ATI AT522NC Stereo Amplifier Review

[March Audio]

I get that tweeters - as far as I am aware - have no response at that frequency, but isn’t there energy there that must be dissipated somewhere, like in the tweeter? Would this cause some heating of the voicecoil or some component in the system?

Yes you are correct. However a tweeters impedance rises with frequency. An 8 Ohm tweeter at 1kHz may well be 60 ohms at 450KHz. I did do an example calculation with real tweeter somewhere here, I will try and find it. Then you have the crossover in front of the tweeter that will increase this impedance further.

The residual of the switching signal in hypex designs about 350mV, so what current that ends up flowing in the tweeter and therefore power dissipated is totally insignificant. You are talking about a few mW. I think @SIY measured 1mW recently.

The tweeter frying class d amp is a myth.

 

[March Audio]

This is a measurement of one of my power amplifiers into 0R22 resistive load (0.22 ohm). What do you think?

View attachment 41498

Nice

 

[March Audio]

It might be "incompetently engineered", as you are saying, but once you bring your amp into the comparative test you do not like to end up with saying a phoney express like "the speaker used is incompetently engineered". You want to show that you are able to drive it regardless its challenging complex impedance. This is the case for the amp designer.

Where do you draw the line though?

Where does it stop being a "difficult" load that an amp should be able to cope with and just become plain bad design that requires a "specialist" amp?

If you look at say the quad esl they all manage to stay in within what I would call "sensible" parameters, so why the free pass for designs that dont do this?

I recently had a conversation with Alan Shaw of Harbeth speakers on precisely this subject. His comment was very interesting. Paraphrasing he essentially said "why would I limit my market by designing a speaker with pathological impedance parameters that require a specialist or limited range of amps that can drive it? It's bad engineering and business sense."

 

[March Audio]

It was one of the recent Martin Logan ESLs, maybe the new 15A? I'd have to dig... And some of theirs dip to ~0.2 ohms at 20 kHz or so.
<pause> https://www.stereophile.com/content...-renaissance-esl-15a-loudspeaker-measurements states 0.52 ohms at 20 kHz from manuf data but does not show the curves.

IME, which is dated now, the impedance magnitude for ESLs gets low at HF but phase angle is not horrible because the transformer drive compensates much of the panel's capacitance.

Big Maggies (2.xR, 3.x, 20.x, and now 30.x) dip below 3 ohms due to the ribbon tweeter but phase angle is near 0 degrees (almost purely resistive).

I'm just going to ignore the early Apogees -- can't imagine too many of them around now, and no new ribbons as pathologically low AFAIK.

Re what I said above, like SIY I think that's just bad design to get to 0.5 ohms.

The Australian Maggie distributor was in the room opposite me at the Melbourne hifi show. He uses class d for them and swears by it.

What I'm interested in, as @amirm doesn't have a power cube, is establishing a non pathological fixed reactive load that he could use for test. It could give us more insight into amp behaviour without making a massive additional workload for Amir.

 

[amirm]

What I'm interested in, as @amirm doesn't have a power cube, is establishing a non pathological fixed reactive load that he could use for test. It could give us more insight into amp behaviour without making a massive additional workload for Amir.

Anything additional is well, another thing that takes time. My loads are Kelvin types which means that I have to reconnect a bunch of cables to test with a different load. Then capture and document it.

The bigger deal here is the probability of damaging amplifiers. I have already killed two amplifiers with standard loads. Fortunately one was a cheap AVR that I bought and the other the company made good. But I had to pay for shipping, customs, etc. and bunch of aggravation for them and me to repair the unit.

In general, I am not here to provide full explanation of either feature set or provide reliability testing. If that data is needed, either buy something you can return, or get the company to respond if they support such loads.

And oh, the last time I tried to build a capacitive load, I got an earful from a manufacturer saying it was not a representative load of real speakers.

Finally, we had an effort to build a powercube like load. It died. Anyone who wants such testing done, needs to put their energy and money toward that effort, than arguing here over (I know you are not).

