[sdiy] my vco is TOO alive

[Dave Magnuson]

Hi Dan,

If you're using the scope on the power rails, you want to see an absolutely 
flat line.  Any twitching, modulation, glitches, etc will effect the VCO 
pitch.

You'll want to try fairly high magnification and a variety of sweep times. 
Remember that your voltage rails might be modulationg slowly (from an LFO's 
current consumption) or quickly (a brief voltage drop during a trigger 
pulse).   This means there's no ideal sweep frequency to use (Try them 
all!).

As another list member mentioned, a voltmeter will work great for the slow 
fluctuations, and an analog meter would work fine for seeing spikes.

I wish my old analog meter didn't croak... I really miss not having one, 
they're great for things like this.

Dave Magnuson

----- Original Message ----- 
From: "Dan Snazelle" <subjectivity at hotmail.com>
To: <kingravine at comcast.net>; "sdiy" <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, December 11, 2008 12:16 AM
Subject: RE: [sdiy] my vco is TOO alive



thanks for the great advice

this might be a good time to get more used to my scope

let me ask...i am still VERY new at using my scope.

what am i looking for ideally on the power rails? and what sort of settings 
are good for this?

in the last year i have been so busy that my scope hasnt seen nearly as much 
use as i would like and
i am still a bit unsure of it at times

thanks

--------------------------------------------
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> From: KingRavine at comcast.net
> To: subjectivity at hotmail.com; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] my vco is TOO alive
> Date: Wed, 10 Dec 2008 17:57:20 -0500
>
> ----- Original Message ----- 
> From: "Dan Snazelle"
> To: "sdiy"
> 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
>