IOM 500s Stereo Amplifier Review

[Hart]

For similar price the Apollon NCx500ST still seems to be the best option.

Apollon NCx500ST Stereo Amplifier Review

This is a review and detailed measurements of the Apollon NCx500ST stereo class D amplifier based on Hypex NCOREx NCx500 modules. It was kindly drop shipped from the member and costs 1,090.00€ (US $1,168) with standard opamp. While the case is stamped aluminum, it is a heavily customized one...

www.audiosciencereview.com

Need an Apollon NCx500ST with large meters. I'm in. Also I agree with others, I think the class D amp folks are sometimes using this as an exercise in seeing how small they can make a powerful amplifier. I would rather see a well designed faceplate and room to breath inside. It's still going to be multitudes smaller than an class A Krell, it does not have to be the size of a pack of cigarettes. I would come up with a good logo/name for the amp, cut the name or logo out of a thick piece of aluminum stock, back the cut out on amp side with diffuse glass or plastic, back light with red LED. Adjustable brightness. Might add $100, but not a deal breaker at $1,200 amp selling price. Benchmark has a good logo and it is cut out, I would have back-lit it, would look great. Looks matter.

 

[amirm]

Many quality preamps won't even drive that. So why test there?

Because many of its competitors with fixed gain are in that region, including the reference design which came at 11 dB gain.

 

[Sokel]

Exactly. There's no point whatsoever.

This "low gain to extract the best numbers for an ASR review thing" has gotten completely stupid. As you say, absurd.

Don't take any notice of it, or the results. Demand more representative levels/gains and testing for typical usage scenarios. What's next? Take the 26.7V APX555B analyzer maximum output and do a unity gain, 178W@4R "power amplifier"? That will surely top the charts. I can't wait.

The consumer world of HiFi is not low gain. 99% of it is unbalanced and will remain so for decades to come. Standard levels have been creeping up since CD in 1982, but anything over 2V unbalanced and 4V balanced is not going to be remotely compatible with the vast majority of HiFi made in the past, the present, or the future.

There was an after-power amp,power amp in the past if I remember well.Quad maybe?
I remember they where can-like?

These ultra low gain ones should fall in this category

 

[Velocipede_Acoustics]

Because many of its competitors with fixed gain are in that region, including the reference design which came at 11 dB gain.

I think it stands to reason that the overwhelming majority can't feed this thing more than 2v or 4v and would have the gain either maxed or near it, especially for inefficient speakers. I appreciate what you do, hower, I think this is pretty odd to present the amp this way.

 

[martijn86]

It's too bad you didn't get a chance to test this beauty...

View attachment 384681

Put a WiiM Ultra with cover art on top and you have a really pretty stack in my opinion.

 

[pma]

TI OPA1656 on the buffer board, which is a good option.

However, not with that SMD to DIL adapter board.
RCA messy spectrum indicates to design issue.

 

[restorer-john]

There was an after-power amp,power amp in the past if I remember well.Quad maybe?
I remember they where can-like?

Like a unity (or less) gain power stage after a voltage amp? The gain has to be somewhere, unless you are doing flea-watts.

 

[pma]

Like a unity (or less) gain power stage after a voltage amp? The gain has to be somewhere, unless you are doing flea-watts.

Certainly. The idea that in case of 4V DAC balanced output we need only 12dB gain is completely wrong. People tend to forget there are also speakers with lower than usual sensitivity and that not everyone listens to DR5 music that is always almost clipping.

 

[amirm]

I think it stands to reason that the overwhelming majority can't feed this thing more than 2v or 4v and would have the gain either maxed or near it, especially for inefficient speakers. I appreciate what you do, hower, I think this is pretty odd to present the amp this way.

I am not clear what you are asking me to have done. As I explained, I have tested a number of amps in this range of gain. The next on up would have been 22 dB on this amp which is quite an oddball and would have gotten people complaining that they can't compare it to reference design. Or other amps for that matter since 22 dB is not a common gain.

The review gives you the performance at both 11 and 16 dB. You can deploy the amp that way and see if it gets as loud as you want it. This is eased by good number of high performance DACs producing nominal 5 volts. If you can't get there, then dial it up one more notch. That is what the feature is for.

 

[restorer-john]

Certainly. The idea that in case of 4V DAC balanced output we need only 12dB gain is completely wrong. People tend to forget there are also speakers with lower than usual sensitivity and that not everyone listens to DR5 music that is always almost clipping.

So true.

I reckon there's half of ASR's members leaving most of their power off the table. You know, the ones who get out their calculators to work out how much gain they need based on full scale 0dBFS output voltage of their DAC...

Then they play a nice digital recording from the early 1980s where there is 8-10dB headroom to 0dBFS as the recording engineers were conservative and it's mostly quiet anyway and wonder why their new "power" amp isn't loud enough even in the loud bits. LOL.

 

[Sokel]

Like a unity (or less) gain power stage after a voltage amp? The gain has to be somewhere, unless you are doing flea-watts.

Pff,it's been years.I just remember them siting behind the speakers after the power amps and they were boosting (?) them as I was explained.

They were round and had heatshink on the back.
Not sure at all it was Quad.

