OP amps are not quite a differential amp. It takes 3 OP amps to make a differential amplifier. An Instrumentation Amplifier has differential inputs and differential outputs.
Audiophiles are very picky which OP amplifiers they use. (A-B) * (some big number) is not the same as (A-B) * ( a known number).
Op amps have gotten a whole lot better in 30 years.
My Audio amp is based on this design:
Leach Amp Plans - Part 1
Which was describe in Audio Magazine in about 1976.
It boasts about 100 W/Ch with a 100 V/us slew rate and about a 0 to 1 Megahertz bandwidth, intentionally rolled off to 0.5 Hz to 44 KHz. Needless to say in 1980, about when I built mine, nothing came close. It boasts low Transient Intermodulation Distortion.
Almost all metal film resistors, 4 independent supplies of 50 volts and 40,000 uF of capacitance. It still rocks.
Comes close to a tube amp in listening tests. Tubes drive horns better and the Leach has better bass performance. Tube and classical go together and so does the Leach, dome tweeters and Folk music.
Linear Mode
