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

Mike Bryant mbryant at futurehorizons.com
Thu Jun 16 03:04:17 CEST 2022

I can't remember the original details or the circuit, but have you tried replacing whatever creates the exponential conversion ?    It may be the gain of it changes at higher input voltages more than any correction circuitry allows for.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Neil Harper via Synth-diy
Sent: 16 June 2022 01:32
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] VCO that goes SHARP in highest octaves??

On 6/15/22 09:48, Michael E Caloroso via Synth-diy wrote:
> Just a wild shot - did you check for oscillation on the line that 
> supplies bias for high frequency compensation?

I scoped the output of IC2b and didn't see any oscillation, I also completely disconnected the HF compensation (removing D1) and didn't see any change in the problem.

I also replaced the reference voltage source (the -15V going through R43
(1.5M) with a -5V reference voltage going through a 470k resistor.
Scoping the -5V reference and I don't see any oscillation happening there either.

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

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