ATI AT6000 Signature Amplifier Review

ATI is a well-known and regarded amplifier manufacturer building amps under their own brand and for other manufacturers that include Lexicon, Outlaw, SAE, and most recently Monoprice. 

After more than a decade, ATI has replaced their well-regarded AT3000 and AT2000 amplifiers with the AT6000 and AT4000 Signature Series. At first glance, their specification and respective power ratings are similar. The AT6000 is still rated at 300 watts into 8 Ohms and 450 watts into 4 Ohms. The ATI6000’s are fully balanced class A/B design using two toroidal transformers and independent secondary windings to provide separate power supplies for each channel. The new amps have much more attractive anodized aluminum faceplates and sport two power cords, dual 15 amp power cords for 2 to 4 channel versions and dual 20 amp power cords for 5 to 7 channels.

Not only are the AT6000 visibly imposing but moving these amps around is a 2-man job (at least for this man). At 96 to 143  pounds, this amplifier is a beast among beasts. So let’s dig into what makes these “American Muscle” amps perform like a cross between a ballerina and a sumo wrestler.

Beastly Design

Amplifier technology is moving forward with Class-D challenging long-established designs in audiophile performance. ATI has a line of N-Core amps as well. This ATI6000 “Signature Pure Balanced Amplifier” is a fully-balanced Class-A/B amplifier with a linear power supply. These audiophile amps are purely about performance: extremely low distortion, incredibly low noise floor, and power provided multi-channel configuration.

Many balanced amplifiers are balanced bridged using two complimentary amplifier channels. ATI takes a different approach using a single 4-quadrant input stage per channel. A single input stage drives complimentary output stages that reduce noise by 50% This requires current (rather than voltage) feedback and dual DC servos per channel to keep DC offset in the tenths of a millivolt range. These amps use ThermalTrak devices with the temperature sensor in the same package as the output so there is no thermal lag and bias is updated in real time. This provides a new level of performance in a multi-channel amplifier.

The outward design is a step up from ATI’s traditional utilitarian designs but remains skewed toward functionality. Still, W.A.F. (Wife Acceptance Factor) approval may require some wining and dining. All AT6000 amps sport large front handles which help immensely in moving these behemoths into place. They are removable and ATI will supply (upon request) shorter screws if you chose to remove them; it’s best to wait until the amps are in place.

The black anodized aluminum faceplate sports a backlit ATI logo, descriptive text, and a large signature, “M”, from ATI founder and designer Morris Kessler. The white lettering on black calls more attention to the map than I would like, but I have gotten used to it.  

I thought it be useful to get a woman's perspective so I asked my wife for her opinion:

When I first saw these amps with the handles I thought they belonged in a mechanic’s shop – they were NOT pretty!  With the handles off, they actually look pretty cool together on the bottom of our shelving, despite the oversized logos.

The ATI logo backlight can be toggled on/off with a touch, but when power is lost, the logos return to their lit default. There is an attractive touch-capacitive blue power switch that is not overly bright. There are also two small orange LEDs: “Stand by” if the amp is off and “Peak” which flashes when the amplifier is clipping. Peak indicators are a feature that I’d like to see on all amps, including AVRs (doubtful that this will ever happen).

There are balanced and single-ended connections controlled by a switch for each. Both may be connected and switched which may be useful for connecting a separate 2-channel system. The shielded 5-way binding posts are solid and make tight connections with my banana plug connects. The Outputs are numbered and ATI recommends using the outer channels for the mains (for heat distribution). The dual power switches are also magnetic breakers replacing the power fuses found on many amps. An optional ground thumb screw is provided as well as a single trigger input.

EDIITORIAL NOTE ON TRIGGERING

When I first received the AT6000’s the trigger functionality required pressing the power button to complete the power cycle. If the power ever went out the amps would not turn on until the power button was pressed. This is not “family friendly.” Updated control boards unconditionally power-on from the trigger, eliminating instances of pops on power up, and also improving the soft power-up process. During power-up, the AT6002 did not draw more than 120 watts before settling at 75 watts idling and the AT6006 did not draw more than 260 watts before settling at 150 watts. The idle power usage is similar to other class-AB amps that I have owned. The two power cords are imposing but ATI tells me that they can both be plugged by a single outlet. The extra power-cord assures that all channels can be driven at their maximum rated power, although this does not happen in real world applications.

The soft-startup avoids overloading circuits during power up. It takes a few seconds for sound to emerge while the amplifier completes the power-up process.

The AT6002 dual-mono amplifier with two 900 kVa toroidal transformers.

 

The AT6007 7 channels (fully loaded) with 59,400 microfarads capacitance per channel.

 

The AT6007 massive heat sinks occupy most of the internal volume.

Packaging and Setup

These amps are packed in very large double-boxes. The six and seven channel models are shipped freight because they exceed the standard carrier 150 lbs. maximum weight. I tested the ATI6002 in a variety of configurations and it was superb in every one.  The minimalist system has an AT6007 connected to 15-amp circuit directly connected to an Oppo UDP-205 balanced and unbalanced inputs. This 5.1 system includes Revel Salon2s (bi-amped), Voice2, and Gem2. This is a wonderful combination for those who want a simple system and do not use equalization or room correction.

