ARC LS25 mkII noise level

I did float the ground on the ls25. Also on the power amp. No change. I'll test by disconnecting all sources one by one to see if there is any change.

Your setup's noise level is what I would expect. I do think there is something going on here on mine. But if I take the LS25 out and replace with a solid state preamp, the noise is gone.

I have the LS-25mkII and have had it for about 5yrs. and have never had any issues with noise. I'm talking standing right next to speaker with ear to tweeter!
Sounds like it could be in the power supply(just guessing)
If you can do without for about 3 weeks, I would send back to ARC.

The hum/hiss is also speaker dependent. The higher the sensitivity of the speaker (92db vs 87db example) the more likely you are to hear the hiss.

What you are hearing is precisely why I have changed over to a solid state preamp. I have the tubes in the amp. It is even more troubling when listening to a tube phono preamp. The tube noise of the phono signal is very noticible. I prefer solid state phono pre for that reason. Amplifying the signal through a preamp is where you do not want extra noise. Finding good tubes that are quiet enough for preamp use is a particularly difficult feat. They may advertise them as quiet, but when you exchange out the tubes for solid state, the difference can be pretty significant.

@ee3: That is what I suspect. I'll check a few more things along with a new set of 6h30 tubes. If that does not do it, I'll send it to ARC for a complete checkup. What amp are you pairing it with and how sensitive is your speakers?

My Focal 1027 Be are 91db.

@tzh21y: The LS25 MKIK does not really use tubes for gain. It is used for cathode following circuit. So, I don't think new tubes will have much effect although you never know. It's interesting in that some people will say their tube preamp is dead quiet and some will say it is much noisier than solid state. I might go passive preamp or solid sate but I'll give LS25 mkII a chance first.