Build a buchla 208 rev2

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Wracked with Guilt
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Post by Wracked with Guilt » Fri Jul 13, 2018 11:36 am

tarandfeathers wrote:
Wracked with Guilt wrote:Hi, it looks like the original link to Roman's BOM is dead. Would anyone be able to kindly send me a copy please? Thanks in advance :guinness:
https://electricmusicstore.com/blogs/bu ... -model-208

BOM links look like they are working to me...
Thanks a lot!

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dingebre
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Post by dingebre » Sat Jul 21, 2018 6:48 pm

Is there a dedicated build thread for the "Touch Activated Voltage Source 218" project? There is some information in this thread and other 208 DIY threads, Dave Brown is always an excellent source, but I have not found much information on the EMS 218 (Roman's right?) project. the information on the EMS site is pretty sparse and my PCBs did not come with any hard copy information. I've found the BOM and the "build" documents on the EMS site.

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boops
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Post by boops » Sun Jul 22, 2018 6:55 am

Look for
Emcloned site
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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dingebre
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Post by dingebre » Sun Jul 22, 2018 11:49 am

Brilliant!!
Thank you!
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Chaotic
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Post by Chaotic » Tue Jul 24, 2018 6:26 pm

One problem left with my friend´s Easel. Have fixed the other problems. It was not neat build and had several issues when he bought it.
I´m getting no sine from the CO. Only a clean tri. The trimpot dont have any effect on it.
Have read somewhere that the Q1 on card 8 have to be selected. Its not easy when I have no spare.
But the question is: Can it be some other parts which course the problem or do we have to get a new tranny?
Tried to use my own card 8 in his 208 and then I got a pure sine.

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Post by papz » Tue Jul 24, 2018 7:34 pm

Is IC2 on the faulty card 8 a 4016 or 4066 ? Should be a 4016, in many cases a 4066 doesn't work properly there.
Swap the ICs of both cards 8 to check all are ok.
Double check the solder joints and resistors value on the faulty card 8.
Compare the diodes with multimeter with the other card.

If none of the above helps, Q1 is probably the culprit.
Get a few new 2N4339's, select the best working one and if needed tweak R41's value.
If you have a proper desoldering tool, you can also unsolder the good card's Q1 and test it on the other card before purchasing new transistors, to confirm it's the cause.
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Chaotic
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Post by Chaotic » Wed Jul 25, 2018 5:40 pm

Swapped the two 2N4339 trannies between card 6 and 8. Got a decent sine. So for me it seems to be the transistors.

Have also another question about the in/out switches on the osc.
Without the keyboard attached the tone altering a semitone when I use the switch. Is this normal?

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Post by papz » Wed Jul 25, 2018 5:50 pm

Yes

Yes
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Post by Chaotic » Wed Jul 25, 2018 6:08 pm

papz wrote:Yes

Yes
Thanks. Now Im done with my friend´s Easel and next will be to finish my papz 208
Have tested my cards #1 to 10 on his main board and all of them seems to be ok :nana:

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208 Card 12

Post by davebr » Wed Sep 12, 2018 4:03 pm

I just spent way too much time troubleshooting card 12. The LM380s were horribly unstable and would break into oscillations which would ripple through the power supplies and affect everything. Typically this is a wrong component but they were all fine. The LM380s were soldered to the PCB. It was the FLUX. It provided enough leakage that with any signal one or more would oscillate at a very high frequency. Very nasty.

I've always suggested using water wash flux and cleaning boards. Here is another reason to do so. I continue to find and fix a small number of problems simply by cleaning the board. Besides, it makes searching for poor solder joints much much easier.

I'll add this to my 208 page.

Dave

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boops
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Post by boops » Tue Mar 05, 2019 2:23 am

Happy builders

Some diy/built:
buchla small case (208 alone,easel,2x4u)HQ psu,
208 card12 upgrade
Reverb mix level pot CV Pcb
pcbs available


viewtopic.php?t=211862&highlight=

viewtopic.php?t=210317&highlight=

Good built!!!!

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Last edited by boops on Sat Jun 08, 2019 12:39 am, edited 1 time in total.
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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d.simon
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Post by d.simon » Mon Jun 03, 2019 11:56 am

is there another option/source for the sliders other than Farnell?
I don't want to "go cheap" but at the same time trying to not spend more than I have to.
especially for the US because freight charge is $20.

I heard the board might have another footprint for the sliders for example, where I annotated yellow vs the ALPS blue.
Picture file
Image


I found some BOURNS, but their leads seem to be at the end of the sliders as opposed to the alps, which have the leads recessed from the ends (plus some sort of mounting pins). :sad:
other than that they seem to have the right dimensions : 45mm travel, 60mm total length...as shown in the datasheet PTA453
https://www.mouser.com/datasheet/2/54/ta-778345.pdf

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Post by captnapalm » Mon Jun 03, 2019 3:18 pm

d.simon wrote:is there another option/source for the sliders other than Farnell?
I don't want to "go cheap" but at the same time trying to not spend more than I have to.
especially for the US because freight charge is $20.

