[sdiy] CA3094 Darlington Question

harrybissell at prodigy.net harrybissell at prodigy.net
Mon Feb 17 16:57:45 CET 2003


Hi Nils...

no reason you can't sub the CA3080 and use an external darlington.

You could also use the LM13700 (still made by NJR) which is a dual
and has the buffer on board.

The LM13700 is very similar but also has the linearizing diodes which
you could use, or ignore.

The LM13600 darlington buffer has a different configuration (it is biased by the Gm input... not a fixed resistor) so it would not be
a direct choice.

What is your project. I'd like to hear more (having just finished a
big guitar project like yours) you can see a photo at www.wiseguysynth.com in the AHMW2002 photo section...

H^) harry

>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?
>Bye,
>- Nils


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