ATI AT6002 Multi-channel Power Amplifier Review Highlights
The ATI AT6002 is a fully balanced amplifier that produces 300 watts per channel into 8 ohms and 450 watts into 4 ohms. The fully balanced design reduces THD while increasing SNR, and it is an innovative amp that offers incredibly high performance.
ATI AT6002 Multi-channel Power Amplifier Highlights Summary
- Two-to-seven channels as a choice
- 300 Watts into 8 ohms, 450 watts into 4 ohms
- Fully balanced, dual-mono design
- Incredible power reserves with dead silent backgrounds
- Very heavy to move
Introduction to the ATI AT6002 Multi-channel Power Amplifier Review
You may be familiar with Amplifier Technologies, Inc. (ATI), but perhaps not with its founder and designer, Morris Kessler. Since Morris started building amplifiers at age 18, he has been designing some of the more innovative amplifiers in the A/V world. ATI also builds amplifiers for other companies, such as Theta Digital, Dynaco, Adcom, Aragon, Crestron, and more.
Now comes the first amplifier to bear his signature on the front panel, the ATI AT6002. A fully balanced, dual mono amplifier with high-end build quality, the AT6002 feels like a statement product. Even better, it sounds like one as well.
ATI AT6002 MULTI-CHANNEL POWER AMPLIFIER REVIEW SPECIFICATIONS
- Design: Multi-channel Power Amplifier
- Inputs: RCA, XLR
- Outputs: Five-way Binding Posts
- Output Power: 300 RMS WPC into 8 Ohms, 450 WPC RMS into 4 Ohms
- THD+N: 0.03% at Full Output
- SNR: 128 dB
- Size: 9.5” H x 17.25” W x 18.5” D
- Weight: 88 Pounds
- MSRP: $3,995 USD (Two-Channel Version)
- SECRETS Tags: ATI, AT6002, Multichannel, Power Amplifiers
I’ve never felt as bad for my FedEx delivery person as I did when the AT6002 arrived. It isn’t the largest package I’ve ever received, not by far, but it might be the most dense. It took the two of us just to get it from the truck to the front steps. Moving the amplifier from the living room into the basement was much easier by utilizing the rack mount handles on the front panel.
Design of The ATI AT6002 Multi-channel Power Amplifier
The AT6002 design is unusual for ATI. For one, it is a true dual mono configuration. There are two amplifier modules, two power cords, and even two power switches. There are also dual toroidal transformers in the front, which help contribute to the massive weight of the AT6002. The modular nature of the AT6002 puts the two amplifier channels on their own cards. This allows ATI to use less point-to-point wiring, which can be a common point of failure, and rely more on PCB boards for reliability. It also allows taking a single channel of the amplifier out and replacing it if necessary.
This daughter-board design allows the AT600x lineup to support between two and seven channels. The $3,995 AT6002 has two channels, capable of 300 watts into an 8 ohm load and 450 watts into a 4 ohm load. The $7,995 AT6007 delivers the same power, but into seven channels instead of two. With dual AC inputs, each capable of a 20 amp load from an individual circuit, there is plenty of power to drive the AT6007.
There is far more to the internal design of the AT6007 than what I am presenting here, but in the Bench Test section, Dr. David A Rich will take you through the design choices made along with the Pros and Cons of each.
On the outside, the AT6002 is simple. Finished in a powder coat black, the front has rack handles to let you position this incredible beast. Each channel has RCA and XLR inputs with a switch to choose between them. A 12V trigger input lets you have it power on with your preamp or receiver. Five-way binding posts for each channel accept banana plugs, spades, or bare wire.
Impressively, the AT6002 design lets you update it down the road if you desire. Additional channels can be added for $800 each, with the work done at ATI. Since the upgrade requires new transformers and a new rear panel, it cannot be done at home. With no price penalty, other than shipping fees for doing the upgrades down the road, it provides you with security if you want to start with fewer amp channels at first.
I did most of my testing of the AT6002 with a pair of Revel f208 speakers. I used a wide variety of source components to test both RCA and XLR inputs. A Marantz AV7005 and Anthem MRX 510 was used with RCA inputs, while the AURALiC Vega DAC, AURALiC Taurus Headphone Amp, and Oppo BDP-105 Blu-ray player were used with XLR inputs.
