Buchla Q: Noisy & Quiet Ground

[Grant Richter]

The Noisy and Quiet grounds ran all the way back to the supplies on separate
wires and were joined at the supply terminals. Quiet ground was mostly used
as the reference for the + terminals of op-amps and carries no significant
current. Anything that switched any significant amount of current connected
to noisy ground so the IR drops wouldn't show up as signals in the audio
path.

Today they are called "Analog (quiet)" and "Digital (noisy)" grounds. They
are usually connected at the input ground terminal of the PC board. That
works fine for the most part.

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>From: "Romeo Fahl" <8brain at spiritone.com>
>To: "synthdiy" <synth-diy at node12b53.a2000.nl>
>Subject: Buchla Q: Noisy & Quiet Ground
>Date: Tue, Sep 5, 2000, 9:30 PM
>

> I've been going over some 200 series Buchla schematics and have noticed that
> most modules that use Vactrols have a "Quiet" ground in the audio path and a
> "Noisy" ground in the CV section.  I'm guessing this has something to do
> with the Vactrols, which are supposed to isolate the control voltages from
> the audio path very well....  How are the two grounds related?  Are they
> kept separate by low value resistors?  I would assume that they terminate in
> the same area of the power supply, but that's probably oversimplified.  If I
> were to build a Lo-Pass gate for example, would I get in trouble if I simply
> ran both grounds together?  Can one of you experts clarify this for me?
>
> Romeo
>