[sdiy] Circon Controller questions (Moog's circuit)

[Mike Beauchamp]

Hey All,

I've recently built the Circon controller as described on Wendy
Carlos' page (just the pitch portion):
http://www.wendycarlos.com/circon.html

This was origionally designed by Bob Moog.
Bob's description:
http://www.wendycarlos.com/other/BMCircLetter.jpg
Schematic:
http://www.wendycarlos.com/other/BMCircCircuit.jpg

I changed the bottom part (labelled Voltage Source for Min) a bit, so
that it is just a potentiometer connected between GND and +15V with
the wiper going into an Opamp setup as a voltage follower. I'm pretty
much a noob, and this was simpler for me to understand.

So I figure my setup is basically Bob's "temperature controlled
current source" using the 2 transistors as the max voltage. Then my
part as described as the min voltage. The pot that I spin to "play"
the circon sits inbetween and goes to another opamp setup as a voltage
follower for a buffer before going to my VCO.

Here's a schematic of the circuit I made. Bear in mind, this took
countless hours to meticulously illustrate in photoshop:
http://mikebeauchamp.com/dump/circonish.gif

I have a few questions about this circuit.. the way I have it setup,
is this a bad?

Also, is there any recommendations maybe you guys could make that
would improve the circuit that Bob Moog has designed here? Stability
is very important here.. Is Bob's "temperature controlled current
source" the best way of doing this?

Ideally, I'd like to set my "low" and "high" adjustments once only
with trimpots.. so the range of my "frequency pot" is the way I want
it. Then I'd like it to be pretty much accurate, with the only
adjustment necessary being the tuning of the actual VCO.

Also, maybe some people on this list have built this type of
controller already? I just want a really playable portamento interface
using a pot.. and ideally be able to select the low and high range of
it (or the scale and tuning) once only and have it be accurate.

Thanks in advance!


-- 
Mike Beauchamp