Audio Research Reference 160S power amplifier

This, our February issue, is the first Stereophile issue to arrive during the year 2020, which marks the 50th anniversary of the founding of Audio Research—in my view one of the key events in the history of high-end audio. So it makes sense for this issue to include an Audio Research review—in this case, of the $20,000 Reference 160 S stereo amplifier.

Following an auspicious start, hi-fi in the ’60s got complicated. It went backward by going forward. Hi-fi expanded to reach a larger audience. But it did so partly by going mid-fi, with a focus on style, convenience, and broad appeal. Technological advances also took hi-fi back. Believe what you want about today’s tube-vs-transistors debate: Back then it was no contest. “Solid state” audio—remember that trademark on all those cheap plastic radios?—made things smaller, lighter, sleeker, and cooler—that last one in both senses of the word—but it damaged sound quality. And yet, even though transistors were not ready for audio prime time, tubed electronics already were looking like yesterday’s technology.

That was the world Audio Research Corporation (ARC) was born into. From the start, ARC and its founder, William Zane Johnson, embodied values that have come to be embedded in high-end audio’s fundamental ethos.

“Bill’s goal was simple: to constantly advance the state-of-the-art in music reproduction,” David Gordon, Audio Research’s current brand ambassador, wrote to me in an email. “He did this through innovative new circuit design combined with new transformer and custom parts designs.” For a company to design its own internal parts was unusual—and remains so—as was the notion that specific capacitor and wiring choices could affect the sound quality of an amplifier. ARC would soon be designing its own capacitors, wire, and transformers.

Also new was the idea that measurements should not be the final arbiter—that the best way to hear things was with our ears: another idea Johnson advocated

The ARC Reference series
“As an engineer, [Johnson] believed each product must have good specifications as a foundation, but good specifications alone did not assure good sound quality,” Gordon’s email continued. “As a pianist, Bill wanted to replicate the sound of live music, which required wide bandwidth and big power supplies with lots of regulation. Audio Research tube products were not meant to act as euphonic filters; they were meant to be transparent, with great bandwidth, and the regulated power supplies allowed the micro- and macro-dynamics to bring music to life.”

Over the years, Audio Research has produced many amplification products, but a handful stand out, most of all, perhaps, the Dual 150 “High Definition” stereo amplifier, from 1975. The D-150 weighed 115lb, and, with its meters, knobs, and front-panel fuse holders, resembled a piece of precision scientific equipment.

Sonically, too, the D-150 aspired to precision—to precise reproduction of the input signal. The notion that precision and musicality are aligned, not opposed, was one of Johnson’s key commitments.

J. Gordon Holt apparently was convinced. Writing in Stereophile, he described the D-150 as sounding like “Nothing. Nothing at all. If it has any sound of its own at all, we were unable to hear it, on the most revealing speaker systems we could round up.” This was the tube amplifier that, more than any other I’m aware of in the whole history of hi-fi, made the case that sonic accuracy and not a euphonic, romanticized presentation was the route to musical enjoyment. It also helped make the case that transistor-based amplifiers weren’t gettin’ the job done circa 1975. The D-150’s high aspirations were clear from the product brochure: “Only a few audiophiles will pay the price for a product that is ‘state-of-the-art’ in performance and quality.” No surprise: In his review of the D-150, JGH called its price—$2685, or about $13,000 in today’s dollars—”murderous.” Sounds like a statement product to me.

But at some point over the next 20 years—perhaps as they began to consider the introduction of the new Reference series—a new theme emerged at Audio Research. In a 1994 Stereophile interview with then–Technical Editor Robert Harley, Bill Johnson said that it hadn’t made sense to make a no-holds-barred product until a reliable supply of high-quality tubes could be secured. That had happened the previous year, when a Russian version of the 6550C tube was (re)introduced. Two years after that, Audio Research released its first Reference-series component, the Reference 600. If the price of the D-150 was murderous, the Reference 600 monoblock was a Gatling gun. A pair of Reference 600 monoblocks cost $29,990/pair, about $50,000 in today’s dollars. Circa 2020, there may be much more expensive amplifiers on the market—including the $170,000/pair darTZeel monoblocks we put on the cover of our December issue—but in 1995 that was an impressive price. (That year’s Stereophile Amplification Component of the Year was another Audio Research amplifier, the much cheaper—$11,990/pair—VT-150 monoblock.)

2020, then, isn’t just Audio Research’s 50th anniversary; it’s also the 25th anniversary of the company’s Reference line. And the product I’m reviewing—the Reference 160 S—is that line’s newest component. This is its worldwide review debut.

And while it’s hardly inexpensive at $20,000, in a historical context it looks like a relative bargain.

