[sdiy] VCO Tuning goals

[Dave Leith]

Hi David

It's hard to be general here but way back in the 70's I worked as a
tech and tuned a lot of analog synths. If there are no instructions I
would usually tune the 0 -  3 or 4 CV volt range with the scale trim
then tune the higher octave(s) with the hi track. I always first
earball the initial octave settings rather than use a tuner as it will
get things in the right range faster (see note below about it getting
worse with each adjustment)

Usually pin bottom note then play octaves getting higher and higher
until the upper notes are too flat to be pulled in reasonably with the
scale. I would not re-tune the VCO when returning to the pinned note
but re-adjust the tuning device. This is usually just easier and
faster. Then use the hi-track. Finally reset the basic VCO frequency
which will have shifted during the tuning process. This shouldn't
affect the scale or hi-track.

Sometimes due to circuit design one needs to pin a hi note then use
the scale to track a lower note. This would apply if each time you
make a tracking adjustment the tuning gets worse rather then better.
(I.e. an ARP pins lower and I believe the Mini Moog is reverse)

For a tuning device I use a Yamaha PT4 which is a very accurate strobe
tuner made for tuning acoustic pianos.

Dave

On 10/1/09, David Ingebretsen <dingebre at 3dphysics.net> wrote:
> Ian,
>
>  Thanks for the suggestion. I know there are many designs out there and have
>  read the information on your site and looked at your designs as well, very
>  nice.
>
>  Do you have any suggestions for my question though? I have several different
>  oscillators, each with different features and behavior. Some better
>  tracking, some less which is fine. I don't necessarily always want dead
>  accurate tracking. My question was really meant to be more to the general
>  "best" way to approach tuning to get the most musically useful VCO.
>
>  Thanks
>
>
>  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
>
>
>
>
>
> ~~ -----Original Message-----
>  ~~ From: Ian Fritz [mailto:ijfritz at comcast.net]
>  ~~ Sent: Thursday, October 01, 2009 4:02 PM
>  ~~ To: David Ingebretsen; 'SDIY diy'
>  ~~ Subject: Re: [sdiy] VCO Tuning goals
>  ~~
>  ~~ 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
>  ~~ >
>  ~~ >
>  ~~ >_______________________________________________
>  ~~ >Synth-diy mailing list
>  ~~ >Synth-diy at dropmix.xs4all.nl
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>
>
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