[sdiy] Consensus on what to do with unused op amps, trannies

[Ken Stone]

>1) We learned from Tim about tying the subrate line of a CA3083 to the neg 
>rail. I'm guessing this also applies to the CA3046, but there the emitter 
>of Q5 and the substrate share a pin, so that seems to limit the 
>flexibility of Q5. Is tying the common Q5 emitter/substrate pin through a 
>resistor to ground OK, so you could use it, say, as a buffer?

Use the transistor in the position in the circuit that has the lowest
emitter voltage.

>2) What's the best thing to do with unused trannies on a CA3046/CA3083?

With the exception of Q5, leave them unconnected. They are physically
isolated little pockets of doping on the die. Nothing will be happening if
the leads are not connected. As already noted, the emitter needs to be at
the lowest circuit potential applicable. That doesn't mean just tying it to
the negative rail either, as that may exceed that device specifications.

>3) On op amps, say a quad, if you're not using all the op amps, what's the 
>best thing to do with the unused opamps?

Output connects to inverting input. non-inverting input goes to ground. This
sets the op-amp up as a voltage follower following 0 volts. Also you could
put a resistor between the output and the inverting input. That way if you
need the device for a mod later, the feedback resistor is already there.

_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au
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