Hiss / buzz , how to get rid of?

[Confused]

A shorted input should be silent (or very close to silent). Any noise on a shorted input indicates a fault of some kind. I don't use the phono input myself, but I've followed the 'noise threads' for some time. It seems that some have a noisy phono input and some don't. If that is the case there is a variable in production that Devialet has to fix

I’ve tried shorted RCA plugs on phonostage input. No difference. The stage has the same amount of hiss as with the phono leads from the arm connected. My speakers are 4 metres from my listening position. Hiss becomes audible at -23dB and increasing as the volume is turned up. This is on my D250 Pro C/I. I had exactly the same issue with my previous D220 Pro C/I.

I tried this test a while ago, for me the hiss was audible at about -21dB, so a very similar result to yourself.  This is with the KEF Blades, which have a quoted efficiency of 91dB 1W/m, so in this regard very similar to your speakers, and the Ortofon Cadenza Black, which has a lowish 0.33 mV output.

All very consistent I think.  I will be switching to my new Ortofon Cadenza Bronze this weekend, which has a slightly higher 0.4mV output. (so about 20% higher output than the Black) This will obviously decrease the level of hiss, but I will be interested in just how much of a difference it makes in terms of how subjectively obvious the hiss is in normal use.

I have mentioned before that the hiss does not bother me when actually listening to records, I am just aware of it when cueing up and so on.  It obviously can't be helping the ultimate level of sound quality though.  I did try a Tom Evans Groove phono stage with my old D800.  Whist this eliminated the Devialet hiss issue, I found that the Devialet phono stage ultimately sounded better.  The Tom Evans was good though, so this is probably a subjective preference rather than one being definitively better than the other.