My main system has each Salon2 bi-amped by an AT6002. An AT6006 drives the Voice2 center channel and the Studio2 rear speakers which are also bi-amped. Each amp is connected to its own 20-amp circuit. This is complete overkill but since my house was converted from electric heat, it was a simple task to repurpose excess capacity. The amps are connected to the Emotiva XMC-1 but were also driven directly from the Oppo HA-1 and Sonica DACs. All pairings were excellent.

I can’t hear you...

These amps are QUIET. I have moved 5 different amplifiers through my system over the years and there has always been some 60 Hz buzz that was easily heard from the center and rear channels. This was cured by the AT6000’s. When I press my ears to the tweeter, there might be something and this is when the entire signal chain is powered on. With my ear to the amps, there is some faint transformer hum but nothing bothersome.

Revel Salon2 Bi-Amplified

Bi-Amping

Bi-amping is relatively simple and inexpensive experiment that one can try at home. Armed with stacking banana connectors, it is very simple to stack them to single-amp and switch to bi-amping. I conducted single-blind-tests using a single Salon2 with 3 different listeners. At modest listening levels (low 80 dB range at best), all were all able to differentiate between bi-amped and single-amped, although preferences varied. A surprising result since at these volumes the amps are practically idling. This was sufficient for my buying decision, all of my Utlitima2s are bi-amped using AT6000’s.

Listening Tests

Two-channel Listening

There are a number of tracks that I use to test an amplifier for room-rattling power. The first is Sarah McLaughlin’s “I Love You.” The heavy bass line remains well delineated from the close mic’ed sibilants. This track momentarily illuminates the peak indicator at about -5 on the XMC-1 volume control. This is far beyond enjoyable levels. The walls and floors are shaking (I think my house settled). Even at the maximum output, the AT6000 sounds great and it did get warm but not hot to the touch.  As expected, bi-amping preserves the upper frequency clarity and removes a slight hint of compression even at these levels.

The Cowboy Junkies Crossroads is also a bass heavy track with an occasional explosive guitar pluck. When Margo Timmin’s vocal emerges it is just right with all sibilants and decay preserved but no added hardness. The individual notes from the electric guitar are delivered with all their ferocity.

Beck’s Sea Changes (HDTracks 192 kHz) is a superb recording where the strings and baseline seem orchestrated to be played on the AT6000 and Salon2’s. When seated precisely between the mains, the, imaging is spectacular. Beck’s deep vocals are precisely locked into the center appearing to come from the Voice2. All the while, the acoustic guitar, and orchestrations are mixed and moved between the front channels. Beck’s mixes are engrossingly moving from quiet patches to layered complexity. The soundstage is deep with instrument placement that is right-on. The AT6000 neither adds or removes anything. What more could you ask for from an amp?

Home Theater

The AT6000 excelled at delivering the smallest detail to the thunderous explosions. For this test, I ran all channels full range (although not recommended for the Voice2). The opening vignette from “Star Trek into Darkness” on UHD is demo material. Even on my 5.1 system, the Dolby Atmos effects work. The spears seem to fly over you as they move from front to back channels. The shuttle spins around the room and the crackling of a freezing volcano are pure fun. The orchestration remains distinct and detailed. The Voice2 is allowed to shine delivering male voices with authority. The sound-track is delivered effortlessly, remaining only warm to the touch after watching the movie at volume.

Revel Salon 2 & Voice Speakers with 3X ATI 6000 Series Amplifiers

The RED and RED2 (4K UHD) Atmos tracks have numerous scenes where hundreds of rounds are fired including gunshots directly from the center channel. Honestly, I did not know the Voice2 could produce those sounds. I watched this film at -20 DB below “reference” which is loud in my room and received no complaints from my family, testament the AT6000 low distortion even during those thunderous dynamics.

Recently, the family watched “The Crown” seasons 1 and 2 on Netflix with the volume much louder than usual for this type of material; our American ears benefited from a 3 dB increase to the English dialog. I sometimes sit nearer to the rear channel and what a joy it is to hear them used for a full range music delivered completely from the rear channels. There are some very enjoyable DD+ sound tracks available from streaming services. Streaming video and audio quality are almost always better than my cable system. There is no question these amps make the Utlima2’s shine. With music or movies, the AT6000s never exhibited any hint of any stress, distortion, or limiting. They are a pleasure.

Conclusion

The ATI AT6000 series amplifier performance is as massive as its dimensions and weight; and yet, completely silent -- delicate enough to deliver the softest passages and explosive enough for the loudest. Their performance matches and exceeds many mono-blocks while versatile enough to support bi-amplified and multi-channel audiophile systems. Sonically, these amps disappear.

There are some very competent and affordable multi-channel amps available but the ATI6000 the combination of performance, power, and build quality are unequaled.

These days many audiophile amps are raising prices and the AT6000 series are not inexpensive but I’d rather bi-amp AT6000’s than place mono-blocks on stands next to the Salon2’s. If you are looking for this level of performance and they fit your budget, you can’t go wrong. Just make sure you have some help moving them around. I liked them so much, I bought 3. If you buy them, you’re in for many years of trouble-free operation and audiophile performance.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.