[sdiy] pin 5 3080

[>>>marjan<<<]

> The 3080 is not being used as an opamp in the MicroMoog -- it's being
> used as an instrumentation amp.  Very different.
> 
> The "opamp equivalent" would be two voltage followers to buffer the
> signals off the ladder and a third opamp connected as a difference
> amp.  The OTA approach is far more elegant and doesn't require closely
> matched resistors.

That's it. Taurus used single 3080 stage (being full of cheap solutions)
used as instrumentaion amp, and I didn't get it until I got MG1/Rogue
schems where this 3080 was used as VCA and it had opamp buffers from
both ladder legs (micromoog was something inbetween as it had taurus
style instr opamp and separate 3080 for VCA, first one being buffered
with some dual FET). Now, Taurus simplest solution seems to sound
the best (after the mini discrete). I guess some nice modern instr opamp
from AD or BB could be used.
Instr opamp is needed for both ladder legs to see the same large imput
impedance, and that reminds me on that thread about new elektor ladder
VCF having opamp in diff stage, with one leg to + in (high impedance)
and other to - input (with impedance determined by resistor).
Now, that's bad (at least for this list, as it may actualy work).


cheers,

marjan