Apollon NCx500ST Stereo Amplifier Review

[pablolie]

The test results at Stereophile are hardly linear or good. Nor do they indicate good low impedance drive capability.

NAD Masters Series M22 power amplifier Measurements

Sidebar 3: Measurements I performed a full set of measurements on the Masters Series M22, using my Audio Precision SYS2722 system (see the January 2008 "As We See It"). As the M22 has a class-D output stage, for almost all measurements I used an Audio Precision AUX-0025 passive low-pass filter...

www.stereophile.com

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Show us a Class A that pumps out that power into ²ohms and we are in business...

 

[pseudoid]

Can you link me to the link?

Within post #1 of this thread.

 

[Buckeye Amps]

Earlier post? I have no idea where that is located. You might be opening a pandoras box because if that's the thread where I calculated the min impedance drive to be ~3 Ohms and then confirmed it at the data sheet to be ~3.2 Ohms that might be counterproductive. I checked the data sheet today and at the amp's Max 40A output at even the lowest possible voltage it outputs ~700 Watts RMS @ 0.9 Ohms. It's good but there is significant roll-off of the power output. Again I have doubts about the heatsink clamping integrity and there is a nanny circuit monitoring the amp and power supply operating conditions to compensate for this lack of low impedance drive capability. There seems to be lots of commentary around my doubts and I want to make sure that you are aware that I like and support class D but I am not going to give them low impedance drive ratings because I have not seen that proven yet or actually tested. All I have seen are failures when tested or operated that way. For a real solid test they need to drive less than 2 Ohms and do it into loads with a proper soak test and not a blip of a test sine wave etc and then they can compete with the big boys that do drive low impedances.

It was a few posts back in this thread.
I am merely giving you an example of a Class D amp that is for a fact handling sub 1ohm loads in real world usage, whereas a lot of "robust"/well know Class A/B amps this person had been using before would often fault/go into protection.

Do what you want with that, but just giving an example you asked for.

 

[Buckeye Amps]

Further examples would be a handful of customers from my very early days who are running 2ohm subwoofers using 2ch NC502s. Nearly three years and not an issue with those yet.

I’ve also had two customers run (against advice) bridged NC502s with 4ohm subs without issue.

 

[Doodski]

Show us a Class A that pumps out that power into ²ohms and we are in business...

I'm not up to speed memorizing models numbers and names of amps that excel at low Z drive but for example there are Krell and Threshold models out there doing it. Yes, they cost a arm and a leg even used and require lots of energy for operation. We know this but you asked for a example.

 

[Doodski]

Within post #1 of this thread.

I can barely remember the original question because I am multitasking but here's a rough go at those figures from the reactive load test. The amp is not very linear into 2 Ohms capacitive Z but does a very admirable job from 8 Ohms to 4 Ohms and into a 2 Ohm inductive load. As I mentioned somewhere around ~3 Ohms is about the limit before the power supply sags too much or the amp current nanny circuitry engages and limits performance.
Max power output at 54.4 Volts 8 Ohms 60 degree capacitive is 185 W RMS at best. (Very good.)
Max power output at 53.7 Volts 4 Ohms 60 degree capacitive is 360.5 W RMS at best. (Very good.)
Max power output at 34.1 Volts 2 Ohms 60 degree capacitive is 290.7 W RMS at the worst. (Lacking.)
Max power output at 47.2 Volts 2 Ohms 60 degree inductive is 557 W RMS at the best. (Very good.)
So dependent on the capacitive or inductive reactance that power amp can have difficulty into 2 Ohms or it can excel. ~3 Ohms Z seems to be about the good spot for this amp as does other better class D offerings. Is this the newer design of amp and power supply PCBs where they added additional clamping screws/bolts?

 

[restorer-john]

Show us a Class A that pumps out that power into ²ohms and we are in business...

The NAD 2R test was with one channel driven only. Not stated, but implied: That means it likely shut itself down when two were driven.

Amir is now testing the power cube with dynamic, which I presume is the old EIA or now CEA burst. (1kHz 20/480- 0dB/-20dB)

Plenty of 1980s and 1990s power amplifiers will exceed this Appollon in dynamic capability, continuous power, noise etc.

Random Yamaha example:

Another:

Note: The continuous Yamaha specs are FTC rated, which means continuous, from 20-20kHz and from 250mW to rated power AND with preconditioning. They greatly exceed those conservative figures when simple short, 1kHz tests are used.

 

[pseudoid]

Plenty of 1980s and 1990s power amplifiers will exceed this Appollon in dynamic capability, continuous power, noise etc.

Thank you but it is your fault that I have to ask the following question?
Whatever happened to specifications such as the "Dynamic Headroom", "Damping Factor" and even "Dynamic Power" or ""Slew Rate"?

 

[Rick Sykora]

Whatever happened,it should shut down,plain and simple.
There was something odd about it even at warm up,the graph is strange.

Ideally, you are correct. However, sometimes electronics have early mortality. If the defect was in the thermal behavior, it may not have tripped the protection enough or not at all. If electronics were fully reliable under all circumstances, then no need for warranty coverage. Having worked in automation applications that require fault tolerance, can assure you that such equipment is very expensive.

I have multiple high power test cycles on an identical Buckeye amp and it still is fine. If @thin bLue was able to articulate the conditions that resulted in the failure, would be willing to try to reproduce. In the end, whether Buckeye’s amps or any other reputable product, would not expect the supplier to stop shipping over a single reported issue. One does not need a degree to know that a single point does not make a (trend) line.

 

[restorer-john]

Whatever happened to specifications such as the "Dynamic Headroom", "Damping Factor" and even "Dynamic Power" or ""Slew Rate"?

