ARC Ref 6 Tube Microphonics

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 ;)

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.

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.

@agbrace That 32dB amp gain is definitely higher than average, though not unheard of. This is certainly boosting your audible "chime"! In my case I was running Rogue Apollo Dark monoblocks with ~33dB gain. At times it felt like ungodly amounts of gain. Anyways, inline attenuators (say 10dB) placed between preamp and amp can reduce the chime proportionally if you have the gain to spare (you do, between 14dB Ref 6, plus 32dB Hegel) - BUT most ready-made attenuators are RCA, and you have to deal with the old "does this extra connection & resistor reduce sound quality" thing we all torture ourselves with here (in reality, it’s a negligible impact).

That Hegel’s 9.4K input impedance (XLR) is almost shocking. Much lower than I’d expect or want. That said, it’s a marginal mismatch, but not enough to have bearing on the tube chime issue. The Ref 6 is cap coupled, so maaaaybe you start losing some bass power due to the low input impedance, depending on the value of those caps. Which is a shame because the Ref 6’s "proper" bass is amazing.

The single ended connection between the Ref6 and H20 appear to be much more cooperative at 300 ohms / 50k ohms. 

Wow, that's a world of difference. I believe Ref 6's circuitry is optimized to normally be best from XLR outputs (whether using SE or balanced sources), but yours might just be the rare scenario where SE wins. You might ask ARC what they think of using a Jensen ISO-MAX XLR-to-RCA transformer box to potentially get the best of both worlds here. That still won't address the tube chime issue lol. 

This thread highlights the diversity of sensitivities we have to various noises and operational issues. Some manufacturers really need to add an alternate "high sensitivity speaker" reference rig to expose noise issues. Not ARC though - they’re doing just fine; their tube gear is already as quiet as can be wished for, in the ways that count.

Reports are consistent that 6 => 6SE upgrades are currently VERY fast. Anyone who’s thinking about it should take advantage of that now. The out-of-warranty repair queue is more concerning...6 months? Don’t send your 6 or 6SE in for the 6H30 ping-tshhhh "issue". Btw it’s really a long decay on that "tshhhhh" part - that’s the 6H30 for you. New set of tubes at most. I guess it’s possible if your PCB board is coming loose somehow, that could exacerbate the 6H30 / relay noise. Everything needs to be tight inside.

I don’t expect the 6SE upgrade would impact the 6H30 microphonics or the output impedance. It’s purely for quality of sound.