[sdiy] help with clicks on VCA

[Tom Wiltshire]

Dan,

Thinking formally for a minute, tremolo is amplitude modulation, so  
it'll make sidebands. Any high frequency content in the modulating  
signal is going to show up in the audio. That'll include abrupt  
transitions in any wave. A ramp wave at 1Hz has a 200th harmonic at  
200Hz. So adding some filtering on the CV input might help - Slewing  
the control waveform is one way.

In practice, though, I doubt that's what's going on. I rather suspect  
that the problem is with the LFO, not the VCA. The fact the problem  
remains with two different VCA designs might also point in this  
direction. Comparators can generate a good 'click' when they switch,  
and this can get coupled through to the power rails. Does the LFO  
include a comparator? Is the Tremolo's power supply well isolated?  
decoupled? Have you tried sending the VCA a control signal from a  
unit with an independent power supply? (so they only share a ground  
and CV line).

I'd stick 100R resistors followed by whacking great capacitors in  
both rails of the VCAs power supply to filter any noise there out. If  
that cures the problem, then you can try some more calculated and  
careful approach.

It is possible to build a quiet tremolo, so don't give up hope.

Regards,
Tom

On 17 Aug 2009, at 13:11, Dan Snazelle wrote:

>
> it happens with square waves too
>
> even with saws
>
> from what i have been reading this is a very common problem with  
> tremolos
>
>
> thanks
>