[sdiy] Oscillator question

Magnus Danielson magnus at rubidium.dyndns.org
Mon Nov 3 22:31:39 CET 2008


Antti Pitkämäki wrote:
> Hi!
> 
> A few days ago I asked about a problem on my Vox Continental II. I have an idea on how to fix it, but I still want to ask one more
 > time to be sure:
> 
> If you have analog audio oscillators that have an input for pitch modulation, and if all of the oscillators are being modulated
 > simultaneously by the same low frequency oscillator (for vibrato), 
and if some of the oscillators have much heavier (deeper)
> modulation than others as a result, can the source for this problem be in the low frequency oscillator? Or is the problem more
> likely in the audio oscillators?
> 
> Quickly thinking, it would be weird if the LFO was the source of the problem, but the whole problem of greatly varying vibrato
> depth is also quite weird, considering I have tried changing some of the components that should affect the depth, but that didn't
 > help.

Just with this information at hand I have a little to little information 
(such as schematics) to really say, but I would say that I would look 
after other problems.

I would start by looking at the power lines as a reality check. Correct 
voltages and no excess hum or noise.

While the LFO could not be ruled out, I'd check the signal from it and 
then the oscillators. One technique is to just stick a probe in there in 
the middle, and decide if the problem is there or not. If not, it is 
later down in the signal chain. If it is there, go up in the signal chain.

Also, check that you don't have a connector or cable problem.

I know it is not much, but a few things to check at least.

Cheers,
Magnus



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