[sdiy] LFO's showing up on VCO

Simon Brouwer simon.oo.o at xs4all.nl
Wed Nov 12 00:09:27 CET 2008


I'd look for varying current into the ground. Even though the ground 
conductor has a small resistance, it is not zero, so current running 
across it will result in a voltage difference. Thus the ground of the 
circuit that generates your CV and that of the VCO's may not be at 
exactly the same potential. Assuming no current in the CV conductor, the 
potential of the CV will be the same on both sides. So the CV that the 
VCO sees (referenced to its ground) will include the error voltage.

Does it help if you disconnect R515 and R615? These would inject about 
2mA p/p of square LFO output into the ground.


Dan Snazelle schreef:
> I am not sure of the technical name for the problem of circuits (lfo's especially) influencing your Main VCO'/'s, but it's a problem i have had before. The difference this time is I am working with a pcb (asm2) that 
> has all of the circuits on ONE board, utilizing a single PSU but with a +/-10 v reference for the VCO. ( i had hoped the reference would get rid of this sort of problem)
>
> Now that all the circuits are working, i am finding myself pulling out my hair due to HEARING the other periodic circuits making my VCO output unstable. (even with the CV's disconnected, i can still hear them messing with the waveform)
>
> at this point i am not willing to add a second power supply to this board and i dont think it would fit anyway.
>
> SO...i am looking for ideas. 
> I tried removing the LEDS attached to the LFO  but that didnt seem to help. 
> HOWEVER i am wondering if giving the LEDS their own ground (straight to the PSU) would help.
>
>
>
>
>
> I am using a power one +/- 15 volt supply
>
> here is the link to the circuits:
> http://www.elby-designs.com/asm-2/asm2.htm
>
> thanks so much
>
>
>
>
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>   


-- 
Vriendelijke groet, 
Simon Brouwer. 

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