Music in the Round #83: ATI & Monoprice 3-Channel Amplifiers

The power-amp saga continues. For months, I've been plowing through the market, searching for something to drive my three front speakers. (I use a two-channel amp for the surrounds.) It can be a three-channel amp or three monoblocks—it just has to sound great with my speakers, and be light enough that I can lift it by myself when I need to rearrange my system. I'd finally settled on Classé's Sigma Monos for their transparency, and because I can manage their weight, one at a time. At the CEDIA Expo in September 2016, I saw two more candidates worthy of consideration. Review samples of both arrived here almost simultaneously.

ATI AT543nc three-channel power amplifier
Amplifier Technologies, Inc. (ATI, footnote 1) is a well-established company founded by Morris Kessler, who first made a splash in audio in 1967 when he co-founded SAE. ATI makes a wide range of audio devices under its own name, as well as under brand names it has acquired, including B&K and Theta Digital, as well as SAE. In addition, it has produced amplifiers for many other companies which I will tactfully not list. Until recently, ATI expended all of its efforts on producing class-A/B amplifiers of solid engineering and performance, but Kessler and Theta Digital's Dave Reich have now stepped boldly into class-D with Theta's impressive Prometheus monoblock and Dreadnaught D modular multichannel amp, both based on Hypex's NCore technology. Larry Greenhill raved about the Prometheus, and I was as enthusiastic about the Dreadnaught D.

Class-D amplifiers, particularly those based on Hypex NCore modules, come in many flavors, depending on the manufacturer's choice of power supply, input stage, and bridging, and careful listeners have found that these can sound as different from each other as can conventional class-A/B amps. The use of conventional linear power supplies based on heavy-duty toroidal transformers results in amplifiers that are nearly as heavy as class-A/B designs of equivalent power. For example, the three-channel, 225Wpc Dreadnaught D weighs about 90 lbs—too much for me.


So when I heard about ATI's new line of NCore amps, I figured that the same expertise was behind them, and that there should be some cost savings, particularly as they lacked anything like the Thetas' elegant cases. ATI's new line borrows from the flexible modular designs of the Dreadnaught D and so is quite comprehensive, comprising 200Wpc models of two through eight channels ($1895–$3995) and 500Wpc models of two, three, and four channels ($2595–$3995), in two sizes of case. All cases are 17" wide and 5.75" high, but can be 10.625" or 15.5" deep. I opted for the three-channel, 500Wpc AT543nc ($3295, plus $95 for optional rack-mount kit), which weighs 57.5 lbs—no lightweight, but I can move it when I must.

Description: Inside the AT543nc are two modules, one with two amplifiers and the other with only one. Each amp has a pair of NCore NC500 boards that are fed via ATI's custom input/gain stage and bridged for the high rated output. These are powered by a conventional linear power supply with a 950kVA toroidal transformer to power the two-channel module (with separate windings for each amp), and another 650kVA toroid for the single-channel module. This results in a theoretical difference between the single channel connected to the smaller transformer and the two that share the larger one; with that in mind, I used the latter to power the left and right speakers and the former to run the center—though it's unlikely that this strategy is of practical significance.

At the left of the AT543nc's interior is a self-configuring power supply, which first ascertains the available supply voltage within a range of 90–135V or 200–260V, then configures the transformer taps for local usage. Only the fuse and the power cord might then need to be changed. This power supply also senses and protects against over/undervoltage, overheating, DC faults, and overload. The three small input boards are affixed to the rear panel, the amp modules to the bottom plate, and its two large toroidal transformers near the front panel.


On the right rear of the AT543nc are, from bottom to top: an IEC AC input, an AC fuse post, a ground terminal, and a 3–24V remote trigger input. The rest of the panel has, for each channel, unbalanced (RCA) and balanced (XLR) input jacks and a pair of multiway speaker terminals. Next to each RCA input jack is a little toggle for switching that input between unbalanced and balanced operation. Into the XLR inputs I plugged AudioQuest Earth/DBS and connected the speakers with AudioQuest Oak/DBS biwire, but none of my standard power cords fit the AT543nc. ATI uses a standard 20 amp IEC power inlet, type C20, with three heavy, flat, parallel blades, to ensure that no user substitutes an unsuitably lightweight cord. The provided cord, with matching C19 connector, was barely long enough for me.

