Clean & dirty ground connections

[Uncle Krunkus]

Something very interesting I've discovered over the past few weeks is the idea of a clean ground (for audio chips etc) and a dirty ground (for logic chips) it stops the logic chips from contaminating the op amps with logic spikes.
To implement it on a synth you need to run a new dirty ground to every logic chip and take it right back to the main filter caps, where you have a common conection to the clean ground.
I don't know whether it is feasible (or even needed) to put this on the SL, but I thought I'd share the idea with you all just in case you didn't know about it.

[etaoin]

I must say that I hadn't heard of separate grounds before. It would be very, very tricky to connect anything if you can't connect the grounds. In your example, the grounds are still connected, albeit somewhere else. It might do something, but my guess is that it doesn't make much difference. Also, as I understand it, logic spikes are in your power lines, not in your ground.

But having separate power supplies for digital and analog stuff is pretty common. I'm building some boards from Ken Stone at the moment en he recommends a separate 'dirty' power supply for everything digital.

[Uncle Krunkus]

Yeah,
My initial thought was that it wouldn't make much difference. I definately don't know the details of it, but I want to look into it. I think the idea is that spikes from the logic chips will go down the path of least resistance which is to be soaked up by the filter caps (as they would hit them first). The separate run back to the caps would have it's own inherent capacitance as well, albiet very small, but that's fine when you're trying to take the edge off a very short transient.
I'll look into it a bit more and let you know whatever I find out.

[mosc]

If I remember correctly, the Buchla 200 Series modules had clean and dirty grounds.

[etaoin]

[etaoin]

I should say "use", as they are still in production. If you have a bit of spare cash...