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[ORDER] OCTOGINTA-II Digisound 80-2 eurorack version
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Author [ORDER] OCTOGINTA-II Digisound 80-2 eurorack version
whoop_john
I have been working on a compact version of the Digisound 80-2 VCO module. As I am sure everyone is now aware, the infamous CEM3340 VCO chip has now been remanufactured by no less than three different sources and this project takes advantage of the rock solid tuning on these VCO chips.

The module is in a compact 10HP width, ie 2". We envision that a complete DIY VCO build should be possible for under GBP £50, including the VCO chip, PCBs and front panel. This may depend on where you source the VCO chip from.

Particular care has been taken to provide an easy build for the DIY community - I have now built five with no difficulty. All components are through-hole in a straightforward layout. No inter-wiring of panel components is needed. The trimmers afford ease of access.

I would like to thank Julian for collaborating on the front panel design and David 'mrmrshoes' for his beta testing and modification suggestions for 12v use.







Julian will be able to ship both PCBs and panels together for a saving on shipping costs. The cost of the PCB set is GBP £9 and Julian's front panel will cost GBP £20. PCB shipping will be £1.50 in the UK and £3.50 elsewhere in the world.

Kits may be offered in future, or complete builds, if people would rather have one-stop shopping or a complete plug in and go module. Please message me if this is more attractive for people and I will work out costs.

The only issue arising has been that on a 12v supply rather than 15v the raw saw wave output has an amplitude of around 7.6 volts rather than 10v. The other waveforms have been buffered and adjusted to give nearer 10v to be more faithful to the original. It would be possible to adjust the other waveforms so they matched the 7.6v, but the team's view has been to keep things as they are as waveforms will usually be attenuated further down the signal chain anyway.

Documentation
The original ETI magazine article is here ETI article
The original Digisound article is here Digisound article
Pav
I'm interested in PCb+panel . I could not view the articles from my iPad for some reason. I see the links on BT cloud...but clicking on link fails. I'll try from PC later. Will these be the BOM to work from?
whoop_john
Pav wrote:
I'm interested in PCb+panel . I could not view the articles from my iPad for some reason. I see the links on BT cloud...but clicking on link fails. I'll try from PC later. Will these be the BOM to work from?


No, I will do a correct updated BOM for 12v in due course. Links to the documentation now changed and should work.
Sparkey
Hi John,
I'd be interested in getting the PCBs and panel. If a there was enough interest and kit happened before I was ready to purchase, I'd certainly look at that, but I'm not desperate to have everything handed to me.

Cheers,
Alyn
Ayab
Excellent features and very compact - Good work. I love it! Very neat panel too.

Did you use a cool audio 3340 (which Julian is proposing a group sale of on another thread on here)? Was it easy to tune?

I would like three pcb sets.
whoop_john
Ayab wrote:
Excellent features and very compact - Good work. I love it! Very neat panel too.

Did you use a cool audio 3340 (which Julian is proposing a group sale of on another thread on here)? Was it easy to tune?

I would like three pcb sets.


Yes I used the Cool Audio version of the 3340. Setting up the sine wave shape and zero point is easy and the tuning should pose no problem if the correct procedure is observed. Once the low frequency span has been set then the high frequency compensation can be adjusted.

It is suggested that the coarse knob is set to off and the fine tune knob be disconnected until tuning has been set up.
whoop_john
Thank you to all those who messaged me and have ordered PCBs. Your PCBs will be in the post to you tomorrow and your support and encouragement for the project is very much appreciated.

I have just a few PCBs left still if you wish to be an early adopter. I have more PCBs on order, coming in about 10 days, so don't worry if you didn't order one yet, I will have plenty and Julian will have stock for those that want to get a beautiful alumin(i)um engraved panel and PCB together, to save shipping.

A BOM will follow very shortly.
cretaceousear
Nice job - good to see Digisound designs gettting a new lease of life!