Plus ça change
The 160 S has an antecedent that’s much more immediate than the D-150 or even the Reference 600: the Reference 160 M reviewed by Jason Victor Serinus in Stereophile‘s October 2018 issue. In fact, the 160 S is so like the 160 M—or, rather, like two of them stuffed into one chassis—that I considered writing this piece as a Follow-Up review. But stuffing two channels in one chassis is a nontrivial exercise, and there’s a lot to say about the 160 S. So I decided to write a full review.

Audio Research has stuffed two 160s in a case that’s only a little bit larger than one 160 M case—the same width and height, but 3″ deeper. Those extra inches make the 160 S exceptionally deep: With the added rear handles, the 160 S extends 24″ front to back. That shape gives it a unique look and could create placement challenges. Before you buy, figure out where you’re going to put it. You may need to acquire an extra-deep component rack or amplifier stand (although the feet will sit on a normal 21″ stand).

Otherwise, there are few important differences between the M and the S. The M, of course, has a separate power supply for each channel, and separate power cords, whereas there is one power transformer in the 160 S and one power cord (footnote 1). The output transformers are mounted higher up on the S than they are on the M, to make room for some extra power supply capacitors underneath. Also, here, the transformers are covered by a perforated metal cage—not so on the monoblock version. The M version has handles only on the front, but the S version adds handles on the back to help with handling the longer, heavier, back-heavy product.

Some owners of the 160 M have learned that they can get away with leaving the cooling fan turned off, as long as they keep the cover off so that heat can dissipate quickly. The S version, though, with twice as many tubes in about the same area, requires fans; there is no “off” position. I was able to keep the 160 S’s two fans on “low” throughout my listening, however, and I didn’t once hear them.

Perhaps the most important difference between the 160 S and the 160 M is the price: A pair of monoblocks will set you back $30,000, but when you buy the single-chassis version, you get the same features, same power, and nearly the same performance—”sonically they’re very close,” Gordon told me—for $20,000. Buy one channel, get the second channel at 50% off.T he things that set both Reference 160 models apart from their Reference-series forebears are far more significant than the differences between the S and the M. To wit:

• The 160 power supply is more robust.

• Those house-made passive components have been tweaked for better sound. That includes transformers, which are made to spec by a domestic company; some of these have been improved compared to previous Reference-series parts.

• The auto-bias circuit has been updated, resulting, Gordon says, in longer tube life and, it is claimed, better sonics due to a reduction in residual DC currents in the output transformer.

• Gordon told me that the 160 M and 160 S both use a new, four-layer circuit board, “which allows for more optimal signal routing, with a smaller footprint, and less noise, thanks to the separate ground plane.”

• A single-ended (RCA) input has been added—a first for an ARC Reference-series amplifier.

• The 160 M and 160 S amps are the first Audio Research amplifiers to allow switching between triode and Ultralinear operation.

Those early ARC amplifiers, especially the D-150, could be tricky to use. It was necessary to bias the tubes, of course, but D-150 users also had to select, via a front-panel knob, the correct AC operating voltage for their locale—the setting closest to but not lower than the actual voltage going into the amp, which was displayed on the middle of three meters.

In contrast, using the Reference 160 S could hardly be simpler. You, or your dealer, must install the tubes—and then there’s almost nothing else to do, other than to replace them every few thousand hours (footnote 2). Back-panel mechanical toggle switches let you set the fan speed, activate the auto-off feature (which, when activated, turns the amp off after two hours with no signal, extending tube life), and choose between the balanced (XLR) and unbalanced (RCA) inputs. You can read the number of hours your tubes have been in use from a recessed back-panel LCD display.

On the front panel, you can set the brightness of the lit-up power meters or turn those lights off completely. You can push the Tube Monitor button to check tube operation: If all is well, eight green lights light up on the front panel, one for each KT150 tube.

And then there is the big decision: triode or Ultralinear?

Tube-audio experts, please indulge me while I briefly explain what this means. The KT150 tube is a tetrode, which means it has two grids instead of just one as in a triode. You can turn it into a triode by electrically connecting the screen grid—the grid closest to the plate—to the plate. Alternatively, you can apply a constant voltage to the screen grid and you have pentode operation, used by many Audio Research amplifiers.

Footnote 1: The 160 S’s single power cord is thick, apparently well-shielded—and terminated on the amplifier end with a “C19” IEC connector. Gordon told me they chose the C19 connector because it “makes a very solid chassis connection and sounds better than the C15″—C15 is the standard IEC connection used by almost all other audio components. This is something to keep in mind if you’re accustomed to using aftermarket power cords, since the standard ones won’t work here.

Footnote 2: 4 ARC says the KT-150s should be replaced every 3000 hours, and the 6H30s every 4000. There’s an hour meter around back.

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Audio Research Corp.

6655 Wedgwood Road N., Suite 115

Maple Grove, MN 55311

(763) 577-9700

audioresearch.com

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