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

Ian Fritz ijfritz at comcast.net
Thu Jun 9 08:52:58 CEST 2022

What do you have in there for a tempco resistor?


> On Jun 8, 2022, at 9:59 PM, Neil Harper via Synth-diy <synth-diy at synth-diy.org> wrote:
> 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
> https://www.onsemi.com/pdf/datasheet/mmbt3904lt1-d.pdf
> Q5/Q6 (expo) were 2N2906 (handmatched) in TH and DMMT3906W (matched
> pair) in SMT.
> https://www.diodes.com/assets/Datasheets/ds30312.pdf
> 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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