While getting mine back into action a few years ago I had a brief discussion here on MW about the zero based outputs:
https://www.muffwiggler.com/forum/viewtopic.php?t=110511

I concluded Mr Blakey should have made the four base outputs bipolar and then added 0-10 for the pulse.
No other designers seem to have followed this positive going output format - do you have an opinion or is it neither here nor there?
whoop_john
cretaceousear wrote:
Nice job - good to see Digisound designs gettting a new lease of life!

While getting mine back into action a few years ago I had a brief discussion here on MW about the zero based outputs:
https://www.muffwiggler.com/forum/viewtopic.php?t=110511

I concluded Mr Blakey should have made the four base outputs bipolar and then added 0-10 for the pulse.
No other designers seem to have followed this positive going output format - do you have an opinion or is it neither here nor there?


Food for though certainly. I was trying to be faithful to the original. Perhaps if I do a second iteration I will address this issue. What do the others think?
Synthsense
Interested in x2 PCB + Panel Sets please Guinness ftw!
whoop_john
A BOM and information on sourcing the components is now available. View or download the information in PDF form.
Modulart_JP
Have been offering a version of the module since last year:
http://www.pharmasonic.jp/vcolfo_e.htm
jaidee
Quote:
Have been offering a version of the module since last year:


... but not any DIY option as far as I can see.

If you are supplying DIY PCBs and panels, particularly for the VCDO (and the appropriate eprom) I'd be very interested - otherwise I'm not sure what this and your other post is doing in this DIY thread.
Modulart_JP
Well...
The Eagle files to make your own PCBs and the FPE file to make your own front panel are available to download.
If that's not DIY then what is it ?
flts
Easy links to board file and panel here: https://www.muffwiggler.com/forum/viewtopic.php?t=197467

Having trouble finding them on site as well!
Modulart_JP
flts wrote:
Easy links to board file and panel here: https://www.muffwiggler.com/forum/viewtopic.php?t=197467

Having trouble finding them on site as well!

OK, let's continue there then.
I just wanted to point out that there was another incarnation of the module in eurorack.
Didn't mean to troll.
Mine sticks to the original design and parts when whoop_john's one has been slightly adapted to "modern life".
It is good to have a couple of alternatives to this nice design.
julian
When you say that John's is an adaptation, can i ask you what you mean?

So far as im aware the only changes made were to allow the unit to run on 12v. I would assume that your unit required the same alterations?
unrecordings
I've got far too many unfinished projects, but...

John - It looks like the PCB is '15V Ready' with an MTA156 footprint - is that correct ?

Would you simply sell a circuit pcb without the panel pcb so that us 5U types can panel mount our pots etc ?
julian
edit - misread question
unrecordings
Thanks Julian
I might have misunderstood your answer though - I would only be looking for the one pcb, not the panel pcb and not the panel (I don't need the pcb for the panel mount components because I can simply wire everything from the long header on the main board)
julian
It was my fault - i read your question incorrectly.

I cant be sure, but i think John gets the pcbs made in sets that contain both boards as one (and then are broken along the score lines).

...but, at £9 for the pair, even junking the panel board, although wasteful of resources, is hardly a cost consideration?
julian
The foils for the original 80-2 modules are here -

http://www.digisound80.co.uk/digisound/modules/80-2_files/80-2&3_PCB.g if

Years ago, i used one to isolation mill a 1-off of the ring modulator -



ie from this file -

http://www.digisound80.co.uk/digisound/modules/80-11_files/80-11A_PCB. gif


I reckon though, unless youre proper keen on etching etc, it would be way more bother than just junking the panel board from John! : )
unrecordings
julian wrote:

...but, at £9 for the pair, even junking the panel board, although wasteful of resources, is hardly a cost consideration?


Yeah I know, It's just the whole waste thing. I'd rather pay the £9 and insist John keep the panel boards as spares though...

I don't need two more VCOs though (inner voice is naysaying), but I've run out of things to solder and it's been too cold to make panels...

John - are you going to move further into Digisound modules ?
whoop_john
unrecordings wrote:
I've got far too many unfinished projects, but...

John - It looks like the PCB is '15V Ready' with an MTA156 footprint - is that correct ?

Would you simply sell a circuit pcb without the panel pcb so that us 5U types can panel mount our pots etc ?


