Music in the Round #83: ATI & Monoprice 3-Channel Amplifiers
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 lbstoo 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 lbsno 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 centerthough 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 90135V or 200260V, 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 324V 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 voicemale or female, high or lowwas 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: www.ati-amp.com.