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absolute phase

post #1 of 109
Thread Starter 
This ought to spark some lively debate...

So i was looking thru a few OTL tube amp schematics and i noticed
that virtually every tube headphone amplifier inverts phase. A quick
glance at a number of solid state units and none of them invert phase.

So that got me to thinking whether or not absolute phase really
makes a difference. Certainly many of the record companies go thru
great effort to maintain correct phase, especially on classical performances
so there must actually be something to this. The first high end grado
headphones had phase switches.

So when comparing a solid state and a tube amp at the same time, some
of the differences you hear may also be phase related.

Amplifiers known to invert phase

Ray Samuels Stealth
Singlepower (all models)
Woo Audio
Eddie Current
Wheatfield HA2
Rudistor RP4

Amplifiers known not to invert phase

Ray Samuels SR-71 (and presumably all his solid state models)
My amplifiers (both tube and solid state)
melos (balanced input models could actually be wired either way)
cmoy, meta42 et all...

So all you people out there with tube amps and sennheiser headphones,
flip those connectors around and see if you can hear the difference.
post #2 of 109
My Quicksilver Audio preamp inverts the phase (as stated in the manual and by the dealer). My Rotel DAC has the ability to invert phase on the fly as well.

Depending on the music, it can make a difference or sometimes very minimal difference.

A very interesting find that all these tube amps do this.
post #3 of 109
Dr. Gilmore - Are you saying L and R channels are reversed? Or are you saying the Phase of the output is off by 180 degrees compared to the phase of the input? These are not the same things but my knowledge is limited.

If the phase (by my definition) is reversed then swapping headphone connectors will not change anything - it will only mix the L and R signals. What you will need is a phase change of 180 degrees to be introduced.

I'll come up with some waveforms just to show-off my noobiness

IIRC - One of the Grado headphones had a phase switch - is this WHY it had a phase switch?

I am just a little more than confused
post #4 of 109
Thread Starter 
yes 180 degrees. Not Left/Right.

On sennheiser headphones you can unplug the connectors at the
headphone end and reverse them for 180 phase.
post #5 of 109
I didn't know that the Sennheiser plugs were polar.
I better take a closer look. How do you tell which is which?
post #6 of 109
One of them is smaller than the other Utep. At least on my headphones

I am testing ...

Its a NO-GO for me The diameter of the pins is also different
post #7 of 109
It is an interesting subject... Just to add to the list:


Creek OBH-11


Creek OBH-11SE (both A and B versions)
Creek OBH-21 and 21SE

My new ANT "Amber" is also inverting.

post #8 of 109
I'm an idiot. Should have known this.

If one is smaller then the other, does plugging them in in reverse, screw up the plugs? I'l' have to check when I get home.

Look forward to your 'out of phase' impressions GS.
post #9 of 109
Thread Starter 
On the original sennheiser cable one pin is slightly a smaller diameter
than the other. ( i measured it) but on the cardas cable both pins seem
to be exactly the same size.
post #10 of 109
Unless I'm mistaken (and I frequently am), I think he's referring to the effective reversal of the positive and negative terminals, and not to the reversal of left and right channels.

I too, have a DAC with on-the-fly phase reversal. I tend not to use it because to me, it seems to "warm" the sound. Just a matter of personal taste maybe.

Then again, out of phase speaker cones would surely be pulling instead of pushing?

Tom McQ
post #11 of 109
Originally Posted by kevin gilmore
This ought to spark some lively debate...

So all you people out there with tube amps and sennheiser headphones,
flip those connectors around and see if you can hear the difference.
Do you just flip the connector on one channel or on both?
post #12 of 109
Thread Starter 
You flip it on BOTH channels. If it does not fit in easily, then do not
force it!

Let me explain a little further.

Take a snare drum with a single diaphram. Put one microphone pointing
at the top of the diaphram. Put one microphone pointing at the bottom
of the diaphram. When you hit the drum the bottom microphone will output
first a positive signal (increasing pressure) while the top microphone
will output a negative signal (decreasing pressure)
post #13 of 109
Sennheiser is a NO-GO because the diameter of the pins is different. They will not go in the other way

Qualia looks like a possibility because they appear to be the same dia...not sure again.


Two pins to each channel - one is live and the other is "return" right? Both returns from left and right merge into the ground ??

Can someone draw the schematic of a Sennheiser Headphone Cable?

post #14 of 109
I have used/owned a lot of equipment that is capable of switching phase, both digitally and analog. I have not once convinced myself that I hear a difference eventhough I know I can hear differences between cables, tweaks, etc. Supposedly it is only relevant for rooms with horrendous acoustical problems and is therefore not applicable to headphone listening.

Here's an even bigger brain buster. My Wadia 12 DAC can invert phase digitally and my Krell preamp can do it analogly (is that the right term?). I wonder if someone can supposedly tell apart all 4 possible phase combinations?
post #15 of 109
This must be a real hoot sitting back and listening to the responses. If it really made a difference it seems to me that it would have been sorted out long ago and one way would be accepted and the other discredited. Smells more like a red herring to me.
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