Decoupling Caps on Power Rails

Broadwave · Posted: Sat Jan 22, 2011 2:49 am Post subject: Decoupling Caps on Power Rails

In the excitement that all my modules actually work, I've ignored the fact that I'm getting LFO and Envelope modulation breakthrough on my VCO's, even though they're not patched in... which is now becoming annoying.

The main PSU is well smoothed, but even if I'm only running one VCO and one LFO, I'm still getting a very, very slight modulation on the VCO output.

All my individual module power rails are decoupled with a 10uf elec cap (most of Ray Wilson's circuits use this, so I presumed it would be ok), but I'm wondering if it's enough, as I noticed that the original circuit I have for the Korg LFO is decoupled with a 100uf cap followed by a 100n poly.

Is there a cure for my woes?

Andy.

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

Hello,

What oscillators do you listen the modulation?
What LFOs or envelopes modulate the VCO's?
What power supply are u using?

Could you check with a oscilloscope the positive and negative rails? In which of them is present the modulating signal?

LektroiD · Posted: Sat Jan 22, 2011 5:23 pm Post subject:

I had the same problem, it turned out the PSU just couldn't cope with the draw all the circuits were pulling from it.. try disconnecting a couple of hungrier modules and the problem should subside. If this is the case, a second supply is needed.

frijitz