[sdiy] Easy-to-interpret example of triangle VCO?

[Aaron Lanterman]

Hi there - today's lecture in ECE4803: Theory and Design of Music 
Synthesizers was on sawtooth core VCOs. I have a million other 
research-related things going on so I didn't have a lot of time to 
prepare, alas, but I think I muddled through it OK, as I had the example 
in Chamberlin work from.

On Wednesday, I'd like to talk about triangle core VCOs. I'm having more 
trouble here finding one that's clear and easy to explain - I find these 
harder to interpret.

I'm looking for a classic OTA based one (I'm going to point them to Ian's 
CMOS switch VCO for further study). I know Buchla uses triangle cores, so 
I looked at Buchla diagrams, and even though I've gotten used to reading 
them, I hit road blocks trying to interpret what he's doing in the 
discrete OTA stage (there's this JFET buffer kind of thing sitting at the 
output of the OTA, which confuses) me... I found a nice design by Jim 
Patchell:

http://www.oldcrows.net/~patchell/jp2rest/dualvco.pdf

Last Wednesday I lectured on OTAs and even showed how to do them with BJTs 
in a differential pair/mirror combination, so I could use this, but I was 
hoping for something a bit simpler even...

I also found the Bergofotron triangle VCO core (wow, that full VCO looks 
like the Mother of All VCOs):

http://hem.bredband.net/bersyn/VCO/VCO%20Buchla%20core.gif

Again, that's another discrete OTA design...

Do any simple triangle VCO schematics come to mind? Something that maybe 
uses a 3280 or something?

Oh, BTW, in case anyone is curious, I've got the first two homeworks 
posted:

http://users.ece.gatech.edu/~lanterma/ece4803/

Some of y'all make an appearance in HW #2. ;)

- Aaron

P.S. I really need to get off my duff and order the Electronotes 
collection.

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Dr. Aaron Lanterman, Asst. Prof.       Voice:  404-385-2548
School of Electrical and Comp. Eng.    Fax:    404-894-8363
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