On Thu, 12 Apr 2007 16:08:23 GMT, SparkyGuy
Gave us:

Why?

My bench power supply's transformer is coupling hum into my breadboard. Yes,
I can move my circuit farther away, but I'd rather solve the problem (short
of replacing an otherwise good supply) than the symptom.

It's a 70's vintage lam transformer with half a dozen secondary windings. I'd
prefer a toroid, but it will be cheaper to simply shield this one.

Make sure you simply twist your output lines from the banana jacks,
right up to the circuit under test. Your noise figure should drop a
lot on that act alone. A couple turns per inch... not too damn loose
or it does no good.