Accustic Arts Audio Mono II monoblock power amplifier

Accustic Arts of Lauffen, Germany, was founded in 1997 by Fritz Schunk, who sold the company to Hans-Joachim "Jochen" Voss in 2016. Voss's professional background had more to do with sweet spreads than sweet sounds—he spent 20 years doing sales and marketing, including with the Ferrero Group, which produces Nutella—but he happened to own some Accustic Arts components, and as a music-loving consumer with a special fondness for rock, had been in touch with Schunk for many years before the company went up for sale.

In an extended Skype conversation with Voss and Sebastian Ruhland, a technician at Accustic Arts, I learned that the 55lb, 300W (into 8 ohms), solid-state Mono II ($24,900/pair) was released six years ago but has been unavailable here for much of that time, owing to a lack of distribution: It and the company's other products have only recently been brought to the US market. Incidentally, the Mono II's predecessor, the 121lb Amp II stereo amplifier, has been a company staple for almost two decades, while the larger Mono III, a far heavier (132lb) and higher-powered (650W into 8 ohms) mono amplifier, came out in 2016.

According to Voss and Ruhland, Accustic Arts amplifiers are improved over time; the Mono II's most recent upgrade involved a change to the toroidal transformer core to deal with hum issues that developed in countries with widely fluctuating voltage. "We optimize the product all the time," Voss said. "For example, we recently upgraded the circuit boards without telling anybody. If we changed the amp's name with each improvement, it would be Mk. XX by now." If you're shopping for a used Mono II, be sure to note the serial numbers and check with the company to confirm its provenance.

The Accustic Arts website says that the Mono II includes 12 "selected" MOSFET output transistors; a magnetically shielded and encapsulated toroidal-core transformer with a capacity of 1200VA; more than 80,000µF of power-supply capacitance; a "very high damping factor for perfect speaker control"; capacitors by Fischer & Tausche, from the northwest corner of Germany; "generously dimensioned" heatsinks; and two pairs of gold-plated speaker terminals, for biwiring. In addition, Ruhland said, "To drive the MOSFET amplifier, we use a current mirror, in which the same current that flows through one transistor also flows through the other.

"We don't use the voltage amplifier to drive the MOSFET; we use the current mirror. I have not seen that very often—only one company does it somewhat the same way. Using the current mirror, you don't need MOSFET driver ICs that make more noise and add distortion. Using the current mirror lowers distortion and raises signal-to-noise ratio."

Installation and setup
After I recruited a friend to help move my 125lb reference Dan D'Agostino Progression Mono amplifiers out of the way, setup was simple. Positioning the Mono IIs on my Grand Prix Monaco amp stands was easily accomplished, as was attaching the same Nordost Odin 2 balanced interconnects, speaker cables, and power cables as I use with my reference amps. (While I did try the surprisingly thin, molded-plug AC cords supplied with the Accustic Arts amps—see below—I stuck with my reference Nordost Odin 2s for 99% of my listening.) Given that the amp's speaker lugs are easy to loosen and tighten, and that the two sets of speaker terminals are identical, you need only make sure to attach your speaker cables in phase and depress the Input Selection button on the monoblock's back panel to the correct position (Balanced/XLR or Unbalanced/RCA).

The handsome front panel includes three LEDs, used to indicate whether the powered-up Mono II is in warm-up mode or ready to play; once you depress the sole on/off button—there is no standby power switch on the amplifier's rear—the light show lasts five seconds and then the amps start producing sound. I always reserved at least an hour for warm-up, which I hastened by playing demagnetization and break-in tones from my Nordost System Set-Up & Tuning CD.

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I asked Voss about power conditioning during our Skype interview. "It's up to you," he told me. Ruhland noted that in some locales, large voltage swings or DC offset on the line—or a proximate hair salon—could make a power conditioner necessary: "When you use a hair dryer next to your amp, maybe you'd better use a power conditioner." Even though my system gets its AC via a dedicated 8-gauge line and special AudioQuest outlets, experience suggests that the music room's second breaker panel picks up noise from both the panel in the main house and the transformer in the street. So for most of the review, I plugged the Mono IIs into the same AudioQuest Niagara 5000 noise-dissipation system fed by the same AQ FireBird HC power cables I use with the Progression Monos.