Manufacturers got lazy and the marketing people (with no engineering background) took over.

In the background all those parameters were/are tested and specified, but just don't make it to pretty looking webpages, instruction manuals or advertising.

HiFi is dumbed down these days.

 

[Doodski]

Thank you but it is your fault that I have to ask the following question?
Whatever happened to specifications such as the "Dynamic Headroom", "Damping Factor" and even "Dynamic Power" or ""Slew Rate"?

Slew rate is the same as frequency response bandwidth. The slope is the bandwidth. So it's nice having both if a person prefers one over the other but bandwidth is more natural for handling.

 

[pseudoid]

Slew rate is the same as frequency response bandwidth. The slope is the bandwidth. So it's nice having both if a person prefers one over the other but bandwidth is more natural for handling.

I really don't know how this stuff gets in my brain OneNote...

Practical Amplifier Slew Rates
It’s been established that, above some frequency point, the slew rate of an amplifier will play a major role in distorting the signal.
The equation to find the minimum slew rate of an amplifier is as follows:
Slew Rate = 2 π • Frequency(max) • Voltage(peak)
So, what would be a bare minimum amplifier slew rate?
Remember that the slew rate specification, though it may seem like it has to do with dynamics, actually has more to do with high-frequency distortion.
From <https://mynewmicrophone.com/what-is-amplifier-slew-rate-does-it-affect-performance/>
Measuring Slew Rate or Rise Time
Slew rate is specified as a change in amplitude with respect to time (dV/dt), typically shown as V/µs. Slew rate is considered a large-signal performance measurement, as opposed to rise time which is a small-signal performance measurement.
From <https://www.ap.com/blog/measuring-slew-rate-or-rise-time/>
Dynamic Power
The dynamic power of an amplifier is measured by repeatedly feeding a 1000 Hz signal for 20 milliseconds (or another short amount of time) followed by 480 milliseconds (or another longer amount of time) of no signal.
The amplifier volume control is turned up until the amp reaches the clipping point. At that point, the amp has reached its instantaneous peak or dynamic power output.
This rating, again, is listed t boast higher power rating numbers in order to make the amplifier look more powerful than it is.
From <https://mynewmicrophone.com/complete-guide-to-power-amplifier-specifications-data/#Dynamic-Power>

 

[restorer-john]

Slew rate is the same as frequency response bandwidth. The slope is the bandwidth.

To determine full power bandwidth using slew rate, you need to use this formula:

Slew rate is proportional to the frequency and the amplitude. Big amplitudes' slew rate is obviously greater.

You can determine an approximate -3dB point from the rise time of a waveform (10%-90%) using this:

 

[restorer-john]

Dynamic power testing is valid, useful, and can tell you a lot about how an amplifier will sound at high powers in the real world of dynamic musical content. It is not a substitute for continuous output testing, but an additional measurement.

An amplifier with deliberately high rails, which are 'soft' (dip down under heavy loads) can deliver high dynamic outputs for relatively low additional costs. NAD employed that idea with their early amplifiers and then refined it for their 'power tracker' designs.

 

[ItSoundsNatural01]

The build quality is impeccable!

 

[David_M]

A decent price for this level of SOTA performance and power. Thanks to whoever sent this one in and @amirm for the testing.

The case, connectors and design in general seem most professional. It's good to see XLR and RCA too as well as the gain settings. Also, @Apollon Audio nice job.

JSmith

Love the clean layout and the thick (low gauge) and short high current twisted pair wires to the speaker connectors that do their best to avoid interference with the low voltage Sparkos opamps for optimum crosstalk.

 

[ivanj]

Amir, thank you for using Power Cube in your testing!
Apollon offers a higher input voltage option for better performance ala Benchmark Media. I wonder how the Apollon would pair with an HPA/LA-4 at a nominal 120V mains?
So which are the preferred op-amps - I may have missed this in the discussion?

 

[Hart]

A little off topic but after seeing so many bad AVR tests it would be nice to see someone build one with class D amps, and better specs. It seems like it could really sell: very high power, cool running, smaller sized. I think except for a couple Denons they have all been not very great, even brands I thought would test well.

 

[David_M]

Each amp has a different gain. Trying to equalize that to the same would be a lot of work. Nothing exciting is happening there anyway. The graph simply continues on that trajectory as we are noise limited. On lower gain amps, the measurement does go to much lower levels. I just don't show it on the graph. Here is that for this amp:

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I wasn't aware these amps have lower distortion and higher power than the newer Purifi amps, by 5dB at least up to 20W. Most music listening (daytime) in your home uses on average, under 5W. Imagine a speaker with an efficiency of 92dB/W...sitting less than 6 to 8 ft away at 92dB SPL is pretty loud...and only demands 1W of amp power, on average.

A less efficient speaker at 88 dB/W demands 1W from the amp for the speaker to produce an 88dB SPL. Increase that power to 2W ==>91dB SPL, which can be loud...and much lower at night, maybe at 0.5W from the amps.

The point I'm trying to make is that amps, on average, are run at low power levels for normal listening SPLs in your room, hence the need for them to have lower noise and distortion specs at low power levels as I consider these (IMHO) more important than the high power specs.

Even when watching movies, the sound, being very dynamic and louder, would, on average, consume about 10W with occasional maybe full-power peaks for those base thumps and other side effects.

So where is the Purifi advantage here? Can you tell the amps apart by listening to them?

 

[David_M]

All our enclosures are made out of aluminium. The weight of this amplifier is 2.9kg.

Just curious ...why don't you offer the low-distortion OPA1612 buffer option anymore and instead offer a higher-distortion OPA1656 version?