Review and Measurements of Nord One NC500 Amp

[McFly]

I love the hypex amps. Small, cool and powerfull. These measurements are great too if not as good as the NC400's.

Off topic-ish; I bought the NC400 monoblock kit halfway through last year. I remember hooking them up and being very impressed. They did everything right from top to bottom, I heard none of the "class D" cliches I had psyched myself up about. But, something with drums was just not right. Snares and hi-hats especially. I told myself it was just the ultimate clarity and transparency of the amplifier. I used them until last week to get used to the sound.

Switching back to the class AB amp was a real "Ahhhh" moment. There were the snares, hats. Bass guitars even had a bit more flesh and crunch. If living with the hypex was like sleeping in a 5 star hotel It was like coming back home to my own bed. It seems theres no place like ...class AB amps. For me anyway. Call it me enjoying distortion or whatever but the AB amp just sounds more right, if not as transparent and powerful.

 

[gvl]

Is the switching noise visible on the analog waveform with filtering removed? I presume the level of the switching noise goes up and down with the actual signal, right?

 

[Bamyasi]

Drop him a note to see what he says.

Sure, I will.

 

[McFly]

I think the switiching noise is only visible at very small levels and does not increase with output. Im on phone so im struggling to quote but see the NC400 thread

https://audiosciencereview.com/foru...and-measurements-of-hypex-nc400-diy-amp.5907/

 

[amirm]

I think the switiching noise is only visible at very small levels and does not increase with output. Im on phone so im struggling to quote but see the NC400 thread

https://audiosciencereview.com/foru...and-measurements-of-hypex-nc400-diy-amp.5907/

That's correct. The NC400 though was tested using the AES filter, this one is not. The filter reduces the spectrum quite a bit.

 

[tohoho4]

Is the switching noise visible on the analog waveform with filtering removed? I presume the level of the switching noise goes up and down with the actual signal, right?

In my amplifier (TEAC AX-505 using Hypex NCore module), large switching noise is superimposed on 1 kHz sine wave at TEAC AX-505's speaker out.

 

[gvl]

In my amplifier (TEAC AX-505 using Hypex NCore module), large switching noise is superimposed on 1 kHz sine wave at TEAC AX-505's speaker out.View attachment 27058

Yuck, does the width of the modulation stay constant with varying of the output level?

 

[tohoho4]

Yuck, does the width of the modulation stay constant with varying of the output level?

Yes, the width of the modulation stay constant with varying of the 1kHz sine wave level.

 

[March Audio]

Yuck, does the width of the modulation stay constant with varying of the output level?

The switching frequency is at around 450kHz. The scope sees it but it does not translate into audio band noise. A speaker simply can't reproduce it. It's filtered out.

 

[Deleted member 2944]

The polarity reversal thing might be expected if there were a single power supply driving both modules.
In that case, you would also see a concurrent polarity reversal on the input jack as well to achieve the double-reversal.
In this case, it's puzzling. Just an assembly mistake I guess.

Dave.

 

[gvl]

The switching frequency is at around 450kHz. The scope sees it but it does not translate into audio band noise. A speaker simply can't reproduce it. It's filtered out.

I get it, but I like my sine waves clean How big is the amplitude of the switching frequency, in Volts?

 

[March Audio]

I get it, but I like my sine waves clean How big is the amplitude of the switching frequency, in Volts?

With respect I don't think you do understand it. The sine wave, within the audible band is clean. What gets reproduced by the speaker is clean. There is no trace of the switching frequency being reproduced.

Very few speakers will get to 45kHz let alone 450kHz

 

[gvl]

With respect I don't think you do understand it. The sine wave, within the audible band is clean. What gets reproduced by the speaker is clean. There is no trace of the switching frequency being reproduced.

Very few speakers will get to 45kHz let alone 450kHz

I meant for my eyes, not my ears. Most of the tragedies we see on this forum are for the eyes anyway.

 

[March Audio]

I meant for my eyes, not my ears. Most of the tragedies we see on this forum are for the eyes anyway.

Yes this is true. We sometimes obsess about some of the visuals of graphs without assessing the real audible impact.

If SFDR of a piece of kit is above say 110dB why should we care? Good kit has got there.

 

[Music1969]

With respect I don't think you do understand it. The sine wave, within the audible band is clean. What gets reproduced by the speaker is clean. There is no trace of the switching frequency being reproduced.

Very few speakers will get to 45kHz let alone 450kHz

I've seen posts like this around, about issues with Class D amps affect tweeters:

https://forum.audiogon.com/discussions/pop-crack-on-power-up-followed-by-audible-tweeter-hiss

Another discussion here, where Ribbon tweeters are less susceptible to this "issue" by ultrasonic switching noise:

https://forum.audiogon.com/discussions/anyone-using-a-class-d-amp-w-ribbon-tweeters

 

[amirm]

The hiss would have to be inside the audible band and indicates a noisy amplifier. It has nothing to do with it being a switching/class-d design.

 

[March Audio]

I've seen posts like this around, about issues with Class D amps affect tweeters:

View attachment 27060

https://forum.audiogon.com/discussions/pop-crack-on-power-up-followed-by-audible-tweeter-hiss

Another discussion here, where Ribbon tweeters are less susceptible to this "issue" by ultrasonic switching noise:

https://forum.audiogon.com/discussions/anyone-using-a-class-d-amp-w-ribbon-tweeters

Anything can be badly designed. You have to separate that and not generalise.

One potential issue is that intermodulation can result *IF* an input signal is close to the switching frequency. However a good design will ensure that the input is filtered and doesnt let signals close to switching frequency in. 450kHz ish in the case of Hypex amps. This is well up into RF range.

I will get the scope on.

 

[gvl]

So, the switching noise, it's a constant. What voltage is it in absolute terms? Nano? Milli? Kilo?

 

[Music1969]

One potential issue is that intermodulation can result *IF* an input signal is close to the switching frequency.

Possible with a DAC is connected direct to power amp?

Especially DAC's that up-sample to high sample rates? Many up-sample to 384kHz and above these days, before converting to analogue?

 

[tohoho4]

I get it, but I like my sine waves clean How big is the amplitude of the switching frequency, in Volts?

In my amplifier, the amplitude of the switching frequency is about 620 mVp-p. I don't know the sound quality is accurately transfered to you on youtube, but the sound quality is excellnt.