2. amps-preamps
  3. 163013-122347

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

Showing 5 responses by brskie

brskie OP
66 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
brskie OP
66 posts
 
@atmasphere 
Hello again. In your response:
"...A 5-pin DIN connector like on the Linn is a balanced connection. Pin 3 of the connectors becomes the shield of both channels and ties to pin 1 of the XLRs at the other end of the tonearm cable..."

However, the Linn arm cable terminates with RCA not XLR.

Then you said:
... while the grounding wire/grounding post becomes the tone arm/turntable chassis ground connection common to BOTH channels?
No. The ground is independent and not common to either channel.
"This is begging for clarification! The ground (shield of both channels of the interconnect cable, pin 3 of the DIN connector) is grounded to the chassis of the phono preamp. In the case of the ARC, it should not contact the sleeve of the RCA connection in any way. But obviously since its tying to chassis, its by definition common to both channels. "

So does this mean that to send a balanced signal to the phono pre I should connect that "weird 3rd ground wire" to the ground post on the ARC, or, should I ignore it and tape over the end so it won't ground to the chassis of some component.

Thanks again Ralph for all you give to everyone in this community.

Bruce
brskie OP
66 posts
 
@cleeds 
So I just have to figure out my tonearm wiring to get the balanced signal into the ARC RCAs.
Thank you again for so freely giving your help.

Bruce
brskie OP
66 posts
 
@cleeds
 So this is the crux of my delima. Since the AR Phono 3SE is a fully differential phono stage, and, since it ONLY has RCA inputs and a ground post then:
      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 is the only way I can logically assume that the input to the ARC phono stage occurs since there are only 2 connections on an RCA to begin with. Unlike an XLR that has 3 connections.
So then, does Linn's email response:
   
"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."

mean that the signal going from the DIN to the phono stage IS balanced? Or, do I have to assume that I would not be able to use a factory Linn tonearm cable and have to arrange for some kind of bespoke wiring in my arm so as to feed the ARC phono stage a balanced signal to begin with???
I can see why there is so much confusion around this topic of balanced/unbalanced signals with the unwillingness of audio companies to follow a strict set of standards.
Thank you for taking the time to respond. I really do appreciate it very much @cleeds 

brskie OP
66 posts
 
WOW
Thank you Ralph for the detail here. Now I Understand the mechanics, and I believe, the theory too. This is the clearest explanation I have found in a week of searching.
Be well, stay safe and Better New Year everyone !

Bruce
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