August 2020

Audio Research Reference 160M Monoblock Amplifier
Another home run from Minnesota!
Review By Rufus Smith

  I was reintroduced to Audio Research around two years ago when I had the opportunity to review the outstanding LS28 / VT80 combination for Enjoy the Music.com. In the past, I have found Audio Research's amplifiers to be very analytical but somewhat sterile sounding. The ARC LS28 / VT80 (reviewed here) still had all of the traditional ARC sounds, but they now had developed some of the classic euphonic conrad-johnson sounds. For me, this combination was heaven on earth. It was the best of both worlds. I ended up buying the combination and have used it as part of my reference system for the last three years.

The Audio Research VT80 amplifier was powered by four KT120 vacuum tubes, which has much higher bass slam than the 6550s I was used to with ARC amplifiers in the past. The increase in the bottom end was due in large part to the greater plate dissipation of the KT120 tube. In November 2017, Audio Research announced the upgrade to SE status for the VT-80 with the addition of the KT-150 tube. ARC favors the sound of this tube as it is used in every other amplifier in the line, except for the VT-80. The upgrade consists of removing the KT-120s and replacing them with the 150s. The two tubes are interchangeable, and with the VT-80's auto-biasing design, the circuit automatically adjusts for the new tubes operating parameters. The advantage of the 150 is longer tube life, 3000 hours compared to 2000 hours for the old 120 tube.

After the untimely failure of one of my KT-120s, I decided this would be the perfect time to send the amp back to ARC for a checkup and the upgrade to the KT-150. In my opinion, the KT-150 brought improvements in tonal color, detail, and overall dynamics to the amplifier. There was also a very noticeable improvement in the overall presentation of the music. Of course, this led me to think about what one of the Reference Series Amplifiers with KT-150s would bring to the system. So a call went out to David Gordon, the Managing Director of Sales for ARC. David has been with Audio Research for almost 25-years. He knows the products as well as anyone as he has been with the company when owned by founder William Z. Johnson through the purchase of the company in 2008 by what is now the McIntosh Group. David graciously offered to lend me a pair of the Reference 160M monoblocks as he felt that they would be a good match with the Verity Otellos (review forthcoming) that were occupying center stage in my listening room.

Two weeks later, I was standing in my garage, looking a pallet with two large boxes sitting in my wife's parking space. Oh lord, I thought, this is going to be fun getting these into the house before Julie got home. Naturally, a call went out to all my friends for help. They can sense whenever I need help moving stereo because they all seemed to have disappeared. Getting them into the house proved more straightforward than I thought after removing the boxes from the pallet and making use of my trusty old hand truck. Now I faced step two of the process, which was getting the amplifiers up to my second-floor listening room. Step two was solved by a trip back in time to my high school football days. I discovered that the box would lay over several of the treads without getting stuck. My solution was to get low to the stairs and pretend that Coach Herring was on the blocking sled yelling at all of us offensive linemen. "Move those knees and keep those feet moving," implored Coach. Keeping low and keeping my feet moving, I drove those boxes up the stairs. The Coach would have been very proud.

Time For Installation
Installing the Audio Research Reference 160 monoblock amplifiers into my system was very straight forward. Measuring 10" high by 19" wide by 19.25" and weighing 56 pounds, making it easy to handle by one person. After unboxing the amps, I installed them on a pair of Sound Anchor Amp Stands that were initially built for a pair of Pass Labs Aleph 1.2s. In moving the amps, you need to pick them from the front and the back because the majority of their weight is located in the rear underneath the transformers. To install the tubes, one removes the covers using the supplied screwdriver and placing the two 6H30 driver tubes and the four KT150 output tubes. When reinstalling the well-ventilated cover, remember to plug in the 12V lead for the built-in two-speed fan into the socket on the amp.

