to be weird. I'm not measuring it with anything except my ears and eyeballs (through the O'tool) but it seems to have roughly the same pot response as my Quad slope or maths.

Oh well, alls well that ends well right? Guinness ftw!
Ginko
pre55ure wrote:
Ok well now I'm totally confused. I actually did use 47k resistors across the pot terminals as stated on the wiring diagram. So my apologies for making this potentially more confusing for others to follow along with. Dead Banana

Anyway, even with the 47k resistors across my pots I still don't find the curves to be weird. I'm not measuring it with anything except my ears and eyeballs (through the O'tool) but it seems to have roughly the same pot response as my Quad slope or maths.

Oh well, alls well that ends well right? Guinness ftw!


Hmm, very weird seriously, i just don't get it - what value pots did you use? It definitely made a big difference for me - I used 50K pots

EDIT: I should probably say that Toppobrillo has now confirmed that the documentation IS CORRECT. So 47K is the right value to use. There must be some other cause to the problem in my build, but meh... It works exactly as described so I won't be poking it anymore... At least until I decide to do the capacitor cycle self-trigger mod...
bezier
Hi everyone,

I "think" i have my mouser cart almost together by now, but i'd much appreciate a little help with two parts.

First, i couldn't find the semiconductors "PN4393, MPF4393" on mouser, which are used instead of "MPF-102"s.

Also, i am confused by the IN914/4148 Diode, as it says "SILICON DIODE" on the BOM sheet, but my parts don't seem to bear the term silicon anywhere. Would this part be correct: http://de.mouser.com/Search/ProductDetail.aspx?R=1N914BTRvirtualkey512 10000virtualkey512-1N914BTR

Any help would be highly appreciated. My questions might be dumb as this is my first self-sourced project, but i can't solve these last things on my own unfortunately...
FetidEye
yes that diode is fine

and here:
http://de.mouser.com/ProductDetail/ON-Semiconductor/MPF4393RLRPG/?qs=s GAEpiMZZMv4z0HnGdrLjnwNZ9rg4nWlJDIFw88rBT8%3d
bezier
FetidEye awesome, thank you!! screaming goo yo
Navs
Just finished one of two 281 boards - I like these! The peak out, especially when cross-modulating, is loads of fun. I'll post some build pics and thoughts soon, but first have a question regarding the auto-loop mod.

I followed Camelneck's scheme, as per this post:

https://www.muffwiggler.com/forum/viewtopic.php?p=1021533#1021533

Because of the way I'd wired my module, I made the capacitor connections directly on the switch lugs that offered the relevant connections. So, one end of the 47nF to the cycle contact of the mode switch and the other connected to the lug carrying 10V on the quadrature switch.

This works for a while after initial power-up. After about 10 minutes - regardless of whether it's engaged or not - it ceases to have an effect. To get it going again I have to apply a trigger.

Any ideas why? Is it because of the circuit in general or because of the way I've wired it i.e. there's some unwanted interaction? As you can see in the bottom of my pic, I anchored the capacitor to the unused lugs of the dual pole 'mode' switches I used (didn't have any single pole to hand). Could that be disturbing the circuit or is the mod itself, as Josh suggests, not ideal? If it's the latter, I can live with it, else I'd undo the mod.

Thanks!

Emalot
I don't know if ot's the good place to ask this but...
I 'm making 1/2 of 281 with toppo rev3 PCB.
I ask me what's the J2, J3, J3 etc in these boards ???
I also found only 6 1N4148 in each board, no 9 like Toopo write in the BOM...
Somebody built this rev 3????
Thank you very much.
Navs
Navs wrote:
... question regarding the auto-loop mod ...


Lil' bump for any ideas help

It seems triggering the envelope after it ceases to auto-loop can reset its ability to self trigger. Not immediately and not every time, but sometimes seriously, i just don't get it lol
bkbirge
Where did you guys get the pn4393's for your builds? Mouser is out of 'em. Almost done with a pair of these and getting the euro specific parts together.

Edit: nevermind, saw the link to the Deutschland mouser earlier in the thread, here's the part number for USA mouser if anyone needs it...
863-MPF4393RLRPG
bkbirge
In progress pics, my smt soldering sucks balls but no bridges so hopefully it's ok, just waiting on parts to finish, I'm going to change out the large alpha pots with some minis...



Arnoid
I skipped the smd decoupling caps the module is working so I guess they're not needed ?
bkbirge
Arnoid wrote:
I skipped the smd decoupling caps the module is working so I guess they're not needed ?


Probably not as I think they are just power supply filtering caps for the IC's but I wanted the practice soldering smt.
Emalot
SOmebody knows what's the PI/PO in the board Rev3?
And the ARI/PKO? (they look like OUTput but what's difference?)
Navs
Emalot wrote:
SOmebody knows what's the PI/PO in the board Rev3?
And the ARI/PKO? (they look like OUTput but what's difference?)


https://www.muffwiggler.com/forum/viewtopic.php?p=1550769#1550769

confused

bkbirge wrote:
Where did you guys get the pn4393's for your builds?


I got my MPF4393 and other parts from http://www.uk-electronic.de/onlineshop/index.php/

It was the first time I'd shopped with them and I was very happy with the turnaround thumbs up

Now, has anyone got an idea why camelneck's self-starting loop mod is intermittant or whether it might be disturbing the circuit?

https://www.muffwiggler.com/forum/viewtopic.php?p=1546581#1546581

Third time lucky, eh? hihi
Emalot
When you put the Cycle mode, do you need one first TRig/gate to make Cycle or not? Because mine need this first trig/gate.
BUt i feels like when i built only one channel, it worked in Cycle mode without first trig...
Arnoid
Emalot wrote:
When you put the Cycle mode, do you need one first TRig/gate to make Cycle or not? Because mine need this first trig/gate.
BUt i feels like when i built only one channel, it worked in Cycle mode without first trig...

Yes it needs a trigger to cycle but somtimes it cycles when powering up
Emalot
...OK. Somebody knows why in DUSG Cycle doesn't need a trigger to cycle, and why inthis 281, it needs one?
bkbirge
Emalot wrote:
...OK. Somebody knows why in DUSG Cycle doesn't need a trigger to cycle, and why inthis 281, it needs one?


