[isw]

In article , Randy Yates
wrote:

In the past we were told that negative feedback in an amplifier (power
amplifier) was bad. I believe the old charge was that it produced
excessive "transient intermodulation distortion."

Can someone please explain, using as much engineering-speak as necessary
(i.e., don't sugar-coat it - assume an audience of electrical engineers)
what this was all about?

If you stick a signal that's beyond its bandwidth capability into an
amplifier, that amp will "outrun" its own feedback loop in an attempt to
handle the signal (i.e. some stage -- usually the input one -- will
either saturate or cut off before the correcting feedback can arrive to
prevent that). The result is distortion, but only until the feedback
*does* arrive; hence *Transient* Intermodulation Distortion.

The solution is to band-limit the signal *before* it gets to the amp, or
alternately, to use an amp with a large enough bandwidth.

In this kind of situation, an amplifier's bandwidth can vary with signal
level, so that an amp may perform fine for low-level signals, but not
for high-level ones.

Isaac