SV: [sdiy] FORMANT VCO restoration and improvement

[Ingo Debus]

Am 18.10.2006 um 10:52 schrieb HA.Synth at t-online.de:

> I found the pulse with the method Paul suggested. It is about 40mV.  
> I think it
> is easier to derive sync out from an other waveform then amplifying  
> this
> pulse.

I'm curious, how did you measure this pulse, what kind of scope, and  
which probe? I can't remember having ever measured the output pulse  
of the 7413 in the Formant VCO (although I owned one many years ago),  
but I find it hard to believe that the pulse has such a low  
amplitude. Maybe the bandwidth of your probe or scope is too low? Did  
you use a 10:1 probe?

> Third Question: Any other iprovements?

I'd replace the coarse/fine potentiometer combo with something more  
practical. Perhaps a rotary switch with octaves or octaves/fifths  
steps and a pot with range of one octave.

Err, you're talking about the "old" Formant VCO from 1977, yes? Be  
carefulnot to fry the 726.


Ingo