SV: [sdiy] FORMANT VCO restoration and improvement

[Scott Gravenhorst]

HA.Synth at t-online.de wrote:
>Hallo Ingo,
>
>wer "misst misst Mist" Sorry don't know it in english. Anyone?

If that's German, I think the noun Mist means "manure"...


>Am Mittwoch, 18. Oktober 2006 20:05 schrieb 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?
>
>You are right here.
>
>I have had a second look today. I think i have reached the limit of my 
>equipment. I use a dual channel 15MHz scope from Metrix, build 1984. Probes 
>from Monacor and Velmanns.
>
>Now i can see the pulse. Nearly 3,5 V at the falling edge (output VCO).
>
>Method:
>VCO pitch 24kHz. Synced Channel A with the regular output of the VCO. saw or 
>square. Time base set to 2uS. Now I can see the pulse thin as an hair. No 
>chance to measure the width (time). 
>
>Thanks to make me think again!
>
>
>>
>> > 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.
>
>Already done, works great. 
>>
>> Err, you're talking about the "old" Formant VCO from 1977, yes? Be
>> carefulnot to fry the 726.
>
>Yes I try.
>>
>>
>> Ingo
>
>
>Harald
>

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