They are different circuits. The 281 is based on a Buchla circuit, the DUSG is a Serge design. According to Ken Stone's site about the DUSG "If the TRIG IN jack is connected to the TRIG OUT jack, the DSG will oscillate with a waveform and frequency set by the RISE and FALL knobs."
Navs
Emalot, have you read the thread? angry lol

I think part of the difference is that the End Out of the Serge DUSG/ VCS is a gate, whereas the Pulse on the 281 is a trigger. So, if you 'miss' the pulse, the EG will not loop. On a Serge End Out, this is high for as long as the EG is idle i.e. you can't miss it.

This might also explain why camelneck's cap fix doesn't work reliably ...

I have now de-soldered what I outlined here. I found that when looping with these caps fitted, the 281 outputs trapezoids not triangles. Maybe it was just the way I'd wired it.

My new solution was to tap the 10V, as before from the quadrature switch, and to wire it via a momentary button/ switch and 10K resistor to the switching contact of A + B's trigger input jacks. Basically, I wired a manual gate to both jacks. This means I can fire both envelopes or get them looping. Ideally, I would like external triggers to also be 'multed' to both EGs in a switching scheme, but I think this is no longer possible hmmm.....

Anyway, now I have a new question lol

The 281 stops responding to external triggers after a certain frequency. Can someone suggest why e.g. is there a HP filter/ gate-to-trigger converter at work and, if so, do I need to make that trigger shorter? I have a hunch this is what it is. After all, when looping, the 281 runs at 500Hz, triggered by its own End Pulse, right?
bkbirge
Finished up a pair of these today, here's some detail pics. One has blinding white led's and one has mellow red led's that's the only difference. Great module, the effort is worth it.

Getting better at wiring, things are more organized, could trim some slack but the length is good for unfolding the board and troubleshooting...


Wires all connected from underneath...


Obligatory front side...


Inside...


Here's a little detail of the B+ buss I made, you can see above the B level pot, all the B+ connections meet there, from the LED's and the attack/decay pots, so only one wire needed to go to the PCB.
twospartans
blbirge,

looks nice!
really excited to get started on my pair!
w00t
bezier
bkbirge thank you for uploading photos, really helpful. I see you stuffed the L+/L- pads as well, are those ferrite beads? I'm just curios for i couldn't find any information in the docs, but have some spare beads i could use.
bkbirge
Yeah those are just ferrites.
bezier
bkbirge thanks, will put them in right now thumbs up
davidschwan1
I used to think ferrites were overkill until I started doing wireless design at work. I'm a firm believer in ferrites, they kill any unwanted RF signals.
Navs
Tidy, bkbirge thumbs up

I'm glad to see I wasn't imagining things with the Greyscale panel, though - it's too small for all-16mm-Alphas, right? I went with 9mm.

Now that I've used mine for a while I think the panel led me astray on another point too: the 281 really wants a couple of attenuverter/ mixers per channel too to give you contour plus VC length. A manual gate is pretty much essential too given the non-selfstarting loop mode and unreliable cap mod. hmmm.....

It's lovely to have & behold, but was there some poll to keep it at 16HP or something? confused
pre55ure
Navs wrote:
Tidy, bkbirge thumbs up

I'm glad to see I wasn't imagining things with the Greyscale panel, though - it's too small for all-16mm-Alphas, right? I went with 9mm.


Actually, for anyone else wondering- I did mine with 16mm alphas and they fit just fine.
drip.feed
pre55ure wrote:
Navs wrote:
Tidy, bkbirge thumbs up

I'm glad to see I wasn't imagining things with the Greyscale panel, though - it's too small for all-16mm-Alphas, right? I went with 9mm.


Actually, for anyone else wondering- I did mine with 16mm alphas and they fit just fine.

Yep, 16mm pots fit fine.

bkbirge
Nice, that's some serious attention to detail with the shrink tubing on everything!
drip.feed
Here is an accurate Mouser project for the 12V build of Toppo's dual 281 pcb.

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=09c22 8a627

It contains everything except jack sockets - Mouser didn't seem to have a great selection of them. Please copy it into your own Mouser cart before making changes.

The caps were chosen to have a minimum lifetime of 4000 hours - our modules are gonna live forever, right?


3.5mm vertical jack sockets:

Synthcube (USA)
http://synthcube.com/cart/index.php?route=product/product&filter_name= 3.5mm&product_id=208

Erthenvar (USA)
http://erthenvar.com/store/jack35mmv

Thonk (UK)
http://www.thonk.co.uk/shop/pj301bm-3-5mm-jack-sockets-x50/
drip.feed
bkbirge wrote:
Nice, that's some serious attention to detail with the shrink tubing on everything!

Gots to have me some strain relief, brother! Guinness ftw!
drip.feed
Here a some further clarifications.

Pot lugs: the yellow boxes show which pot lug corresponds with which wire. The LED polarity is also clarified.




Non-symmetrical pads: the CYC and END pads are not in the same locations on both sets of solder pads.

flab
cheers drip.feed for spending some time to share BOM + notes, i have the pcbs , i ll start a quad version next month
logicgate
One less project in the backlog!! nanners nanners







Working nicely! Phew...
Ginko
How are you guys / gals getting on with the pot range? As in do you get a smooth change in attack / release time as you turn the pot? I had to change the parallel pot resistors to be much smaller in order to get a good response, but Toppobrillo says I must have made a mistake somewhere else. Mine seems to be working fine now anyway though I did have to replace an LED that burned out (first time that's ever happened to me!)
drip.feed
Ginko wrote:
How are you guys / gals getting on with the pot range? As in do you get a smooth change in attack / release time as you turn the pot?

As usual Ginko, I haven't really played with mine yet; I have no room left in my rack! Dead Banana

I am busy building a second, spillover rack right now. When that is ready I'll get a chance to properly try out a few modules that are sitting on my shelf.
Ginko
drip.feed wrote:
Ginko wrote:
How are you guys / gals getting on with the pot range? As in do you get a smooth change in attack / release time as you turn the pot?

As usual Ginko, I haven't really played with mine yet; I have no room left in my rack! Dead Banana

I am busy building a second, spillover rack right now. When that is ready I'll get a chance to properly try out a few modules that are sitting on my shelf.


lol
Ginko
I just got a DHL notification that my LP-1 is on the way from Italy, which means this rack plan is finally about to be complete:



I am going to buy one of the Ginko Synthese case kits next week, going to 12U x 86hp screaming goo yo
Navs
drip.feed wrote:
Yep, 16mm pots fit fine.