Although Voss confirmed by email that the amps had been broken in at the factory, Accustic Arts' US rep, Randy Forman, told me that, in his experience, an extra 100 hours was needed. I played break-in tones 24/7 for five days. I encountered just two issues with the Mono IIs. The first was minor: The on/off buttons didn't always depress smoothly. Although neither ever got stuck, they felt a bit chintzy. More concerning, the left-channel amp began to hum audibly on my last day of listening and continued to do so even when I removed it from the Niagara 5000 power conditioner and plugged it into the wall outlet. I checked to see whether appliances were running full force in the main house—the eightfold assault of washer, dryer, dishwasher, electric range, refrigerator, heat pump, and two computers—but the three wire-haired terriers had once again failed in their ongoing attempts to turn everything on and burn down the house. (They love the chorus of Aretha Franklin's "Think," which they bark in cadence, but have yet to embrace the notion of "Respect.") Perhaps John Atkinson's measurements will detect what the hum was about.

Yippee, it's time to listen
Because I review music for Stereophile, my first listens were to unfamiliar recordings. Lacking a baseline reference, I may have been a bit at sea, but that didn't stop me from loving what I heard. The clarity, beauty, and exceptional smoothness of Jim Anderson's engineering revealed itself as I auditioned Patricia Barber's Higher (our September 2019 Recording of the Month). The glorious voice of soprano Lise Davidsen singing Wagner and Strauss (24/96 WAV/ProStudioMasters, Decca B003030802) sent me into an ecstatic whistling frenzy, and I was deeply moved—chilled—by the suffering and grief that sang through the recording, by Mirga Grazinytè-Tyla and the City of Birmingham Orchestra, of Weinberg's final Symphony, No.21 (24/96 WAV, Deutsche Grammophon). And if I didn't wax ecstatic about the recording by Sasha Cooke, Kelly Markgraf, conductor Steven Osgood, and the Fry Street Quartet of the chamber opera As One (24/96 FLAC), that was due solely to the music—not the sonics.

COMPANY INFO
Accustic Arts Audio GmbH
US representative: Finest Fidelity
3 Sagebrook Drive
Bluffton, SC 29910
(386) 341-9103
ARTICLE CONTENTS

COMMENTS
JRT's picture

I would like to see Stereophile subjectively and objectively review and test a ~$3k Rotel RB-1590 stereo amplifier, claimed to be two separate monoblocks in one enclosure. Rotel rates it at 350W/channel into 8_Ohms, 4_Ohm min load, 120_dB s/n A-weighted (presumably referenced to full power), 0.03%_THD over the range of 20_Hz to 20_kHz, frequency response 10_Hz to 100_kHz ±0.5dB.

It would have been interesting to know how that $3k Rotel subjectively and objectively compares to this $25k/pair Accustic Arts Audio Mono II monoblock power amplifier, after being rebuilt with proper power supply transformer (these big mistakes are not confidence building). More than 8x the price should buy some nontrivial improvement, else the opportunity costs need further consideration.

Bogolu Haranath's picture

For $3,000, we can also get PS Audio Stellar mono-blocks (Stereophile Class-A) 350 WPC 8 Ohms and 700 WPC 4 Ohms :-) ...........

Ortofan's picture

... following are a couple of other subjective and objective reviews to tide you over:

https://www.bwgroup.ch/wp-content/uploads/2016/11/Hi-Fi-News-11-2015-Test-Rotel-RC-1590-RB-1590.pdf

https://hometheaterhifi.com/reviews/amplifier/preamplifier/rotel-rb1590-rc1590-preamplifier-power-amplifier-review/

JRT's picture

I had not seen those.

Ortofan's picture

... in the Mono II's price range, you know what to do next."

Permit me to finish that thought.
Buy a pair McIntosh MC1.25KW or a pair of Pass Labs X600.8 amps.
Or, if you can live with a two-channel amp, then a Pass Labs X350.8 or a D'Agostino Classic 2 will save you about $10K.
Better yet, save another $10K with a Parasound JC5.

Bogolu Haranath's picture

You could also consider the new Krell Duo 300-XD stereo-amp ($10,500), 300 WPC into 8 Ohms :-) ........