 

[DonH56]

Re what I said above, like SIY I think that's just bad design to get to 0.5 ohms.

The Australian Maggie distributor was in the room opposite me at the Melbourne hifi show. He uses class d for them and swears by it.

What I'm interested in, as @amirm doesn't have a power cube, is establishing a non pathological fixed reactive load that he could use for test. It could give us more insight into amp behaviour without making a massive additional workload for Amir.

Maybe, but you can find a number of ESLs that are in that range, and as a panel guy I choose not to dismiss them and their listeners. That impedance is at 20 kHz where there is not a lot of power in normal music. But I am not the guy doing the work, have enough of my own, so in the interest of not continuing the argument or adding to Amir's workload I'll drop this.

 

[bigguyca]

ATI specs for the AT522NC are 200 WPC into 8 Ohms and 300 WPC into 4 Ohms FTC with <0.03 THD average power.

View attachment 39651

Does this indicate some kind of averaging the power over the entire frequency range to achieve this spec?

- Rich

I was reading over this interesting thread and came to your question.

Average power, or "Continuous average sine wave power" per Bob Cordell's latest book, is the name for the power that you'll see in power amplifier measurements. It's based on P = I^2 x R, or P = V^2 / R power.

At times you will see the term RMS power, but this is not correct. To paraphrase the excellent wording in Wikipedia, the RMS value of a power waveform can be calculated (and would be larger), but it is meaningless.

 

[DonH56]

I was reading over this interesting thread and came to your question.

Average power, or "Continuous average sine wave power" per Bob Cordell's latest book, is the name for the power that you'll see in power amplifier measurements. It's based on P = I^2 x R, or P = V^2 / R power.

At times you will see the term RMS power, but this is not correct. To paraphrase the excellent wording in Wikipedia, the RMS value of a power waveform can be calculated (and would be larger), but it is meaningless.

Yes, basically all power is rated as the product of RMS current and RMS voltage perhaps using impedance magnitude in ohms. RMS = root-mean-square, the square root of the mean-squared values over time (https://en.wikipedia.org/wiki/Root_mean_square or any one of a bazillion other references). Average power is Vrms * Irms, or using just resistance Pavg = Vrms^2 / R = Irms^2 * R. There is no such thing as RMS power (you can do the math, but it has no real meaning, and is not what is specified in the data sheet).

 

[RichB]

Yes, basically all power is rated as the product of RMS current and RMS voltage perhaps using impedance magnitude in ohms. RMS = root-mean-square, the square root of the mean-squared values over time (https://en.wikipedia.org/wiki/Root_mean_square or any one of a bazillion other references). Average power is Vrms * Irms, or using just resistance Pavg = Vrms^2 / R = Irms^2 * R. There is no such thing as RMS power (you can do the math, but it has no real meaning, and is not what is specified in the data sheet).

Here is the statement on ATI's site.

*EIA 1kHz Power refers to maximum average power in watts at 1kHz with 0.005% THD + Noise. **FTC Full Bandwidth Power refers to maximum average power in watts from 20 Hz to 20 kHz with 0.03% THD + noise. ***Other voltages available on request.

This specification looks comprehensive since it is FTC. I don't follow the math, but the concept of a "maximum average" seems odd. Perhaps, this means that this specification is at the voltage to achieve the maximum power. If this is correct this is not an indicator for the THD + Noise at 1 watt and below, for example.

- Rich

 

[DonH56]

Here is the statement on ATI's site.

This specification looks comprehensive since it is FTC. I don't follow the math, but the concept of a "maximum average" seems odd. Perhaps, this means that this specification is at the voltage to achieve the maximum power. If this is correct this is not an indicator for the THD + Noise at 1 watt and below, for example,

- Rich

Don't get hung up on the verbiage. Average power is just the product of RMS current and RMS voltage to produce an average result. The RMS values are those that would equal a DC (constant) voltage or current that produces the same amount of heating in a (ideal) resistor. Power changes with time so the average power is the average of power over time. It is what most people describe simply as "power". There is average power, apparent power, instantaneous power, peak power, real power, imaginary power, etc. all with technical definitions. Plus a few less rigorously defined like "dynamic power", "peak dynamic power" , "peak instantaneous dynamic power" -- usually used to provide some indication of how much power an amplifier can put out for a short time and often without specifying distortion.

