AC phasing in hi fi system

marcok

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#1
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
 

oldphaser

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#2
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
 
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jbeckva

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#3
I guess I'll beg the question lol.. why is that? I get that reversing the plug basically reverses the phase, but the primary side is pretty much isolated. Is it because of how basically one side of the primary really is neutral, and depending on the wiring scheme that "hot" side can pass across the back wall several times versus a straight shot on the other side (thinking of the outlet with the 700's)? :scratch:
 

oldphaser

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#4
I guess I'll beg the question lol.. why is that? I get that reversing the plug basically reverses the phase, but the primary side is pretty much isolated. Is it because of how basically one side of the primary really is neutral, and depending on the wiring scheme that "hot" side can pass across the back wall several times versus a straight shot on the other side (thinking of the outlet with the 700's)? :scratch:

Dean had told me he never got a good answer from the engineering department. I will have to go through all the documents I have been gathering again. Somewhere is a good explanation I found that I should have bookmarked.

In the meantime...... here is something I found in Ben Duncan's book "High Performance Audio Amplifiers": "...hum and EMI are often highest around about the midway gain setting, particularly if the pot wiring runs by the mains transformer." In the case of the Phase 700's the input (low level) wiring runs near or next to the line supply wiring.

It is also interesting to note that if you perform an AC leakage test you may find that when the amplifier is at its quietest that you will have a higher AC leakage than that when you have the line cord reversed. (NOTE: You may need to re-read the previous sentence a couple of times.....)

Now I've got you really scratching your head.

Ed
 
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marcok

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#6
Thank you guys !
Anyway my question was related to all gears .
The web is full of articles that say that if all the gears are in phase the sound
is better .I'm very skeptical but it's always better to ask .
Another hifi fashion , just like oxigen free cables , biwire and so on ( IMHO )
Ciao
Marco
 

Netfly

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#7
It's most important in live gear. Most guitar amps have a polarity reverse switch. You don't want to be grabbing a mic in a rain storm and have the polarity of the mic and the guitar reversed...ouch. On home gear I always consider grounding the chassis together if hum is a problem and observe polarity if it presents. Separating cables - power form speaker from siganls can sometimes help too.
 

Gepetto

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#8
Thank you guys !
Anyway my question was related to all gears .
The web is full of articles that say that if all the gears are in phase the sound
is better .I'm very skeptical but it's always better to ask .
Another hifi fashion , just like oxigen free cables , biwire and so on ( IMHO )
Ciao
Marco
If you run on balanced power, it probably will not matter much or at all. Most utilities in the US and Europe are not balanced though. A neutral and a hot line.

Depending on how the wiring runs internally through the equipment chassis, phasing could make a difference. A long run of AC wire inside the chassis could run near other signal wiring or PCB wiring and it would be good to have that long run be the neutral wire than the hot wire. The current running through either the neutral or hot wire is the same, however the voltage potential isn't which could set up small electrostatic (capacitive) coupling mechanisms with the hot wire.
 

marcok

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#9
Correct Joe !
My AC line is unbalanced .
My question was : Can you hear the difference ?
To be honest I am not able to .
Ciao
Marco
 

Lazarus Short

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#10
This is one of those audio issues I never worried about. Another is the gauge of the AC line cord, especially after seeing the skinny, skinny cord on Lee's PL 400 loaner...
 

Gepetto

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#11
Correct Joe !
My AC line is unbalanced .
My question was : Can you hear the difference ?
To be honest I am not able to .
Ciao
Marco
Hi Marco
i believe this has always been about background hum, reversing sometimes has an effect on that. No possible with modern 5-15P plugs since they have started polarizing with a wider neutral blade.

I don’t think it ever affected sound quality other than signal to noise.
 

marcok

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#12
Hi Marco
i believe this has always been about background hum, reversing sometimes has an effect on that. No possible with modern 5-15P plugs since they have started polarizing with a wider neutral blade.

I don’t think it ever affected sound quality other than signal to noise.
In my systems I have no hum or better :
-Carver C 4000 hum at 4 o'clock position on phono amp with Dynavector step up transformer . (Cart Dynavector Karat 17 ds )
-Dynaco Pat 4 hum 5 o'clock position on phono ( Ortofon 2M red )
Phase Linear 4000 no hum on phono . ( Grado Z1+ in one system and in the other one Stanton CS 100 )
In all cases listening level is 11 - 1 o'clock position
The position are related to master volume control .
I believe it's normal .
Ciao
Marco
 
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