The ARC 160M amplifier follows what has become the standard aesthetics, and they are available in the classic silver or the optional black finish. The review pair was finished in black. I am not a fan of black components, but these really grew on me over time. The front panel features two handles, and four pushbuttons sit centered under what may be the coolest feature of the amplifier, the GhostMeter. The GhostMeter serves two purposes: First, it serves as a window that allows the listener to enjoy the glow of the tubes from the listening position and, second, it serves as a power meter. Constructed of two plates of acrylic, one side is etched with the markings for the meter. The needle is sandwiched between the two plates and with illumination provided by white LEDs below the meters resulting in an optical illusion of the meter floating in space. The only way I know to describe the look is "sexy as hell."

The four pushbuttons below the meter are labeled Power, Meter Light, Tube Monitor, and Ultralinear / Triode Mode. Pressing the Power Button fires the amp up and illuminates a green LED that blinks for approximately two minutes until the voltages stabilize, indicating that the amplifier is ready for operation. The next button, for the Meter Light, toggles you through the three brightness levels for that sexy meter. Pressing and holding the Tube Monitor Button lights up the associated LED for each tube. Green indicates that the tube is okay. The last button switches the amplifier from ultralinear mode to triode mode. Triode operation is indicated by the color of the LED above the button changes color from green to a light blue/white color. The switch from ultralinear to triode drops the power from 140 Wpc to 70 Wpc.

The top of the amplifier has the sockets for all the tubes, as well as two E-Core transformers. It is these transformers that account for most of the weight of the ARC 160Ms. The E-core transformers are favored by ARC for their sound and are preferred over toroidal transformers because of their sound. All transformers utilized by ARC, regardless of their type, are designed in house and are custom manufactured by USA-based third-party manufacturers.

The rear panel features the hookups for the speaker cable utilizing taps for 16, 8, and 4 Ohms and common ground. ARC recommends that you play around with the connections to find which works best with your speaker.  Centered on the rear are both balanced and single-ended inputs with a toggle switch to select the input in use. There are two more toggle switches to set the fan speed (slow or high) and one that enables auto shut-off, which was defeated for the duration of the review. There is also a digital display that tracks the number of hours on the output tubes. The display is a godsend for us folks that can't keep track of the number of hours that are on the tubes. Last of all is the connection for the 20-Ampere IEC power cord.

The Reference 160m is the first Reference series amplifier to utilize ARC's new auto-biasing circuit that debuted on the VT-80. The system ensures that the KT-150s operate at their peak efficiency throughout their life span. It also allows for the use of 6550s, KT-88s, KT-90s, or KT-120s, but that brings up the question of why you would want to. As noted above, all of the company's transformers are designed in-house but are built by US-based subcontractors. The same is true for the capacitors and wiring used in the design. The amps also make use of a four-layer PCB board, which is a first for an ARC product. The boards are hand assembled in-house using a special solder. According to Dave Gordon, the use of a properly laid out circuit board outperforms a board that utilizes point-to-point wiring, which can act as an antenna attracting noise to the circuit.

Time For A Listen
Now on to listening. Immediately on firing the amps up, all of the attributes that I loved with the VT-80SE were there but were considerably better. I expected improvement, but not this. Simply put, the 160m's are a revelation. I began my listening with Chelsea Williams' LP Boomerang [Blue Elan Records, BER1047]. This album beautifully blends the three styles (indie-folk, country, and pop) that have defined her career. Each song flowed from a darker background that allowed the beauty of her voice to shine. Instruments were more clearly defined, and it was easier to follow the individual lines played. I love the sound of a harmonica, and it is nice to see one used to such an effect. Ross Garren's playing on this album is virtuoso. On quite a few records, I find harmonicas to be somewhat bright and edgy. Not valid when reproduced by the Audio Research Reference 160 monoblock amplifiers. They nailed it.