So, maximum average power is the maximum (average over time) power the amplifier can deliver -- just leave out the word "average". Or pick up an engineering textbook, or read the Wikipedia article, to see how average power is defined. ATI is (unlike some companies) being careful to define exactly what power they are measuring.

You have posted footnotes so I do not know what they are referencing. Taking them in order:

*EIA 1kHz Power refers to maximum average power in watts at 1kHz with 0.005% THD + Noise.
- This is the maximum power the amplifier is rated to deliver at 1 kHz whilst meeting their 0.005% THD+N spec. EIA defines it at 1 kHz.

**FTC Full Bandwidth Power refers to maximum average power in watts from 20 Hz to 20 kHz with 0.03% THD + noise.
- The FTC defines full power over a bandwidth of 20 Hz to 20 kHz (the audio band). This is typically a little lower than the single-frequency 1 kHz measurement, and THD+N is a little higher (feedback, which reduces distortion, falls at high frequency and so HF distortion is typically higher, plus wider bandwidth means more noise is captured).

***Other voltages available on request.
- I have no idea what this relates to; my guess is that this footnote relates to the mains (wall) voltage. Most amplifiers use unregulated output supply voltages so maximum power will vary a bit with wall voltage. Or it could just mean it is set up for 120 Vac but other voltages such as 240 V are available (e.g. by changing a switch or transformer tap). Or something else.

HTH - Don

 

[RammisFrammis]

I just packed the heavy thing. It is actually going back to ATI because of faulty design of the trigger. So testing wouldn't have done any good.

If the power button is still pushed in and the trigger voltage is present, the amp will power up after a power failure. The amp senses the range of the incoming AC (120 VAC or 240 VAC), selects the appropriate primary tap on the power transformer, then cycles through soft start.

 

[nick-v]

Would this amp be a good match for the Denon AVR-X3700H pre-outs?

1.6 volts for full-rated output, so I'm thinking it should be a pretty good match. The Benchmark AHB-2 is a little too rich for my blood.,

 

[Matias]

Would this amp be a good match for the Denon AVR-X3700H pre-outs?

1.6 volts for full-rated output, so I'm thinking it should be a pretty good match. The Benchmark AHB-2 is a little too rich for my blood.,

You can get much cheaper from VTV or Audiophonics.

 

[MakeMineVinyl]

After a power outage the AT4007 defaults to standby, and you can only turn it on from the front button. The trigger is effectively disabled. That's my only functional complaint about the AT4007. This quirk has led to angry phone calls from my wife while I was abroad on client matters, because the TV would turn on but no sound would come on. ATI asserted this behavior is for safety reasons, but my old AT2007 would come back on from the trigger after a power outage. Then again, I replaced the AT2007 because the trigger circuit went bad after ~7 years of use. So maybe they're saving the trigger circuit with this behavior?

This behavior is because of the kind of power switch the amplifier has. The 6000/4000 have a sensor type power switch which resets when power is completely removed; since the power switch itself relies on power, it has no other choice. The microcontroller also has no other choice than to reboot when AC power is restored. The trigger input cannot override the front panel power switch because of safety; you must always be able to shut the amplifier down by that switch.

ATI amplifiers including the AT NC5xx series use a physical latching ON/OFF switch which obviously remembers its state when AC power is once again restored. The microcontroller reads the latched power switch's stage and the amplifier powers up.

 

[jhaider]

This behavior is because of the kind of power switch the amplifier has. The 6000/4000 have a sensor type power switch which resets when power is completely removed; since the power switch itself relies on power, it has no other choice. The microcontroller also has no other choice than to reboot when AC power is restored. The trigger input cannot override the front panel power switch because of safety; you must always be able to shut the amplifier down by that switch.

