To: Aaron Lanterman lanterma@ece.gatech.edu,
From: Donald Tillman don@till.com,
cc: synth-diy@dropmix.xs4all.nl,
Subject: Re: [sdiy] Buchla 144 dual square wave oscillator
Date: Fri, 03 Jul 2009 15:28:53 -0700

---

> From: Aaron Lanterman <lanterma@ece.gatech.edu>
> Date: Fri, 3 Jul 2009 16:47:14 -0400
>
> This is a really curious circuit:
>
> http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_1440_1_200.jpg200.jpg

>
> Any inklings on how this works?

Oh man, that is strange! Okay, here goes...

Q1 is a temp compensated reference of sorts for Q2.

Q2 is an exponential converter. The Q2 collector connection to the
positive rail is an error, and instead it sinks current from C3 to
control the oscillator frequency.

C3 is the cap for the oscillator. There will be a descending sawtooth
voltage here.

Q6/Q7 (over on the right aways, "are you following me camera guy?") is
a source follower with a beefup transistor.

Q5/Q4/Q3 performs the reset. R18 sets the trigger point, Q5 conducts
at the trigger point, Q4 feeds that to Q3 which resets C3, up to
positive. C5 provides Schmitt action.

The reset pulse is coupled via C6 to an olde world flip flop (Q8 and
Q9).

Q10 buffers that square wave.

Q11 creates balanced push-pull versions of the AM input. Diodes
CR4/CR5 clamp the signal level of the square wave to those +/- points.

R46 is a hack to mix in a little of the inverse square to increase the
dynamic range of the AM.

Q12 is an emitter follower.

Whew!

-- Don

--
Don Tillman
Palo Alto, California
don@till.com
http://www.till.comBR> _______________________________________________
Synth-diy mailing list
Synth-diy@dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diyBR>