As i said this is a first thing to do and if you only can buy this Test Record it will be easy http://www.cardas.com/music_frequency_sweep_lp.php to check In Phase / Out of Phase and Polarity (Both channels in positive polarity) / Out Of Polarity (Both channels in reversed or negative polarity Spiral). There is also 13 strikes on a high "B-flat" on a piano Note: The last of the 3 strings are brought into zero-beat, dead-on tuning. Listen for the impact of hammer on string, quickly followed by room reflections mingling with one another, followed by a keener sense of the piano sound itself, as the ring-out time of the string exceeds that of the reverb time of the room.
... and many more features on this test LP
... and many more features on this test LP