[sdiy] New VCO... maybe...

Aaron B. aaron at zadzmo.org
Thu Dec 10 00:19:54 CET 2020

On Wed, 9 Dec 2020 22:56:22 +0100
Roman Sowa <modular at go2.pl> wrote:

> I haven't used that phrase for long, so here it goes:
> Comments welcome!

I've got something similar in my notes: I used an MCP602 wired as a
comparator as well. I only used one opamp section; the integrator was
just a capacitor to ground, fed by a current source, discharged through
a 2n7000. No waveshaping as I was intending to drive a digital shift
register circuit with it.

Messy hand-drawn schematic here: https://ircz.us/AdY3JZw1

I abandoned it as I had a spare LM13700 section and used a simple
triangle core design with that instead, which performed much better.
The thought of using the other half of the MCP602 as an integrator
never occured to me.

In general, I like the idea of 5 volt oscillator cores. Build it around
it's own TO-92 voltage regulator and basically eliminate power supply
tuning and coupling issues, then have a TL072 or whatever scale the
waveform to normal modular levels.

Also the trapezoid generator mentioned on the page but not in the
email: those are underrated waveshapers. Very musical, interesting
timbres; low parts count; easily made voltage controllable with a VCA.
They work equally well with sawtooth waves too.

Aaron B. <aaron at zadzmo.org>

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