You call that fine? lol

Nice work on the notes thumbs up
kssm
Hey everyone, I'm in the middle of building one of these beauties and am looking at the bom v1.0 (link from Thonk's site).
What is the purpose of the 0.1uF ceramic caps that are listed on the BOM? It also says "surface mount, install on bottom of PCB". Are they decoupling caps? There is no information that I can see in the rest of the Build Bundle about them. Anybody install these 7 ceramic 0.1 caps?
kssm
Well that was solved quickly, oops. Upon looking closer, I see the tiny SMD pads that are filled on the bottom of the PCB. So glad I don't have to install those suckers.
Synesthesia
ahahah the bom I am using is all over the shop with the numbers - that's fun wink

Guys, why the 4.7K are not needed i you use banana ? seriously, i just don't get it
pre55ure
Synesthesia wrote:
ahahah the bom I am using is all over the shop with the numbers - that's fun wink

Guys, why the 4.7K are not needed i you use banana ? seriously, i just don't get it


I think... That this was because banana output levels are typically higher than euro levels. I saw this mentioned somewhere that it was just to bring the pulse level down a bit.
existenz81
hi where i can find the blue buchla style knobs or make noise style knobs? and the panels as well please?
Synesthesia
There is an upcoming group buy for the blue Rogans existenz81

Board populated, panel ready ... let's take a break.


ehochstrasser
What are the dimensions of these boards?

I've tried sifting through this thread and the documentation, but can't find the answer. I'm trying to cram some 258's and a little extra onto one panel and this would be a good addition.
Jop
Dimensions are:

76x107
ehochstrasser
Thanks Jop!

Sounds like the PCBs are Euro-friendly in all orientations.
Synesthesia
Did anyone figured out what to do with the second row of LED with the RSFC panel + how to wire them ?
djs
Synesthesia wrote:
Did anyone figured out what to do with the second row of LED with the RSFC panel + how to wire them ?


are you referring to the quadrature leds, or something else?
Synesthesia
djs

Not sure smile

on the Buchla panel, there is 2 LED under the trigger out . One is the same than on the GrayScale panel.... but what about the second ?
djs
The second LED is to indicate whether the quadrature mode is "on" for that channel. What I did on mine was to use the quadrature switch to also send some voltage (i think the 10v line) to the LEDs lined up for that channel.
Synesthesia
djs - That will do me smile Thank you !
existenz81
Hey folks, i have problem in sourcing pn/mf4393, but i actually have some mpf102.... I can use them anyway or zeners are changed to accomodate 4393? I use 12v...
bkbirge
existenz81 wrote:
Hey folks, i have problem in sourcing pn/mf4393, but i actually have some mpf102.... I can use them anyway or zeners are changed to accomodate 4393? I use 12v...


Here's the part number for USA mouser...
http://www.mouser.com/ProductDetail/ON-Semiconductor/MPF4393RLRPG/?qs= %2fha2pyFadui5HRvnVEEExr0ybSRPQwVeEvo4xsvy%252bUkxHA%2f5E5p7kQ%3d%3d
existenz81
bkbirge wrote:
existenz81 wrote:
Hey folks, i have problem in sourcing pn/mf4393, but i actually have some mpf102.... I can use them anyway or zeners are changed to accomodate 4393? I use 12v...


Here's the part number for USA mouser...
http://www.mouser.com/ProductDetail/ON-Semiconductor/MPF4393RLRPG/?qs= %2fha2pyFadui5HRvnVEEExr0ybSRPQwVeEvo4xsvy%252bUkxHA%2f5E5p7kQ%3d%3d



Thank you bkbridge, but since i have mpf102 and i don want really Place an order from mouser usa here in europe only for 2 trannies, i'd really like to know if i can use mpf102 with 1n4235 or i have to use 1n5240... What do you think about?
bkbirge
I don't know about substitutions but I originally got that number from a post earlier in the thread that pointed to mouser Germany so I'm sure you can get that in europe no problem, go back through the thread.
bkbirge
Here's the earlier post that shows the Germany link...

FetidEye wrote:
yes that diode is fine

and here:
http://de.mouser.com/ProductDetail/ON-Semiconductor/MPF4393RLRPG/?qs=s GAEpiMZZMv4z0HnGdrLjnwNZ9rg4nWlJDIFw88rBT8%3d
existenz81
Many thanks man! thumbs up
existenz81
Synesthesia wrote:
There is an upcoming group buy for the blue Rogans existenz81

Board populated, panel ready ... let's take a break.




Hi, i'm building a quad module as well, which wiring diagram did you followed? I wonder if there is a particular wiring for quad module, something to link the two double module each other in order to get special functions, or they remain two indipendent double modules in the same panel and all i have to do is to follow the normal wiring doc, for both the pcbs?
Thanks!
djs
existenz81 wrote:
Hi, i'm building a quad module as well, which wiring diagram did you followed? I wonder if there is a particular wiring for quad module, something to link the two double module each other in order to get special functions, or they remain two indipendent double modules in the same panel and all i have to do is to follow the normal wiring doc, for both the pcbs?
Thanks!


This is what i used to build my buchla clone 281.
http://www.sdiy.org/toppobrillo/DOWNLOADS/2812_DUAL/Dual%20281%20PDF.p df

Technically they are independent boards, except that I wired the power (plus 10v) from one board to the other so that it all runs off of one power connector.
cleaninglady
I Just finished building these but it seems the suckers dont cycle with the switch in the upper position.

Should they ? It would be very handy not to have to trigger then externally. Dead Banana
rico loverde
cleaninglady wrote:
I Just finished building these but it seems the suckers dont cycle with the switch in the upper position.

Should they ? It would be very handy not to have to trigger then externally. Dead Banana
its a know issue, there's a thread somewhere in the DIY section that discusses some work arounds. I can't seem to find the thread but that more likely due to me being on my phone
logicgate
It's not an issue, I believe it needs a trigger to jumpstart the cycling
rockwoofstone
Navs wrote:
Because of the way I'd wired my module, I made the capacitor connections directly on the switch lugs that offered the relevant connections. So, one end of the 47nF to the cycle contact of the mode switch and the other connected to the lug carrying 10V on the quadrature switch.

This works for a while after initial power-up. After about 10 minutes - regardless of whether it's engaged or not - it ceases to have an effect. To get it going again I have to apply a trigger.

Any ideas why?


