[sdiy] my vco is TOO alive

[Dave Magnuson]

----- Original Message ----- 
From: "Dan Snazelle" <subjectivity at hotmail.com>
To: "sdiy" <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, December 10, 2008 2:11 PM
Subject: [sdiy] my vco is TOO alive


>
> one of my vco's, a CGS (ken stone) vco, which is being run off a +/- 
> 12volt supply and has a tempco in place, lately has been exhibiting a LOT 
> of instability. This started a few months ago and it sounds like there is 
> a gremlin inside of it that is messing with its stability.
>
> i am all for organic VCO's but this is too much. The note you are playing 
> almost always starts dipping in pitch after a few seconds.
>
> it's not that it isnt IN TUNE with itself, it is, and the last time I 
> checked i think i was getting around4 ot 5 octaves of tracking.
>
> The issue is more about WARBLE. the notes droop and have odd amounts of 
> vibrato added as i hold a note.
>
> so..my question is...what could cause a healthy VCO to start sounding like 
> it's dying?
>
>
> I have about 5 or 6 other modules running off the same PSU and none of 
> those modules are showing any of the same problems.
>
> Could it be
>
> Bad caps?
> Ripple?
> (the PSU is rated for at least .7 amps)
> Or something I cant even fathom?
>
> Up till this point, i had been very happy with this VCO and found it very 
> flexible.
> But now that i cant hold a note for too long without it dipping in 
> frequency, it doesnt work too well with my other VCO.
>
>
> ANY advice appreciated!
>
> thanks
>



Hi Dan,

I'd start simple:

jack is dirty / corroded?
Loose wire to the CV jack / tuning controls?
Bad tuning pot?

Use a voltmeter or scope on the CV summer and see what's happening. 
Also, look at the power rails with a scope

I'd also try disconnecting every other module from the power supply to see 
if the problem goes away.

Dave Magnuson