Polymoog Resonator (Polymoogerfooger)

[MC]

If you want the complete schemo for the resonator, the service manual is online. I don't remember the url.

Yeah, the Polymoog is a strange beast as evidenced by the +Vch virtual ground in the resonator/mode filters that is not the same potential as chassis ground or earth ground. I never did see the logic behind that, and Luce liked to develop complex circuits where a simple one would have sufficed.

[jhaible]

If you want the complete schemo for the resonator, the service manual is online. I don't remember the url.

Yeah, the Polymoog is a strange beast as evidenced by the +Vch virtual ground in the resonator/mode filters that is not the same potential as chassis ground or earth ground. I never did see the logic behind that, and Luce liked to develop complex circuits where a simple one would have sufficed.

I have the service manual - thank you!
The reason behind the +Vch, as I see it (just guessing - I haven't read the whole text of the servie manual):
(1) Keeping it separate from GND (separate connection) means keeping it clean. So the "real" (0V) GND can act like a "dirty GND" or "wastebin GND", which might make a huge difference in such a vast instrument.
(2) Raising it to 4.85V allows electronic switches to be powered from +15V and 0V. (No 30V types available at the time). You still have to divide down the signals before routing them thru a +15V/0V powered CD4016, but after dividing it down (with the lower leg of the divider at Vch, not GND!) the signal not just becomes smaller, it also becomes all-positive!
Having said that, I must add that there are other electronic switches in there, which are powered from "artificial" supply rails, like -3.1V and a positve voltage smaller than 15V, for other parts of the circuit, so the strategy isn't overly consistent.
The result of this "raised GND" (almost +5V) is a very unsymmetrical headroom. If that circuit clips, even harmonics come earlier than odd harmonics. Not sure if this sounds good or not (I'll see / hear when I've built my prototype), but that's how the original behaves. And slew limiting distortion will certainly come earlier than voltage clipping for harmonically rich signals, too!
I'll offer an option on my PCB to use a modern 30V electronic switch and a 0V GND instead, and modern opamps, too. But just as an option!

JH.

[MC]

I have the service manual - thank you!

Do you have the schematics or both volume 1 & 2 of the service manual?

Volume 1 reads like a college textbook and I haven't seen that online yet.

[jhaible]

I have the service manual - thank you!

Do you have the schematics or both volume 1 & 2 of the service manual?

Volume 1 reads like a college textbook and I haven't seen that online yet.

297 pages, yes!

http://rapidshare.com/files/247069146/a ... ual.pdf%0A

I suppose this is where I originally got it from. Just google'd for the file name. I wouldn't know how to upload these 180 MegaBytes ...

JH.

[dslocum]

I had a Polymoog long ago. It had belonged to David Sanchez. It was modified several ways by Doug Slocum. For one thing, some the LEDs were replaced with green and amber ones so that you could tell if each section was on or off while on a dark stage. That and some other mods - like routing the sample and hold to the keyboard so that each key pressed triggered a different frequency... that was sort of neat. Hmmm... can I do that on a Voyager? Sample and hold stepped once for each key press?

Actually, I did that mLED mod on two PMs for David (Sancious). Anyone know what ever became of them? Just curious.

[dougt]

Can anyone re-post the PM service manual I and II again? I'm missing part I and the link above is dead...

Thanks