[sdiy] CA3094 Darlington Question

Nils Pipenbrinck np at inverse-entertainment.de
Mon Feb 17 16:20:16 CET 2003

Hi Folks,

I have a rather large project in the planing (a big guitar synthesizer
inspired by the EH microsynth inspired circuit).

The original circuit uses a lot of the old and expensive CA3094 OTA's. Half
of them don't even have the darlington in use, so I'll use the cheap CA3080
there. The only difference between the OTA cores is the bandwith (30Mhz or
the 3094, 2 for the 3080).

Now I wonder if I couldn't simply "emulate" the 3094 by using a 3080 and put
a darlington tranny behind the output. It's only used as a emitter follower,
so I don't expect any problems here.

There is however one thing that I don't understand:

The built in darlington has a 47k resistor between the second transistors
base and emitter. I'm not sure about it's function: My guess is, that this
resistor will trade some gain for speed. Is this correct, and I can just use
a faster darlington transistor like a BC517, or does this internal resistor
has a different purpose?

- Nils

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