Cap Q's

[tomg]

On 19-Nov-98, Andrew Schrock wrote:
>All, 

>I finally have the time to finish up my tomg-design VCO-2a's. They tune
>and scale ok, but one problem I'm having is that when an ADSR fires (for
>example) it sets my VCO off a bit, likewise when I feed the VCO into a
>VCF the pitch goes down a couple semitones. The LFO's don't seem to affect 
>them at all... I don't really have any regulation on the modules
>themselves, although I probably should. Would bypass caps help me out? 

>Also, my LFO's are ASM-1 design. I'm having a bit of trouble getting the
>period as long as I would like... it doesn't seem to want to go past maybe
>6Hz or so. Perhaps a different type of cap would help? I think I'm using
>10uF tantalums. 

>Thanks, 
>Andrew

It sounds like you need to add a resistor and cap to the adsr +V
to provide a little reserve.


+V ------/\/\/\----+--> adsr
                   | +
           100    ---
                  ---
                   |
                   |1OO
                  ---
                   -

Bypassing the VCO is not a bad idea 10uf/35v is ok but use 
standard electrolytics, I have found too many tantalums 
shorted on supply lines. 

The ideal would be to bypass every single IC. This is a 
good idea for just about everything that uses op-amps of 
any kind. I should do it more often.


+V ------/\/\/\----+--> IC + pin
                   | 
           100    ---
                  ---
                   |
                   |0.1
                  ---
                   -
-V ------/\/\/\----+--> IC - pin 
                   | 
           100    ---
                  ---
                   |
                   |0.1
                  ---
                   -



-tg