3 interesting articles from AES, Journal of Elect Engineers, Eric Barbour

[300A]

Most of the tests done by reputable reviewers run a square wave through the amplifier. Is it incorrect to assume that an amplifier that is passing a sqaure wave intact with no ringing is also playing all frequencies evenly across the audible sprectrum? And as far as the phase distortions you claim are utter nonsense. Do you realise what kind of phase shifts even the best of speakers have? Frequency response is what is important. Even a 1st order x-over is going to have a 90 degree shift. It's very simple. An amplifier with zero feedback is going to have extremely soft bass and a rolled off treble. If you like tube amps that's no problem. But please don't try and tell me that from an engineering standpoint that tubes are superior.

I guess the first, and last comment I will make is to listen to a well designed tube amp with a properly matched speaker system. Much more inner detail, no black zone behind the instruments, no grunge, no harshness/zing in the highs, no brittleness when cymbals clash. Truly natural sound.

True, some use square waves to look at the phase response, but we are looking at the basic "fundamental" waveform, not what happens down to the noise floor, which a scope won't display.

If we want to check the basic response to, say 50khz, we need a square wave to only about 5khz as this will give us the phase response to 50khz. 2khz if we only want to see the phase response at 20khz.
Good tube designs give better, more natual highs than SS ever will. I don't think you have ever listened to a good tube amp or preamp.

"An amplifier with zero feedback is going to have extremely soft bass and a rolled off treble."

I don't know where you got this idea, but it is false in many tube designs. I see tube amps with responses to 80khz and more, so the highs are there.

As far as soft sounding bass, it depends on the speaker, the power supply design, and parts quality. Electrolytics "loosen" the bass because they don't charge and discharge properly.

Most speakers made nowadays, for SS amps, need low output Z amps because speakers are not damped properly. They underdamp them so the response goes lower and need high damping to quell the boom. A properly designed speaker, they are out there, doesn't need a low output Z as it is self damping.

One can do a simple battery test on ones own speaker by, first disconnecting the amp, and simply switching on a 1.5 volt battery across the speaker and then switching it off (open load on the speaker when switched off). The woofer should give the same clicking sound when connecting and disconnecting the battery. But what you will usually find is a "click" when the battery is connected and a thud or boom when disconnected, a sure sign the box isn't designed properly for the driver.

As far as speaker crossovers are concerned, many now use phase correction to limit this problem. But the caps are often times worse than the cure. Go figure.

Yes, there are alot of poor tube amps out there that have limited frequency response, high distortion, and claiming the "midrange" magic. But I have come to dislike those, just like you do. They miss so much of the music that one aspect won't cover all the losses from other areas of the music. So now I listen to PP amps.

I guess the last comment I will make is to listen to a well designed tube amp with a properly matched speaker system.