 

[restorer-john]

I am not clear what you are asking me to have done. As I explained, I have tested a number of amps in this range of gain. The next on up would have been 22 dB on this amp which is quite an oddball and would have gotten people complaining that they can't compare it to reference design. Or other amps for that matter since 22 dB is not a common gain.

The review gives you the performance at both 11 and 16 dB. You can deploy the amp that way and see if it gets as loud as you want it. This is eased by good number of high performance DACs producing nominal 5 volts. If you can't get there, then dial it up one more notch. That is what the feature is for.

So Amir, tell me why this test makes any sense, other than presenting the best figures the "amplifier" is capable of by deliberately running at the lowest gain.

11dB with even your 5V source at full blast output knobbles the output to 39 Watts at 8 ohms.
13dB with your 5V source at full blast output knobbles the output to 62 Watts at 8 ohms.
What exactly are people buying a power amplifier for again? (that was a good pun- for a gain)

Based on your power output graph, it achieves 210W@8R at the knee. That's 41V RMS. So it would need 18dB+ for your 5V source, 20dB+ for a 4V source and 26dB+ for a 2V RCA source. And you tested at 11dB and 13dB...

 

[JeremyFife]

Pff,it's been years.I just remember them siting behind the speakers after the power amps and they were boosting (?) them as I was explained.

They were round and had heatshink on the back.
Not sure at all it was Quad.

Was it this - Musical Fidelity "supercharger" ... I always wondered what these were really for! https://www.stereophile.com/solidpoweramps/907mf/index.html

 

[Sokel]

Was it this - Musical Fidelity "supercharger" ... I always wondered what these were really for! https://www.stereophile.com/solidpoweramps/907mf/index.html

Yes!
I had a look around and couldn't find it,thank you!

 

[Sokel]

Yes!
I had a look around and couldn't find it,thank you!

To complete,at the same house I got my love for semi-actives,they had 2 meter tall Magnats with at least 15" opposed side woofers.
Dynamics were insane even at the most moderate levels!

 

[JSmith]

you tested at 11dB and 13dB

11 & 16dB from what I am reading?


JSmith

 

[restorer-john]

Was it this - Musical Fidelity "supercharger" ... I always wondered what these were really for! https://www.stereophile.com/solidpoweramps/907mf/index.html

2.23V line input for full rated power of 550W@8R. That's 29.5dB gain.

The "speaker" level inputs are just padded down like a powered subwoofer in/outs.

I love JA's underplaying of the shutdown event and failure to hit spec:

 

[restorer-john]

11 & 16dB from what I am reading?


JSmith

Yes, correct. 16dB on the switch setting. Still way too low for even Amir's 5V example. It can never reach anywhere near rated power- that's the point.

 

[Velocipede_Acoustics]

I am not clear what you are asking me to have done. As I explained, I have tested a number of amps in this range of gain. The next on up would have been 22 dB on this amp which is quite an oddball and would have gotten people complaining that they can't compare it to reference design. Or other amps for that matter since 22 dB is not a common gain.

The review gives you the performance at both 11 and 16 dB. You can deploy the amp that way and see if it gets as loud as you want it. This is eased by good number of high performance DACs producing nominal 5 volts. If you can't get there, then dial it up one more notch. That is what the feature is for.

It seems clear to me. Test it at the two highest gain where I, and just about about everyone's else, read 99th percentile, will have to use it because we have preamps/dacs hay only output 2 or 4v, which is about as close to an unofficial standard we have.

I don't think we're being obtuse about this.

 

[ryanmh1]

Because many of its competitors with fixed gain are in that region, including the reference design which came at 11 dB gain.

Hypex ships the NCx500 from the factory with the "buffer", which is really akin to the voltage gain stage in a traditional amplifier, set at a level sufficient for 27dB overall gain for the package. The gain on the preamplifier stage itself is lower, but it does ship by default with that stage applied, and the bundler must either it strip out or modify it to change this. Many "tweak" this to provide their own "signature" on the amplifier, I assume. While it can be used without one, and will measure better, it is not intended to be used as such in a home audio application. No reasonable amplifier requires well over 10V to drive it to full output.

When Benchmark sold (and arguably unintentionally started this with) a low gain amp, that was technically a professional product. Fair enough. Select maximum gain mode, and you still get a reasonable home audio component. Now, it seems home audio resellers bundling Hypex modules (along with Topping's LA90) have now realized they can pump the numbers (and sales to suckers who will buy whatever measures "top of the chart") by using extremely clean signal generators to do the voltage gain job for them on measurements. It's cheating, and I suspect they're doing it specifically to try to use that SINAD chart to sell product. Personally, I wouldn't tolerate that, but it's your ballfield, and maybe it is fair allow using a signal generator for the voltage gain. Tough call.

FWIW, a home audio product should be providing at least 24dB gain for a 100W/8R product, and closer to 29dB for a 300W/8R product, which is the gain required to drive to full rated output with 2V from an RCA jack. If a home audio product cannot be driven to clipping with 2V of output, it's badly designed, plain and simple, and ought to be pilloried as such. If it allows that but offers other options as "cheat modes", that's neat, but a curiosity and not really a reasonable test setting, in my view. Has a manufacturer really achieved anything technically impressive by using an APx555 for its gain stage? Not really. They've just designed something that will probably cause a lot of people to clip their preamps.