[sdiy] Sic Transit OTA Mundi

[Harry Bissell Jr]

--- Antti Huovilainen <ajhuovil at cc.hut.fi> wrote:

> What are the main differences in the OTA core
> between 3280 and 
> 3080/13700/5517? (ignoring buffers etc)
> 
> Less CV feedthrough? Distortion?

13600 - Dual OTA with linearizing diodes and
controlled impedance buffer.  Good buffer performance
at low bias levels, but a rapid change in bias could
feed through

NE5517 - Similar to 13600 with a different buffer
scheme... current mirror from Gm bias drives the
buffer.  I saw little difference from the 13600
in evaluation.  I'd consider it a sub.  I did get
some odd bleedtrhough when it should have been cut
off. Not enough to consider it a serious bug, just a
curiousity.

13700 - Dual OTA with linearizing diodes and fixed
impedance buffer. Less CV bleedthrough in the buffer
for fast control signals, poor buffer performance at
really low Gm biases.

CA3080 - The classic single OTA with no diodes. 

CA3280 - Dual OTA with linearizing diodes fed from an
internal current source. No buffers. Very low offset
variation with Gm bias. Can use this as a control VCA
feeding mod signals to a VCO without tuning shifts
with
mod level... any other critical applications. Makes
the best VCA (low distortion and almost zero control
feedthrough of level shift.

H^) harry