I've just finished building a pair of these modules, and everything works very nicely, trimmed to 500Hz at the fastest speeds.

Like Navs, I applied the cycling fix, and for mine, it appeared to work wonderfully. However, I did notice (and unless you're looking for it, you might not see this), that the highest speed of each cycle is reduced to around 170-180Hz with the capacitor fix applied and that the envelope shape at this highest speed becomes trapezoidal, rather than triangular. Things get back to normal at around 100Hz or thereabouts.

So, if you've applied this fix, it would be interesting to know if the maximum speed has been affected for you. For now, I've removed the fix, but would be good to find an alternative...
logicgate
Why is it considered a "fix"? As far as I know it's not defective, it behaves like the original... lol


I would call it a mod
rockwoofstone
Well, OK - that's just semantics! So, same question, but substitute "mod" for "fix" ;-)
cleaninglady
I have noticed that if i have the Trig Input of the First section (A) and the Trig Out of the Last section (D) connected with a Banana Cable and it is in Quadrature Mode (ie : switches ON , so A triggers B and C triggers D ) , the thing will cycle.

Can someone else try this and confirm your findings here ?

EDIT : It seems this also needs Trig Out of B to be connected to Trig In of C.
Cycling Only starts on power up and will cease if this chain is broken.

Maybe not so great after all but at least something...
drip.feed
I've just built a new one of these. But I only get a steady -9.8V from Peak Out waah

Everything else seems to work. Hopefully I only have a broken IC, but which one?

seriously, i just don't get it
rockwoofstone
If you've got one that already works, just systematically swap each if the ICs into the one that works if you suspect that's the problem. If the problem doesn't migrate to your working module, you know it isn't an IC causing it. thumbs up
drip.feed
rockwoofstone wrote:
If you've got one that already works, just systematically swap each if the ICs into the one that works if you suspect that's the problem. If the problem doesn't migrate to your working module, you know it isn't an IC causing it. thumbs up

Well, yeah, my next step is to swap all the ICs one by one and hope that it starts working. I just thought some superstar schematic reader could take an educated guess. lol
Ginko
EDIT: I would say, check the TL061 and orientation of the diodes around it - that is almost certainly the summing mixer for the peak out - check your soldering around that area

Good luck!
drip.feed
Ginko wrote:
EDIT: I would say, check the TL061 and orientation of the diodes around it - that is almost certainly the summing mixer for the peak out - check your soldering around that area

Good luck!

Nope, can't see anything wrong around the 061. I have now replaced all the ICs and the problem is still there: -9.3V steady out of Peak Out.

If I remove the 061 I get -12V steady out of Peak Out.

It's almost like neither A or B OUT signal is getting to that mixer... seriously, i just don't get it
NS4W
Thanks for the BOM and diagrams drip.feed w00t
drip.feed
I cross-posted this elsewhere on the DIY forum but nobody has responded so far. I'm hoping that some of the subscribers to this thread will see this.

--------------------------------------------------

I have another 281 build gone wrong.

The output from channel B is slightly unstable. With the Attack and Decay at minimum, and the channel trimmed to 1ms rise and fall, I should get a nice 500Hz triangle wave from the Cycle output.

Instead I get a triangle wave that varies in pitch a tiny bit around 500Hz. Here is a WAV - it is very distinct. Over a longer period of time the beating effect varies in speed: it slows down and speeds up.

B Channel unstable wave.wav


Also, the LED for that channel is permanently lit, and is not as bright as its the LED on channel A.

Does anyone have any ideas where I should start looking? I have scanned for obvious short-circuits and all the components are brand new from Mouser.

Toppo doesn't supply any schematics for this dual PCB so here are the ones for the original, 2-board build. Hopefully they might help (because I can't really read schematics), though they might not since the original build was for 15V and mine uses 12V.

SCHEME B BOARD v3.pdf

SCHEME A BOARD v3.pdf

help
pre55ure
drip.feed wrote:
I cross-posted this elsewhere on the DIY forum but nobody has responded so far. I'm hoping that some of the subscribers to this thread will see this.


I hate when that happens... Anyway, I didn't respond because unfortunately I don't really have any good ideas. My plan would probably be to take the functional one, and start poking around with my multimeter, and then to start comparing the voltages between points on the working one and the non working one until you start to find differences between the two. Of course then you get to try and trace the problem upstream as far as possible...
Dead Banana

Good luck!
cane creek
Slowly getting there, like many on here I've got about 6 different DIY builds on the go Mr. Green

NS4W
I don't have any ferrite beads at hand, what do they do and what happens if i just put jumpers there instead?
cane creek
NS4W wrote:
I don't have any ferrite beads at hand, what do they do and what happens if i just put jumpers there instead?


you must either use Ferrite bead or 10R resistor, if you just add a jumper then theres nothing to suppress high frequency noise in the circuit.
NS4W
ok. will install 10R then while waiting for some beads. Thanks! thumbs up
Jerem
Hi to everyone! I am a little lost with the 0,1uf ceramic caps. Where I have to solder these 7 components? Thank
woodster
They are the 7 SMT spots on the solder side of the board.
logicgate
Is it normal behaviour to only one generator work in cycle mode if both generators are set to cycle mode?


I noticed this today.


If I have A & B set to cycle, only A will loop. If I change the mode at "A', then B starts looping. I can't have both looping at the same time, or perhaps there's a wiring mistake somewhere? I already checked and all seems to be fine, even so because the module works perfectly, I just happened to notice this behaviour because I never used both generators on cycle mode at the same time before.


Thanks!
drip.feed
Yeah both will cycle independently, unless you have the module in Quad mode, in which case A and B are combined into a single function generator.
logicgate
@dripfeed

Thanks mate! thumbs up
milkyjoe
Has anyone figured out why the loop mode does not work right and if it's fixable ?

On A buchla 281e, the loop mode always works no problem....
xahdrez


Just finished my wiring on this today and the little beaut fired up properly first time! Many thanks to drip.feed for your diagram above - I'm certain I would've made some healthy mistakes if I'd done it without that!
keninverse
milkyjoe wrote:
Has anyone figured out why the loop mode does not work right and if it's fixable ?

On A buchla 281e, the loop mode always works no problem....


