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Balanced Phono question - forgive my ignorance

So if you have a balanced phono stage (and I'm not re-hashing the argument whether it matters, is better etc. - I think that's been done), does the wiring from the arm to the phono then have a balanced connector, or is the balance achieved through attaching the ground wire to the phono, and then a balanced cable out to the pre-amp?

Sorry if this shows a complete lack of understanding of what balanced is, I was just curious from a wiring perspective. My system is completely using balanced connectors, and I'd like to not change anything, so a balanced pre may be in the cards.

Best wishes & thanks.
hatari

Showing 2 responses by dgarretson

dgarretson
2,588 posts
 
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.
dgarretson
2,588 posts
 
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
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