The ATI AT6002 Multi-channel Power Amplifier Review In Use
No matter how much power any amplifier has, there is a limit to how loud we can listen to it at. Despite this limit, the ATI AT6002 has the largest dynamic range of any amplifier I have ever heard, because when it is quiet, it is dead silent. I could place my ear next to the tweeter of the Revel f208 and hear nothing when the system was idle. Not even a slight hiss. No amplifier has ever been this quiet in my system. The amplifier itself is also as quiet as can be (no noises made by the physical structure). There are plenty of amplifiers that produce a slight sound in use, though it is usually buried under the music. The AT6002 is so quiet, you wouldn’t know it was on if not for the LED light up front.
Using the AURALiC Vega to deliver the new Led Zeppelin high-resolution masters, the AT6002 pounded through these classic re-releases without issue. From the opening chords of “Whole Lotta Love” to the final notes, every note was clear and precise. The dual 8” woofers of the Revel f208 strain receivers, even high-end ones, when pushed to high output levels. The AT6002 had no problems here, and there was no harshness or break-up as it powered through the best of Plant, Page, Bohnam and Jones.
ATI also states that the design of the AT6002 is for the demands of modern film soundtracks. So why not push the volume all the way to reference levels (85dB with 105dB peaks) and listen? When the opening Kaiju attacks San Francisco in Pacific Rim, a deep guttural roar filled my listening room and scared the hell out of me. Having seen this film a dozen times, it shouldn’t surprise me anymore, but it managed to do so by filling my room in a way it hadn’t been done before. The roar even managed to wake up my kids, sleeping two stories above.
With female vocals, the AT6002 brought out the clarity of their voices. Compared to my Parasound Halo A31, the ATI AT6002 removed a layer of granularity. Like a pale warm sky at dusk, vocals were a little bit smoother than before. Natalie Merchant’s vocals in Carnival offer a bit more than I’ve heard before, and I listen to the track at least once a week. The A31 is already a good amplifier, but the AT6002 offers just a little bit more resolution than it does with the Revel f208.
A unique aspect of the AT6002 is how much reserve power it has. Even after I switch the amplifier off, it will continue to play music for a good 10-15 seconds just off the extra current stored up. This amp is as overbuilt as a 110 pound movie starlet with 6 pounds of breast implants. With ttge AT6002, you worry about the glassware falling out of the wine rack, not the amplifier running out of slam.
I tried to push the AT6002 as much as I could, including tracks from the metal band of all metal bands, Metallica. No problem. Massive Attack and their repeated 40 Hz notes into the Revel f208? Child’s play for the ATI. Miles Davis and a double bass? Why don’t you keep turning up the volume, I don’t mind. Morris Kessler plastered his name on the front of the AT6002, so I knew I could put the pedal to the metal. I just could not make the amplfier lose its cool.
The ATI AT6002 Multi-channel Power Amplifier Review on the Bench
By David A. Rich Ph. D.
We want to thank Audio Precision for the loan of the test equipment used in this review. Chris Heinonen did the measurements.
AC Watts are measured in average power rather than RMS. Only AC current and AC voltage are RMS quantities.
All numbers in this report are for the worst-case channel. Channel match in these tests was excellent.
The noise level of the amplifier is very low. We measured 17.8µV of noise at the speaker terminals with the input grounded. This measurement was flat from 20Hz to 20kHz. Using this noise value, the SNR can be calculated to different reference values.
SNR 95dB at 1VRMS
SNR 104dB at 1 Watt into 8 Ohms (2.8VRMS)
SNR 128.7dB at 300 Watt into 8 Ohms (49.2VRMS)
SNR 127.6dB at 470 Watt into 4 Ohms (43.3VRMS)
The 128.7dB SNR at 300 Watts has a bit equivalent of 21 bits, which is better than any DAC now on the market. As you can see, the numbers go up at full power, and this will vary with the maximum voltage the amplifier can swing before clipping The ATI 6002 can swing 50VRMS. Using the standard 1 Watt reference, the SNR is still remarkable high. Again I point out these are not weighted numbers. Every noise source in the amp’s first gain stage has to be carefully considered to achieve these noise levels.
The gain of the unit with RCA in was 27.1dB (22.55V/V)
The frequency response at 8 Ohms is shown below. It is ±0.22 dB
The crosstalk in the worst channel at 10kHz was -101.966 dB.
