[sdiy] IN your mind, what is ....

[Steve Ridley]

> So where does one find a nice description of the magic things
> it does?  I have tube, but have never used one.  Now I'm not
> sure why I would want to, given the low gain (compared to an
> opamp) and low input impedance (input signal current eater) ?
>  I've got the National data sheet which has a ton of circuit
> examples in it, but they like to use it as an opamp in most
> of them.

Start with Nat. Semiconductors application note AN-72.  

Then dig out the vintage Serge and PAiA schematics.  Most of 
the first generation Serge modules (1973 - 75) used them with
varying degrees of success (the waveshaper is good, the VCO 
is pants).   Also dig out US patent 4,306,480 for an explanation
of the Serge waveshaper.

It might help you get your head around the circuits if you redraw
them as a current mirror on the front of an inverting amp, like in
the Serge patent.

My own vote for my favourite IC is the THAT/dBx 2080 VCA.
Great audio performance, exponential control over a huge range
(sadly not temperature compensated) and most importantly still
widely used in current pro audio equipment - so I don't expect 
them to go out of production in the near future.  


Steve

P.S.  If any _UK_ DIYers agree that the CEM3396 is their favourite
IC, I have a couple of tubes of NOS ones.  Email me privately.