[sdiy] Buchla VCOs

[Grant Richter]

> The VCOs have NO straight 1V/Oct inputs! On the dual 258s, there are 2
> exponential FM ins (both
> on reversing attentuators, with a coarse AND a fine adjustment) and on the
> linear FM. just a
> straight attenuator.

Don't forget Don started designing these units in 1963. The 218, 219, and
237 keyboards which have the "black and white" layout use a 2.5 volt per
octave standard. Don patented the use of keyboards with velocity and
aftertouch for the Kimball Organ company in 1963. The 237 keyboard was a
polyphonic "black and white" keyboard with velocity and aftertouch produced
in 1968.

In the Buchla gestalt, a keyboard is a "Kinesthetic Input Port" and
specifying pitch is only a small part of it's duties. The Model 219 you have
is the most advanced of the designs, it has 38 voltage and pulse outputs,
only 4 of which concern pitch (4 voice scanning polyphonic).

The 208 Music Easel was the first modular synthesizer with patch storage, it
was produced in 1974.
> 
> I suppose the thinking was to use the combination of Coarse/Fine attenuators
> to get to 1V/Oct,
> but this is a doomed operation.

You can add pull switches to 258's that select a calibrated 1V/Oct input.
It's not really worth the effort since it's simple enough to amplify the
1V/Oct signal up to the 2.5 volt per octave Buchla standard.
> 
> The actual circuitry is a straight-forward 726 heater expo converter, a hand
> selected
> hi-frequency track resistor (about 3M) with LM741 CV mixers (ugh).
> 
> It's obvious from looking at 1/2 of the modules that Buchla loved the military
> surplus stores :)
> The boards are a hodge-podge of decent 1% RN resistors mixed with carbon comp.
> The VCO trimmers
> are not precision, but cheesy ones. Every board uses different transistors.

Modern stuff is so well engineered it's no challenge or fun to restore.
Restoring a Buchla is like restoring an Avanti or Vespa, rather than buying
a Honda off the lot. I would expect MOTM or Wiard modules to have a 100 year
lifespan or better due to the high quality of modern process controls.
Modern semiconductors can have a 1 million hour MTBF, which is 114 years.

Not true for the semiconductors Bob and Don had, impurities from primitive
process controls could cause failures in the thousands of hours.

> Trimmers are use in
> some modules (the frequency shifter has like 8 of them), but I guess I'm not
> into the 'West Coast
> Sound'.

It is true the "West Coast Sound" considers chromatic scales to be rather
boring. There is a mind set that considers Western Orchestra music as
"industrial fascism". That is why there is little emphasis on it in the
system design, there was little demand for "black and white" style keyboards
with chromatic tuning.

> I think a 1V/Oct input with a 10-turn trim would be nice.....and
> knowing Don, he probably
> did this *on purpose* to cause 'interaction' to 'find your own center of VCO
> happiness'. Whatever
> :)
> 
It takes a long time to set up because of the trimmers on the faceplate, but
I have played 4 Buchla oscillators polyphonically over a 4 octave range. It
sounded fine. The emphasis in the Buchla designs is for an Electric Music
Box which controls itself by aleatoric methods, rather than a keyboard
synthesizer. This is what Pauline Oliveros, Ramon Sender and Morton
Subotnick were specifying as design parameters. If they had wanted
traditional tunings, they would just have worked with existing orchestral
instruments.