[sdiy] Polyfusion LFO with voltage controlled start point

[Magnus Danielson]

From: mark verbos <a0284520 at addcom.de>
Subject: [sdiy] Polyfusion LFO with voltage controlled start point
Date: Fri, 09 Feb 2001 16:40:34 +0100

> Hi!
> 
> I just finished the Polyfusion 2003 LFO circuitboard I bought from Bruce
> Duncan 3 years ago. It is cool because it has a control for the start
> time. So when you send a trigger to synch it it will reset to the part
> of the cycle that you set the start time control to. Since Bruce didn't
> think it was important to throw in a schematic I strted to wonder. Does
> anyone know what is actually happening in there?  I would love to see
> the schematic. I have tried to reverse engineer it, but just seeing the
> real thing would be much nicer.
> 
> It is cool as both an LFO and an actual oscillator, a totally different
> kind of modulation (sweeping the start time while the oscillator is
> slaved I mean). Maybe if it used a matched transistor pair and a tempco
> it would be a contender for the coolest oscillator award. I guess the
> Buchlas still hold the tittle.

Hmm... I have been thinking about this problem and come to think of
it, it sure does provide some interesting features. First of all, you
actually trigger your oscillator... oh dear! ;)

Well, taking just an ordinary oscillator core, precharging the
capacitor should be easy enougth to do. You could use a CA3080 as a
switchable precharging enforcer. The CA3080 would when started be
"open" and the initial value CV would go straight thru to the cap.
Then, at the trigg, the CA3080 would be closed, and the oscillation
could be allowed to run from there. You should be able to do this
trick on several diffrent oscillator cores.

Hmm... doesn't sound too difficult.

Cheers,
Magnus