Apollon 1ET6525SA ST Amplifier Review

[slm0x]

Note from hypex: The NCx1000 OEM is not for sale yet. However, we expect to ship it in Q3, 2026

Should be on sale very soon )

I have an NCOREx 500 stereo amp. I'm waiting to purchase the NCx1000 (now the NCx1400) as my next amplifier purchase. Release date keeps getting moved back by Hypex. Dylan at Buckeye also hasn't heard anything on a release date.

Really anxious to get my hands on some of these monoblocks.

 

[dcolak]

Wait, what's this?! I've been eyeing for a quiet woofer/subwoofer amp, but this hints that many amps suck at low frequencies. Does your old reviews have this information in other charts?

That's why I always go back to the AB class amps.

 

[Matias]

That's why I always go back to the AB class amps.

Have you seen which amp class tops the charts? Yes, class D.

 

[Mort]

That's why I always go back to the AB class amps.

I'm sorry to hear that.

 

[Sokel]

Have you seen which amp class tops the charts? Yes, class D.

To be fair, top ten (10, but not physical 10, it's about the gain tricks) at your list are not class D.

 

[harkpabst]

To be fair, top ten (10, but not physical 10, it's about the gain tricks) at your list are not class D.

Power output into low frequencies has nothing to do with "gain tricks". We're not talking SINAD here.

 

[Sokel]

Power output into low frequencies has nothing to do with "gain tricks". We're not talking SINAD here.

I'm probably the first that pointed that out, as soon as Amir started measuring this way.

No nice votes from me if a power amp is not delivering the same power across all spectrum.
That's its one job after all.

 

[Matias]

Remember that the power measurement is defined by a given threshold of distortion %. And all amps have different frequency x distortion characteristics, no matter which class.

 

[Jukka]

Okey so please explain the apparent mismatches between these four graphs from this thread:

And doesn't change much in bass either:

8 Ohm naturally has less power but most speakers are 4 ohms or lower:

I tested its ability to drive one channel with 2 ohm. While it did that superbly, it did not result in a lot more power:

Our sweeps with respect to frequency show the common rise in distortion at higher frequencies. But this is still excellent performance:

The first graph doesn't state conditions other than 40 Hz (load, channel count, distortion).
The 8 Ohm test is clear, voltage limited.
The 2 Ohm test is close to first graph, but not a match, so what's different?
Fourth graph gives about 230 clean Watts (before the knee) between 20 and 200 Hz. This is the value I've been looking at for subwoofer amps. Why is this wildly different from the first graph? Which one is actually meaningful? I would guess the latter one is better because conditions are stated. The first graph is just too vague.

 

[Matias]

IMO you should compare the 40 Hz Max Power to the regular (1 kHz) Max Power on the left.
Which for this amp is 352 versus 372 W, pretty close.

 

[Jukka]

IMO you should compare the 40 Hz Max Power to the regular (1 kHz) Max Power on the left.
Which for this amp is 352 versus 372 W, pretty close.

Nobody cares about 1% distortion power, the ability to generate more voltage swing stops at the knee. After that it's just more distortion and no fundamental.

 

[Matias]

Nobody cares about 1% distortion power, the ability to generate more voltage swing stops at the knee. After that it's just more distortion and no fundamental.

You need to compare apples to apples. If the 40 Hz uses 1%, then we should compare to 1 kHz 1% too. We don't have the data for knee on both frequencies. And comparing knee versus 1% is wrong.

 

[David_M]

Nobody cares about 1% distortion power, the ability to generate more voltage swing stops at the knee. After that it's just more distortion and no fundamental.

What??? ... If the knee is at 0.0001% at 100W, a 200W output after the knee at 0.005% distortion is still clean output power with greater voltage swings than it had at 100W with clearly inaudible distortion...in fact, you have the same chance of hearing 0.0001% THDN as you would at 0.005% THDN. The very nature of the power curve says the 0.005% THD spec was also reached at a wattage of say 50W, before the knee. Both sides of the knee produce clean audio power.

Voltage output stops increasing when the peak rms output voltage reaches and tries to exceed the power supply rails. The peak of the output voltage waveform flattens out, ceasing to be sinusoidal and becoming more of a rounded-topped square wave. That usually happens at the 0.1% THDN and higher... and that's why the audio industry has set maximum power to be spec'd at 0.1% THD, a spec that has been in existence for decades. Very smart engineers at the FCC and many audio companies agreed on this specification for a reason.

Tube amps were set at 3% THD for some reason as their max power rating, but that is another topic for another day. Bob Carver himself told me this when I bought one of his VTA series tube amps.

 

[Jukka]

That usually happens at the 0.1% THDN and higher...

That might have been the case half a century ago. Modern transistor amps are better than in the past, so a fixed point is simply not applicable. You did explain it correctly, the fundamental stops growing and all that follows are HD as it happens with square waves. The HD consumes power too, so power graph keeps rising, but the height of the wave does not increase. If this clipping took place at 0.1%, it would show up in the graphs as increasing distortion increment rate from that point on. As you can see from the power vs distortion graph, nothing changes at 0.1%. The clipping, rising distortion, starts earlier, at the knee, where distortion begins to take a moon rocket trajectory. That's a clear change in the curve. With many amps the knee is not as distinct as with this one.

