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

There is little, if any, advantage to XLR on short runs.

danvignau

There is little, if any, advantage to XLR on short runs.

That’s a pretty broad statement and it isn’t clear exactly what you mean. As I’ve already pointed out, the use of XLR connectors does not necessarily mean that the unit is true differentially balanced.

There is great potential advantage in using differentially balanced circuitry and connections in a phono preamp. In addition to the increased immunity to noise, there’s a 6 dB increase in gain. That’s a huge advantage in a phono section!

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).