On the front panel, from top to bottom at center, are the ATI logo, LEDs for Peak level and Standby, and an illuminated power switch. When the AT543nc is plugged in, the power switch pulses dimly blue to indicate standby mode. Push the button, the Standby LED lights up, and a few seconds later goes dark as the blue power LED glows full: the amp is ready. After 10 minutes without an input signal, the AT543nc shuts down all its high-power functions and goes into Sleep mode; when it senses a signal, it powers itself back up. It has a soft start to minimize power surges, but was so efficient that I found no need to use my 12V trigger wire.

Listening: The AT543nc's sound was immediately appealing in terms of both balance and clarity. In orchestral recordings, the individuation of lower strings and winds and their melodic lines was notable. There was plenty of weight at the bottom end, but it was taut, with no loss of control at any volume level. The same was true of the upper midrange and treble, which were open and airy, but with no glint of brightness.

I played all the reference recordings I've used to evaluate other amps, but the AT543nc was not to be faulted. Every recording of solo voice—male or female, high or low—was reproduced as I would want it, and as I have heard it through this system with the very best amps I've tried. As I played recordings of larger and still larger ensembles, I heard no diminution in the AT543nc's clarity and balance. Power was generous; I got the Peak LED to wink only once, and it was my own fault: with the gain set very high, I switched sources. The AT543nc's recovery was instantaneous and without consequence.

That brief paragraph characterizes the AT543nc's sound quality but is insufficient to distinguish it from other amps. With my Bowers & Wilkins 802 D3 speakers, the AT543nc ran toe to toe with the Classé Sigma Monos, except that the ATI was marginally less detailed in the upper midrange. This was not a significant problem except with some high-resolution files, such as the Color Field Quartet's recording of James Matheson's String Quartet (multichannel DSD256 download, Yarlung YAR25670/NativeDSD), and even those sounded startlingly transparent through the AT543nc.

Footnote 1: ATI Amplifiers, 1749 Chapin Road, Montebello, CA 90640. Tel: (323) 278-0001. Fax: (323) 278-0083 Web:

Odin 412's picture

Thanks for reviewing some power amps at less-than-insane prices! The Monoprice amp sounds like a huge bargain. Great sound at around $1K? I'm interested - I only wish that the amp was a bit smaller. I'm also not sure how "conducive to relaxed, extended enjoyment of music" can become a negative, but to each his or her own.

Kal Rubinson's picture

"Conducive to relaxed, extended enjoyment of music" is not a negative but it does not encompass the full range of my listening experiences.

billtheblizzard's picture

Mr R. reproaches the Monolith as "conducive to relaxed , extended enjoyment of music." He writes "(it) does not encompass the full range of my listening experiences."

Would that full range of listening experiences, by corollary, extend to the obverse of "relaxed, extended enjoyment of music" -- tense, brief and displeasurable? For that is what Mr. R seems to imply. True stereophiles, it seems, listen to music not only for mere pleasure, for that would be bourgeois and pedestrian, but also to wallow (as a masochist) or revel (as Nietzschean Superman) in discomfort, anxiety and unease.

True seekers like Mr. R. understand that a good HiFi set up will be analogous to putting on your hair shirt or flagellating yourself like a devout penitent. One might say: the greater your suffering the superior your system. That which best reproduces nails on a chalkboard is next to godliness sayeth the wise.

"ATI makes a wide range of audio devices under its own name, as well as under brand names it has acquired, including B&K and Theta Digital, as well as SAE. In addition, it has produced amplifiers for many other companies which I will tactfully not list."