AT6002 Power Output into 8 Ohms
At 310 Watts (50VRMS), the THD into two channels was 0.012%. THD+N was also 0.012%, reflecting the units low noise. The spectrum is below:
We note the odd-ordered harmonics are significantly larger than the even-ordered harmonics, as expected for a balanced amplifier. The origin of the small spurs, which are spaced at 120Hz (the full wave rectifier fundamental frequency), is not clear. Note that the side tones are on the fundamental test tone frequency (1kHz) and the odd-ordered harmonics.
Given the importance of the distortion structure in the balanced amplifier, I have listed the harmonics below. The odd harmonics are dominating out to the 9th harmonic.
1.0k 2.0k 3.0k 4.0k 5.0k 6.0k 7.0k 8.0k 9.0k 10.0k
-0.00 -94.80 -80.75 -112 -95.76 -129 -89.26 -133 -89.03 -135.83
Below is a spectral plot under the same conditions from 0Hz to 1kHz, to illustrate any hum spurs.
No power supply hum spurs are seen above -135dB, a remarkable result for a power amp at full power. Two spurs at 780Hz and 880Hz are the full wave rectifier fundamental frequency (120Hz) modulating around the 1kHz test tone. The origin of these modulation spurs is unclear and may be at the experimental site.
IMD, using 19kHz and 20kHz, was 0.086% for the first 3 IM products in the worst case channel.
The individual products are shown below. The 1kHz the 2nd order IM is very low, but the 3rd order IM tones at (18kHz and 21kHz) are higher than expected. ATI provides no specification for this test.
The 2nd harmonics of the tests tones (38kHz and 40kHz) intermodulate with the 19kHz and 20kHz test signals to produce the 3rd order 18kHz and 21kHz IM tones (do not confuse the order of the IM tones with the order of the harmonics). The 2nd harmonics of 19kHz and 20kHz were down -80dB, so it is unclear what is causing 3rd order IM tones to take on the value below.
1.0k 18.0k 19.0k 20.0k 21.0k
-105 -67.92 -6.01 -6.02 -67.05
Next, we reduced the power to 12.5 Watts into 8 Ohms (10VRMS) to examine the edge of the crossover distortion region. The 12.5-Watt spectrum is below, and it indicates a very well designed power amplifier.
The THD is 0.0047%. As expected for a balanced power amp the odd-ordered harmonics dominate, and it is mostly the 3rd harmonic at 0.0038%. The 5th harmonic is 0.0021% , the 7th 0.0011%, and the 9th 0.001%
At 3.1 Watts (5VRMS) the THD went up to 0.0051% as a result of an increase in the 3rd at 0.0044%
The minimum THD was at 34 Watts at 0.0032%. The third harmonic drops 15dB (0.00053%) with other harmonics similar in value to the 12.5 Watt (10VRMS) spectra . The 5th harmonic now dominates at 0.002%
At 1.1 Watts the THD begins to decline again (not shown) reaching a minima of 0.0018% at 20mW. This shows low level crossover distortion is well suppressed. The origin of the bump from 180mW to 34 Watts is not clear. The maximum is 0.0052% at 1.1Watts which is still very low.
The 19kHz / 20kHz IM was 0.023% for the first 3 IM products in the worst case channel at 12.5 Watts. The individual products are shown below. The 1kHz 2nd order IM is very low but again note the values of the 3rd order IMs.
1.0k 18.0k 19.0k 20.0k 21.0k
-121 -79.13 -6.0 -6.0 -77.61
For the 34 Watt level, which yielded the minimum THD the 19kHz / 20kHz IM was 0.037% and at 0.023% at 3.1 Watts.
The 19kHz / 20kHz IM monotonically decreases with power but is significantly higher than the 1kHz THD in all cases. These large differences are not typical.
AT6002 Power Output into 4 Ohms
Into 4 Ohms, the frequency response is ±0.293 dB 20Hz – 20kHz, and the crosstalk is 81.518 dB at 10kHz (both numbers in the worst channel).
The spectra below is at 470 Watts into 4 Ohm (43.3VRMS)
THD+N Ratio was 0.019% and THD was 0.019% again reflecting the low noise of the amplifier.
Again we note the odd-ordered harmonics are significantly larger than the even-ordered harmonics, as expected for a balanced amplifier. The origin of the small power supply related side tones is not clear. As in the previous case, the side tones are on the fundamental test tone frequency (1kHz) and the odd-ordered harmonics.