Yes I stuck an alternative MOTM style power socket there. I can sell a PCB without the panel PCB but the cost is still £9. After all, what am I going to do with the spare front panels and no main PCB? The PCB is 15v ready, it just needs the original component values installing.
whoop_john
Modulart_JP wrote:
Have been offering a version of the module since last year:
http://www.pharmasonic.jp/vcolfo_e.htm


I am all for diversity and choice. If HP is an issue then my version saves you 2HP. I am considering offering complete built modules, but the cost won't be anything like $240.
unrecordings
Well if someone is going to fuck it up, they can thank me for the spares hihi

Will PM you shortly

Do you have a list to hand of the component changes you made for 12V - will make cross referencing the ETI docs so much easier
Pav
Hi WhoopJohn , Julian .. may i inquire what is the status on ordering
OCTOGINTA-II with panels ?
julian
Pav wrote:
Hi WhoopJohn , Julian .. may i inquire what is the status on ordering
OCTOGINTA-II with panels ?


I cut the panels last week, but ive done nothing with them at all, due to being sucked into other things!

Theyre identical to the photo John posted, except for "10" has been changed to "+" on the outputs. Ie "10vsin" becomes "+vsin" (etc)

I have parts for all those who have previously expressed interest, including yourself.


John told me yesterday that the pcbs are on their way to him, and should be with him in a couple of days. So, you can order from him, or wait, and he will send me a bunch to go out with panels, if that is better for you (saves a touch on postage)

They will also turn up on my website in due course.
Pav
Thanks for the update Julian ..I can wait and order from you both PCb and panel.
whoop_john
I was notified that PCBs are on their way 6 days ago, but I have not yet received them but expect to do so in the next few days. Customs delay no doubt.

As soon as I get them I will send some to Julian so that he can send out PCBs and panels together so you save on shipping cost.

If you want bare PCBs only, then message me.

PCBs through Julian or me will be the same cost to you.
whoop_john
.    
julian
I now have the pcbs from John, so can start sending out pcb / panel combos.
nobody
Nice work. Ive been working on building my own port of this but fuck, looks like two people beat me too it. Good thing is its a nice design smile

Im interested in the PCBs, I want to do my own panels though. Couple of questions:

1)I saw you tested these with the cool audio chips. Have you tried with the rev G chips?

2)Do I get a bulk sale price for 20 PCBs?

3)Is there a parts list / schematic somewhere?

4)Are your pcb / schem designs available in case I just want to steal them and do my own run (for myself)? Imitation is the highest form of flattery. smile

Only thing I wish it had was an LFO switch....
julian
I think this is your link to the schematics -

http://www.digisound80.co.uk/digisound/modules/80-2_files/80-2.pdf

This is the 80-2. I have in mind that there was an 80-2 point "something" which is a switchable lfo version, but i feel like im going a bit mad, as i cant find it now??

So far as im aware, the schematics are the same for this version as the original, and the only difference is some component changes for running on 12v.

Really though, all i do is chop metal, so this may all be nonsense!
unrecordings
You need to go back a couple of levels and find the ETI article:

http://www.digisound80.co.uk/digisound/modules/80-2_files/80-2&3_ETI.p df

I'm building a 15V version, so John kindly put a graphic together with the changes he made so I could go and cross reference them against the ETI article

I was looking to use Rev G chips, but Thonk have sold out, so I'm temporarily stuck
nobody
unrecordings wrote:
so John kindly put a graphic together with the changes he made

And those are located where exactly? I cant seem to find them. I found John's website but all the "muff" files are hidden.
julian wrote:
So far as im aware, the schematics are the same for this version as the original

Ok good to know. Wonder if he would share his board files...I like the pcb design.
unrecordings
With John's permission, here's that graphic with the +/-15V resistor values dropped back in and marked in red

unrecordings
A couple of people PMed me about the Rev G CEM chips

Well Thonk have them back in stock again at £10.60 a piece (plus VAT so that's £12.70 ish)
unrecordings
WARNING FOR 5U BUILDERS

Just putting the final components together and hit a snag - the power header is way too close to the bottom set of trimmers. I did a quick fit tacking the components in place, and although they'll fit, you'll eventually kill the trimmers trying to force a power cable onto the header. I'm using bourns trimmers and MTA156 headers. You may be okay with a Molex connector, or just a raw header - but for those who use MTA156 - watch out
julian
Could you put the trimmers or the headset on the other side of the board, as a work around?

