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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
oldhvymec
5,101 posts
 
If your looking for confusion you came to the right place.. Get a hold of PASS and talk to them.. Call Nelson Pass get his number at First Watt and ask HIM.. It’s been a few years, he has always been available for his products in one form or another.. I’ve seen him weigh in on a few DIY treads just to help out..

You know horses mouth stuff..

Regards
lowrider57's avatar
lowrider57
5,417 posts
 
This was the response:
     "No. RCA shield and ground lug are contiguous connections."
In an unbalanced (RCA) cable there are only 2 wires, a signal and a ground (which acts as the return signal). The cable has a shield wrapped around the conductors, which can pick up interference which results in noise.

In balanced cables there are 3 wires in the cable, 2 for signal and one ground. There is a shield wrapped around them. The two signal wires carry a sine wave which is 180 degrees out of phase from each other. When this cable is connected to a fully balanced component, the 2 signals are put back in phase.



lowrider57's avatar
lowrider57
5,417 posts
 
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."

This statement is unrelated to the balanced vs. single-ended (unbalanced) operation. Pass is referring to the grounding of a component. The signal ground is the end point for the cable that is plugged into the component, whether it is balanced or unbalanced. The designer grounds this wire to a designated area inside the unit.
He refers to chassis ground which is more commonly known as safety ground or earth ground. This is the wire that travels all the way back to the ground in the service panel where it connects to the neutral wire.
Safety ground is attached to the metal chassis and runs down the power cord (the 3rd prong on the PC connector) 
for safety reasons such as a shock to the body since current is flowing through the components and cables.
In a proper design, such as a Pass amp, the signal ground and the safety ground never meet.



lowrider57's avatar
lowrider57
5,417 posts
 
I looked at the Pass phonostage and it is designed for an unbalanced connection from the turntable. Your LP12 is single-ended. The ground screw on all phonostages is for the ground wire from the TT to prevent noise and hum. There are balanced outputs to go to your preamp.
I checked the AR and it is the same unbalanced design. Outputs are SE and balanced. Again, the LP12 is not balanced, it is single-ended like 90% of turntables.


brskie OP
68 posts
 
@lowrider57 
Thanks so much. Therefore, according to your response and my research, each of these phono stages must somehow convert an unbalanced incoming signal into a balanced outgoing signal internally. This is what was so confusing to me. I thought that the balanced 4 pin signal from a cartridge had to remain balanced throughout the electronics. I didn't know it could be converted to unbalanced at the tonearm DIN connection and then back to balanced again inside the phono stage.
Again, thank you for your very helpful response.

Bruce
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