"anahata"


What you're saying is that the amplifier should be driving a realistic
load for a test to be maningful, and of course you're quite right.

This kind of test has been done before, by potting down the amplifier
output to the same level as the input and using a differencing amplifier
to compare the result with the input signal. You put the "real load"
speaker in another room where you can't hear it, and listen to the output
of the differencing amplifier.

Once HF phase shifts and gain had been balanced out, the result in the
tests I've read about was silence. It was also instructive to investigate
the dramatic sudden noises that would occur in the difference signal if
the amplifier under test was driven to clipping, or if it was class B and
the quiescent current reduced to produce crossover distortion.



** The only folk to ever carry out the above ( it is very tedious to do )
and publicly demonstrate the result was the UK Quad firm. The test
procedure was suggested by Peter Baxanadall:

http://www.dself.dsl.pipex.com/ampin...o/subjectv.htm

Quad demonstrated their model 303 amp as passing the test of "no audible
distortion".



.......... Phil