I'm not suggesting it's ideal, but as a solution?
unrecordings
Yep you could indeed do that

I just found a couple of Molex connectors in a long forgotten box - they could work (and I know a lot of people use them in place of the MTA156) but I personally don't like them

I think I'm going to hard wire a long power cable, like I do for most Euro conversions, but yes - reverse mounting is definitely an option
Pav
Hi John,Julian,


first a heads up to any builder that the holes in my panel are drilled with the 9mm alpha plastic shaft in mind. The holes are 1mm too small for the metal shaft variety where the thread cannot get through.
Easy enough to fix with a file.

Food for thought in a future batch production.

Question for John ..

I have a large stock of PJ301BM aka "earthnvar" sockets ..im wondering if i can snip off the earth tags.. and just solder the signal and switch pins. Im looking at the layouts posted by "unrecordings" and it doesnt appear that any ground pins are connected. suggesting this might be ok.

However i may be completely wrong as i do not see the ground pins of the power header connected by track to anything either ..which is confusing me a little ..unless there is pcb circuit layer not shown just for ground.

If no - ill go order some PJ301M thonkicon.
whoop_john
Pav wrote:
Im looking at the layouts posted by "unrecordings" and it doesnt appear that any ground pins are connected. suggesting this might be ok.

However i may be completely wrong as i do not see the ground pins of the power header connected by track to anything either ..which is confusing me a little ..unless there is pcb circuit layer not shown just for ground.

If no - ill go order some PJ301M thonkicon.
The diagram showing the component changes for 15v omitted the top copper layer for clarity. The earth pads are indeed connected. I don't personally use thonkicons, I use the ordinary tag socket versions.
whoop_john
Pav wrote:
The holes are 1mm too small for the metal shaft variety where the thread cannot get through.

Point noted. I am using plastic shafted pots which are both ubiquitous and cheap. Search for RV09 and a bunch will come up.
Pav
Hi,

I notice that the 2 x 22pf and 1 of the 4 1nf capacitors C7 in the original digidesign doc has them as polystyrene.

Q1: could u point out which of the 1nf caps is C7 by its relative pcb position ?
Pav answer Pin 11 of cem is timing acc to schematic..

Q2: what are the roles of the 22pf caps C11,12 ? Not mentioned in the old doc. ?
Pav answer is they are parts of opamp feedback loop removing hi freq oscillation..maybe.

I am aware that a COG (NPO) ceramic will give similar stability today as polystyrene did in the past and usually cheaper.

I see the prototype pictures do not show polystyrene so it may not be essential ..but i do like my vcos to be stable.



Thanks
Pav
Hurrah, my Octaginta is working fine first time of asking nanners ...just need to finesse the tracking calibration.
whoop_john
Pav wrote:
Hurrah, my Octaginta is working fine first time of asking nanners ...just need to finesse the tracking calibration.


Well done Pav. Once calibrated please do a video.

Best wishes,

John
unrecordings
I'm lagging badly behind on this - I have two boards completely finished, and the pots to wire one of them up, and the panel blanks but now the weather is better, I'm also badly behind on my other hobby - gardening. It'll all even out in a few weeks - although a robin has nested in my workshop, so that might put the skids on making any panels until September Dead Banana
julian
After saying i wasn't going to do any more colours / finishes, i ended up with a bit of space on a run, so these exist -



Same price as the silver, but wht you see is what there is (ie when theyre gone...)
Ayab
Dammit Julian those are fine looking B&W panels.

Did not know you were doing them when I ordered.

(I think he mentioned them to me me in a pm but my mind must have been elsewhere I did not look at the thread very frustrating )

Still very excited to be receiving my Octaginta VCO's soon!
Pav
whoop_john wrote:
Pav wrote:
Hurrah, my Octaginta is working fine first time of asking nanners ...just need to finesse the tracking calibration.