ATI amplifiers including the AT NC5xx series use a physical latching ON/OFF switch which obviously remembers its state when AC power is once again restored. The microcontroller reads the latched power switch's stage and the amplifier powers up.

I thought there was a fix for this defect.

I haven't pursued it of yet mostly because I'm totally unexcited about removing such a heavy amp from my media cabinet. But is it inaccurate that ATI has fixed this problem on the 4000/6000?

 

[RichB]

I thought there was a fix for this defect.

I haven't pursued it of yet mostly because I'm totally unexcited about removing such a heavy amp from my media cabinet. But is it inaccurate that ATI has fixed this problem on the 4000/6000?

Correct. This was a problem with my AT6000s. It took a board swap and two firmware updates to finally get them to operate from the trigger after a hard power loss. If this is a problem, you should contact ATI. ATI can send you a board or a firmware updater, of arrange for service.

Also, when I reviewed the AT4000 a couple of years ago, it did not have this problem so the newer builds do not have the issue.

- Rich

 

[MakeMineVinyl]

I thought there was a fix for this defect.

I haven't pursued it of yet mostly because I'm totally unexcited about removing such a heavy amp from my media cabinet. But is it inaccurate that ATI has fixed this problem on the 4000/6000?

I never heard of any defect that needed fixing on the 4000 6000. The 4000 and 6000 series use a powered on off switch which resets if it loses power. I am the person who designed that control system and wrote the software for it and I've never heard of anything being wrong with it. From what you say it seems to be working normally but when I get a chance I will look at the source code and double check.

 

[jhaider]

The 4000 and 6000 series use a powered on off switch which resets if it loses power.

That is the defect. Even though I haven't yet inquired about the fix for my own amp out of laziness, I hope Rich is right that this defect has been fixed.

 

[MakeMineVinyl]

That is the defect. Even though I haven't yet inquired about the fix for my own amp out of laziness, I hope Rich is right that this defect has been fixed.

There's nothing that can be done about that. The switch requires power to work and if it loses power it has no other choice but to reset. It's just the nature of a solid state switch. The software could be rewritten to override the power switch with the trigger cable but that's not my call to make.

 

[jhaider]

There's nothing that can be done about that.

[note - wanted to send you a DM but you have them disabled]

Half-apologies in advance for going full-Karen about this defect, but it represents one of those things I just don't understand about late stage capitalism.

There is an existing technology (here, the rocker/spring loaded physical push switch) that just works, has no apparent functional or aesthetic drawbacks, has one really nice advantage (haptic feedback), and is presumably cheap.

So obviously the late-stage-capitalism answer is to engineer a complicated new design with unclear functional or even aesthetic benefits, and a glaring practical flaw - it breaks the commonly used control mechanism if it loses power! The new design is also inherently wasteful, because it draws power the alternative doesn't. I assume the vampire draw is negligible, but it is there.

Maybe if the ring around the switch were an OLED wattmeter or something like that that danced to the music, one could say there is an aesthetic benefit. However, it's just an illuminated ring to tell you the operating state. Physical switches can have rings around them too.

Consider that many of these amps will not even be in the listening room. An expensive, super-high-performance multichannel amp is likely to be mounted in a remote rack, or placed in equipment cabinet. If I were a CEDIA guy, the first service call I received because a family's speakers didn't work after brief power interruption would make the very last time I sold any customer that amp - even if it is in every other way a product with superior performance and reliability - until the company repaired the obvious design defect that caused my customer to call me!

The switch requires power to work and if it loses power it has no other choice but to reset. It's just the nature of a solid state switch..

If a switch is going to destroy the functionality of the 12V trigger if the power goes out for a split second, there should be battery backup to power said switch for a time included in the circuit.

The good thing about this exchange is you've reminded me to contact you guys about the fix for my AT4007. It's good on ATI that they've realized they made a design mistake and (per @RichB) put in the time and effort to correct it.