[sdiy] Polymoog resonator question

David G Dixon dixon at mail.ubc.ca
Sun Oct 14 10:18:59 CEST 2018

Hi Tim and SDIY Team,
Tonight I finally finished the resonator board, but it's useless without
controls of course, so I have just laid out a 4" x 4" panel PCB with all of
the necessary panel components on it (16 pots, 4 DPDT On-On-On switches, 2
SPDT On-On switches, and 6 jacks).  I'll try to make that tomorrow, but I
have to buy some 10k pots, as I only have 100k on hand but the resonance
circuit needs 10k, so I'll probably have to wait until Monday when I can
make a trip to Lee's in Vancouver.
Concerning the ARP Soloist filters, I have an old and very broken Soloist
sitting under a cabinet in my living room collecting dust which I acquired
from Dave Leith.  The main reason I wanted this beast was so I could play
with the filters, and this was entirely because I love the sounds that Tony
Banks obtained on those old Genesis records (Riding the Scree, Blood on the
Rooftops, etc).  It was going to be a project for last year when I was on
sabbatical, but I never got around to it.  I'm going to try to do something
with it in the next couple of months, though.
The ARP resonators are completely non-adjustable.  They are just fixed
T-filters with different component values.  There is a resonator switching
logic circuit (with NAND gates and NOT gates) which turns these resonators
off and on.  The resonators take a pulse waveform in and are arranged in
parallel.  The inverters of a 7405 (which have open-collector outputs) are
connected directly to the filters, and I believe that they ground the signal
when on to turn off the resonator, but when off, they have little or no
effect.  That's how I interpret the schematic, but it is 1:00 am and I'm not
really familiar with 7405s, so I could be misinterpreting it badly.  It's
probably some trick that every "grey eminence" knows very well, but that I'd
have to spend an hour or so trying to understand.


From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tim
Sent: Saturday, October 13, 2018 11:00 PM
To: Tom Wiltshire
Cc: synth-diy at synth-diy.org DIY
Subject: Re: [sdiy] Polymoog resonator question

Just a thought: skip the voltage control, put in digipots for the panel
controls, and make the whole thing programmable. Especially for use as a
resonator, it would be cool to dial in several acoustic instrument responses
and then be able to bring them up quickly. Okay, maybe keep voltage control
of the center frequency for nifty sweep sounds.  

And while we're talking about resonators and the ARP 2700 (over on AH), has
anybody ever found schematics for, and successfully duplicated the fixed
filter / resonator section of the ARP Soloist and Pro Soloist? Seems like
that has a history of pretty useful acoustic instrument responses. Also, has
anyone ever run a poly synth through a Soloist resonator section? Also also,
how does the Soloist switch presets? Are there a bunch of relays or
transistor circuits in there switching different resistor and cap values

Tim (on a questionable question quest) Servo

On Fri, Oct 12, 2018 at 1:52 AM Tom Wiltshire <tom at electricdruid.net> wrote:

> On 11 Oct 2018, at 18:31, Rutger Vlek <rutgervlek at gmail.com> wrote:
> That video is also my sole reason for wanting a resonator. I'd actually
hope for the resonator to also be able to track keyboard moderately well to
(optionally) maintain a fixed interval between notes played and resonant

That's possibly useful, but missing the point of a resonator, I'd say. The
idea is that we're modelling the resonances of a instrument body in some
way, and those are fixed for a given instrument. That's a key part of what
gives one instrument a different character from another.

> My suspicion is that Elhardt identified a very small number of sweet spots
that are very well tuned to the input signal as well as to the reverb on
top. I believe it's only partly thanks to the resonator, but also thanks to
his craftsmanship (or many hours of exploration) that he can make it sound
this good.

Certainly his playing is a big part of the success of that video. He takes a
"trumpet-like" sound, but then does a very good job of playing it like a
trumpet. If you'd done the "Jump" chords (for example) instead, it wouldn't
have sounded half as good.

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