[sdiy] Best AVAILABLE OTA for building new designs?

Fri Apr 10 20:12:25 CEST 2026

Thanks, Ben.

I resolved the power issue with two 15V-5A switching supplies from Makewell.  These things are brilliant – they don’t create noise, they run cool, and they are very small and light.  I’ll never go back to linear supplies.

Concerning the fanning out of 1 control to 48 destinations, local buffering is the key.

Concerning the mixing of up to 48 signals, the simple solution is to put each voice output through a pretty small gain so that many voices can be summed without clipping, then turn it up afterwards as necessary.  Based on the science of sound (I guess), I can play 10 or 20 or 40 keys at once, and it doesn’t sound “louder” than 1 key.  So, as long as the output signal doesn’t clip against the rails, everything is OK.

Finally, the circuitry doesn’t seem to generate much heat, except for the local buffer opamps on the control signals, and then only when their faders are fully OFF (which is when the 2164 control voltages are at a maximum, and given the less-than-5k input impedance of the 2164 control pins, this adds up to a significant amount of current, even though I’ve limited those “OFF” voltages to 3V or less).  I have purchased these cute little heat sinks to stick on top of the buffering TL072s, but I haven’t bothered yet, and they don’t seem to get too hot.  Actually, only 2 or 3 of the TL072s get warm anyway, and they don’t get that warm (certainly not too hot to touch or anything).

Finally finally, I was a little bit concerned that I was going to spend lots of time and $$$ building this thing, and that it was just going to be a big, meh, vanilla waste of space.  However, I can now report that it is actually really cool, it makes a lot of very interesting sounds, and it is an absolute blast to play.  And I only have the polyphonic core finished.  I still need to design and build the resonators, effects, etc, etc, and, of course, I still need to create a front panel and put the whole mess into a case.  I am retiring from the university at the end of this summer (and I am effectively retired as soon as I give and mark my last final exam next week), so I will have lots of time to spend doing just that.

From: Ben Stuyts <ben at stuyts.nl>
Date: Friday, April 10, 2026 at 2:44 AM
To: "Dixon, David" <david.dixon at ubc.ca>, "synth-diy at synth-diy.org" <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Best AVAILABLE OTA for building new designs?

[CAUTION: Non-UBC Email]
I see you have solved the problem :-)
https://youtu.be/lbtxMdQE64A

What a wonderful project, amaze amaze amaze!

Ben

On 11 Aug 2024, at 22:13, David G Dixon via Synth-diy <synth-diy at synth-diy.org> wrote:

I'm actually building my own version of the Korg PS-3100.  I'm calling it the Sketchy Labs DS-3100.  However, mine will have some unique features: Saw, Tri, and (fully PWMable) Pulse waveforms will be blended with faders.  Also, HP, BP, and LP filter responses will be blended with faders.  Finally, two complete and independent ADSR EGs per key (with hold functions), one for the filter and one for the VCA, rather than just one.  Also, the filter ADSR control will be bipolar for weird negative envelope effects.

Each ADSR requires one 2164, the filter and VCA together require one 2164, and the waveform and filter response faders each require one 2164, per key.  That's five 2164s per key, times 48 keys, so there will be 240 2164s just on the voicecards.  I'm presuming another 10 or so on the front panel controls for a total of 250.  It may be slightly more or slightly less.

My worries with this beast are: 1) How much heat will the circuitry generate?  I'm going to install a fan inside the case, but I don't know whether it will be sufficient, particularly since many circuit boards will be stacked about 1 cm apart.  2) Will a 3A+3A power supply be sufficient?  3) Will there be a problem mixing 48 key outputs together?  Will clipping be a problem?  Obviously, all 48 keys will never be played at the same time, but still.

This is a project that I have dreamed of doing ever since I started doing synth DIY.  I know it's stupid and ill advised, but it has been a lot of fun so far, and that's really the whole point.  It's going to take me months to build, and that's also sort of the point.  I've designed the VCOs and the voicecards, and built prototypes that I'm happy with, so once my huge 2164 order arrives, I'll start building.  I still have to design the circuitry downsteam of the voicecards, and figure out the front panel, but I'm not too worried about that.

________________________________
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Ingo Debus via Synth-diy
Sent: Sunday, August 11, 2024 2:50 AM
To: Synth DIY
Subject: Re: [sdiy] Best AVAILABLE OTA for building new designs?
[CAUTION: Non-UBC Email]

Am 10.08.2024 um 20:48 schrieb Mike Beauchamp <list at mikebeauchamp.com<mailto:list at mikebeauchamp.com>>:

My latest project is going to require about 250 2164 ICs.  That's not a problem given what I'm paying for them.  Yes, in all but the filter
I don't think I'm the only person here interested in hearing more details about your project that uses 250 quad VCA's…

A Hammond B3 style organ, where every key contact is replaced by a VCA? 2*61 keys, 9 contacts per key?

Any other ideas?

Ingo

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