Hi all ,
some of you can hear the difference in sound when you change the polarity
of AC plug ?
To be honest I have never seen any difference .
My systems have no ground connections at all : no hum , no buzz , nothing .
Ciao
Marco
Marco,
With regards to Phase Linear amplifiers like the 400 and 700's..........
The 400 series amplifiers typically did not have this problem. Probably because of the way the amplifiers were wired. That is the line supply cord, B+ and B- are all on the same side of the amplifier as that of the transformer. The 400's also did not have a power switch on the front panel (which would have required additional line level voltage wiring to be running around inside you amplifier).
The 700's series amplifiers did. More so with the 700 series 2's that used twisted pair wire running to the pc board. The earlier 700's and 700B's with shielded wire running all the way from the volume pot to the pc board weren't as bad.
If you were to measure the noise floor "unweighted" you might experience a difference of approximately 5 or 6dB when the line cord is reversed.
The old method to measure the noise floor was with the input jacks shorted or fully CCW. Some of the newer standards (after 1977/8) have a variety of ways to measure the signal to noise ratio. These newer methods were with the following; 1.) no input shorting, 2.) volume pot fully CCW, 3.) at 12 o'clock, 4.) fully CW, 5.) or with a 1,000 ohm resistor installed across the input jacks. The Phase 700's were noisiest with the volume pots at 12 o'clock.
One of the ways to evaluate the noise floor is to listen to your speakers with your ears next to the speakers with no input (music) running into your amplifier. Reverse the line cord and listen again. If you are playing your amplifier with music playing through your speakers at any moderate level, the music will mask the noise floor.
I hope this helps to answer your question.
Ed