How do you measure output impedance?

It is very simple if you can hook up a potentiometer to the output of the preamp. Use a value that has a maximum value at least 10 times the estimated output impedance, 25K ohms should be enough.

Feed the preamp a fixed level signal such as a reference 1,000 Hz tone or pink noise from a test CD.

Turn the resistance to maximum and measure the AC voltage across the pot. Then turn it down slowly until the voltage drops to 1/2 the initial value. Disconnect it from the preamp and measure the resistance, it will be equal to the output impedance of the preamp.

Contact me if you wish and I can fax some drawings if you need them.

Actually, Herman, that all sounds pretty intimidating to me. I'd need a lot of hand-holding, plus a pot. Thanks for posting it, though.

Drubin, may I ask - if you feel intimidated by having to measure some voltages, why do you need it? What are you trying to achieve?

Maybe he's trying to feed a low impedence input power amp, like an Aleph, known to be tricky with unruly pre's?