While the Amplifier Technologies, Inc. brand is a relatively “recent” entry in the contemporary audio scene, its owner and founder Morris Kessler is most assuredly no neophyte. Kessler’s design and manufacture pedigree goes back more than forty years to the legendary S.A.E. amplifiers. Now, he and his team do what they do best—make well-built and great-sounding power amplifiers. ATI has entered the world of multi-channel amplifiers with a vengeance and their newest AT52XNC line range from two-channel to eight-channel models with X representing the number of channels onboard.
During his long and innovative journey, Kessler has explored amplifier designs, ranging from Classes A, A/B, and more recently, D. Also known as “switching” amplifiers, Class D designs are highly efficient, saving on both size and heat production. Class-D amplifiers generate a train of square pulses of fixed amplitude but varying width and separation, reflecting the amplitude variations of the analog audio input signal that can be maintained and manipulated in the digital domain. While such amplifiers have long been used in automobiles and mobile phones, the past decade has seen their application to high-end audio components. ATI has been behind the development of Theta Digital’s Prometheus Class D monoblocs that, depending on speaker impedance, can crank out up to 850 watts per side.
The AT52XNC amplifiers all incorporate the same innovations that include microprocessor control for turn-on delay, and automatic AC power recognition (117V or 230V, nominal power). These amplifiers also incorporate a novel “sleep” circuit when no signal is present for 10 minutes. Power is then removed from the output modules and a front-panel LED begins to flash. Normal playback resumes as soon as a signal is detected at any of the inputs. Regardless of how many channels are included, all the AT52XNC series are rated at 200W per channel into 8 ohms.
With a product slogan of “American Muscle,” all ATI amplifiers are built in the USA to strict specifications, starting with toroidal power transformers with MOH cores and “bifilar winding” that ensures each channel has a separate power supply. Hypex N-Core NC-500 Class D amplifier modules power each channel and are considered to be among the very best in the business. The chassis is cold-rolled steel (CRS) that receives a smooth powder-coated finish. Gold-plated RCA jacks are mounted directly to the rear panel. Double-sided glass epoxy circuit boards and premium components with clean-as-a-whistle wiring complete the picture. Optically coupled circuits that are entirely out of the signal path protect each amplifier.
Out of the box, at just north of fifty pounds, this amplifier can be placed on a rack or stand with a modest amount of physical effort. The Amplifier Technologies Inc. AT524NC façade comes in a standard black finish (silver is a $100 option) and has a central logo, status lights, and power button. The rear panel has two rows of inputs, RCA and XLR, that can be selected by small toggle switches next to each input. Below the inputs are speaker connection posts that can accept bare wire, spades or banana plugs. On the far right is a 12-volt trigger input (a 3.5 mm mini-plug cable is supplied), a ground terminal, fuse holder and 20A power cord receptacle. A true plug-and-play component, once the input modes are selected and speaker cables and power cord attached, you push the on-button and the sound emerges.
During this review, I used a Casablanca IVA controller as the preamplifier (same parent company) with digital sources that included an Oppo BDP-105 and PS Audio PerfectWave Transport and matching DAC. My second listening room is 18’ x 12’ x 8’ (L x W x D) and already houses a pair of Totem Mani-2 Signature speakers on custom Sound Anchor stands. Because these are bi-wireable monitors, I used all four channel of the AT524NC to light them up.
Hearing is Believing
Having lived with the Amplifier Technologies Inc. AT524NC for several weeks, driving relatively insensitive speakers (85dB at 1m), it was clear that I was on to something good. With the transparency of the Casablanca controller, any colorations or flaws in the presentation of recorded sound that are due to the next link in the sound chain, i.e. amplification, would become readily apparent. Voice reproduction is my gold standard for evaluating audio components. Starting with Radka Toneff’s 44.1kHz/16-bit version of “The Moon is a Harsh Mistress,” a breathy, warm ballad was placed firmly into the middle of my room while pianist Steve Dobrogsz provided well-balanced accompaniment. Speaking of the piano, this instrument presents a huge challenge to recording studios, regardless of medium used to capture it. Aussie pianist Fiona Joy has had the good fortune to hook up with Cookie Marenco’s Blue Coast label and the DSD recordings that have resulted are simply sensational. Any of the cuts from her recent SACD Into The Mist will serve as a tutorial on how to record a piano, getting the percussive elements, soundboard overtones, and pedal decays just right. The dynamic demands placed when heard at life-like levels often push lesser amplifiers into clipping: here, no problem whatsoever.
Larger scale works included a stunning program of Stravinsky orchestral pieces, rendered by Eiji Oue and Minnesota Orchestra on a Reference Recordings DVD-R (176.4kHz/24-bit) disc. The Firebird Suite blasts out of the gates at the nine-minute mark and there was no shortage of bass slam from my smallish monitor speakers. Having heard so-called high-end Class D amps before, I was simply unprepared for how well this passage was conveyed via the AT524NC with headroom to spare. Numerous listening sessions concluded with a DSD64 hi-res download of legendary bluesman David “Honey Boy” Edwards and friends on “Shake ‘em on Down.” The capture of every musical nuance, foot tap, spittle, and head movement resulted in a very realistic program laid down in APO’s Blue Heaven Studios in Salinas, Kansas.
The Final Assessment
At $2599 (for four channels, as reviewed) and $1895 (for two channels), the Amplifier Technologies AT524NC Class D amplifier’s high performance level certainly justifies its purchase for a first-rate stereo or multi-channel home theater system. Highest recommendation.
(Special thanks to Craig Shumer at Theatermax for providing us with sample for this product review)
- Analog Audio Inputs
- One RCA and One XLR per channel
- Input Impedance/Sensitivity
- 47 K Ohms/1.5V (200W RMS)
- Power Output (per channel, all driven)
- 200W (8Ω 20-20kHz, <0.02% THD)
- Intermodulation Distortion
- Frequency Response
- +0, -5dB, 5Hz-20kHz, load independent
- Damping Factor
- >5000 at 100 Hz; >1500 at any frequency up to 20kHz
- S/N Ratio (IHF “A” weighted)
- Slew Rate
- >60V per microsecond
- Power Requirements
- 117V AC, 230V DC, 50/60 Hz
- Power Consumption
- Less than 1W at Standby; 1800W maximum
- Power Requirements
- 117 volts, 50-60 Hz
- 19.5 kg (43 lbs)
- Dimensions (W x H x D)
- 432 mm x 145 mm x 270 mm (17” x 5.6” x 10.6”)
Amplifier Technologies, Inc. AT524NC Power Amplifier is available from authorized ATI dealers at an MSRP of $2599
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