[Eeyore]

isw wrote:

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,

Where would you get one of those (signals) ?


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.

And of course with audio band-limited signals and decent modern circuitry such
a thing NEVER happens. National's recent LM4562 and LME49710 family op-amps
have no less than 55 MHz gain-bandwidth. Talk about overkill !

Another popular myth dies a death.

Graham