Well done Pav. Once calibrated please do a video.

Best wishes,

John


Heres me picture plus a video testing sync with triangle (30 seconds long from phone)

https://youtu.be/wjEY6U3gx2U

Ayab
Got back just now from a long day out and was greeted by a package from Julian. John's Octaginta PCB's and Julian's Panels.

Looking forward to getting some soldering done this weekend. Gorgeous panels (black text on aluminium) very happy SlayerBadger!

Have a good weekend
julian
Suddenly all the 3340 vco threads have been bumped to the top of the list, so i figured i should do John's build for him also!

: )
whoop_john
julian wrote:
Suddenly all the 3340 vco threads have been bumped to the top of the list, so i figured i should do John's build for him also!

: )

Thanks Julian. It would seem that there are a variety of 3340 build options for people to choose from. I still have stocks of PCBs and so does Julian for the Octoginta-II project. It should be easy to do a build for under £50, $68, €58 and that includes the Gucci Julian engraved panel.
Snatti
Is there a Mouser cart for this build, or the possibility of buying a parts kit?
loderbast
Hi,

i am in the process of soldering my ocataginta.

i noticed there are 9 resistors marked 100k on the pcb (bom says 8)
also there is also 0ne marked 150k (bom says 2)
whats is up with that?


cheers Paul

edit:
i just saw there is also a 1m2 resistor on the silkscreen (in ther bom there is no 1m2)

obviously i am missing something..
is there different revisions of the bom/pcb?
whoop_john
loderbast wrote:
i noticed there are 9 resistors marked 100k on the pcb (bom says 8)
also there is also 0ne marked 150k (bom says 2)
whats is up with that?


A legacy from the original PCB build I guess.

R15 on the original Digisound 80-2 schematic has been changed from 100k to around 145k-150k to get the gain near +10V for TRI-Out 10V. So there are now 8 x 100k and two x 150k.

R11 on the Digisound 80-2 has been changed from 1M5 to 1M2 for 12v operation.

BOM is here: https://www.dropbox.com/s/1y74ptq6iksvwki/OCTOGINTA-II%20BOM.pdf?dl=0
loderbast
thank you, John!!
whoop_john
I have just updated the BOM. R4 is marked on the PCB as 100k - this should be 150k and now matches the BOM.

I have added layouts showing component names and values. These are correct and reflect the above change to R4.

PCBs I am sending out from now will have a tiny black dot against R4 for ease of identification. All other components are marked correctly on the PCB.

Revised BOM:
BOM URL
nobody
For the love of god I can not seem to get the pulse output working. Is there something special I need to do? Sines, saws, and tri's are working, but I have not yet tuned them. I ripped out all the components On the pulse circuit, checked the pin itself, and even tried a different chip.
, and replaced the pulse circuit with new components. Nada. Any suggestions?
Pav
At risk of suggesting things you had already tried, I would start with ruling out connectivity to the pulse jack from the connecting pin header joining the PCbs. Then work backwards on the component PCb checking continuity on pulse signal path from/to connecting header. I suspect the joining of the boards is likely cause now you have replaced components.
nobody
I tried it but I'll try it again. Does anyone know the minimal components I need on the pulse circuit to see an output? If I take off the pull down and the zener should I see something directly on the CEM pin, or do those components need to be there? Is tuning an issue as well?

Like I said, everything else is working, and if I look directly on the cem pulse pin I have no signal.
Pav
The ETI article description says the pull down is a must have. Zener just sets range.
I didn't need to do any tuning to get pulse with all components in place.
I did wonder if the pulse width cv range setting at extreme cow or cw if out could be silencing the cem...but could be another straw I'm clutching.
whoop_john
I just got back from overseas where I've had no interwebs. I'll have a look at my Octoginta-II builds and see if I can fathom out what is happening. I built 5 so far and I had a beta tester also do a build and comment back to me. One way or another we shall get to the bottom of this, I am sure.
nobody
Ok, I removed the front panel, and depopulated the 2k resistor. Then connected pin 1 of that 2k with a 10k and connected the other end to a ground pin on the breakout header, top side. So basically pin 4 of cem has a 10k pull down. Still no square, connectivity checks out ok... about to poop on this thing.
whoop_john
nobody wrote:
Ok, I removed the front panel, and depopulated the 2k resistor. Then connected pin 1 of that 2k with a 10k and connected the other end to a ground pin on the breakout header, top side. So basically pin 4 of cem has a 10k pull down. Still no square, connectivity checks out ok... about to poop on this thing.

