Polymoog Resonator

Being a big Numan fan and him using the Polymoog early on I crave the sound of its filter. But it’s a fairly unusual 3 band unit.

If I could built this on a Shruthi-1 board I would be happy, probably a big job though :slight_smile:

Sounds impressive though:


It’s more of a resonant EQ than a filter.

Whatever it is, it sounds great!

I had never heard this filter until just now. This is a very awesome sound processing device! I might try to start making a filter board out of this. It will require some software modifications. I was thinking something along the lines of the Dual SVF where you use the software to select the filter and the mode. You use the page button to select the filter, and the knobs to control the parameters. Seems pretty simple? Right?

The filter is one reason why you can’t really reproduce some of the polymoog sounds on other synths. The Vox Humana preset is one of the more famous ones.

It might require a slightly larger case and sliders perhaps?

The power supply looks to be the hard part, the usual +15 -15v arrangement.

Also, the Shruthi only has a few CV channels? I think you need about three for this in total, it will need one for each band, then there’s the mode selector.

If someone got it working then I’d buy one :slight_smile:

In fact, you may need up to 9 or more controls argh.

There’s a front panel design here showing all the controls:


The Polymoog resonator is not a controllable device. The pots are directly modifying stuff in the audio path - there’s no CV-controlled gain elements. There is no way to control it other than with knobs (well, OK, vactrol or digital pots might be used in place of the pots).

Supply voltage is not an issue if you can deal with lower signal levels.

I suppose it would be possible to make a circuit that did have CV inputs though? a much bigger task of course.

I had a look at the schematics, each resonator is a full-blown SVF. So you can start from the dual SVF schematics ; and adjust the resistor / caps value to reflect the change in Q range and signal levels.

You’d need to add a third SVF though.


Will that work in the same way? As far as I understand the resonator sliders adjust the gain at the given frequency.

This is a bit different to a usual filter where the knob adjusts the cut off point and the number of poles affect the gain.

On each column:

  • Low / Med / High = Cutoff frequency of the SVF
  • Gain = gain of the input signal (there must be a VCA at the input of each filter to provide this kind of attenuation)
  • Emphasis = Q of the SVF

Thanks :slight_smile:

I’m not sure how much of a difference the gain makes.

actually the gain here is a volume, and as olivier has stated somewhere (can’t remember sorry), the input volume in a resonnant filter has a huge impact, it controls the way the resonnant frequency and the original signal interact.

vox humana is a unique preset hardwired (all presets are circuit boards on polymoogs). It is on the model that does NOT have a resonator. The names are confusing but basically model one has nothing to the right on teh panel, model two has different presets and all the extra modulators resonators and 24 db low pass filter. Many fellah and gal polymoog clubbers have talked about making a vox humana for the more complex second model polymoog but the machines are physically different and to my knowledge no one has ever succeeded in getting it out of the more complex Polymoog. On person about 6-8 years ago actually had everything on teh polymoog brought out to pots. Basically the sound is the polymoog vox human processed through the MXR digital delay. If you want an interesting resonator read up on teh one in the modular 900 series Moog. The frequencies were chosen to aid in making acoutic classical string instruments. 9 filters I think.

Yeah, I’d read something about the various models. It is quite a poor synth really, but the early numan albums that use it are quite ground breaking.

Many who own them complain about the almost constant need for repair.