[sdiy] Aries 317 VCO

[Harry Bissell]

In practice, the dual core works 'sort of' well. The sawtooth is derived from a slave current output from the expo converter and
is reset by the triangle core, Errors in the matching of the two cores show as amplitude error in the sawtooth, not bad for listening
but a problem if you use the sawtooth for something like driving a Wiard MiniWave (which needs a stable amplitude to avoid distortion, well OK... to avoid 
abnormal distortion...)

H^) harry


----- Original Message -----
From: Donald Tillman <don at till.com>
To: lanterma at ece.gatech.edu
Cc: synth-diy at dropmix.xs4all.nl
Sent: Wed, 30 Mar 2011 02:58:45 -0400 (EDT)
Subject: Re: [sdiy] Aries 317 VCO

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




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-- 
Harry Bissell & Nora Abdullah 4eva