Are you still having problems with your pulse output? If you don't see it then it may be possible that something in the pulse width circuit is pulling it either end of its limits and it has disappeared.

The CEM3340 datasheet seems to suggest the output on pin 4 should operate correctly with nothing connected to the pulse width pin5, although it does not explicitly say so it shows a connection diagram without anything on pin 5.

Pin 5, the pulse width, is designed to operate from a voltage from 0-5 volts. The PWM pot is connected between the positive rail and normalised via a 47k resistor through the PWM jack. After the jack there is a further voltage divider which would reduce a maximum of 10v into the jack or via the pot to a 5v max at pin 5.

We are operating at 12v for eurorack rather than 15v, but I can confirm that on the six builds I have done to date that the PWM pot range will change the pulse width from 0% to 100%, so the resistors do not need to change, although we should only be getting a max of 4v on pin 5, being a third of 12v. The chip itself is designed to operate at down to 10v, so it seems the voltage requirement on pin 5 also scales.

I would check that you are indeed getting a voltage change on pin 5 from the PWM pot, via the PWM jack. 2v here will give something near to a 50% square wave and should certainly make the pulse visible on pin 4 by probing that pin directly on a scope.

nobody
Thanks for the post. Was able to get a square wave out when I disconnected the control board and put a voltage on pin 5. I must have a short or open somewhere. More debugging to do but at least I know it works now. Thanks!
whoop_john
nobody wrote:
Thanks for the post. Was able to get a square wave out when I disconnected the control board and put a voltage on pin 5. I must have a short or open somewhere. More debugging to do but at least I know it works now. Thanks!


If there is not an obvious short somewhere on the control board then I would suspect the normalising on the PWM input socket. If this does not make connection then pin 5 will pull to 0v via R20. Check the adjustable voltage on the PWM pot on the normalising and signal pins of the socket to check it's getting through OK.
unrecordings
Just finally finished my two MOTM versions this week, but it's been a little too overcast to take a photo.

I dispensed with the panel board and point to point wired everything that wasn't on the main board. All in all very easy to port back into the 5U domain and kudos to John for putting this together, they are superb VCOs and I'm yet to fully explore the sync possibilities. If I were starting over I might lose the Coarse Tune switch, put an attenuator over the PWM CV In and maybe crowbar in a switch and a couple of components to allow use as an 80-3 VCLFO

Hoping to get a photo sorted this week :-)

Edit: Try this...

whoop_john
unrecordings wrote:
Just finally finished my two MOTM versions this week, but it's been a little too overcast to take a photo.

I dispensed with the panel board and point to point wired everything that wasn't on the main board. All in all very easy to port back into the 5U domain and kudos to John for putting this together, they are superb VCOs and I'm yet to fully explore the sync possibilities. If I were starting over I might lose the Coarse Tune switch, put an attenuator over the PWM CV In and maybe crowbar in a switch and a couple of components to allow use as an 80-3 VCLFO

Hoping to get a photo sorted this week :-)

Edit: Try this...



Well done, that looks great. Neat, sweet and petite.

I still have PCBs. If anyone wants PCBs plus panels then Julian has them Here.
unrecordings
whoop_john wrote:
nobody wrote:
Thanks for the post. Was able to get a square wave out when I disconnected the control board and put a voltage on pin 5. I must have a short or open somewhere. More debugging to do but at least I know it works now. Thanks!