I have listed the harmonics below. Only the odd-ordered harmonics are significant. The level of odd-ordered harmonics does not change much out to the 9th harmonic.
1.0k 2.0k 3.0k 4.0k 5.0k 6.0k 7.0k 8.0k 9.0k 10.0k
0.0 -96.2 -77.5 -118 -84.9 -123 -83.3 -136 -83.6 -137
Below is a spectral plot under the same conditions from 0Hz to 1kHz
The 120Hz harmonic is at -130dB, a remarkable result for a power amp at full power. The origin of the two spurs, which are modulation of the full wave rectifier frequency (120Hz) around the 1kHz fundamental, is again unclear.
19kHz / 20kHz IM was 0.15% for the first 3 IM products in the worst case channel.
The individual products are shown below. The 1kHz IM is very low, but the 3rd order IMs are higher than expected.
1.0k 18.0k 19.0k 20.0k 21.0k
-105 -62.8 -6.00 -6.00 -61.9
Next, we reduced the power to 25 Watts into 4 Ohms (10VRMS). The spectrum is below:
The THD is 0.0058 %
As expected for a balanced power amp, the odd order harmonics dominate and are significant out to the 9th harmonic.
1.0k 2.0k 3.0k 4.0k 5.0k 6.0k 7.0k 8.0k 9.0k 10.0k
0.0 -106 -87.9 -128 -91.28 -132 -94.78 -133 -97.0 -133
At 49 Watts, which yielded the minimum THD, was 0.004%. The 3rd harmonic is down 10dB from the 25 Watt result.
At 6.2 Watts (5VRMS) the THD went up from the 12.5 Watt level to 0.0085% as a result of an increase in the 3rd of the and 5th harmonic by 2dB
At 2.2 Watts, the THD begins to decline again (not shown) reaching a minimum of 0.0025% at 20mW. This indicates low level crossover distortion is well depressed. The origin of the bump from 90mW Watts to 49 Watts is not clear, but the 0.0084% maximum level is low.
The 19kHz / 20kHz IM was 0.035 % for the first 3 IM products at 25 Watts.
The individual products are shown below. Note again the values 3rd order IMs (18kHz and 21kHz).
1.0k 18.0k 19.0k 20.0k 21.0k
-113 dB -76.0 dB -6.0 dB -6.0 dB -74.5 dB
The 19kHz / 20kHz IM was 0.035 % for the first 3 IM products at 49 Watts and 0.035 % for the first 3 IM products at 6.2 Watts.
The 19kHz / 20kHz IM is constant for 49 Watts to 5 Watts.
In summary, the only blemish in the AT6002s performance is the higher than expected values in the 19kHz / 20Hz IM tests, which ATI does not specify. The amplifier’s spectral performance clearly shows the advantage of the fully balanced topology, and THD at 1kHz is low, regardless of the level we looked at. The power supply hum at full power is almost non-existent, putting some preamp designers to shame. The noise of this amplifier is remarkable low, giving rise to SNR values at the 21-bit effective level of a digital component.
Design Technology in the AT6002
ATI supplied a complete schematic. I thank them for the openness they provided on the design.
This section assumes the reader is familiar with the introductory presentation on balanced amplifiers:
The ATI AT6002 is a full balanced non-inverting amplifier. As explained in the introductory article, this is the approach you need to take if you want low noise without an additional buffer stage before the amplifier.
Also, as explained in detail in the introductory article, the problem with a balanced non-inverting amplifier is that it needs two positive inputs and two negative inputs. Solutions in the IC design world do not translate to the world of discrete power amplifiers. Matching of the individual components in a discrete design is the most significant issue that must be overcome. The best discrete solution I have seen was published in the reference below and was discussed in detail in the introductory article.
Bongiorno, J. “Ampzilla III” The Audio Amateur 15.4 (September 1984): 7 – 19
Outside the complementary four input core stage, this is a pure Morris Kessler design. This is not the area of the review that I can discuss the designer of the product in detail. Morris does deserve more space than I can give here, and you can find a reference to a 16 page interview of him referenced on the ATI website.
Morris is a master amplifier designer you may never have heard of. He keeps a very low profile and lets the products speak for themselves. He has been producing amplifiers for 50 years.