Ortofan's picture

... four fans. No thank you.

Bogolu Haranath's picture

For most of the listening levels those fans probably won't turn on ........ Even if they did, the noise levels would be low enough, not to interfere with the listening to music ......... See Stereophile review of albeit more powerful older model Krell Solo 575 mono-blocks .......... MF did not mention any thing about fan noise interfering with his listening :-) ..........

Bogolu Haranath's picture

Or, you could also consider McIntosh MC462 stereo-amp ($9,000, Stereophile Class-A), 450 WPC 2, 4 or 8 Ohms :-) ..........

Ortofan's picture

... high enough into lower impedances. Good try, though.

Bogolu Haranath's picture

450 WPC 2, 4 or 8 Ohms ....... For most of the music, for most listeners, for most of the listening levels, with sensitive speakers, we probably don't need more than 450 WPC :-) .........

Bogolu Haranath's picture

McIntosh MC462 can deliver more power than specified 450 WPC ........ See Stereophile measurements :-) ..........

Bogolu Haranath's picture

Or, you could also consider Bel Canto REF600M mono-blocks ($4,990, Stereophile Class-A), 300 WPC into 8 Ohms :-) ..........

Ortofan's picture

... emits ultrasonic switching noise. Strike three.

Bogolu Haranath's picture

No human being can hear that high ultrasonic switching noise ......... No tweeter can reproduce that high ultrasonic switching noise ........ No music extends into that high ultrasonic switching noise ........ See Stereophile measurements of Bel Canto REF600M :-) .........

Ortofan's picture

... what we can or cannot hear. No audio amp should be radiating RFI.

Bogolu Haranath's picture

Ok ..... Don't use your smartphone or AM/FM radio or turn on your TV, while listening to music :-) .......

Bogolu Haranath's picture

If you insist on high power, in addition to the amplifiers you mentioned above, we can also consider the Bryston 28-B/3 ......... 1000 Watts into 8 Ohms and 1800 Watts into 4 Ohms ....... $24,000/pair ....... See Stereophile review of older model Bryston 28-B :-) ..........

Ortofan's picture

... suggestion. Even the 7B³ would be sufficient to far exceed the power ratings of the Accustic Arts amp, plus the Bryston 20-year warranty is not to be sneezed at, unless you're afflicted with upgrade-itis.

Bogolu Haranath's picture

Thank you ....... I could finally appease you :-) .......

Bogolu Haranath's picture

I think that 20 year warranty is also transferable :-) ........

georgehifi's picture

"Manufacturer's Comment
Editor: The lack of performance of the Accustic Arts Mono II power amplifiers was caused by the fact that we unfortunately installed wrong transformers."

When sending a product sample to be reviewed and thoroughly bench tested to Stereophile, one would think that a company would give it's very best sample, (even "cough" better spec'd) than a production one, to be showcased in a magazine that will make or break that product.

this sort of answer happens way to much for my liking
Cheers "cynical" George

georgehifi's picture

"Bel Canto REF600M .........
Submitted by Bogolu Haranath on October 4, 2019 - 2:26am
No human being can hear that high ultrasonic switching noise ......... No tweeter can reproduce that high ultrasonic switching noise ........"

You are correct, but you can hear the effects of the Class-D's output filter that has to get rid of that switching noise, with phase shifts that are large (up to 70 degrees!!!) that reach down to 1khz. That's why many complain about the upper mids and highs with class-D.

(copy and paste this link to your browser)
https://ibb.co/hd9qNC7

Cheers George

Bogolu Haranath's picture

There are/were several Class-D amps and integrated amps included in the Stereophile recommended component lists ....... Many of of them earned Class-A distinction in sound quality and in measurements ....... Bel Canto models are one among them ....... Why is that? ........ Heaven forbid, you are not questioning the hearing ability of the Stereophile reviewers, are you? :-) .......

georgehifi's picture

Reviewers have subjective outlooks, each to his own, but surely no one would turn a blind eye to the phase graph linked in my last post above?

Cheers George

Bogolu Haranath's picture

That one is above my pay-grade ........ May be JA1 with his technical expertise could shed some light on that particular topic :-) ..........

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