[sdiy] VCO that goes SHARP in highest octaves??

Neil Harper metadata at gmx.com
Thu Jun 9 05:57:28 CEST 2022

On 6/8/22 23:40, Ben Bradley via Synth-diy wrote:
> Rereading the original, it seems reasonable to assume at least one
> component is different in SMT from thru hole. I'd start replacing SMT
> parts with thru hole and see what happens. I can't quite say why, but
> I'd start with Q5 and Q6, and if no change then Q1-Q2. From there I'd
> do the other active parts. After what you've already tried, this does
> not have an easily identifiable solution.

thanks ben, yeah I'm at a loss with this one and I agree that those are
the next things to look at.

Q1/Q2 (schmitt trigger) were 2N3904 in TH and MMBT3904 in SMT

Q5/Q6 (expo) were 2N2906 (handmatched) in TH and DMMT3906W (matched
pair) in SMT.

I'll start with Q5/Q6 as you said. I have used DMMT3906W as an expo pair
in another oscillator type and didn't experience the high-freq-boost
that I'm seeing in this one.

/// Neil Harper
/// Every Wave is New Until it Breaks

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