[sdiy] THAT VCAs for VCOs? (was: Hopf bifurcation VCOs)

[jhaible at debitel.net]

Zitat von Ian Fritz <ijfritz at earthlink.net>:

> Don't know yet.  I'll try to have a look today.  There will be offset 
> issues, as usual with OTA-based circuits.  My present circuit has a small 
> offset on one of the outputs.  The OTA's have been trimmed, but for another 
> application; I just rewired that to make the quad osc.

I wonder if these THAT (formerly DBX) VCAs would be a good solution here.
>From the data, they should. The Blackmer gain cell also puts out a current
like our standard OTAs, but with its internal linearity doesn't require
small input voltages which so much magnify the offset voltage of OTAs.
I guess that will be the next thing I'll try, if it's possible to make a
good VCO (or QVCO) with these. The expo function is built-in. which is
an advantage in VCA applications, but might make accurate tracking, and HF
tacking, in a VCO harder.

Has anybody on the list tried a THAT/dbx/Blackmer cell for VCOs already?

A QVCO from built from two THAT2180's and three AD633's might give decent
results even without trimpots, except for V/Oct tracking.

JH.


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