[sdiy] Aries 317 VCO

[Donald Tillman]

On Mar 29, 2011, at 11:01 PM, <lanterma at ece.gatech.edu> wrote:

> See here: http://synthfool.com/docs/Aries/AR317s.gif
> 
> It's pretty interesting! It looks like it has a triangle core, with a 3080 OTA dumping current into a cap - but it gets kind of weird from there. There's a second OTA and a weird NPN/PNP (Q5/Q6) pair that I, uhm, think is acting as a comparator, but I'm not sure. 
> 
> Has anyone dug into this? Does it have pros and cons?


Hey Aaron,

It's arguably a dual core, a triangle main core and a second sawtooth core sync'd to the triangle. 

U2 is the bipolar current drive for the triangle core, U4/Q5/Q6 is the triangle core comparator, which also triggers Q7/Q8, the reset circuit for the sawtooth.

It has the advantages of a triangle core (better tuning because there's no retrace, and you don't have to derive the triangle waveform from a sawtooth) and at the same time he doesn't have to derive a sawtooth from a triangle and deal with a glitch at the zero crossing.

   -- Don

--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com