That's funny because I thought the job of a reviewer/journalist was to be as transparent and informative as possible. MR R. though must undoubtedly have the best reasons for his policy of obscurantism. It would be jolly arrogant of the Stereophile reader to expect the reviewer to risk embarrassing certain manufactures by revealing the OEM behind a given product and, de facto, the all too obvious massive mark up that comes with the cache of a big name. Heaven forbid the reader be more informed at the expense of a reviewer daring to be untactful! Why should the unwashed readership expect full disclosure from anointed gatekeepers like MR. R?
In the same diplomatic-let's-not-rock-any-boats-"tactful" vein, Mr. R. also does not mention that ATI is the OEM for the Monoprice Monolith Amps. Because how could anything be more tactless than revealing the provenance of a made in the US, $1,000, 200W, class AB amplifier, exhibiting excellent measured performance (see review in sister publication Sound and Vision)that commits the sin of making good music for so few dollars. Strike one: Monoprice (shush about ATI dammit!)Strike two: it's really affordable (What! The peasants have a better amp than my gold plated piece of audio jewelry from Geneva?). Strike three: The amp sounds too nice and fails to give aural ascetics the hair shirt feel they crave and demand.

Kal Rubinson's picture

First, I do often listen to music that is intense, disturbing and aggressive. The Monolith tends to soften those attributes and, thus, it does not serve all of my listening needs.

Second, this is a review of the Monolith and not investigative journalism. ATi makes a wide range of OEM products over a wide range of prices and one should not suspect that they are equal nor that they are intended to be. The Monolith is a remarkable product for the price regardless of its source.

HammerSandwich's picture

Kal, I doubt you could lift such a beast. Perhaps 950VA?

Kal Rubinson's picture

Yup. Almost 1kvA.

HammerSandwich's picture

...your conclusion about the Monolith seems more absolute than warranted by:


So when I say that I hear a change in balance with any new component other than a speaker, that's based on what I hear relative to the component that the review sample has replaced, and not on any absolute reference.

Especially when auditioned with only 1 model of loudspeaker!

System synergy makes sense, but it works only when we remember that we always evaluate systems.

Kal Rubinson's picture

Good point but there were several previous amps around for contrast: ATI, Classe and Parasound. It was a consensus.

ToeJam's picture

Mr. R., I understand the differentiation you make between the subtle (or otherwise) variances in how the Amps sound relative to each other. I hear you saying that the Monoprice sounds good and pleasant, but lacks some of the refinements the ATI and Parasound present.

I appreciate your careful articulation of what you discerned because it helps me decide if I want to invest more to obtain the specific improvements you describe.

Kal Rubinson's picture

Almost all the stuff we play with is pretty good and screaming about HUGE differences is rarely called for.

NiviM's picture

Hi Kal,
How do you compare the sound of the Nad M27 to the ATI AT543nc ?

TJ's picture

... when I ordered a new ATNC522 stereo amp after reading your review. Within days I discovered three product defects, all intermittent (mechanical transformer buzz, protection circuit instability during normal playing, occasional ground loop) in a high end system that's always been completely stable and has never had a grounding problem. It's possible of course that these intermittents might be the consequence of rough handling during shipping. I was also disappointed to find an IC op amp buffer stage (not discrete class A like Nord Acoustics and others) and with B&W 805 speakers, more than a "slight tilt" in the tonal balance that you noted with your speakers. Too bad, it seemed promising.

JRT's picture

While I do appreciate Kal's opinion, appreciate his sharing his perspective, and his efforts in reviewing interesting things in his recently ended column, I think that reviews of audio electronics and loudspeakers should be both subjective and objective, so this review of the ATI amplifier remains half of a review without the associated objective measurements.

This family of amplifiers using Hypex NC500 amplifier modules is still a current product, and seems worthy of a deeper dive in another review, maybe for a larger segment of Streophile readers in two channel configuration. I would like to see JA1's measurements of an ATI AT52xNC and/or AT54xN, regardless the number of channels, bundled with another review.