[sdiy] Polymoog Resonator - no-pots equivalent

Tom Wiltshire tom at electricdruid.net
Mon Aug 21 19:46:07 CEST 2017

Hi Steve,

Yes, three multimode filters would be the same as the PolyMoog resonator. That’s what it is:


Note that the schematic shows us that the filters are state-variable filters (which we’d guessed anyway because of the HP, BP, and LP outputs) and that they’re *not* VCFs. They’re just based on op-amps. You also mention the slopes. A 12dB SVF has 6dB slopes for the BP output. That’s normal, since that’s a 2-pole bandpass filter, and it’s a 2-pole filter. The way I think about it is that you need to filter off both the low and the high frequencies, so you have to share the poles out to do the job!

The Moog schematic is about as simple as such a thing could get, since it is pretty much just the three SVFs joined together. Personally I don’t like the way you have to change the response of all the filters together instead of individually, but that would be easy to change. Compare with this schematic:


Obviously you could go wild with this. Some years ago I built SVF+VCA modules around the 2164. This would be perfect for this, since you get a 2-pole VCF with VC resonance and a VCA all on the one chip.


I don’t seem to have the schematic online, but ask me if you’re interested.


       Electric Druid
Synth & Stompbox DIY

> On 21 Aug 2017, at 17:16, Steve <sleepy_dog at gmx.de> wrote:
> Hey experienced SDIYers,
> say, would slapping together 3 {VCA, multi-mode VCF 12 dB/oct with Q control} combos be the functional equivalent of the Moog Resonator? (with modified VCF control ranges, limited to 1 of those 3 bands each)
> Although I faintly remember some of those multi mode VCFs having only 6 dB/oct slope on BP. Maybe not those. Are there designs with the same slope for all, or is this a general feature of such VCFs?
> My goal is to make something that can shape sounds similarly to the Moog thing, as demo'ed on YT by some guy enhancing vocal and brass sounds.
> https://www.youtube.com/watch?v=_XUiJi5153Y
> But in a much smaller box, without the battalion of pots.
> I thought about just taking J.Haible's schematic and replacing all the pots with MCP41HV digipots, but that'd be 14 (some are stereo), a bit expensive *and* wiper noise, that doesn't taste well together ;)
> - Steve
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy

More information about the Synth-diy mailing list