In article ,
Theo wrote:
"Dave Plowman (News)" wrote:
An audio circuit I found online and have been playing with has an odd
design (to me).

It's op-amp based running off a (separate) +/-15v supply.

There are on board caps across the supply, which is common enough. 10
and 0.1uF in parallel. But instead of going to ground, they are wired
across the +/-15v. Does that do the job as well? Or serves a different
purpose?

Is the opamp powered off those +/- rails? In dual-rail circuits often
power is drawn from the + and - rails, and the GND rail acts as a handy
halfway reference point but doesn't actually source/sink much current.
That means switching transients are taking gulps of current between +
and -, and so decoupling caps are placed between + and - to provide them.

Yes. There are a total of 7 opamps. All powered +/- It is an audio
filtering device with unbalanced in and out so a good ground important.

If instead of +/-15v you thought of the circuit as 0/+30v with a PNP/NPN
stack of transistors between +30v and 0v you might see that even if
there's a +15v wire it's largely irrelevant as most of the current is
going through the transistor pair.

I can see that. Just odd I've never seen it used before.

--
*Succeed, in spite of management *

Dave Plowman London SW
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