I spent several hours at CEDIA 2012 and 2013 with Morris, discussing his general design philosophy as well as the ATI6002 circuit design in detail. This is not a circuit that gives up its secrets easily, and despite years of looking at this topology, I uncovered a couple additional aspects of the ATI6002 implementation as I studied it for this review.
Design Methods for High Reliability
What distinguishes a Kessler design is robustness. Since 1963, he has produced 500,000 units ranging from two to sixteen channels. In that type of volume you cannot afford an amplifier design that is a frequent flyer back to the factory for service.
The output stage is the area that needs the most attention to prevent a service calls. These are the transistors that drive the current to the load and dissipate the thermal losses. The data sheets for the output transistor provide complex curves to set the Safe Operating Area (SOA) of the transistor.
Cordell, B. Audio Power Amplifiers McGraw Hill, 2011, 186 – 190
Selection of a robust transistor is the first step, monitoring the output transistors’ voltage and current over time to determine if the SOA is exceeded, and the final step is stabilizing the thermal properties of the transistors. Morris has placed an emphasis on finding robust output transistors over ones with slightly better specs.
Thermal stabilization of the amplifier is significantly improved using ON Semiconductors ThermalTrak transistors which imbed the diodes of the thermal feedback on the die with the output device. Thermal feedback is much faster than when the diodes are on the heat sink. In addition, they are an exact match to the transistor. The thermal feedback is so fast, distortion of the amplifier can actually be reduced at low frequencies.
A power amplifier’s unity voltage gain current amplifier stage must be designed to have good linearity. Many designs for the output stage to improve linearity exist but some can break into parasitic oscillation dependent on the load. Some nice looking designs on paper can even break into oscillation without a load connected if the transistors arriving at the shipping doc do not match parameters of the ones used for the prototype.
The Kessler current output stage design starts with a triple emitter follower configuration with a large number of passive components wrapped around the outputs to prevent parasitic oscillation. The protection circuit in the ATI6002 also senses parasitic oscillations and shuts the amplifier down. Most amplifier do not protect if a high frequency oscillation occurs on the speaker terminal.
The output stage of the current amplifier has 4 transistors in parallel. Since this is a balanced and complementary 16 transistors are connected at the two speaker terminals. 8 transistors are on each side of the speaker terminal.
In the ATI 6002 the entire amplifier is surrounded by optocouplers to the protection circuit. Information coming across optically includes the output stage current flow, output transistor voltage, and the presence of high frequency oscillations.
If any fault is detected by the protection circuitry on the other side of the optocouplers the differential pair tail current source is shut down. That brings the whole amplifier to close to zero current draw protecting itself from an external fault very quickly. Unlike CMOS analog opamps which may need extra circuits to make this work, the bipolars are frozen since they get no base current. The circuit that cuts the bias current to the amplifier is also optically isolated. At the same time, the power rails are disconnected by the standby relay. Thermal shutdown is also part of the protection system.
If the fault is outside the amp, such as a short on the speaker terminals or the output transistors were being run outside the Safe Area of Operation (SOA), the protection recycles, waiting for the user to fix the short or resolve other issues. If the problem is inside the amp, such as the rare shorted output transistor, the protection circuit senses the current flow on recycle and keeps everything off until the unit is fixed. If you power cycle the amp after it goes into protection mode, it will go through the whole process again and shut down.
Although it is rare in some amplifiers, the failure of an output transistor may take out the speaker with a large DC voltage applied across the speaker terminals. The protection is not fast enough to get the amp shut down.
The complete optical isolation of the protection system from the amplifier in the ATI Signature series amplifiers allows the eliminatioin of the relay between the amplifier output and the speaker terminals. This relay itself can be a source of failure. Note that some amplifiers are missing the relay on grounds that it affects the sound, but have not taken the steps to ensure the amplifier will not take out a speaker when the relay is removed.
The protection circuit on the other side of the optocouplers calculates how long high current has been flowing in the amplifier with a high voltage across the output devices. This condition can be the result of a complex speaker load. The protection does not activate until the SOA is exceeded. Some protection circuits are too trigger happy.
Common Mode Feedback, DC Servos and Other Circuit Highlights.
The four input core stage has the interesting property that its AC common mode rejection is high, but it has no DC rejection. Moving both input base terminals together (+ and -) will also move both speaker terminals at very low frequencies. Applying a differential DC signal to the + and – input base terminals results in a differential movement of the speaker terminals. The base terminal input pair thus allows four-quadrant control of the speakers’ DC voltage.
