Audio Research Reference 110 / KT 150 Review

I’ve never owned an ARC power amp and I don’t recall ever having heard one in any system, anywhere. That’s rather odd given the status of Audio Research and their position as one of the top tube amp manufacturers in the US marketplace. The reason I’d never sought out a listen to an ARC is perhaps due to my carrying the prejudice of believing that ARC amps were all rather lean sounding, and that the warmer more musical sound that I tend to prefer could only be had from something like a CJ, or a Jadis. But still.

I did own an ARC LS5 preamp for a while, and it struck me as fast, detailed, quite transparentTransparent / Transparency - A clear view into the recording space, no opaqueness, just openness and clarity., but not very tube-like.

So a few weeks back I was at my local Hifi Dealer in Raleigh, NC, when I spotted the unmistakable classic ARC silver faceplate, attached to a rather bulky looking power amp. Getting closer I noticed the ‘Reference’ moniker and thought to myself, “hmmm, what have we here?”.

One scorched credit card later and I was hauling the Audio Research Reference 110SE back to my listening room.

SE / 110 / KT120 / KT 150 etc

There was a mistake made by the dealer when I bought the unit, but I wasn’t ARC-savvy enough to recognize it. Without getting into too much detail here, the unit was sold to me as an ARC Ref 110SE, a model which, in actual fact, does not exist. Other Reference series amps could be internally modified to accept the more powerful KT150 tubes, a modification involving component changes, and the supply of a set of carefully matched KT150 tubes directly from Audio Research. This modification awards the donor amp ‘SE’ status, special-edition, or whatever SE stands for. But in the case of the Reference 110, no modification is needed to run KT150’s, they can be installed in the stock amp*.

So what my dealer had said to me was incorrect, and the source of a lot of frustration on my part. They had not upgraded this amp to run KT150’s, what they had meant to say was that they’d installed a set of KT150’s in the stock Reference 110.

Setting Up the ARC Reference 110

Back at base I heaved this 85 LB beast of a unit onto my component rack and dredged out an old pair of Audioquest balanced IC’s from the closet. I had a better 20A PC than the one the amp came with, but not much better. So the first order of business was to order up a set of balanced IC’s – Acoustic Zen Matrix, along with a Cardas Clear 20 amp power cord.

Getting the ARC hooked into my Allnic Audio L-5000 DHT preamp and wired to the Sonus Faber Cremona Auditor M took a half hour or so, at which point I was ready to flick the power switch on the big boy. I’m always nervous switching on a tube power amp, even if it’s one that I’ve owned for a while and has never previously shown a proclivity for spontaneous combustion. I’m happy to say that the ARC’s little green light lit-up, without additional pomp and fireworks. Ne’er so much as the hint of a ‘pop’ passed through to the speakers. So far so good then.

Listening to the ARC Ref 110

I played an album side to let her warm-up then sat down for a listen. Hmmm. Interesting. First impressions were one of a nicely detailed presentation, plenty of air and space, good stage depth and width, but a little on the lean side. After 35-45 minutes or so the sound fleshed out quite nicely and it became more pleasant to listen to. But it still sounded a little analytical. And this was with the warmly balanced Sonus Faber Cremona Auditors, so there was no way this amp was going to work with my Dunlavy SC-3.

Over the next few days I was in and out of the music room, spinning vinyl and the occasional CD, but I was never really able to connect with the music at any kind of emotional level. There was just a little edge to the sound that distracted me during longer listening sessions. This couldn’t be right.

A few days later the Acoustic Zen XLR’s arrived in the mail and in they went. An instant and noticeable improvement. Hopefully, they would continue to evolve the sound in that same direction during break-in, since they were new from the manufacturer.

A few days later the Cardas Clear PC arrived in the mail and in it went. Voila. Another small but worthwhile improvement. I was now hearing more flesh on bone and gone completely was any sense of an etched presentation. I gave the XLR’s 20 hours of playtime, during which I tried not to form any lasting impressions. Sure enough, the sound continued to evolve, gaining more presence, more solidity, and just becoming generally more pleasant to listen to.

A couple of weeks later a new PS Audio P10 powerplant arrived, and I spent several hours getting it wired into the system. The effect of the PS Audio P10 was positive and the whole system moved to a new level of performance. I have not really messed with the P10, plugging and unplugging components to see how each individual component’s sound is shaped by the P10, and I doubt I ever will. Nor have I messed with different filters or curves or whatever the term is, perhaps I’ll do that at some point since these changes can be implemented via the remote.

So all further comments on the Audio Research Reference 110 are with the Cardas Clear PC, the Acoustic Zen XLR, and the PS Audio P10 in circuit.

What Makes The Ref 110 Special?

1. It has an effortless presentation and never holds back on loud complex passages.
2. It presents detail but given adequate warm-up time and suitable ancillaries, the detail is never etched or clinical sounding.
3. It has a large enveloping soundstageSoundstage - The overall size and shape of the musical “space” a system creates, including width, depth, and height., particularly front to back, with good image placement and plenty of air and space around elements in the soundscape.
4. It provides a good, solid bass foundation, better than most tube amps that I’ve heard to date.
5. It is remarkably transparent. Speakers are able to disappear unimpeded and the window into the music is clear, without any discernible opacity.
6. It has dynamic drive and punch and is great with rock music, but if the recording is bad, it isn’t going to gloss over the fact.