There isn't a definite fix for it. At the moment the best method is to send a short trigger/pulse to the input either externally or with a momentary switch sending 10V from the regulator to the input. I'm adding this to my modules since it adds some playability to the module.
flab
hey guys , do you think i can replace the the pn4393 with the http://uk.mouser.com/ProductDetail/ON-Semiconductor/2SK596S-C/?qs=sGAE piMZZMv4z0HnGdrLjvvqag9lmLhH4KASp%2f9etKw%3d because thats what i have at the moment ? will it work ?
cheers
flab
i know the pinout is different , anyway i ll give it a try
thrasumachos
keninverse wrote:


There isn't a definite fix for it. At the moment the best method is to send a short trigger/pulse to the input either externally or with a momentary switch sending 10V from the regulator to the input. I'm adding this to my modules since it adds some playability to the module.


having seen the video you psoted, I have to say: my god. this mod is incredible. It's exactly what these needed. I've already built a pair of these, else I would be all over the ones of yours in the bst. Is there any way you could share how you got the led switches wired up?
FetidEye
finished my build.
anyone got some info about how to set the trimpots?
regenbot
I think those control the range of the envelopes, so test which is most useful for you thumbs up

FetidEye wrote:
finished my build.
anyone got some info about how to set the trimpots?
drip.feed
regenbot wrote:
I think those control the range of the envelopes, so test which is most useful for you thumbs up

FetidEye wrote:
finished my build.
anyone got some info about how to set the trimpots?

To calibrate for 1ms rise and fall:

1) Turn the attack and decay pots fully counter-clockwise so they are set for the shortest attack and decay times.
2) Once the attack and decay times are set to minimum, use a scope or frequency counter to monitor the output of the 281.
3) Adjust the trim pot so the frequency of the output signal is 500Hz.
FetidEye
thanks!
clive.grace
There really ought to be some modules that come with a health warning.

Sister Mary Francis that was brutal. The Board is fine but the wire.... and the assymetric pin outs in some places and that 4 pin-no-ground on one side and 5-pin-with-centre-ground on the other... Gawd. @drip.feed your drawing saved my sanity...




Mine is the other way around as i used pin headers on the component side, and glad minded, that board would have been a mess of lifted traces with the errors i made.

Working now. One more into the rack....

Next! o0h J3rk Fadex... Phew I was worrying it might be one of mxmxmx's devices intent on blinding me (squints at world)....
drip.feed
You're more than welcome, Clive.

I built four of these and still had to send two to a guru to get them working properly. cry

I love 'em, but I won't be building any more in my lifetime.
camelneck
Navs wrote:
Just finished one of two 281 boards - I like these! The peak out, especially when cross-modulating, is loads of fun. I'll post some build pics and thoughts soon, but first have a question regarding the auto-loop mod.

I followed Camelneck's scheme, as per this post:

https://www.muffwiggler.com/forum/viewtopic.php?p=1021533#1021533

Because of the way I'd wired my module, I made the capacitor connections directly on the switch lugs that offered the relevant connections. So, one end of the 47nF to the cycle contact of the mode switch and the other connected to the lug carrying 10V on the quadrature switch.

This works for a while after initial power-up. After about 10 minutes - regardless of whether it's engaged or not - it ceases to have an effect. To get it going again I have to apply a trigger.

Any ideas why? Is it because of the circuit in general or because of the way I've wired it i.e. there's some unwanted interaction? As you can see in the bottom of my pic, I anchored the capacitor to the unused lugs of the dual pole 'mode' switches I used (didn't have any single pole to hand). Could that be disturbing the circuit or is the mod itself, as Josh suggests, not ideal? If it's the latter, I can live with it, else I'd undo the mod.

Thanks!




Sorry for the very late reply. smile Unfortunately, I quit following this thread shortly after I made my original post. Thus, I wasn't aware of your post until I just happened to discover it years later.

As for your questions:

You implemented my mod correctly and it seemed to be working just fine.
The only problem was this: you set your expectations a bit too high.

When I came up with this modification, I wanted to find a very simple way to make the 281 start cycling upon power-up (when the mode switch is in the cycle position) without the need for an external trigger to jump start the cycle process. This modification accomplishes that ... plus some.

Plus some? Since the capacitor remains charged for several minutes. the mode switch doesn't have to be in the cycle position at the moment of power-up as long as you move the mode switch to the cycle position before the capacitor discharges.

After several minutes (actually the time varies depending upon the leakage requirements of the capacitor that is used) this mod ceases to work because the capacitor eventually becomes discharged.

As long as you make sure the mode switch is in the cycle position during power-up (or as long as you move the mode switch to the cycle position shortly after power up) this modification will work fine.
pre55ure
drip.feed wrote:


I built four of these and still had to send two to a guru to get them working properly. cry

I love 'em, but I won't be building any more in my lifetime.


Agreed with both of you. I'm now at the point where I have been doing DIY long enough to start forgetting the builds of done in the past. But I won't forget these. Definitely one of the most painful builds I've done in a while. So much panel wiring... Dead Banana
Jop
Just finished one and everything is working great! Wiring is indeed a bit tedious but not that bad if you take your time and make a drawing upfront.

Despite my drawing I managed to put the PCB backward behind the panel, now B on the panel is A on the PCB.. lol I'm not going to change the wiring, it's just a minor thing (and only noticeable in quadrature mode).


Don T
Almost finished with a Buchla format build of these boards. One board finished, one board halfway there, and I think 1/3 of the panel wiring done. Posting a pic of the panel so far. If someone would be kind enough to proofread, I would appreciate it. I'm juggling 5 builds at the moment: This 281, a 266r, a 291, a 258, and an entire ARP 2600 (completely from scratch).

This is not counting a customer's ARP Axxe and Sequential Circuits Pro One in for repair.

So yes, I cannot only not see the forest for the trees right now, I cannot even see the trees for the leaves! eek!





Red = +15V, Black = GND. vertically mounted resistors on the Attack and Decay pots are 47K.

Yes, I know I'm missing a switch, the LEDs, and four banana jacks! I'll need to find some way to glue the 3mm LEDs in, the holes in the panel are slightly too big for a press-fit. The four orange banana jacks are on backorder from Mouser.
fluffybeard
Finished my first Toppo 281. Everything works... except for the led on channel A. The led for the B side is smoooooth, but the other one is either on or off.

I should mention that i accidentally soldered the led transistor on backwards so i might have broken something. Tried switching the op amps to no success.

Any guesses?
bkbirge
fluffybeard wrote:
Finished my first Toppo 281. Everything works... except for the led on channel A. The led for the B side is smoooooth, but the other one is either on or off.

