NC400 FFT Plot

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lowtech

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Re: NC400 FFT Plot
« Reply #20 on: 5 Jun 2012, 06:21 am »

mgalusha

Re: NC400 FFT Plot
« Reply #21 on: 5 Jun 2012, 11:33 am »
Makes SpectraPlus-DT look like a genuine bargain.   :wink:

A very different instrument though there is some overlap. One can purchase the dScope without the digital analysis options and  save either $2K or $4K depending on other options.

ChrisPa

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Re: NC400 FFT Plot
« Reply #22 on: 7 Jun 2012, 01:44 pm »
Mike, the FFT looks pretty good, the higher harmonics should be attenuated by the output filter so they will look increasingly better as the frequency goes up.

That should only relevant above 20k. Anything lower than is in the audio band and so unattenuated

Quote
It's certainly hard to find fault with how this amp measures.
Thanks for the new data, this is the first FFT I have seen of Brunos's new baby.
Scotty

agreed

*Scotty*

Re: NC400 FFT Plot
« Reply #23 on: 7 Jun 2012, 03:49 pm »
Here is a link to a Harmonic overtone calculator. http://www.sengpielaudio.com/calculator-harmonics.htm
As you can see from the calculator about the time you reach 5Khz to 6kHz the higher harmonics above the 3rd overtone fall at or above 20kHz.
 The output filter will quickly become a factor in your measurements as you look at the THD the amplifier might have at frequencies above 5Khz.
Of course the bottom line is, the amplifier sounds good in addition to doing well on the test bench.
Scotty

ChrisPa

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Re: NC400 FFT Plot
« Reply #24 on: 10 Jun 2012, 12:52 am »
Here is a link to a Harmonic overtone calculator. http://www.sengpielaudio.com/calculator-harmonics.htm
As you can see from the calculator about the time you reach 5Khz to 6kHz the higher harmonics above the 3rd overtone fall at or above 20kHz.
 The output filter will quickly become a factor in your measurements as you look at the THD the amplifier might have at frequencies above 5Khz.
Of course the bottom line is, the amplifier sounds good in addition to doing well on the test bench.
Scotty

Okay, to be pedantic. Mike's original plot was for a 1kHz fundamental. Harmonics will occur at every 1 khz. The output filter won't have any attenuation until (approximately) the 20th harmonic (20 khz)
 
For higher fundamentals (eg 6 khz) the output filter won't have an effect until the frequency of the harmonic exceeds the corner frequency of the filter, or. 20 khz, which for 6 khz will be 4th harmonic (24 khz) upwards

So the output filter won't have any practical effect on the harmonics in Mike original plot

*Scotty*

Re: NC400 FFT Plot
« Reply #25 on: 10 Jun 2012, 02:54 am »
Correctamundo, Mikes 1kHz FFT will not show the effects of the filter. The filters effect however can be seen on the THD measurements presented in the Ncore data sheets.
Quote
For higher fundamentals (eg 6 khz) the output filter won't have an effect until the frequency of the harmonic exceeds the corner frequency of the filter, or. 20 khz, which for 6 khz will be 4th harmonic (24 khz) upwards
From the the online calculator the 3rd harmonic overtone falls at 24kHz.
From the THD graph in the Ncore's datasheet, the output filter's effect on the amplifiers high frequency response can partially explain the reduction of THD seen in the graph as the frequency increases.
Scotty

MoonUnit

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Re: NC400 FFT Plot
« Reply #26 on: 10 Jun 2012, 03:24 am »
Thanks for posting this! Those are very good measurements. Is the noise just over -115 dB part of the noise floor of the measuring device, or is that the noise floor of the amp?

mgalusha

Re: NC400 FFT Plot
« Reply #27 on: 11 Jun 2012, 03:29 am »
Thanks for posting this! Those are very good measurements. Is the noise just over -115 dB part of the noise floor of the measuring device, or is that the noise floor of the amp?

The dScope III has a rated noise floor of -115dB. Not quite as good as the Audio Precision 2700 series but awfully close, the AP is -117.8dB but is about 4x the cost.  :o

If I measured at a higher power level it would likely show a greater S/N ratio since the signal would be higher. I'm still learning how to use it but getting there. :)

ChrisPa

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Re: NC400 FFT Plot
« Reply #28 on: 13 Jun 2012, 03:07 pm »
Correctamundo, Mikes 1kHz FFT will not show the effects of the filter. The filters effect however can be seen on the THD measurements presented in the Ncore data sheets. From the the online calculator the 3rd harmonic overtone falls at 24kHz.

The fundamental, the base frequency, is the '1st harmonic' eg. 6kHz
The 2nd harmonic is 2x base freq ie 12kHz
so 4th harmonic is 4 x 6 = 24kHz

That's why measurements of harmonic distortion always start with '2nd harmonic distortion' and go up

The 'harmonic' is different to the 'overtone'
The 'overtone' is always 1 number lower than the harmonic, ie. the 3rd overtone is the 4th harmonic

So, for example, at 6kHz there will be no attenuation of any 3rd harmonic distortion

From the THD graph in the Ncore's datasheet, the output filter's effect on the amplifiers high frequency response can partially explain the reduction of THD seen in the graph as the frequency increases.
Scotty

That will also apply to any amp with hi-freq roll-off (including most/any class D?)