So overall I would describe the amp as being true to the recording, adding little and taking very little away, It doesn’t do ‘bloom’ to the extent that other tube amps do, it’s fairly neutral, but once warmed-up it is musical and engaging on all but the poorest recordings.

Listening to Rush – Moving Pictures, there’s a great pace and rhythm to the track “Camera’s Eye”, with Peart’s relentlessly perfect drumming pushing the track along and Lee’s bass guitar standing proud and clear in the mix. The synth on “Tom Sawyer” stretches the sound wall-to-wall while Lee’s voice appears center stage with plenty enough substance to avoid the sense of ‘glare’ that can come from his vocals on some systems.

As with most tube amps, the Reference 110 does acoustic guitar beautifully. Playing through several acoustic albums including John Martyn’s “Solid Air”, Nick Drakes “Pink Moon” and the classic “Friday Night In San Francisco” featuring Al Di Meola, John McLaughlin, and Paco de Lucía, the big ARC presented the attack, sustain and decay of notes impeccably, giving the strings just about enough flesh and substance to put the instruments right there in the room.

Conclusion
In a nutshell, I like the ARC Reference 110 with its bold KT150 sound, and I could live with it quite happily for the long term. My next project is to roll-in my newly retubed Thor Audio TPA-60 Monoblocks, and get some ink on paper before I forget just how fantastic those amps sound. So the ARC will be on standby duty for a while as I catch up with my reviews.

In some respects I’ve probably never heard the 110 sound at its best as I didn’t pay much attention to cables or isolation during my time reviewing it, even though it clearly demonstrated a need for good cabling and clean power. Hopefully I’ll have another shot at coaxing the best from the amp before I have to release it back into the ether to fund another review project.

All in all, I think this is an excellent amp, one which can drive a broad range of loudspeakers to high levels without breaking a sweat. It doesn’t bloom in the manner of a classic CJ, but rather remains true to the input signal and presents everything in a clear, open, transparent, and dynamic fashion.

CAH

August 2020

* There’s an amount of conflicting information about this amps lineage wrt its capacity to handle the KT150 in stock mode, and I’ll be reporting back on this in due course.

2026 Update — Reference 110 and KT150 Tube Compatibility

This review has recently been brought back to my attention because of renewed discussion on Audiogon regarding the Audio Research Reference 110 and whether it is suitable for use with KT150 output tubes.

To avoid any possible confusion, I want to clarify exactly what happened, what I was told at the time, and what my current position is.

When I bought this amplifier in 2020, it was sold to me by a reputable dealer in Raleigh, NC as an Audio Research Reference 110 “SE.” I was told that the amp had been taken in on trade and upgraded by the dealer to SE status. As noted in the original review above, I later learned that there was no factory-approved “SE” version or SE upgrade for the Reference 110. That raised an obvious question: if there was no official SE upgrade, was the Reference 110 actually suitable for KT150 tubes in stock form?

At the time, I contacted Audio Research directly for clarification. I also started a thread on Audiogon asking for input from people familiar with Audio Research power amps:

Question For Those In The Know About Audio Research Power Amps

Audio Research replied to me by email on June 30, 2020. The relevant part of that reply stated:

Summary: There was never a proper “SE” update for the REF110. You can use KT150’s in that amp, that is not a problem. The dealer may have called it an SE but technically that is not correct.

That response removed my concern at the time. I continued to use the amp with KT150 tubes for several months without issue before selling it. The next owner also used the amp with KT150 tubes for more than a year, again without reporting any issue to me.

However, on June 16, 2026, the old Audiogon thread received a new post from another user who had contacted Audio Research with the same basic question. That user posted a response attributed to Greg Christensen at Audio Research, the same person who had replied to me in 2020. The email response in this instance is not dated, so I can’t say when it was sent by Greg:

We do not recommend using the KT150 in the REF110 amplifier. The current draw from those tubes is more than the power transformer was designed to handle and using those tubes will shorten the life of that transformer. It is ok to use 6550’s, KT88’s, or KT120’s but we do not recommend other tube types for this amplifier.

I cannot reconcile those two statements. In 2020, Audio Research told me in writing that KT150 tubes could be used in the Reference 110. At some other time, between 2020 and 2026, Audio Research appears to have given the opposite advice, warning that KT150 tubes draw more current than the Reference 110 power transformer was designed to handle.

Because of that later statement, my current advice is clear: I would not run KT150 tubes in an Audio Research Reference 110.

The original review remains unchanged because it reflects my experience with the amplifier as purchased, used, and reviewed in 2020. But anyone reading this review today should treat the KT150 issue as unresolved at best, and should err on the side of caution. Based on the later Audio Research statement, the safer tube choices for the Reference 110 appear to be 6550, KT88, or KT120, not KT150.