I should mention that i accidentally soldered the led transistor on backwards so i might have broken something. Tried switching the op amps to no success.

Any guesses?


I've had that prob on another build (galilean moons) and it was because a leg of the led was touching chassis, I'd check around there.
fluffybeard
bkbirge wrote:
fluffybeard wrote:
Finished my first Toppo 281. Everything works... except for the led on channel A. The led for the B side is smoooooth, but the other one is either on or off.

I should mention that i accidentally soldered the led transistor on backwards so i might have broken something. Tried switching the op amps to no success.

Any guesses?


I've had that prob on another build (galilean moons) and it was because a leg of the led was touching chassis, I'd check around there.


Thanks! I found the culprit. I had used a 10k resitor instead of a 100k. smile
Don T
Getting close to the end of my build, here's where I am:



This looks a lot more fun when it's not you doing it! hihi

I started the panel wiring portion tonight, and I worked the better part of an hour before taking the pic (AND a break!). As I looked at the pic, I realized I was only about 1/4 done with the wiring, because I have yet another board to go, plus wiring up the LEDs. It's a lot of work, and kind of makes me pine for a set of boards that have no panel wiring to speak of, but you can't beat the price!

The two boards and the panel together cost me a lot less than... (wait for it!)...
Don T
Quick update, progress has been made!

Bottom board wiring finished:



Bottom board mounted on standoffs:



It may not be obvious from the pics, but I decided to solder the wiring for the bottom board with the wires connecting underneath. Why? The clearance between the two boards is pretty tight, and I did not want a rat's nest in between the boards.

Top board mounted:



To completely avoid a rat's nest of wires between the two boards, the wires for the top board are mounted in the more traditional way, from the component side of the board:



So, at this point, 3 of the 4 function generators are completely wired. I'm saving the last one until I can get some detachable connectors for the "B" side, so that if necessary, the top board can be laid off to the side for troubleshooting. So far the only detachable connectors are for the power between the two boards, simply for the ability to be able to power up only one board at a time for troubleshooting. Plus, I'm out of small heatshrink and small cable ties, gotta make a supply run tomorrow.

Why not detachable connectors everywhere? When you've done as much repair work as I have, you come to realize that connectors are a big point of failure in many pieces of gear. I've seen more faults due to connector failure than any other single component failure (Especially in the Moog Polymoog and Oberheim OB-Xa). So there!

This actually has gotten to be a lot more fun for me as it progresses, it's turned into a good problem-solving mental exercise to figure out how and where to route wires as neatly and efficiently as possible.
negativspace
Totally agree on the connectors... I wire my multiboard panels so that everything folds out like a clamshell for troubleshooting. I never ever ever use connectors unless I have to. thumbs up
keninverse
negativspace wrote:
Totally agree on the connectors... I wire my multiboard panels so that everything folds out like a clamshell for troubleshooting. I never ever ever use connectors unless I have to. thumbs up


Thousand times yes. It sometimes creates longer wire runs but in the end the wiring is much easier to follow, troubleshoot and repair. Once in a while I'll use crimp terminals and solder the pins to wire but in the end it's time consuming and adds just another point of failure.
bkbirge
keninverse wrote:
negativspace wrote:
Totally agree on the connectors... I wire my multiboard panels so that everything folds out like a clamshell for troubleshooting. I never ever ever use connectors unless I have to. thumbs up


Thousand times yes. It sometimes creates longer wire runs but in the end the wiring is much easier to follow, troubleshoot and repair. Once in a while I'll use crimp terminals and solder the pins to wire but in the end it's time consuming and adds just another point of failure.


True but if you are going after the true memorymoog sound you need them.
Don T
The finished version:

"A" Side:



"B" Side:



If I had to do it over again, I would do things a little differently...

I was somewhat smart in installing the pots and switches and wiring those first before mounting and wiring the circuit boards. I was somewhat stupid for not doing the same with the LEDs! d'oh!

So, if anyone reads this, and it's not already too late, do as much of the wiring for the pots, switches AND LEDs before running wires to the circuit boards!
Navs
camelneck wrote:
Sorry for the very late reply. smile Unfortunately, I quit following this thread shortly after I made my original post. Thus, I wasn't aware of your post until I just happened to discover it years later.

As for your questions:

You implemented my mod correctly and it seemed to be working just fine.
The only problem was this: you set your expectations a bit too high.

When I came up with this modification, I wanted to find a very simple way to make the 281 start cycling upon power-up (when the mode switch is in the cycle position) without the need for an external trigger to jump start the cycle process. This modification accomplishes that ... plus some.

Plus some? Since the capacitor remains charged for several minutes. the mode switch doesn't have to be in the cycle position at the moment of power-up as long as you move the mode switch to the cycle position before the capacitor discharges.

After several minutes (actually the time varies depending upon the leakage requirements of the capacitor that is used) this mod ceases to work because the capacitor eventually becomes discharged.

As long as you make sure the mode switch is in the cycle position during power-up (or as long as you move the mode switch to the cycle position shortly after power up) this modification will work fine.


No probs - I've only just seen this too! Thanks for the explanation.

As outlined here I got rid of the cap and added a button to my front panel to get both envelopes looping.

I'd forgotten this question too - has anyone else experienced it?

Quote:
The 281 stops responding to external triggers after a certain frequency. Can someone suggest why e.g. is there a HP filter/ gate-to-trigger converter at work and, if so, do I need to make that trigger shorter? I have a hunch this is what it is. After all, when looping, the 281 runs at 500Hz, triggered by its own End Pulse, right?


Don T, love the colour of your wires.
Don T
Navs wrote:

Don T, love the colour of your wires.


Thanks! It is more than just for looks, I would've gotten lost in the wiring without at least a rudimentary color code.

Plus, the organ that donated its wiring harness had many, many colors available. I was going to make some kind of lame organ donor joke, but decided not to do so applause

Update: I just tested my completed module, and it all works great! It's peanut butter jelly time!
Mongo1
Hi -
I've been trying to get the cycle problem fixed on my quad 281 using the capacitor method that's been discussed, and I decided it was time for something completely different (cue Monty Python music)

The panel I am using has space for the Remote control switch, which I don't have, so I decided to use that space for something else. Namely:

1) I installed a N.O. pushbutton switch in that location.
2) I wired 10V to one side of the switch
3) I attached 4 1N4148 diodes (anode side) to the other side of the switch.
4) I connected the cathodes of the diodes to the Trigger jacks on each section of the module.