If there is not an obvious short somewhere on the control board then I would suspect the normalising on the PWM input socket. If this does not make connection then pin 5 will pull to 0v via R20. Check the adjustable voltage on the PWM pot on the normalising and signal pins of the socket to check it's getting through OK.


Come to think of it - I think the normalisation for the PWM socket on the original ETI schematic is wrong (???) Although I didn't order a panel board, it looks from the artwork like John corrected it

BTW, if anyone else is building a 5U version with panel mounted pots & jacks, i've a wiring diagram I can post
ApolloView
Hi all,

Great thread. I was just about to breadboard my CEM3340 revG chip using the old Digisound 80 VCO schematic and was planning to stripboard a design, and in the future, I planned to learn to print some PCBs.

But some clever people have done all the hard work for me. Many thanks John! applause

I'm a new Wiggler, I just joined the forum for this thread, this is my first post. So apologies if my etiquette is a little off.

Is there a LFO version too or is this over kill for an LFO?

Please, can I get 3 PCBs and panels in black?

I was planning on running from 15V and have already ordered what I thought I needed to build, did I miss the link to the BOMs somewhere?
julian
I'm not certain I have more panels, but I'll check.

If I'm to cut another batch, does anyone else need any?

John sent me a photo of a couple more boards that he has been working on, only just this morning, so.... : )
unrecordings
I think the LFO version is just a couple of component changes, so you could potentially build an LFO out of the VCO board

I've built two of these reverting to the 15V values. I'll go back to my docs and check the changes later (I've a cabinet to wax while it's still relatively warm & dry)
ApolloView
julian wrote:
I'm not certain I have more panels, but I'll check.

If I'm to cut another batch, does anyone else need any?

John sent me a photo of a couple more boards that he has been working on, only just this morning, so.... : )


Thanks Julian, appreciate it.
ApolloView
unrecordings wrote:
I think the LFO version is just a couple of component changes, so you could potentially build an LFO out of the VCO board

I've built two of these reverting to the 15V values. I'll go back to my docs and check the changes later (I've a cabinet to wax while it's still relatively warm & dry)


Yeah, it's only a few resistor value changes if I remember correctly. I was wondering what people opinions were of the use of the CEM3340 for an LFO or if there were other LFO options out there?

Can someone please point me in the direction of the BOM, I'm probably being stupid, in which case could you please point out my stupidity so I can move on.
unrecordings
I used the original Digisound BOM in the end I think, just swap the CA3080 for an LM13700, think I used a 72 instead of TL082, and ZD1 is a 10V zener

Wouldn't want to step on John's toes, if memory serves he emailed the docs after I ordered, but that's the 12V build

Edited to add: Sorry to sound so vague, but I looked at my docs and found three BOM because I only used the main board

Incidentally I posted in another thread that I just finished a little utility module to go with the 80-2. It's Ken Stone's CGS56 Pulse Buffer/Gate Converter. A very simple circuit to convert 0-10V signals to a +/-5V pulse. Ken's own pcb is a quad version, and you can use one to generate four +/-5V pulse outputs, each having a different duty cycle. I also added four simple 1uF capacitors to AC couple the 80-2 outputs if I want to

(1uF non polar seemed best, 100nf slewed the output a little, 10nF slewed it a lot - you may find 330nF/470nF/680nF is better, I was just lazy)
whoop_john
If Julian doesn't have enough PCBs I have some in stock and can order more if there is demand. I can usually get reorders within 10-14 days.

Those that want PCBs and Eurorack panels should order them together from Julian.

Who has the details for an LFO version? I'll produce a BOM.

Best wishes,

Whoop John
unrecordings
whoop_john wrote:
Who has the details for an LFO version? I'll produce a BOM.


http://www.digisound80.co.uk/digisound/modules/80-2.htm

Very last page on the ETI article linked above

You may find that just changing C7 gives a pretty good result, which could be switchable quite easily from VCO to LFO mode

Also the CGS56 I mentioned earlier naturally outputs -5V with no input. You could in theory use this as a bias voltage to patch into the VCO. Not sure if this is possible with the CEM (runs upstairs to try it...)

