My guess (and I'm sure a dealer or an AA owner will confirm or deny this) is that the phase controller is to help in connection with discs which are recorded in the wrong polarity. There are many who believe that Telarc dics, for example, sound better in inverted (180 degree) polarity. I myself have heard the difference on some discs, not on others (I have a similar phase knob on my Audio Logic DAC); I also believe that there is some list of discs available which sound better in inverted polarity, hopefully one of our commenters can show you where to find that list. The problem in some cases, particularly classical recordings which are multi-miked, is that you can have a jumble of different polarities in the final mix, which kind of makes changing the polarity an exercise in futility. You should try it with some discs and see if you hear a difference, as some people are more sensitive than others to this effect.
8 responses Add your response