They are essentially the same amp in every respect except for a few minor power supply changes. One of the changes allowed them to be quickly turned off and on when using their noisegate (ACM-420). The noise gate turned the amps on and off quickly with the presence (or lack thereof) of an audio signal. There were also some minor power supply upgrades in the .2 series. The .2 series is bullet proof, the A300 was merely bullet resistant.
Can you tell I owned a pair of those amps?
