[sdiy] VCO Tuning goals

[Ian Fritz]

If you used an accurate VCO to start with you wouldn't need to ask these 
questions.  I have several designs that track to better than 0.1% up to 
30kHz - 40kHz.  The largest error is always in the top octave. These 
designs are freely available.

Ian


At 01:07 PM 10/1/2009, David Ingebretsen wrote:
>In brief, I just finished building a trio of MOTM 300 ultra VCO's into a
>Frac Panel
>
>http://www.xmission.com/~dingebre/page8.html
>
>As I have been tuning them, I have a question on the concept of tuning a
>VCO.
>
>I understand all too well the scale will always have errors, and my
>understanding is that an error of +/- 0.2% in the frequency is likely not
>detectable, BUT... as one plays, it seems most successive notes are within
>the same octave and often within a few notes. The question then is:
>
>Is it more important to have better accuracy octave to adjacent octave or
>between 4, 5, or more octaves? That is, when I tune the oscillators, should
>I be more worried about a 0.2% difference between C0 and C1 or C2 and C3
>than between C0 and C5? I hope this makes sense.
>
>I've been making a chart, and have been playing with Paul Haneberg's high
>frequency trim modification
>
>http://www.wiseguysynth.com/larry/mods/VCO_track.htm
>
>or
>
>http://dragonflyalley.com/images/MOTM300/VCO_track.pdf
>
>(but I am using a multi-turn trimmer in series with a fixed 1M resistor
>instead of swapping resistors).
>
>I've noticed there is some interesting interaction between the scale and
>high frequency trim and I just want to make sure I'm approaching the tuning
>in the best musical sense. I'm curious musically/theoretically if it is
>better to worry about the error between several octaves and let the note to
>note difference be what it is, or work on minimizing the "octave to adjacent
>octave"/"note to note" error. Reducing the high frequency error between, say
>C0 and C5, increases the inter-octave error between C1 and C2, or C3 and C4
>somewhat.
>
>The accuracy of the 300 makes some of this argument moot, but I am curious
>about the whole zen of VCO tuning.
>
>David
>
>David M. Ingebretsen M.S., M.E.
>Collision Forensics & Engineering, Inc.
>2469 East Fort Union Blvd. STE 114
>Salt Lake City, UT 84121
>www.CFandE.com
>
>801 733-5458 Office
>801 842-5451 Cell
>
>dingebre at CFandE.com
>dingebre at 3dphysics.net
>
>
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