Edit: Yep that worked - minus 5V into V/Oct
ApolloView
Thanks,

I have the BOM from the original article and ordered all the components. I was actually more curious about the potentiometer, jack form factor and the clever pin and socket system to stack the PCBs. The pots I ordered before seeing this thread, are solder lug type with the round base, which wouldn't fit on the PCB.

I'm a little green to this. My only projects so far have been a couple of guitar pedals, and I learnt a lot while making my own 808 stripboard clone. So far I don't have any experience with Eurorack format. But I have committed to learning/designing Eurorack for all future projects.
unrecordings
I might be speaking out of turn here, but I wouldn't build a Euro format modular powered at 15V, you'll run into compatibility problems down the line...

...If that's what you intend on doing. Let us know and we can advise
whoop_john
ApolloView wrote:
Thanks,

I have the BOM from the original article and ordered all the components. I was actually more curious about the potentiometer, jack form factor and the clever pin and socket system to stack the PCBs. The pots I ordered before seeing this thread, are solder lug type with the round base, which wouldn't fit on the PCB.

I'm a little green to this. My only projects so far have been a couple of guitar pedals, and I learnt a lot while making my own 808 stripboard clone. So far I don't have any experience with Eurorack format. But I have committed to learning/designing Eurorack for all future projects.

There is a BOM with details of pots, jacks etc. at Octoginta-II BOM
ApolloView
unrecordings wrote:
I might be speaking out of turn here, but I wouldn't build a Euro format modular powered at 15V, you'll run into compatibility problems down the line...

...If that's what you intend on doing. Let us know and we can advise


Thanks for the advice, by compatibility you mean just from the power source?

Or would the output be incompatible, voltages too high?

I can totally alter my plan, if it makes more sense to start at 12V. Best foot forward and all that
ApolloView
whoop_john wrote:
ApolloView wrote:
Thanks,

I have the BOM from the original article and ordered all the components. I was actually more curious about the potentiometer, jack form factor and the clever pin and socket system to stack the PCBs. The pots I ordered before seeing this thread, are solder lug type with the round base, which wouldn't fit on the PCB.

I'm a little green to this. My only projects so far have been a couple of guitar pedals, and I learnt a lot while making my own 808 stripboard clone. So far I don't have any experience with Eurorack format. But I have committed to learning/designing Eurorack for all future projects.

There is a BOM with details of pots, jacks etc. at Octoginta-II BOM



Thanks John
unrecordings
ApolloView wrote:
unrecordings wrote:
I might be speaking out of turn here, but I wouldn't build a Euro format modular powered at 15V, you'll run into compatibility problems down the line...

...If that's what you intend on doing. Let us know and we can advise


Thanks for the advice, by compatibility you mean just from the power source?

Or would the output be incompatible, voltages too high?

I can totally alter my plan, if it makes more sense to start at 12V. Best foot forward and all that

Let's start with the Digisound it has +/-5V outputs and 0-10V outputs all powered originally from +/-15V supply rails. John's version tweaks some values so that it works on +/-12V supply rails but the VCO outputs are still the same (+/-5V and 0-10V)

You mention Eurorack which is typically a 3U high panel with +/-12V supply rails (some Eurorack has an additional +5V rail)

+/-15V systems are typically FRAC (also3U panel) or MOTM/MU/Dotcom (5U panel)

There's a graphic somewhere to illustrate this...

So while you can do what the hell you like, as your system expands, or maybe you buy/sell third party modules, you run that problem of 15V supply rails versus 12V

Just something to watch out for when designing a DIY system from scratch

Here's that graphic I thought it had power requirements so there might be another version somewhere. I you're going 15V have a look at the power thread at the top of the 5U forum

https://www.muffwiggler.com/forum/viewtopic.php?t=9323
DSC
Rock solid design of the VCO!!! Here's what I did with four of them.


Synthsense
Looking forward to listen to a demo! hyper
whoop_john
Very professional build.

I may have one or two Octoginta II PCBs left, but I am more than happy to reorder stock if there is a demand. Julian also provides lovely panels.

Whoop John

DSC wrote:
Rock solid design of the VCO!!! Here's what I did with four of them.


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