The result is that when I push the button, a 10V trigger signal hits each of the sections at the same time. If a section is set for cycle, it will begin cycling. Otherwise it just runs through one cycle of its envelope.

Ultimately I would probably rather have 4 buttons, but space being one it is on this panel, that is not possible.

This solution isn't perfect, but I think I like it better than having to insure the cycle switch is set before powering the unit on.

I hope this helps someone....

Gary
flab
i know befaco has a 281 clone ,is this how more or less they dealing with the cycle problem http://befaco.org/img/Modulos/Slope_gen_2/slope_generator_2_2.pdf ? i havent studied befacos project yet,,iam just saying.
search64
So I jumped at the offer currently running at Thonk (free dual 281 PCB with the Grayscale panel).

But the MPF4393 are now also obsolete at Mouser, so what do I replace them with? Are the 2n4393 the same thing? I never know what to look for in a transistor seriously, i just don't get it
Don T
search64 wrote:
So I jumped at the offer currently running at Thonk (free dual 281 PCB with the Grayscale panel).

But the MPF4393 are now also obsolete at Mouser, so what do I replace them with? Are the 2n4393 the same thing? I never know what to look for in a transistor seriously, i just don't get it


Yes, they are the same, but the case and the pinout are different. The MPF4393/PN4393 is DSG, while the 2N4393 is GDS. You'll want to slide some insulation over the Gate lead, and cross it over the other two, as shown below:

Sony Crocket
Finished my dual 281.

Pluged it, and.. it´s dead.

Built using MPF102. I socketed them so I tried different ones... same result.

No hot ICs and the 7810 is cold as ice.

Didn´t soldered the leds but tried with a 10k resistor instead, and no results.

I´ll be glad if someone could help me with troubleshooting.

Thanks!
fluffybeard
Sony Crocket wrote:
Finished my dual 281.

Pluged it, and.. it´s dead.

Built using MPF102. I socketed them so I tried different ones... same result.

No hot ICs and the 7810 is cold as ice.

Didn´t soldered the leds but tried with a 10k resistor instead, and no results.

I´ll be glad if someone could help me with troubleshooting.

Thanks!


Mine was dead.... Until I soldered some ferrite beads in L- and L+. I don't think they are in the BOM. I think some people replace these with 20r resistors as well.

Check that your 7810 has power.
Sony Crocket
Thanks fluffybeard!

That´s embarrassing, hahaha

Seems that I also forgot those ferrite beads. Put 220r resistors and it´s working nice now!

Thanks!
fluffybeard
Sony Crocket wrote:
Thanks fluffybeard!

That´s embarrassing, hahaha

Seems that I also forgot those ferrite beads. Put 220r resistors and it´s working nice now!

Thanks!


No problem! Now go and enjoy your brand new module:)
strat-1
After building the 281 board, I realized that I forgot to buy mpf4393 transistors.
So I compared all the fet's datasheets I have in stock with the original 2n4393.
From all the fet's, 2n5457 was the transistor that suited very well with the circuit.
Here is a picture with the knobs fully counter-clockwise, shows symmetric triangle calibrated at 500hz.
strat-1
After building the 281 board, I realized that I forgot to buy mpf4393 transistors.
So I compared all the fet's datasheets I have in stock with the original 2n4393.
From all the fet's, 2n5457 was the transistor that suited very well with the circuit.
Here is a picture with the knobs fully counter-clockwise, shows symmetric triangle calibrated at 500hz.
a.b.o.z.
Instead of L+ and L- I have 10R resistors. As soon as I plug power on L+ starts to smoke. I unplugged it quickly..only a little of smoke escaped. What would be the obvious reason for this? It is not reverse power...all diodes are oriented as should, ICs also. I havent checked for resistors values yet.
Don T
a.b.o.z. wrote:
Instead of L+ and L- I have 10R resistors. As soon as I plug power on L+ starts to smoke. I unplugged it quickly..only a little of smoke escaped. What would be the obvious reason for this? It is not reverse power...all diodes are oriented as should, ICs also. I havent checked for resistors values yet.


Did you use 1/2 Watt resistors?
a.b.o.z.
nope, reguler blue 1/4 1%
Don T
a.b.o.z. wrote:
nope, reguler blue 1/4 1%


Ok, those resistors need to be at least rated for 1/2 Watt
a.b.o.z.
Ok, will change those. Just now I plugged the module again with fastest cycle setting on both generators just to see if LEDs work. And thing was blinking as should and resistor did not smoke. Weird. I thought I was on hidden camera confused
And quad mode works also.Woohoo. Then I noticed that B attack is no attack. Only decay there. And by turning attack pot up that 10R starts to smoke again. It is CV to SMOKE grin I will deff change those to 1/2 and report back.
Cheers
a.b.o.z.
very frustrating Wiring mistake. Ground was tied to mid lug of B attack pot. It works now! Sometimes it doesn't start to cycle on its own..needs a trigger...I can live with that for now.
bournio
A.B.O.Z.

My 281 doesn't start without a trigger.

Actually. The B channel doesn't start without a trigger, the A channel will start if it's in cycle mode when power is switched on.

No idea why.

It does seem pretty responsive to triggers, as long as it has a good rising edge. Even fairly high frequencies.
a.b.o.z.
Yes, same as mine, A cycles on power on, B needs trigger.
Poldenstein
trying to source parts for this build..
is PN4393 ok instead of the now obsolete MPF4393?
duff
Poldenstein wrote:
trying to source parts for this build..
is PN4393 ok instead of the now obsolete MPF4393?


Yes, PN4393 is suggested in the build notes. I had trouble finding these at a sensible price so went with 2n5457 as mentioned by strat-1 and they also appear to work fine.
Poldenstein
thank you duff!!
spacedog
Poldenstein wrote:
trying to source parts for this build..
is PN4393 ok instead of the now obsolete MPF4393?


http://www.mouser.at/Search/Refine.aspx?Keyword=610-PN4393

Guinness ftw!
Poldenstein
yup thanks..
that's exactly what i added to my project thumbs up
ehafh
i can't seem to get any of these BOM's to load.
when i click on them it just goes to my personal mouser order history etc.

is it posted somewhere in a pdf or plain text without having to log into a site?

edit-
found it here - https://www.dropbox.com/s/80lwyvx3l25x4ru/Buchla_2812.zip

// http://www.toppobrillo.com/twoeightyone.html
househead
Hi all cool

I've built 4 of the dual boards (15v) and I've got the same issue on all boards in that the attack and decay pots don't appear to do anything.... I used the mpf102's as originally specified on the pcb and I know Toppobrillo changed the bom to pn4393's ...

