ARC Ref 6 Tube Microphonics

Hi All, I purchased a used Ref 6 preamp a few months ago, initially everything was fine, tube hours indicator said ~950 hours but not sure if that was accurate. After about 50 hours of use, turning the volume past 0 and the mechanical relay kicks in, a chime is heard coming through the speakers. I assumed one or more tubes had become microphonic. I replaced all tubes with new ARC select from Upscale, 7 Sovtek 6H30Pi, 1 Sovtek 6550WE. I let it warm up for a few hours, turned volume past 0 and the same chime is still there. On the positive side, the SQ improvement was immediately noticeable and outstanding, I love the preamp in my setup but the microphonic chime is annoying. ARC service said that some chime is normal but it still bothers me. Any advice? Ignore it? A new set of tubes direct from ARC? New tube rings? Send in to service? Thanks.


@agbrace definitely not normal. Call ARC and explain it to them. If u do send it expect a long wait But they will tell you to ship it when they will be getting close for your repair so at least you will still be able to use your system If you want to.

ARC recommends a minimum input impedance load of 20k with their preamps. You’re not getting the best out of the Ref 6 with a 9k load. Los your gain is probably too high if you have a 90db higher efficiency speakers 

Yep, I switched from the Hegel to another amp that I have, a Benchmark AHB2, which has an input impedance of 50k ohms and the chime was still audible but very much reduced such that one would not consider it an issue. Speakers are Harbeth 40.3XD ~86 dB Thanks for all the discussion and advice on this issue.

If it only chimes when getting out of zero volume, then I would try to set the volume to last used in the menu and before putting it in standby just lower it to 1. If my memory serves, it’s possible thru the set up menu.

Secondly, the Ref 6 has 15db of gain and you’re not only mismatching impedance with the Hegel amp but also, due to the high gain of the amp you’re limiting the usable volume range. It must be pretty narrow and each step increases or decreases the volume by a lot. Not a good setup.

If you like the Ref 6, and it is a very nice preamp, you should probably match it with either an ARC amp or a solid state amp that presents a proper load and has less gain.

Few other things that come to mind - make sure the Ref 6 has plenty of space around it. Place it on the top shelf if you haven’t yet with nothing above it. Allow it breathe. Are you using the rubber tube rings? If not, you should. Is it plugged into a power conditioner? Try it with the conditioner and direct to wall and see if any change in noise.
And call ARC to get their take on it.

Hello @agbrace

I have the same problem in the last 30 days.

I also have listened a noise coming from the transformer on the right just behind the volume dial if I put my ear very close to the acrylic cover.

Can you check if yours is also doing this noise?

Mine was perfect for the last 4 years and I am sure it is not normal. (Have change al the tubes for ARC grade Upscale tubes with no change).

Kind regards