Richard Strauss' Also Sprach Zarathustra [RCA Living Stereo, LSC1806], as performed by Fritz Reiner and the Chicago Symphony Orchestra, is a sonic tour de force prized by audiophiles for decades. To experience this album, one only needs to listen to the first 21 bars, which opens with a sustained low C (pianissimo) played on the organ, double basses, and the contrabassoon. The opening transforms into a trumpet fanfare proclaiming the "World-Riddle" theme followed by the sharp timpani strikes with their incendiary transients that lead the listener into a rising crescendo of the full orchestra and organ leading to a climax that washes over the listener like a vast tsunami. The ARC 160M amplifiers give the listener a remarkable sense of the not only sounding louder but in a spatial sense as the sound fills the hall.

The tonality of each instrument was realistically reproduced cleanly with no smearing or unnatural artifacts. When the orchestra rose to a crescendo, and the intensity increased, the hard-to-hear details emerged from a dark background with a clarity that is required listening. This amplifier accurately reproduced dynamics from the lowest pianissimo to the loudest fortissimo with no hint of compression. No matter what I played over the three months I lived with this amp was reproduced as the musicians and the recording engineer envisioned it. It did not matter, rock, jazz, classical, bluegrass, or whatever; it is presented in all its glory. This amplifier does not care what you run through it; it will reproduce it as intended.

I did some of my listening with the amp in triode mode. I found the amplifier in triode mode to be warmer sounding than neutral. Overall, instruments sounded a tiny bit flatter with less definition, and colors were not as vivid. It reminded me of the Audio Research of old. It wasn't bad per se, just different. I could listen with either, yet I prefer ultraliner mode. Depending on the recording, there may be times the triode mode sounds better to my ears within my hi-fi system.

For most of the review, I used my Dad's Thiel CS 1.5 speakers as my regular speakers need to have their woofers replaced. I must admit that as good a speaker as that little Thiel is, the Audio Research Reference 160 monoblock amplifiers takes them to a different level. For the first time, I honestly heard them as the late Jim Thiel intended. About a month into the review, I received a pair of the Verity Audio Otello Loudspeakers for review. With the Otello's in the system, all of the attributes of the 160s were still there only better. Bass was lower and tighter, midrange clear and focused, and the highs sparkled with just the right amount of sheen. Soundstage depth and volume were more clearly defined. I am genuinely at a loss for words, but with the Verity's, I had found a match made in heaven.

In Conclusion
What can I say about the Audio Research Reference 160M monoblock amplifiers that I have not already said? It is, without a doubt, the most excellent amplifier of any type that I have ever had in my system. It was a somber day when I had to send them back. Since returning them, I have made some significant upgrades in my system's front end, replacing both my digital and analog systems. Oh, how I wish I had them back. Dave, if you accidentally send another pair my way, I won't tell anyone (hint, hint). They are a fantastic world-class amplifier and are, in my humble opinion, the finest amp to ever find its way out of Minnesota and are a true testament to the legacy of Bill Johnson.

Specifications
Type: Vacuum tube monoblock power amplifier

Tube Compliment: Two matched pairs of KT150 for output and two 6H30 for gain stage. 

Power Output: 140 watts continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% at 140 watts, below 0.04% at 1 watt. (Note that actual power output is dependent upon both line voltage and "condition" i.e., if the power line has high distortion, maximum power will be affected adversely, although, from a listening standpoint, this is not critical).

Frequency Response: 0.5Hz to 110kHz.

Input Sensitivity: 2.4V RMS Balanced for rated output. (25.5 dB gain into 8 ohms).

Input Impedance: 200 kOhms via balanced XLR.

Output Polarity: Non-inverting, balanced XLR input pin 2+ (IEC-268).

Speaker Output: 16, 8, and 4 Ohms.

Output Regulation: Approximately 0.6dB 16 Ohm load to open circuit.

Damping Factor: Approximately 14

Overall Negative Feedback: 14dB

Slew rate: 13 Volts / microsecond

Rise Time: Two microseconds.

Dimensions: 17.25" x 10" x 18.5" (WxHxD)

Weight: 56 lbs each

Price: $30,000 per pair

Company Information
Audio Research Corporation 
6655 Wedgwood Road North
Suite 115
Maple Grove, MN 55311

Voice: (763) 577-9700
Website: www.AudioResearch.com