The $50,000, 176lb Accustic Arts AMP V (pronounced Amp Five) is the heaviest, tallest, most powerful, most expensive stereo amplifier to enter my audio system. With rated power of 900Wpc into 8 ohms, 1360Wpc into 4 ohms, and 1500Wpc into 2 ohms, the AMP V, which stands proud at the top of the Accustic Arts amplifier line, surpasses my reference D’Agostino Progression M550’s rated power into 4 ohms by 260Wpc (footnote 1).
What, if anything, might those extra 260Wpc—and those extra pounds of transformer and heat-dissipating metal—mean sonically in my moderately sized listening room? I was determined to find out.
Rock the joint
“I listen mainly to rock and a few classical tracks—for example, The Planets,” AMP V designer Sebastian Ruland told me during a WhatsApp chat that also included Hans-Joachim “Jochen” Voss, the owner of Accustic Arts. “This is the main thing I was thinking about musically when I was designing.”
“We wanted sound that’s authentic and natural,” Voss added. “Some electronics sound overly analytical. We have tried to make the AMP V sound as natural as live music, from the bass to the heights, without overdoing the bass. Our goal is to produce really solid, good-sounding music that works with all good loudspeakers. For example, we’ve been at AXPONA with Magico and Van den Hul.”
The AMP V is the successor of the AMP III (footnote 2), but almost everything about the AMP V is new. “The AMP III, which was in production from 2011 to 2016, was taller and looked more like a cube. It also lacked sufficient space inside,” Ruland said. With no concern for designing to a price point, Accustic Arts “did what we needed to do [as we] created our biggest stereo amp, with a 30% price increase from the AMP III.”
The AMP V remains a current-mirror, dual-mono MOSFET design. The V has 40 MOSFET output transistors, identical internal cabling, and identical, “improved” printed circuit board (PCB) traces for each channel. The improved tracings are part of a new PCB design that includes gold-coated traces and gold-plated contacts; they’re said to raise the damping factor and improve “other parameters”—that’s from Ruland. Everything is hand soldered. “In the AMP III, there was a problem with high frequencies and high power,” he acknowledged. “The protection circuitry inside the amp would sometimes be triggered if, for example, you took a 16kHz signal with 20 volts on the output. The new PCB addresses this.”
“The gold maintains constant contact resistance. There’s no corrosion or anything like that, and no change over time,” Ruland said.
Two pairs of new, gold-plated WBT speaker terminals allow for biwiring or biamping. The AMP III had only single-ended inputs, but the AMP V is a fully balanced class-AB design with an added pair of balanced inputs. Ruland estimates that as much as 8% of the amp’s output is in class-A. That’s close to 100W.
Ruland designed the amp’s two identical, magnetically shielded toroidal power transformers, which were manufactured in a facility 80 miles away; it’s the first time Ruland has designed the transformers in an Accustic Arts amplifier. Accustic Arts says the power supply has capacitance in excess of 220,000µF. To remove any possibility of hum—I heard none—transformer inductance was decreased by increasing the number of windings. “It’s about the ratio between input windings and output windings,” Voss said. “To get more power, we had to increase the output voltage as well.” The AMP V boasts 40% more power than its predecessor and is, in Voss’s opinion, “more musical.”
Damping factor linearization
New to the AMP V and its MONO 5 sibling is “damping factor linearization,” an option engaged by pushing the Damping Control “On/Off” button on the amp’s rear panel. According to the 1½-page explanation in the AMP V’s well-laid-out, printed instruction manual—it was not available online at press time—modern, high-power transistor amplifiers have very low internal resistance and therefore naturally high damping factors. “These high damping factors are desired because they have a very positive effect on important technical parameters, eg, on distortion characteristics. … The degree and progress of the damping-factor influence … the control of the connected loudspeaker by the power amplifier.
“Claims are often made that a higher damping factor is better for controlling the loudspeaker, and therefore the system sounds better. That is not the case. Correct is that a power amplifier with a very low damping factor is not able to sufficiently control the loudspeaker. It is, however, true that a loudspeaker does not have the best outswing behavior with the maximum damping factor. The truth is that the value of the damping factor should … be within a certain range which is ideal for the loudspeaker and should be linear for as long as possible over the frequency range.
“In order to meet these two requirements—ideal range and linear curve—we lower the complete value of the damping factor slightly to the ideal value and then linearize it over a wide frequency range.” All this happens, of course, only when Damping Control is turned on. When the damping factor is not engaged, “the absolute damping factor is then maximized, but from 5kHz, decreases considerably.”
Voss and Ruland both noted that damping-factor linearization is intended to improve control of difficult loudspeakers. When the damping control is activated, they say, the AMP V will better convey attack on low bass. To quote Voss: “We listened to Outbreak [by Dennis Chambers] in our listening room once with active linearization and once without, and we can hear the difference: Without linearization, the song sounds somewhat held back. Activating the linearization adds more dynamics to the mix. The entire recording gains more openness and room to breathe.”
Setup
Acknowledging my physical limitations, I asked two fully vaccinated weightlifters from my gym to help hoist the AMP V onto the top shelf of my four-tier rack. When they arrived, they saw no way to position it without wedging a hand between it and the D’Agostino Momentum HD preamp that would sit alongside it atop my four-tier, eight-shelf Grand Prix Audio Monza double rack. So instead, they lifted one of the 115lb D’Agostino Progression M550 monoblocks from one of my low-lying Monza amplifier stands onto that top shelf and replaced it with the AMP V.
The AMP V requires two 15A power cables, one for each transformer; their receptacles are positioned one above the other on the rear panel. Also on the rear are three buttons: one to engage the Damping Control, another to engage “Mute,” which keeps the unit at “perfect” temperature for optimized sound and should be used only for “very short listening interruptions,” and a third to choose between the AMP V’s single-ended and balanced inputs.
There are two sets of speaker outputs. Two ground contacts are intended for use with shielded, groundable speaker cables.
Behind the power button on the front plate, the AMP V has two power switches, which operate together to disconnect both channels from the power supply. This is not a standby button but a main power switch.
On the front panel, directly below the power button, is a small blue LED flanked by two red LEDs. The red LEDs light up during warmup, after the power button is depressed, which takes about five seconds. When the red lights go off and the blue LED lights up, the AMP V is ready to play music. If a red LED remains lit, there’s an error on that channel.
Accustic Arts counsels switching on the AMP V last and turning it off first. They also recommend against turning the amp on and off frequently. “The high amount of switch-on current is a heavy burden for the electrical components” and can “shorten the amp’s life.”
One related thing, which the company says is “VERY IMPORTANT!: After switching the unit off, please wait 60 seconds before switching it on again.”
Footnote 1: My Wilson Audio Alexia 2 loudspeakers have 4 ohm nominal impedance.
Footnote 2: The smaller, forthcoming AMP IV is, similarly, the successor to the AMP II.
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COMPANY INFO
Accustic Arts Audio GmbH
US distributor: Rutherford Audio
14 Inverness Drive East, Unit G-108
Englewood CO 80112
(303) 872-6285
rutherfordaudio.com
ARTICLE CONTENTS
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Specifications
Associated Equipment
Measurements
Manufacturer’s Comments #1
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