[Arny Krueger]

"Randy Yates" wrote in message

"Richard Crowley" writes:

The reason this works is that the analog outputs from
most
audio equipment (consumer and professional) is NOT zero
impedance. They all have some amount of output
resistance,
most typically with a simple series resistor in the
output if you look at the circuit schematics. Pro
equipment typically has ~600 ohm resistors in series
with the outputs, and consumer stuff has at least 1K and
likely higher.

Agreed. The part is sometimes called a "building out" resistor. The lowest
I've seen in use might be 70-ish ohms.

Why would they do that?

Stability and reliability.

They'd be derating an ideal
voltage amplifier characteristic (zero output impedance)
that is desirable in such devices.

Simplistic theory meets real world practicality.

Consider the stability of an amplifier with an extremely low output
impedance with that of one with a higher output impedance, achieved
passivly. Note the near-universal use of output inductors on power amps.