The common mode feedback is set by a DC servo at the speaker terminal connected to both base terminals in a negative loop. DC servos also adjust the differential DC at the output to 0. For those not familiar with DC servos, a reference is below.
Cordell, B. Audio Power Amplifiers McGraw Hill, 2011, Chapter 8
As mentioned in the introductory article, the feedback resistors at the inputs of the amp (in the non-inverting case connected to ground) must have a very low resistance values. This presents a problem. Typically a DC blocking cap will be in series with the feedback resistor to ground. This takes the gain of the amplifier from DC to 1, reducing the offset at the speaker terminal to the low level of the differential pairs’ offset. With a feedback resistor in the 100 – 200 Ohm range, the capacitor would be extremely large and introduce distortion. The DC servo, as used in the ATI Signature series amplifiers removes the need for the large electrolytic capacitor in the feedback path.
The output stages are on unregulated rails. The voltage gain stages are on regulated rails. This design approach helps reject power supply noise but can lead to problems if the power supply rails are not turned on in a proper sequence, adding additional circuitry.
The ATI6002 is fully complimentary, meaning that every PNP transistor is matched by an NPN transistor for the entire circuit. The voltage gain stage consists of the four input differential core terminated with resistors. The complementary circuit approach is essential since some DC offsets in the core are canceled. The second voltage gain stage is a standard differential pair, one on the positive rail and one on the negative rail. The complimentary collectors of the second stage differential pairs connect through the output stage base spreading circuit (VBE multiplier). The base spreading circuit, which sets the output stage bias current, uses the diodes in the ThermalTrak output devices. The base spreading circuit is also complementary in the AT6002.
Balanced to Single Ended Conversion Without an Extra Stage of Electronics
Although this amplifier is fully balanced, most users will use RCA inputs because their preamp is likely to have only single-ended RCA output jacks. The standard approach would be to add a circuit in front of the amplifier to convert the single-ended signal to differential. It would be desirable to send the one input directly to the amplifier and set the other input to ground but this will unbalance the amplifier. More closed loop gain will be on the input side rather than one side with the bases connected to ground. In the AT6002, the feedback gain is changed on the side with the grounded input to placet the amplifier back into balance. A relay switches in the resistor which balances the amplifier.
Like any single-ended-to-balanced converter, a common mode voltage will be of the amplifier’s differential pair current source (the tail). The voltage is equal to the input voltage. In balanced mode, no common mode voltage is on the current source.
Design for Low Noise
When optimizing an amplifier to achieve the 130dB SNR that we measured referenced to full power, every noise source must be considered. Most noise comes from the first stage of voltage gain. Low noise transistors are a must, but in a power amp they may see high voltages as they do in the AT6002, limiting the selection process. When designing a very low noise amplifier like the AT6002, resistors can have noise higher than expected from the thermal noise calculation. In the ATI, specially selected metal film resistors are selected for low noise.
Low noise also requires very careful PC board layout, including reducing board resistance as much as possible. Power supply regulation and decoupling must not only produce a stable DC, but they must be low noise over the whole audio band. Power supply rejection of the circuit needs to be very high, requiring all traces of the PC board to be carefully matched and shielded. In the measurements section, we saw almost no hum spurs even at full power. This is not unexpected in a design for high SNR. The fact that ATI designs its own transformers also helps here.
Conclusions about the ATI AT6002 Multi-channel Power Amplifier Review
The ATI AT6002 is completely fitting of its Signature Series designation. It is a giant in the world of power amplfiers, and I have never been so happy to have rack handles on something as I was with this. It handled all the music I could throw at it, and with its engineering pedigree and construction, I was certain it wasn’t going to break down under the stress. What surprised me is how silent it was when it was at idle.
Its modular design means it will support as many channels as any non-Atmos home theater will need. In the stereo, dual mono configuration I evaluated, I don’t have any criticism for the AT6002. It handled all my tests, from music and movies to the Audio Precision. The only problem you will likely have is moving it into place. On a positive note, for a power amplifier, heavy is good.
If you didn’t know about ATI and Morris Kessler before now, you should find out more. The ATI AT6002 Signature Series amplifier is a high-end amplifier that is designed to please and never be replaced.