Why no polarity invert function on Pass Pre-amp?

[jeromelang]

I have upgraded to the X350, and I couldn't be more pleased with my system's sound after the amp is fully run-in. The used Aleph Ono phono pre-amp I picked up earlier has also come good after some initial hiccups. So enthusiatic about having am all-Pass amps in my system that I almost bought the X0 pre-amp on display at the Singapore dealer last month, until I found out that there is no absolute polarity switch on this pre-amp and all other Pass models. Why is that? I would have thought it is a fairly understood matter that a lot of music recordings have been remastered with inverted absolute polarity. The Pass D1 DAC does come with a polarity switch doesn't it? Mr Colburn mentioned that it may possible to add a polarity switch, but I could not find out from him further if he actually meant a switchable type or a permanent one. Appreciate if Mr Pass would advise me. Thanks in advance.

[GRollins]

Every time I have to buy a new car, I go through this same sort of thing. One manufacturer has feature A, another has feature B. But to find a car that has both...it's not necessarily an easy task.
A polarity switch is a nice feature to have. The other side of the coin is that the switch itself causes some degradation of the signal. If you have a circuit with an unbalanced output, you have to stick another device in the signal path in order to flip the signal upside-down; yet another trade-off. In the case of a circuit with balanced outputs (like the X0), you can get away with just a switch.
You can always add your own. Granted, it's a pain in the rump with a manufactured piece of equipment, but it's something to think about. But then you've got to decide whether you want that switch in your signal path...

Grey

[dice45]

Grey and jeromelang,

absolute polarity: necessity IMO.
Additional switch for it :

I use an input selector switch having twice as much positions as need and then two neighbored positions select the same input, one 0° and one 180°. No problem technically on a balanced preamp, but the input selector switch is expensivish. Calls even for changes of the front plate engraving. Ouch!!
But the only proper way to do it IMO. Allen Wright does it that way too on his differential tube preamp.

[GRollins]

Making a vitue of necessity. If you've got to have a switch, make it do double-duty.
I like it.
Of course, then you run into the problem that the switching is done with relays and it will take a whole new board full of relays to get the job done. Bummer.

Grey

[paulb]

I would guess this has been covered before, and if so I apologize for rehashing. But does anybody have a physical explanation for why we can hear inverted polarity? This is assuming we can actually hear it, of course, but I'm not ready to start that [rat-hole] discussion.
Is it like the leading wavefront is compression or rarefaction and the ear can tell the difference, or something to that effect?
Hi Grey, welcome back...

[tschrama]

Hi all,

I think absolute polarity can be distinquist theoretically.

The single-ended nature of the speakers (and amplifier) causes polarity depended compression. But I think this effects is far to small to percieve, but maybe not.

Sound traffeling in air has the same thing going on. I calculated that a 140dB SPL tone = 2x10^2 N/m^2 = 0.5% of normal air pressure*. But again a fluctuation of 0.5 % about the average presure introduces neglectible distortion (and this is at 140 dB SPL). I believe Nelson Pass used this theory to explain why single ended amplifiers are perceived as better sounding. I don't agree. The inner ear produces far more distortion by it self in the transduction of sound to mechanical vibration.

The human inner ear organ (cochlea) phaselocks at low frequencies (up to 500- 1000Hz). Above that, absolute phase information is not transfered through the cochlea. Since the cochlea produces neural signals at one polarity of the mechanically movement, this phaselocking could theorectially produce a perception which depends on polarity.

Actually I don't think absolute polarity is important. Well, just my opinion....greetings,
Thijs


*
'James O. Pickles, 1988, 'An Introduction to the Physiology of Hearing'

[jeromelang]

Dear Mr Pass

I am interested to use your pre-amp to set up an all-Pass Labs amplifier system. Would you be able to provide a switchable solution to the polarity invert function? Because of the higher level of resolution with the X350, I have become even more sensitive to the imaging problems with absolute polarity inverted recordings. The display unit of X0 I was eyeing had been sold during the period while I was waiting for the advise from Mr Colburn. My next target is the X1 pre-amp. Your advise is much appreciated.