ARC LS25 mkII noise level

Thanks all for your response.

I will call ARC tomorrow. I did a voltage check and everything is good. Although I can read schematics and have some tech skills, I can't figure out where in the circuit this noise might be coming from. If the power filter caps were no good, I would think the noise would be louder and the voltages would be off.

I noticed some strange looking powdery dust covering the main board. I wiped away what I could. No change in noise.

Yeah, it has been a challenge. This is my first foray into tube gear. Maybe I am used to dead quiet solid state amps.

I think the culprit here is the LS25 MKII. The VS60 with a solid state preamp is very quiet. So the LS25 might need repair but I'll try getting new tubes for it first. It has 2 6H30 tubes.

Perhaps my expectations are skewed as I am probably looking for the dead silence my solid state gear provided. However, these 2 amps sound really good to my ears.

The noise can't be heard over music. If the room is dead quiet, I do hear the hum and noise very slightly from 3 meters away. With a solid state preamp, the noise is gone.

Yes, there are tube dampers on the 2 6h30s. They are the UltraSonic Hal-o dampers. I will work with ARC to resolve this. It might just need some service.

@Elizabeth I wish it was 3 feet. 3 meters which is about 10 feet away from my listening seat.

It's more of a hum with some hiss and a slight buzzing. I've ordered new tubes. And I'll disconnect all the sources one by one to see if that helps. The spec sheet says 14uV IHF weighted so on paper, it should be nearly dead silent.

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.

@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.

Resolution:

After doing a through noise measurement and consulting with a very qualified tech here in NYC and the head tech at ARC, my LS25 II is indeed within spec. It comes down to my expectation and the fact that the Focal 1027 be's are very sensitive. Although Focal publishes them to be at 91db, it is very conservative. It is more close to 95db or so.

ARC uses as a reference, a pair of 87db speakers. It is quite interesting to me that a low cost Arcam solid state preamp is dead silent. The sound quality is much inferior, however. So like life, compromise is a part of audio as well.

The good news is that there is a simple mod to reduce the gain on the LS25mkii by 6db. My tech is quite sure this will do the trick. So all is well!