Balanced Phono question - forgive my ignorance

Hi Dave, the early BAT must be one of the few! Most of the phono sections I've seen with a balanced output are also balanced in.

TD, There is a way to run balanced operation from RCA jacks from a tone arm, provided the tone arm ground is on a seperate post. In such a case, the idea is to have the arm ground be the shield of both channels, and the barrel connection of the RCA is then the inverting output of the cartridge, going to pin 3 of the XLR. It should on no account be connected to ground. This setup will work fine with no hum problems.

Thanks - I think I get it now. Cheers

TD,

I doubt you're giving up anything with your special cable. My guess is that if you take a multimeter you'll find that XLR pin 2 is connected to RCA hot, pin 3 is connected to RCA jacket, and pin 1 is connected to an RFI foil drain that floats unconnected at the RCA connector. This arrangement is no more or less balanced than using XLRs end-to-end.

Ralph,

My prior phono stage was an early BAT P10, which was balanced except for the first gain stage. At the time of this early production run, BAT favored SE input from tonearm & balanced output to pre. Subsequent P10s are balanced end-to-end. I assume there are other similar hybrid phono circuits still out there.

Dave

I am using the Ayre P-5x phono pre which has balanced and single ended inputs. I use the balanced inputs with a custom made Audioquest Cheeta cables that have RCA connectors on the side that plugs into the VPI Aries (VPI did not have a xlr connection block option at the that time, they do now) and xlr on the other side for the P-5x. This option was described in the P-5x manual as the second best option for connectivity and works well for me.

If you think about it the phono pre end of the cable is like any xlr while the other end the cable the two balanced wires are connected to the rca center hot and the shield. AQ cable are a "balanced" design so it is a slight disadvantage to have the RCAs on the one end.

If I was starting now I would get the VPI xlr connection block, but at this point the things are electrically correct and it works.

TD

Dgarretson's response is correct except for what looks like a typo:

However, some phono stages not balanced all the way through have true-balanced output sections. In this case you will benefit going XLR from phono to pre.

I think the word 'not' goes between 'will' and 'benefit'.

I don't think there are too many phono sections out there that have XLR inputs but are not balanced, so its probably a moot point. We found that most people really didn't understand what we were up to with the balanced input on our phono section; I can't imagine why a manufacturer would take that on and *not* have at the same time a fully balanced (and in our case, differential) phono section inside.

Be sure the preamp you choose is true fully balanced, or there is additional gain opamps involved that will DEGRADE the sound. Over here balanced sounds lifeless as single ended is much more involving. Belles preamp

The ground wire coming from the TT and the tonearm cable's RFI shield are both unrelated to forming a balanced input to the phono stage. The signal from the cartridge is just two wires per channel coil. These two wires can be connected to pins 2 & 3 of an XLR connector, or to RCA hot & shield. The RFI shield in the tonearm cable is mapped to XLR pin 1(acting as a drain to ground), or soldered to one of the cartridge's signal wires connected to RCA shield.

If the first gain stage of your phono section is true balanced, you should use an XLR input. Not all phono stages with XLR inputs are true balanced all the way through. If not true balanced in the first gain stage, then it doesn't matter whether XLR or RCA inputs are used. In fact it could be argued that the reduced metal mass in some nice RCA connectors like the Eichmann or Tiffany might favor RCA over XLR input for phono stages that are not balanced all the way through.

However, some phono stages not balanced all the way through have true-balanced output sections. In this case you will benefit going XLR from phono to pre.

Using an RCA-to-XLR converter plug to adapt an RCA phono cable to an XLR input will incorrectly map the inverted signal carried on RCA shield of the tonearm cable to XLR pin 1 of the phono section. When running balanced you need either to reterminate the RCA tonearm cable or get a new cable.

Either way will work. I get better results (less noise) by using the two wire input to my phono pre, but it is something that you can play with and see if one connection or the other makes any difference.