Anyone know if using the ordinal mpf102's would cause my issue or should it all still function !??

Tanks

keninverse
Wiring is the trickiest part of getting these built. Make sure you double and triple check all of the wiring and also try and make sure you understand what all the pots are doing in the circuit.
Don T
househead wrote:

Anyone know if using the ordinal mpf102's would cause my issue or should it all still function !??


Yes, it should still work.

With these boards, it is very easy to wire the jacks for one section, and the pots for another. In other words, make sure the pots for the "A" section are actually wired to the "A" section on the panel. Quite a few people have accidentally wired their panels this way. They have perfectly working boards, but they think they don't work because they are turning pots wired to the "B" section while testing the "A" section.
woodster
Yep househead, yours sounds like the problem I had.
The cause on my build was not having the B+ connection to the pots.
househead
Great so I don't need to source pn4393's if I've got mpf102's... The wiring thing sounds interesting, I'll double check ...
calaveras
Just finished my 281 and it mostly works!
Woohoo!

Well the bottom "Peak Out" out doesn't seem to be doing much. But after both my recent MST builds were still born it was nice to see things light up, and make a sawtooth on the scope fer sure.
Hilariously my big obstacle now is that I am out of long power cable with the 10 pin connector, and all out of the connectors to make new ones!

After I get it racked up I'll put her through her paces some more to iron out the kinks.
Update:
The peak out and B amount do nothing at all!
I'm having too much fun using this as an oscillator at the moment.
For time being it has to get in line behind my non-functioning SDIY builds.
(but if anyone knows this is an easy fix?)
calaveras
Okay I got the A&B pulse outs working. Turns out I had the op amp (TL072?)at the top next to the VR flipped around wrongways.
Flipped it back and now I can get some more interesting patches happening. Still working on the Peak out. I'm going to carefully separate the two PCBs and verify contintuity with all the pin headers. Also now that I've done one other project with SMT I'm going to revisit the decoupling caps.
angry SMT.
justin3am
I've been using my Dual 291 for a few months now and only just noticed that the Gate/ASR Mode doesn't work on channel A. I'm not sure if it was always this way or not. d'oh!
I mean it works, it just won't hold when the gate is high. I've got the same gate signal going to channel B (which works as expected), so I don't think it's an problem with Gate voltage. Anyway, I've got a momentary switch routing the 10v to the Trig input, so that should be more than enough to hold it open.

I haven't had a chance to troubleshoot the problem and since there aren't many situations where I'd use it in that mode, I may just leave it as is for now.

My question is, can I potentially damage any parts by using that channel while it's not working correctly? If I'm risking further damage, I may just troubleshoot it this weekend, if it doesn't sound like anything serious, I'll just put it off. grin
fluffymuff
So i've just finished by 281 build for Euro (with the barcode Panel PCB) and just realised I used the 1n5240 zeners instead of the 1n5235's recommended for 12v in the BOM. Is this going to cause me issues, or can I leave them as is?
pre55ure
I would swap them.
the ones you put in are designed to regulate 10v and the ones in the BOM are designed for 6.8v. I havent looked at the schematic in a while and don't remember what they do in this circuit... but thats a pretty big difference in voltage.

Edit: Just checked the schematic and the 1n5240 is specified in the original, so It's doubtful that your going to harm anything, but it might not work quite right, or alter the ranges over which it responds etc...
fluffymuff
Thanks pre55ure, I took your initial advice and swapped them out for some BZX85C6V8's which I had in stock (as far as I can tell the same spec as 1n525's) and all seems good. Just need to calibrate and this baby can join his pals hyper
rithma
Hi folks... some of the modded versions of the toppo 281 have a little pushbutton/led in place of the led, and it's set up to trigger.

Anybody know where to source this part or have a part number?



boy am I glad I read through this whole thread before getting started on wiring up my 281.

/Etienne
Fernando
rithma wrote:
Hi folks... some of the modded versions of the toppo 281 have a little pushbutton/led in place of the led, and it's set up to trigger.

Anybody know where to source this part or have a part number?
(...)
/Etienne


Someone gave this link before:

LED Illuminated Pushbutton - 30mm Round
https://www.adafruit.com/product/492
charonme
could you please help me with a replacement for the PN4393 / MPF4393 / 2n5457 from tme.eu or farnell? I can't find any of the suggested ones here on tme.eu or farnell.

how about this one? https://www.tme.eu/gb/details/j106/tht-n-channel-transistors/on-semico nductor-fairchild/

or this? https://www.tme.eu/en/details/bf256b/tht-n-channel-transistors/on-semi conductor-fairchild/
Markat
Are there any calibration notes for this build? What are the trimmers for?
keninverse
In the original buchla modules the trims set freq to match the panel legend so you can set to whatever you like since there's no panel legend on the Euro version. Turn both A and D pots full CCW while in LFO mode and you should hear a tri on the output. Set the trims so you have around around 500Hz-1kHz. It really depends on how fast/slow you want the module to run.
tuukka.j
Is there any reason why I should not take the B+ and GND from one pin on the PCB for all the pots, switches and leds?

Other than the mechanical of course, but as I'm building my own PCB for the panel components (for reasons) that shouldn't be an issue.

So is there any electrical reason for taking the GND and B+ from different spots on the PCB?
Triglav
Is there a trivial way to add LEDs for the PULSE OUTs or would I need to build something like the CGS LED driver?
Triglav
Well, this was a nightmare to wire but it's done:
lasesentaysiete
Triglav
impressive!
Triglav
Thanks!
I do have a couple of questions though.
— Has there been a reliable mod to reliably start the cycle when flipping the switch? Is the mod on https://modularsynthesis.com/roman/buchla281/281_qfg.htm applicable to 12V builds?
— It seems like the outputs are 0-10V is there a simple way to make it 0-8V? The build docs suggest that it should be 0-8V with the 1.33k resistors. EDIT:I have solved this with simple voltage dividers on the outputs. Seems to work fine.

EDIT2: Wiggler cygmu was kind enough to draw up a cycle mod. It's now working like a charm:
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