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Balanced vs. Unbalanced Inputs

I am trying to upgrade to a differentially balanced phono stage to compliment my Pass XP-22 pre and Pass X250.8 amp so as to minimize long cable artifacts and benefit from CMR. I do understand the it is the circuitry and not the input connection that determines wether a signal is balanced or not. I am looking at both a Pass XP-27 and AR Phono 3SE as possible options. Both have RCA inputs plus a ground post only. No XLR inputs. 

As far as my understanding goes, a balanced cable must have 2 signal conductors, a hot (+) and a cold (-) PLUS a ground for EACH channel. So, I sent an email to Pass Labs as follows:  

 ".... I want to confirm that there are TWO signal conductors PLUS a ground for each channel. Specifically, on each of     the RCA inputs, do the center pins and the shields carry the hot (+) and cold (-) signals respectively while the grounding wire/grounding post becomes the tone arm/turntable chassis ground connection common to BOTH channels? "

This was the response:
     "No. RCA shield and ground lug are contiguous connections."

But on the pass website is the following:
     "In order to minimize ground loop issues Pass Labs never manufactures equipment with signal ground and chassis ground contiguous."

When I email Linn about their pseudo balanced  LP12 T cable they responded with:
     "All Linn arm cables are terminated with a 5 pin DIN connector with the center pin being arm ground, which on an LP12 is also used as the chassis ground.  This is separate from the left and right channel grounds and hots which are on the other 4 pins."

Again, there is no (+) signal to be superimposed with an inverted (-) signal separate from ground for CMR. I Do have a technical background but I am not well versed on circuit design so please forgive my ignorance. I did get some very helpful advice from a member here, however, the further I inquired with the manufacturers the more confusing it became. As of now I am wary about emailing AR for fear of even more confusion. If anyone has any advice on how to proceed I would really appreciate it. Thank you all so much.

Bruce
brskie
fuzztone's avatar
fuzztone
5,510 posts
 
The stumbling block here is that the signal "ground" (return) and the (arm, chassis) shield are different. Always.
As Moncrieff recommended 35 years ago put your single ended cables in a mesh tube attached to pin 3 and the amps chassis.
Over and out.
audio2design
1,351 posts
 
The whole point of balanced cable operation is to avoid interconnect cable interaction with the sound of the system and if the tenants of the balanced system are followed, it does this very well. This means that to sound right, the cable does not have to be expensive, it simply has to be correct!


Could you clarify this, because in my mind, the point of balanced is, and has always been common mode noise rejection.  Good cable construction will of course lead to consistency of noise on both cables ensuring common mode rejection.

Now w.r.t. studio balanced connections, i.e. AES compliant, that is not just about balanced, but a drive/load standard that is low enough impedance to dominate over cable parameters.


Technically a phono cartridge is "floating" which means it's neither balanced or single ended. It can be wired either way
This statement is false. A floating inductor like a cartridge is in fact a balanced source.


No, that statement is quite true. A floating source is not the same as a differential source. It would only be truly differential if you center tapped it and connected the shield to the center tap, such that coupling to the cable shield is similar for both conductors. That is not the case for a cartridge.



but the reason there are so few balanced turntables/phono stages is that there is diminishing return on splitting the signal to make it balanced, particularly when the signal from a cartridge is already so weak.


I disagree with the diminishing returns as the two channels are completely separate loops, hence if you connect them to the same ground (single ended), then you loose the benefits of independent floating loops and reduce common mode rejection.

lukaske
307 posts
 
And than, we gonna “hear “the difference  between the 2: for me RCA is more open: good balance, beautiful placement , detailed and holographic. XLR: gives also a good balance, placement:okay, but the openness is less: “flatter” compared to RCA.  Conclusion: I only used RCA. ( my system: CEC cd-player, Auralic streamer, Metronome Technologie C6 (dac), Daniël Hertz M6L ( préamp) Wavac MD 805 m ( monoblocks) and Ilumnia Magister (speakers)
georgehifi's avatar
georgehifi
10,312 posts
 
Balanced vs. Unbalanced Inputs
First off you need to ascertain if they are "real" balanced outputs or "real" balanced inputs.

As many outputs are really SE, and an opamp chucked on to it to give pseudo balanced output, in this case your better to listen to the SE not the balanced.

Same goes for inputs on many amplifiers they are SE input circuitry, and they again just chuck an opamp onto it so you can have balanced, again in this case the SE will sound better also.

Now for the tricky bit, you can only find this out if you know what your looking at, look inside at the input board section, or see circuit diagrams. Because no-way will they state this, in their literature

Cheers George
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clearthinker's avatar
clearthinker
1,582 posts
 
Goodness me.  Opinions here are diametrically opposed on a question that should be straightforward.  The OP says he understands now but if that is the case then he is smarter than I am.

I had believed that running phono fully balanced brings a 6dB noise floor reduction and thus is very desirable given the very low level signals involved.  Having read the thread carefully and re-read it, I no longer clear that a phono output can even be run single ended (because of the cartridge 'floating' idea expressed in two posts).  Nor yet has any view been expressed here as to the respective SQ benefits of balanced vs single-ended operation  (Possibly premature as it has not been agreed what balanced operation is or whether it is possible).

I think I would be a great idea to ask the the great phono cartridge and phono amp designers to clear this up - hopefully they might all agree.  Question: precisely how are cartridge and turntable wired to the phono amp to obtain fully balanced operation?

Also it would be highly instructive to listen to the same system wired single-ended and then fully-balanced and to take noise measurements of each.
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