Using XLR for Phono out

The type of plug does not determine whether a connection is balanced or not. I am using a "balanced" connection from my cart. to my fully differential phono pre. However, by choice, I am using RCA plugs. Why? XLR plugs fitted on my OL arm would not fit through the arm pod on my Nott. table. Balanced or single-ended is a function of the circuit topology, not the type of plug used.

Just to point out a potential fly in the ointment, not all true balanced inputs (outputs too) are created equal. One needs to measure the CMRR (Common Mode Rejection Ratio) at the input. Many manufacturers use OP amps to implement balanced inputs. Most of these have poor CMRR. Also, for good common mode rejection the source impedance of the two halves of the balanced output on the other end should be equal. BTW, though much disparaged by many in the audio community, transformers have some of the highest CMRR ratings and equal source impedance is a given. By my count there are 18 Lundahl amorphous core transformers in the signal path of my system and it sounds great, no noise, hum or RFI interference.

Lewm, of course I was refering to the use of transformers as an input device. That was the context of the discussion. Even when used as the input for a SE (balanced to SE conversion) you still have high common mode rejection. If you apply the same signal to each leg of the transformer primary, as in common mode noise, you cannot generate any magnetic flux in the primary and thus no signal. This would be different if you were to ground one leg. A tranfomer "naturally responds to a differential signal.

Lewm, if you feed a balanced signal to a transformer and the primary winding is either "floating" or wired balanced (CT grounded), you will have CMR even if the secondary is wired SE. If the signal is the same on each leg of the primary (common mode) the potential difference is zero! No magnetic flux, no signal transfer, therefore high CMR. The primary does not care how the secondary is connected as far as CMR is concerned.

Manufacturers do it because SE is cheaper (half the number of parts ;-) ). In phono preamps, designers have traditionally used SE architecture because adding the other half for balanced will increase the inherent circuit noise. That would be a good example. The MC pick-up is naturally balanced. Connecting it that way to the primary of an MC input transformer, then connecting the secondary SE is quite common.