However I believe the good hf distortion figures of the ncore (good distortion figures across the whole audio band) really are because it's highly linear, ie. it really has low distortion.  It has low open loop distortion; and it has even lower closed loop distortion, because it has lots of feedback.  The hf filter will help but isn't the underlying reason

This is why Bruno/hypex publish the 18.5k + 19.5k Intermodulation distortion plots - they let you see the hf distortion reflected back down into the audio band



PS. the freq response is less than 1dB down at 24kHz and less than 2dB down at 48kHz, so it won't be having that great an effect even on the 6kHz 8th harmoinc distortion

The freq response is still less than 3dB down at 60kHz, the 10th harmonic of 6kHz

berni

Re: NC400 FFT Plot
« Reply #29 on: 19 Jul 2012, 08:44 am »
Hi guys,

on this link there is a small signal frequency response for all loads (8, 4, and 2 oHms), but I`m curious what the large signal response would tell for the same loads, specifically, what would be the electrical power into 8, 4,and 2 oHms for 20Hz, 1kHz and 20kHz?

http://www.hypex.nl/docs/nc1200%20folder%20web.pdf

The reason I`m asking is I have noticed non-linear behavior at small and large listening levels with some class-D amps. Some of them sound detailed at low listening levels, but much less at higher ones.

I hope I can get a straight answer.
Thanks!

poseidonsvoice

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Re: NC400 FFT Plot
« Reply #30 on: 19 Jul 2012, 11:37 am »
Hi guys,

on this link there is a small signal frequency response for all loads (8, 4, and 2 oHms), but I`m curious what the large signal response would tell for the same loads, specifically, what would be the electrical power into 8, 4,and 2 oHms for 20Hz, 1kHz and 20kHz?

http://www.hypex.nl/docs/nc1200%20folder%20web.pdf

The reason I`m asking is I have noticed non-linear behavior at small and large listening levels with some class-D amps. Some of them sound detailed at low listening levels, but much less at higher ones.

I hope I can get a straight answer.
Thanks!

I'm not sure why you wouldn't get a straight answer.

Have you looked at this link, and in particular the PDF file, section 9 (Figure 9.2?):

http://www.audiocircle.com/index.php?topic=108251.0

Best,
Anand.

berni

Re: NC400 FFT Plot
« Reply #31 on: 19 Jul 2012, 12:14 pm »
That`s THD versus frequency and it tells nothing about the frequency linearity into various loads at full power.
I would like to see the same frequency graph as in in 9.1, but measured at full power.

poseidonsvoice

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Re: NC400 FFT Plot
« Reply #32 on: 19 Jul 2012, 09:30 pm »
Got it. Sorry, can't find an equivalent with just FR measured...might want to email Bruno directly...

Anand.

mgalusha

Re: NC400 FFT Plot
« Reply #33 on: 19 Jul 2012, 10:06 pm »
That`s THD versus frequency and it tells nothing about the frequency linearity into various loads at full power.
I would like to see the same frequency graph as in in 9.1, but measured at full power.

Maybe, if I get some time. I already owe a friend some measurements that I haven't gotten done yet.  :duh:

So you want to see THD vs Freq at 200W into 8R? By definition that is the clipping point, so it would be more relevant at something less than full power, especially, IMO, as 99.999% of all listening is done at low to medium power, at least in my world. :)

berni

Re: NC400 FFT Plot
« Reply #34 on: 20 Jul 2012, 12:54 pm »
Got it. Sorry, can't find an equivalent with just FR measured...might want to email Bruno directly...

Anand.
Maybe the measurements show the same what I did noticed.
 :roll:

berni

Re: NC400 FFT Plot
« Reply #35 on: 20 Jul 2012, 12:57 pm »
Maybe, if I get some time. I already owe a friend some measurements that I haven't gotten done yet.  :duh:

So you want to see THD vs Freq at 200W into 8R? By definition that is the clipping point, so it would be more relevant at something less than full power, especially, IMO, as 99.999% of all listening is done at low to medium power, at least in my world. :)

no THD, just like I said above.
Freq response at 8,4 and 2 Ohm at full power

The frequency response seems to change with different amount of power. As it does with different impendance.

Thanks!

Davey

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Re: NC400 FFT Plot
« Reply #36 on: 20 Jul 2012, 03:04 pm »
Are you assuming there's a correlation between subjective "sound detail" at low or high listening levels and actual objective non-linear behavior?  I'm not sure a straight answer is attainable when the premise is rather gray.  :)

Anyways, it would be interesting to see the type of test results you're mentioning.  However, it's going to require someone to fabricate a hefty dummy load and possibly reconfigure their NC400 mounting scheme since this testing scenario would be completely different from normal usage.  Type and capability of the power supply could become a big factor in this type of testing also.

Cheers,

Dave.

mgalusha

Re: NC400 FFT Plot
« Reply #37 on: 20 Jul 2012, 03:52 pm »
I have a load capable of absorbing over 4kW, so that part isn't a problem but I may not run it at full power. While I doubt the amp would fail, I am not willing to sacrifice it for something that is not a real world scenario, IE: full power listening. Per the data sheet, the average level may reach 1/3rd of full power when peak clipping is occurring, so in the real world 1/3 rated power for a FR graph would be more useful. However, the datasheet also specifies the FR from 0 to 50kHz as +0/-3dB, all loads.