I heard the board might have another footprint for the sliders for example, where I annotated yellow vs the ALPS blue.
Picture file
Image


I found some BOURNS, but their leads seem to be at the end of the sliders as opposed to the alps, which have the leads recessed from the ends (plus some sort of mounting pins). :sad:
other than that they seem to have the right dimensions : 45mm travel, 60mm total length...as shown in the datasheet PTA453
https://www.mouser.com/datasheet/2/54/ta-778345.pdf
I believe the extra set of footprints on the pcb is for the original-style sliders used on the 1970s Easels. They were far inferior to the Alps; since this is the user's main interface to the instrument I feel like nice smooth sliders are worth the money. Not to mention how much of a pain it would be to remove the front panel and replace one should it go bad.

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Post by d.simon » Mon Jun 03, 2019 7:09 pm

captnapalm wrote: I believe the extra set of footprints on the pcb is for the original-style sliders used on the 1970s Easels. They were far inferior to the Alps; since this is the user's main interface to the instrument I feel like nice smooth sliders are worth the money. Not to mention how much of a pain it would be to remove the front panel and replace one should it go bad.
makes sense...on other projects I've seen/used some sliders that have a similar '1970s-style' footprint (from alibabba) and they do seem inferior.

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Post by ARY » Fri Jun 07, 2019 8:16 am

HI
DOES ANYONE KNOWS WHERE I CAN GET A uA726 IC CAN 10?

THNAKS

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Post by boops » Fri Jun 07, 2019 3:44 pm

pm me please
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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d.simon
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Post by d.simon » Mon Aug 12, 2019 6:02 pm

getting closer to powering this up...at least starting w/ cards 1-4.


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Post by d.simon » Wed Aug 14, 2019 11:30 am

been going through the modifications.

I didn't see this mentioned on the threads...on card 3, the schematics show C11 910pF. But that's not in the Roman BOM or on the layout (that I can see).

Seems to be the same position as davebr 100pF "oscillations in the EG output" mod. (across R17)

910pF seems oddly specific. I guess that lowers the cutoff frequency (compared to 100pF) for stabilization?

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Post by tarandfeathers » Thu Aug 15, 2019 5:48 am

I don't think the value is critical. When I noticed the oscillations (before Dave had that note on his site) I added a 1000pF cap in that position. For some reason Don Buchla often used 910pF in locations where 1000pF works fine. I can only assume he must have bought an enormous lot of them very cheap at some point.

It's not included in the EMS 208 because Roman based the design on an original 208, not the schematics, and I believe this was a very early example, made before several modifications/bug fixes were implemented. You will also notice on the widely available card 3 schematic that there is another C11, 100pF around the logic which is intended to improve the behaviour when in sustain mode (note "improve", not "fix"), plus the entire envelope end pulse out section (feeding pin 7) which is not there at all on the EMS 208 - this would allow a self cycling envelope with a one wire modification to the motherboard, presumably implemented on some later manufacture 208s.
Dunnington Audio - Various Buchla format accoutrements available

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Post by d.simon » Thu Aug 15, 2019 11:20 am

tarandfeathers wrote:I don't think the value is critical. When I noticed the oscillations (before Dave had that note on his site) I added a 1000pF cap in that position. For some reason Don Buchla often used 910pF in locations where 1000pF works fine. I can only assume he must have bought an enormous lot of them very cheap at some point.

It's not included in the EMS 208 because Roman based the design on an original 208, not the schematics, and I believe this was a very early example, made before several modifications/bug fixes were implemented. You will also notice on the widely available card 3 schematic that there is another C11, 100pF around the logic which is intended to improve the behaviour when in sustain mode (note "improve", not "fix"), plus the entire envelope end pulse out section (feeding pin 7) which is not there at all on the EMS 208 - this would allow a self cycling envelope with a one wire modification to the motherboard, presumably implemented on some later manufacture 208s.
Thanks - yea he must have had a surplus of those! :) I was looking on mouser and the 910pF they have seems to be for another type of application...maybe high voltage?

I made that mistake once...I kept buying some high voltage type (maybe 100pF?) for a bus board and they really didn't fit the placement in terms of geometry and lead spacing. I still have a couple bags of them.

Thank you for the other infos...I was wondering about pin 7. Also, I remember seeing something about a EG loop mod. I'll check that out (not sure if it uses pin 7). I kind of knew about the other C11 based on your sustain board and forum posts. I might try to implement something similar.

