DACs driving VCO(s)

[J. Larry Hendry]

> From: Tony Allgood <oakley at techrepairs.freeserve.co.uk>
> And finally, I just have to wonder just how accurate our
> series resitor chains are that sit under our favourite keyboards.

> From: Paul Schreiber <synth1 at airmail.net>
> The argument on DACs driving VCOs always centers around:
> how good is good enough?
---------snip-----------
> BUT.... you CAN hear the difference if you have 3 VCOs in
> your patch, all driven from a common CV, and you tune to
> a *zero beat* at 110Hz then try to play 880Hz. If 1 VCO
> is off about 0.4Hz you will hear that beating.
----------snip-------------
> My Kenton Pro2000 averages about 206uV error over 7
> octaves.

I did some measurements when I was making the adjustments to my MOTM-300
VCO after I completed the construction.  Zero beating was the only way to
get them "just right."  Of course, as I was doing this I discovered that my
controlling source had more error than the VCOs I was controlling.  I
started out trying to beat against a DCO in my Juno 60.  BAD idea !!  That
is not NEAR as accurate as I originally thought.

Finally I ended up using the Kenton pro-2000.  However, even that error was
apparent (zero beating across 7 octaves).  The worst of all was my
MicroMoog resistor dividing network.  It's error was about 4 times that of
the Kenton.

To dial in my tracking, I had to compare VCO to VCO using a divider on one
so I could beat the VCOs several octaves apart.  So indeed I found that the
VCO was the most accurate device in the whole system.  I certainly would
not consider anything less accurate the Kenton as acceptable to me for
multiple oscillators

> Of course, there are arguments for "musical sloppiness" 
> but I don't go down that road much. I prefer "controlled,
> added sloppiness" to "built-in sloppiness" in most cases.

AMEN !
I like to de-tune myself.  But, it should be ME causing the de-tuning, not
my gear.  I admit that I could not follow all the math that has been tossed
about.  But, I can tell you that from my own musical perspective, that the
accuracy of the 14 bits or so of the Kenton is about at my minimum
acceptable level.

Larry Hendry