[sdiy] Re: [AH] Buchla VCOs

[Magnus Danielson]

From: "Paul Schreiber" <synth1 at airmail.net>
Subject: [AH] Buchla VCOs
Date: Sat, 7 Jun 2003 12:19:33 -0500

Hi Paul,

> OK, I'm not a Buchla expert, but I can see an immediate reason it was hard to
> do "Carlos music" on them.
> 
> 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.
> 
> I suppose the thinking was to use the combination of Coarse/Fine attenuators
> to get to 1V/Oct, but this is a doomed operation.

I agree! It's doomed.

> 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).

A'la mode at the time, yes... ;O)

> It's obvious from looking at 1/2 of the modules that Buchla loved the
> military surplus stores :)

Good boy! ;O)

> 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.

Sounds like a real hippie synth (sorry, could not avoid it)!

> 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'.

The trimmers for the frequency shifter is for the dome-filter.

> 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 :)

;O)

> I would have use a switched pot, so that you had a choice of fixed or
> variable tracking. Guess they were out that day when he went shopping :)

That where the day ;O)

Cheers,
Magnus - just back from Budapest this afternoon