[sdiy] Tune VCO

[Scott]

Since you are the only one who replied, it must be easier than I am
making it.  Any CGS vco owners please chime in about how much you should
expect to turn the trimmer to notice a change (I understand it will be
small turns at the end for fine tuning, but for noticeable changes, is
it a few twists or something?), and where it usually ends up..  (towards
the end or middle of the trimmer)
This VCO does have the trimmer tune it to C after it's in tune.  I have
a couple that do have it, and a couple that don't.  On the ones w/out
it, the tune knob on front just isn't dead center when it's tuned in,
but they work fine.

More specifically the problems I have is that I can tune one octave
apart to be exactly one volt apart, but then further down the range it
is off.  Then I can  also tune 6v apart to be exactly 6 octaves higher,
but then some of the notes in the middle drift away from tune.

What I do is as you said, tune it one octave apart, then jump up to
three, then six, and its lost.  If I can get from 0 to 6 in tune, the
middle is gone.

Am I doing something wrong??  
I press a low C, then tune that in w/ the tune pot on front, then I go
to a higher note and get that tuned to what it should be w/ the trimmer,
then I go back to the low C, and tune that w/ the pot on front, then to
the high C and tune that again w/ the trimmer.  Eventually they bounce
back and forth, needed smaller adjustments until I don't need to change
any trimmers to go from a low C to a high C.  YAY..  until I play middle
C and it's out of tune!
If I tune in only a few octaves, I can bring that set of octaves up or
down w/ the tune knob, and they all work fine.  Im just trying to get a
larger range of octaves in tune. (I'm playing around w/ sample hold, and
quantizers.. and yes the note quantizer is putting out exactly what
voltage it should for each note)

Thanks again

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Paul Perry
Sent: Monday, July 02, 2007 2:21 AM
To: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Tune VCO

One really should have TWO adjustments for a VCO,
One to make the frequency double for each one volt increase (that's the
octave per volt) 
And another to make sure that the borttom C is at zero volts.

If you have only one control, then I don't see how it can be tuned
exactly!

But if you DO have two trimmers, then the key is to adjust the oct/v
trim so
that moving from the middle C to the next higher C gives exactly one
octave.

Then, fiddle with the other one until theCs really ARE C's.

You MIGHT have to repeat the procedure a couple of times.. but it should
converge to perfection. If not, there is a problem somewhere..

Paul Perry Melbourne Australia

I

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