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.


That "chime" (ting-pshhhhh) is extremely typical of 6H30, and is quite distinct to that tube type. If it makes you feel better, other brands of 6H30 preamps have the exact same deal - any type of click relay inside such a unit will set it off. The biggest variant is how much gain. Rogue’s Hera II had much higher gain than Ref 6 and was almost unbearable in my system (high gain amps and high sensitivity speakers made for a bad combo here) - in fact it got to the point I could hear the damn chime excited between notes sometimes, at loud playback volumes.

The Ref 6 is below the threshold where you have to worry about this getting excited during normal playback. The relays just set it off because they’re right there inside the box, on the same springy PCB as the tubes. You’re not activating those relays during music playback, so no worries.

As with all tubes, the microphonics can get worse with age, and on/off heat cycles. All the critical tube elements are pressed through those thin mica wafers, and as those holes get stretched you get the inevitable result. Scrupulous sellers like ARC and Upscale will also do a great job screening these tubes and getting you the best, quietest new set.

Tube dampers don’t do a goddamn thing here (I tried Herbie’s etc), so don’t waste any money there. They don’t have enough mass to be effective, nor are they attached directly to the internal elements which do the ringing. I also did not find exotic external isolation platforms or component dampers to have any significant effect.

If you’re concerned that it seems like a sudden onset in your case, it was probably there before and you’re more sensitive to it now. Sometimes the relay will randomly have a louder click / pop effect, and that’s it.

If it still bothers you, the only solution is to move to a preamp that uses a different tube type. The plates of 6H30 are very large for the gain rendered, and physically this is what happens in these scenarios. Tubes like 6922, 12A*7 have much smaller plate structures and can be dead quiet even next to relays (when tightly selected). 6SN7 are another large plate, medium-mu tube that can be very problematic in preamps, but their "chime" sounds much different to 6H30 (more of a tink-thuump vaguely like tapping a microphone). Fewer of the 6SN7 based preamps seem to have relay based switching (old world mechanics for an old world tube type), so I guess fewer people complain there ;)

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.

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 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.

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