T.Henry's VCO Deluxe tuning

[Jim Johnson]

I can't comment on the specifics of the circuit you're working with, but I
can tell you roughly what you're doing wrong.

Tuning an exponential oscillator is an iterative process involving two
trimpots - one for the scale, and one for the base or offset value.
Essentially, the procedure goes like this:

1) You'll need a solid pitch source - either an oscillator that you know is
calibrated, or or another instrument.

2) Listening only to the oscillator you are trying to tune, play octaves on
the keyboard and adjust the v/octave trimpot so that you get approximately
a one octave change for each octave on the keyboard.

3) Play the same low note on both instruments, and use the "offset" or
"base" trimpot to bring them in tune
4) Now play a high note on both instruments, and use the "scale" or "v/oct"
trimpot to bring them in tune.

5) Repeat steps 3 to 4 until done. Garnish with chopped parsley and serve!

BTW - I haven't heard of this circuit. Where'd you get it?

Jim Johnson 
Metaphoric Software
-------------------
Makers of Techno Toys
Software for Electronic Music
http://www.technotoys.com
info at technotoys.com


*********** REPLY SEPARATOR ***********

On 4/21/98, at 5:03 PM, JBaker  wrote: 

>ok, so I tweaked the V/Octave trimpot on the VCO and the DAC calibration
pot on
>the Paia MIDI-CV8 and the first VCO is in tune...then I trimmed the
V/Octave
>trimpot on the second VCO so that the two VCO's were in tune (at a single
>pitch).  I was hoping to hear a perfectly intoned output from both VCO's
for the
>entire range of the MIDI keyboard, but no dice.  The second VCO doesn't
stay
>tempered like the first, so instead of getting that fat dual oscillator
sound I
>get something vaguely remiscent of looney tunes.  Suggestions??
>
>speedy replies encouraged (senior project due Thursday)
>
>thanks,
>Jeff