[sdiy] SSM2164 or THAT2180 as current switch in triangle core VCO?

[jhaible at debitel.net]

I tried a THAT VCA in a QVCO:
http://www.oldcrows.net/%7Ejhaible/matrix_fx/jh_ts_qvco_idea.pdf

Actually, no switching here (sine core, no triangle core), but 
I ran into something that applies to a triangle core as well,
and can easily be overlooked (At least I overlooked it.):

Even though you can apply a CV that is positive or negative (speaking
of the difference between the two control pins), only the negative
range will work as intended.
Why?
In a VCA application, a gain >1 makes sense to bring up a small
input signal. But in a VCO, when your input signal is close to maximum,
a gain >1 means the chip simply can't provide the current it should
theoretically. Again, in a VCA you would _notice_ this immediately
(overdriven output stage), but with an integrator connected there
it's not so obvious.

JH.



> 
> Anyone tried either in place of the usual matched pair expo converter/OTA 
> combo?
> 
> (I'm coming up with ideas for suggested student project, which will 
> basically be along the lines of "try something no one has done before.")
> 
> - Aaron
> 
> -----------------------------------------------------------------------------
> 
> Dr. Aaron Lanterman, Asst. 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
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