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Post by dsf » Wed Aug 28, 2019 3:17 am

tarandfeathers wrote:
Don T wrote:
dsf wrote:Wanted to ask something around, trying to go through and take note of my last unsolved small bugs. I notice three things

1 - MO modulation index has a "dead spot" affecting both AM modulation, at about position 4 of the fader it seems to "kill" the CO signal, it just lowers a lot it's volume or "strength" then it gains again.

2 - MO modulation switch affects CO volume even if Index is not applied (wtf??) with the switch on a.m. COs volume is noticeably higher that when the switch is at Balanced external or f.m.

i guess those are not normal behaviours, but wondering if anybody experienced anything similar
Have you tried swapping the CD4016 on Card 6 (The MO card)?
It seems doubtful to me that the 4016 has any bearing on this. Regarding 1, this might be because the AM symmetry calibration has not been done which can cause a sort of "null" where the modulation doubles over on itself, or it could be a problem with either VT6 or 7 on card 5. With no modulation index, VT7 is all the way on and VT6 is all the way off, with an inverted copy of the modulation index CV driving VT7 and a non-inverted copy driving VT6. VT6 and 7 are used as mix resistors between the non modulated and modulated versions of the complex oscillator signal so it seems likely to me that there is a point in the range of CV where VT7 has mostly turned off but VT6 has not yet turned on enough to pass the correct level of signal (or VT7 is turning off too fast, difficult to say which).

As for higher level when in the AM setting, I think this is somewhat normal though it shouldn't be too extreme, and it could be corrected by adjusting the gain of amplifier 3 in IC5 on card 5, decreasing R29 to reduce the level of the AM path until it matches the level in the FM and balanced settings.
Hey Daniel! long ago you told me this, i finally feel like opening again the case and fix the Fm Am level difference issue (the am mod issue was indeed a problem of proper calibration).
So if i stick a trimmer at r29 i can adjust for the proper value to match fm-balanced external level? Or should i match the vactrols?
right now there is a big volume difference between AM and FM-Balanced ext.

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Post by d.simon » Sat Aug 31, 2019 9:36 pm

dsf wrote: Hey Daniel! long ago you told me this, i finally feel like opening again the case and fix the Fm Am level difference issue (the am mod issue was indeed a problem of proper calibration).
So if i stick a trimmer at r29 i can adjust for the proper value to match fm-balanced external level? Or should i match the vactrols?
right now there is a big volume difference between AM and FM-Balanced ext.
Are you aware of Dave Brown's card 5 modifications? He mentions r29 and a mod on the way the index works (change IC4C from inverting to non-inverting).

https://modularsynthesis.com/roman/buch ... 08spss.htm

Also in the papz thread user Siri on 1/23/2019 quoted some advice from Dave Brown on matching vactrols.

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Post by dsf » Mon Sep 02, 2019 5:25 pm

d.simon wrote:
dsf wrote: Hey Daniel! long ago you told me this, i finally feel like opening again the case and fix the Fm Am level difference issue (the am mod issue was indeed a problem of proper calibration).
So if i stick a trimmer at r29 i can adjust for the proper value to match fm-balanced external level? Or should i match the vactrols?
right now there is a big volume difference between AM and FM-Balanced ext.
Are you aware of Dave Brown's card 5 modifications? He mentions r29 and a mod on the way the index works (change IC4C from inverting to non-inverting).

https://modularsynthesis.com/roman/buch ... 08spss.htm

Also in the papz thread user Siri on 1/23/2019 quoted some advice from Dave Brown on matching vactrols.
Hey, thanks, yes i saw that but didn't went deep into it, i really don't think like matching vactrols, but i think i'll try Dave's mod, i just want to use it :)
Will build boops card12, do card5 Dave mod and hope to end there and concentrate in making music.

Thanks!

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Post by d.simon » Tue Sep 03, 2019 4:50 pm

dsf wrote: Hey, thanks, yes i saw that but didn't went deep into it, i really don't think like matching vactrols, but i think i'll try Dave's mod, i just want to use it :)
Will build boops card12, do card5 Dave mod and hope to end there and concentrate in making music.

Thanks!
I did the vactrol matching, but haven't powered up any of those circuits yet. It wasn't too hard to do.

But I know what you mean...I seem to go recursively farther back in the building process. Right now I'm learning how to use a router, so I can make a homemade fretwire-straightener - this is because I bought some already curved brass fretwire for the 218.

I figure the router skills will be useful in making cases - which was another tangent I went down. But first I want to build a router table.

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Post by jonen » Sun Sep 29, 2019 10:54 am

I am having an issue with my sequencer. After it didnt select the right stages I had to add decoupling capacitors on IC1 between pin 4 and N and on IC6 between pin 5 and N. Now I have this weird issue, that stage 4 and 3 always get triggered at the same time and with faster clocks, only stage 1 and 2 are triggered. Any idea what else to change?

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