I have bench tested some dual mono amplfiiers in one box from other manufacturers (two transformers, two power supplys, etc.) and found many have no performance improvements to justify the cost as crosstalk still exists between the channels thru the common chassis and other coupling effects. However these effects, as in plain old stereo amplifiers, are rarely worst case problems, utterly swamped by things like slew rate limiting on transients, feedback loop failure on transients, underdamped response at the frequency limits, inadequte performance into capacitive loads, and lots of other things that are easy to see and evaluate with a square wave generator and a dual trace scope. Of course the first thing you need to realize is that a real world square wave is not square, the leading and falling edges are exponential curves. Thus when you see an amp or preamp putting out nice ruler straight square waves with straight leading and falling edges, you are seeing slew rate limiting in the internal circuits, not good reproduction of the input square wave.
Of course all these tests and evaluations won't give you a final definitive answer as to if the amp that passes all the tests is going to sound just wonderful, still many variables we don't have a good handle on yet. However, we can tell the amps and preamps that fail the tests probably are not worth considering -- i.e. -- if it tests good it won't necessary sound good, but if it tests bad, it is bad!
So much to learn, so few willing or curious enough to try learning it.
Frank Van Alstine