The reason why this is good with manufacturers is that it allows inflating power ratings. The knee in this threads amp for 20 Hz starts at roughly at 230 Watts. Amirs cursor is at 277. 0.1% is close to 315. 1% is about 350 Watts, which is closer to the standard power measurement values. To me this is a 230 Watt amplifier, because I care not about powering distortion.

PS. I bought this amp to drive a pair of 8 Ohm DIY subs. That one graph shows 158 Watts for that load. I don't feel cheated, I feel like I know what I got and I can trust that this amp delivers just that.

 

[harkpabst]

@Jukka, your argumentation is mostly solid, but some of your criteria are chosen arbitrarily.

There is no amplifier without distortion. Even at 20 Hz 230 W into 4 Ω there still is distortion. It might be as low as -110 dB at 70 W, but it's still as vanishingly low as -97 dB at 277 W. How would you compare the output power at 20 Hz to the plethora of power amps that never reach down to -97 dB THD+N? There has to be a common ground for comparison. If you don't agree with Amir's standards you should complain to him. Don't imply.that the specs of this amp would be made up.

Finally, a higher input voltage (past the point where "the knee starts" in output power according to your strict definition) will still result in higher SPL from the speakers. Do you agree?

 

[Jukka]

There is no amplifier without distortion. Even at 20 Hz 230 W into 4 Ω there still is distortion. It might be as low as -110 dB at 70 W, but it's still as vanishingly low as -97 dB at 277 W. How would you compare the output power at 20 Hz to the plethora of power amps that never reach down to -97 dB THD+N? There has to be a common ground for comparison. If you don't agree with Amir's standards you should complain to him. Don't imply.that the specs of this amp would be made up.

Finally, a higher input voltage (past the point where "the knee starts" in output power according to your strict definition) will still result in higher SPL from the speakers. Do you agree?

Good questions and to be fair, one cannot casually answer. I would compare, how much "clean" power an amplifier products, by how much is there before the knee for a given load. That would in most cases also be the best THD+N for that amplifier. After all, each amplifier has a knee, a clipping point, although it varies how much power and distortion the point has. I also acknowledge that the distortion is wiggly in graphs, so the knee in this thread could actually be at the cursor and not before. Generally the knee should be at most where the power supply limit is, as stated in an earlier reply. I guess it could also be stated as minimum power where maximum voltage is achieved before clipping.

Too high input voltage can overload the input stage and that would cause input clipping and fall short from the amplifiers full potential. But yes within that limit, where the limiting factor is power stage voltage swing (not input voltage or current capacity), increasing input voltage increases SPL after clipping point, because HD generates and is perceived as increased SPL. Harmonic distortion does not, however, make the fundamental (original input signal) any louder (except for H1, if there is such a thing).

 

[David_M]

@Jukka, I'm curious ... where would you place the knee for the 9040BA module power curve below for 8 ohms (black line)? From your reasoning, perhaps at 200W, where the distortion starts to rise? Or 300W or 400W, where it definitely shoots up to the skies? BTW, Purifi rates this module at 375W into 8R at 0.1% or -60dB THD+N. As I explained earlier, this is industry standard, and the FCC has not changed it, as far as I can tell. In fact, a manufacturer is free to rate their amp at any distortion level. Purifi would also be correct if they rated their 9040BA module at 200W with -130dB THD+N or 300W with -125dB THD+N. But that would be 'wasteful' and unrepresentative of the true performance of the module.

Also, a slight correction to a statement you made: "Harmonic distortion does not, however, make the fundamental (original input signal) any louder (except for H1, if there is such a thing)."

When you look at a 100W (~28.3Vrms into 8 ohms) waveform on the scope at -130dB THD+N, it will be clean. Increasing the power to 200W (40Vrms) or 300W(~50Vrms) at higher distortion levels, the primary waveform amplitude (H1 in this case) will linearly increase and will continue to do so at 200W or 300W. By the time it reaches 375W in this case, the input voltage amplitude will not cause a proportional change in the voltage output, but H1 will continue to increase along with higher harmonic products, just not at the rate as the input (and you'll still see a clean looking voltage waveform on the scope) ... until it just stops increasing when its peak voltage waveform is equal to the module rail voltage (typically +/- 46VDC for this module). Then, a rounded sine wave results, as I explained in my earlier post.

Good and interesting back-and-forth, @Jukka !

 

[NTK]

...
BTW, Purifi rates this module at 375W into 8R at 0.1% or -60dB THD+N. As I explained earlier, this is industry standard, and the FCC has not changed it, as far as I can tell.
...

The latest update (2024) to the US FCC rule (16 CFR Part 432) uses 1% THD+N as the limit. See section 432.3 (e).

Federal Register :: Request Access

www.ecfr.gov

 

[David_M]

The latest update (2024) to the US FCC rule (16 CFR Part 432) uses 1% THD+N as the limit. See section 432.3 (e).

Federal Register :: Request Access

www.ecfr.gov

Cool, I stand corrected, thanks! ... so that means one can rate their power amps at any distortion level that must not exceed 1%, correct?

 

[NTK]

Cool, I stand corrected, thanks! ... so that means one can rate their power amps at any distortion level that must not exceed 1%, correct?

That would be my interpretation. For example, if the manufacturer's power output rating of an amplifier is 100 W, then the measured THD+N at anywhere from 0.25 W to 100 W must be less than 1%, from 20 – 20k Hz.

Note that the FCC rule only specifies 8 Ω output, and not for any other load impedance.