SVF calibration help

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mmeixner
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SVF calibration help

Post by mmeixner » Tue Oct 02, 2018 2:39 pm

just finishing quite a lot of Oakley modules - each and everyone working first time, thanks to the great PCBs and thorough building instructions.

Now calibrating the SVF's V/Oct I can't reach 1 octave per volt (this is measuring with a precision lab supply and oscilloscope). I get something around 1050 cents max. Should I try to exchange R29 (120k) for something different?

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Synthbuilder
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Post by Synthbuilder » Tue Oct 02, 2018 4:06 pm

Try changing R29 to 130K. Someone else found the same problem as you are getting and reported it here on the forum a few months ago. I have since changed the Builder's Guide for the SVF (and COTA) to reflect this change.

It is odd that it has taken over ten years for this problem to have come to light. I think it could be that the nominal resistance of the temp co resistors has changed. Which is odd considering it is the same part number I have always sold. I really must investigate this further but 130K is the value that seems to work so that's what I'm recommending now.

Tony

mmeixner
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Post by mmeixner » Wed Oct 03, 2018 2:06 am

Synthbuilder wrote:Try changing R29 to 130K. [...]

Tony
Thanks!
Odd thing with the part number, yes - but as long as it's easily solvable like that ...



(if this is good English, or more Germanglish...)

Schlumpfhut
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Post by Schlumpfhut » Wed Oct 03, 2018 7:58 am

I had a similar problem when trying to calibrate the tracking of my SVF. Solved it by inverting the routine, meaning start at the higher pitch and then go down one octave and adjust the trimmer. No problem ever since.

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