[sdiy] Thoughts on a Polyphonic Synth

[Aaron Lanterman]

On Fri, 24 Mar 2006, jure zitnik wrote:

> what bothers me the most is that it would be necessary to have an
> exponential voltage converter on each card. but i guess you can't
> avoid that huh?

Check out the SSM2164, which is four current-in curren-out gain cells 
each with its own voltage controlled response.

There's one person on the list (maybe a few) who do a lot of SSM2164 stuff 
- I've seen schematics for state-variable and four-pole filters, and also 
a sawtooth type VCO. I'm curious if it could be used as a current switch 
in a triangle-type VCO, but I haven't seen anyone try to do that.

If you think about it the SSM2164 is pretty close in 2040 in terms of 
functionality - the 2040 is voltage in instead of current in, and drives 
everything from a single expo converter unlike the four separate in the 
2164 - and the 2164 needs external op amp buffers (the datasheet makes a 
big deal about the outputs being held at virtual ground, but I don't know 
how important that is) instead of having them built in 2040 - but having 
four of them in one chip is still nice.

(Not saying the sound is similar, of course).

You could build a VCO, a SVF, and a VCA with just one chip.

- Aaron

-----------------------------------------------------------------------------

Dr. Aaron Lanterman, Asst. Prof.
and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
School of Electrical and Comp. Eng.    Fax:    404-894-8363
Georgia Institute of Technology        E-mail: lanterma at ece.gatech.edu
Mail Code 0250                         Web:    users.ece.gatech.edu/~lanterma
Atlanta, GA 30332                      Office: Centergy 5212