Why do most phono preamps lack XLR input even thought cartridges are naturally balanced?

As a counter to that cleeds, and not taking anything away, it is also true that because an RCA connection is used, does not mean that the input is not true differential.

With great gain, comes great responsibility. But seriously, w.r.t. phono, differential gives you the ability to increase gain while decreasing common mode noise, but you are still amplifying differential noise as well as noise internal to the amp. You are not getting 6db for free. You could always crank the gain 6db on a single ended connection, which again, for a cartridge, is already pseudo-differential due to the floating source.

roberttdid4

As a counter to that cleeds, and not taking anything away, it is also true that because an RCA connection is used, does not mean that the input is not true differential ...

Quite so, and I made that same point earlier in the thread (fifth post). The Audio Research Ref Phono preamps are examples of RCA connections into a differentially balanced preamp.

... differential gives you the ability to increase gain while decreasing common mode noise, but you are still amplifying differential noise as well as noise internal to the amp. You are not getting 6db for free.

That's a fair point. There's no such thing as a free lunch. It's still 6 dB.

You could always crank the gain 6db on a single ended connection ...

Actually, no you can't "always" - unless you change preamps. At maximum output you do gain 6 dB with a differential circuit.

Except with a phono input, you don't gain 6db, as it is an application specific input. It amplifies the difference between the two leads. There is no "differential" output that has 2x the signal level (6 db).

roberttdid

Except with a phono input, you don’t gain 6db, as it is an application specific input. It amplifies the difference between the two leads. There is no "differential" output that has 2x the signal level (6 db).

I do not know what you mean by "application specific input" or why this matter isn’t more clear to you.

My phono preamp gain is adjustable and is spec’d up to a maximum of 68 dB single ended and 74 dB balanced. That seems consistent with my experience.

 To clarify, I can only add the specs for my Ayre P-5xe: the gain for the balanced output is 6 dB higher than single ended out for each of the 3 gain selections. However the gain does NOT change with the choice of RCA or XLR inputs. You should be able to look up the specs and recommended phono cable wirings on the Ayre website in the manual download.  The specs are minimal and no S:N specs are given.