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!
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.
The only way to know is to use your own ears. To my ears, it is not even close. In your case, maybe there is something going on inside of the pre that is not right. I love the sound of tubes but I have been turned of by the noise, especially from the preamp. There are some good tube preamps. I have never heard the LS25 but Atmasphere, Lamm and First Sound make some great pre's. The Atmasphere uses the 12au7 and unfortunately, it is getting very hard to find quality 12ua7's out there NOS. Both are pretty much handmade and cost well over $5,000.00. Maybe someday I wlll try one of these pres.
@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.
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.
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.
Also, try to float the AC ground on the LS25 temporarily. See if the hum/noise go away.
The guy you need to talk to at ARC is Chris Ossana. Helpful and technical Guru.
I have a pair of Classic 120's and Ref3 LE both with many upgraded parts in the critical signal path and power supplies. When the amps are on and the Ref3 is off, there is absolutely no noise or hum coming out of the speakers. When the Ref3 is turned on and i select any source (except phono) with no signal and turned the volume to the max, there is only a very faith hiss that i hear when i put my ears to the speakers. Selecting the phono input while the phono stage is turned on with no signal, i can hear hiss or what they call "tube rush". However, that is to be expected from tube phono stage. Mine is a Ref2 Phono. Tube amplification nowadays CAN BE quiet although no quite to the level of a good solid state design. Good Luck.
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.
Maybe a pointless question, but do you have tube dampers on the LS25? I have a LS26 and hear no noise. Maybe the tubes need replaced, take small steps to solve the issue. Possibly vibration dampers under the componet. Mine is on AQ Feet. Contact ARC they are very helpful on the phone, the challenge is reaching someone on the phone as they are very busy. If you are buying new tubes look for the 6H30-DR, I have found them to sound better than the ARC OEM tube.
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.
Your thread on the vs60 having noise issues is now followed with the pre being noisy as well. Sounds like a nightmare trying to listen with all these issues.
Go with Ayre SS, dead quiet and nice sound. The other option is to isolate the tube or circuit that has the issue and repair or seek professional assistance. Also maybe accept that a very low level hiss or whatever might be there and weigh the other benefits of tube gear.
I can't hear anything coming out of the ARC amps and pre I have so you might want to look at some other issues like power as well.
In all honesty you seem knowledgeable but maybe tubes are not for you. Do you hear these sounds over the music, when in idle, or what?
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