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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
agbrace OP
43 posts
 

Thanks for the detailed response. When music is playing, I don't notice anything out of the ordinary and I love the sound of the preamp so maybe I will ask ARC about some of their selected tubes and just live with it. Appreciated.

ghdprentice
7,364 posts
 

I have owned a Audio Research Ref 5SE for many years, auditioned a Ref 6, and currently own a REF6SE for several years. Dead silent. Call Audio Research. I am sure they will guide you. Probably a repair.

mulveling's avatar
mulveling
2,046 posts
 

I have owned a Audio Research Ref 5SE for many years, auditioned a Ref 6, and currently own a REF6SE for several years. Dead silent. Call Audio Research. I am sure they will guide you. Probably a repair.

I would strongly argue against this action. At most, a new tube set is warranted. There is going to be a lot of variance on "sensitivity" to this issue because its impact varies a LOT based on the downstream. Systems with high gain amps and highly sensitive speakers will render the "chime" very prominently, because it occurs AFTER the volume control (i.e. a low volume level does not control it).

In my system (96dB speakers, ~ 30dB amps), there probably isn’t a 6H30 preamp on earth where I wouldn’t notice the chime on relay switch.

carlsbad2's avatar
carlsbad2
1,959 posts
 

Microphonics is a tube thing more than an amp thing.  Don't fix the wrong component.

agbrace OP
43 posts
 

Interesting, I am using the Ref 6 connected to a Hegel H20 and then to a pair of Harbeth 40.3XD. I believe the H20 has higher than average gain at 32dB. Also the output/input impedance matching of the Ref 6 and H20 appear to be just barely OK with the avg. output of the Ref 6 being ~600 ohms and the input of the H20 being 9.4k ohms, I am using XLR. JA's measurements set a recommended lower limit of 10k ohms for amplifier matching so maybe this isn't a very good match. 

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