[rustydoglim]

Q&A for specs.  For your entertainment, see the spec for icepower 500ASP:
http://www.nuforce.com/picts/icepower-500asp-thd-vs-freq.JPG
http://www.nuforce.com/picts/icepower-500asp-thd-vs-power.JPG

[Beano]

Just wondering how the aspect of THD  distortion specifications impacts how well an amplifier would perform soundwise.

Some high end amps like Krells may not have as an impressive THD specs but they are highly regarded. Also I believe tubes amps don't do well in these specs but supposedly their lower order harmonic distortion doesn't make the sound unpleasant to the ear?

[nuforce-casey]

Just wondering how the aspect of THD  distortion specifications impacts how well an amplifier would perform soundwise.

Some high end amps like Krells may not have as an impressive THD specs but they are highly regarded. Also I believe tubes amps don't do well in these specs but supposedly their lower order harmonic distortion doesn't make the sound unpleasant to the ear?

Well this is one can of worms we don't want to touch.  NuForce believes that good amps measure good and sound good.   While amplifiers could 'sound good' without having a good measurement, but it's flaw as far as 'high fidelity' or 'being accurate' are part of the objective.

[vdm]

I just had a look at the Nuforce 8 measurement results on their website. It certainly looks impressive. If it measures like that then I am very curious to hear what it sounds like  

However, I do not see the phase measurement in the frequency response graph. It only shows the amplitude measurement. Since one of the claimed characteristics of the Nuforce amplifiers is the almost zero phase shift in the audio range I would've expected to see the measurement results showing it working as advertised.

Also, the frequency response graph does not indicate into which load it was measured. Was it 4ohm, 8ohm, open load? How does it look into 16ohm?

Similarly the other measurements also do not indicate into which kind of load it was measured. It would be very helpful to show the measurements for 4ohm, 8ohm and 16ohm loads respectively. That'll give a much better indication of how the amplifier might respond under changing speaker loads.

Finally, are their any measurements showing the efficiency versus power output of the amplifier? The efficiency of switching amplifiers are typically very low at low power outputs. It can go down to between 20% to 30% for a power output at 10W. When driving high efficiency speakers (94dB to 100dB) the amplifier typically outputs in the range of 5W to 10W. Such high efficiency speakers also have fairly high impedances (12ohm to 20ohm), which decreases the efficiency even more. This question probably boils down to the abililty of the Nuforce to drive high efficiency and high impedance speakers. Is it going to operate below 20% efficiency most of the time when driving such a speaker? In that case a Class A amplifier will be more efficient  

Ok, I agree that's a lot of questions - I just did a brain dump after looking at the published measurements of the amplifier. I guess I'm in one of my very inquisitive moods today  

[rustydoglim]

If someone could name another manufacturer that provide as much measurement and plot as NuForce, I will like to see what they have done.
Now that I think of it, does anyone even provide any plot?

Come on, we don't sit around all day doing nothing other than taking measurements.  The more data we provide, the more you ask for it  
The FR is taken at 8 ohm load.  Our AP machine is in a lab 120 miles away from our production facility and our CTO have too much work to do. We do new measurements only when we have major upgrade or new product.

[rustydoglim]

NuForce amp has quiescent power around 5W, so in the case of high efficiency amp the max power consumption is about 10W, compared to 100’s of watts for class A amps. Efficiency for switching audio amps are not very important at such low power usage. It is the absolute number that counts.

[Rivendell61]

If someone could name another manufacturer that provide as much measurement and plot as NuForce, I will like to see what they have done.
Now that I think of it, does anyone even provide any plot?

Hi Jason,
Well, since you ask so forcefully....I'll respond!
As a D-100 owner I know CIAudio/Hypex stuff best.  There are AP generated plots for the Channel Islands Class D amps right here on Audiocircle (on CIA Circle)--mainly THD vs Power and Freq. resp. info.
But there are also many Hypex plots for all sorts of parameters out on the net.

I'll link you to a THD vs Freq graph of the Hypex/CIAudio Class D amp module (....since we are already showing other makers plots, e.g., ICE):
http://www.audiocircle.com/image.php?id=5654

It looks quite good....  
That should allow almost exact comparison of Hypex/CIAudio and the NuForce THD vs Freq graph, which is current (7/25) on your web site (and the identical graph on the 6Moons review page):  
The much discussed flat THD vs Freq., @ 8ohms, 1w, 10w, 20w, and 40w--

There are lots of comparative graphs and data out there--

Mark

[vdm]

To add to the above post regarding measurements, have a look at the ICEpower data sheets at the link below:

    http://www.icepower.bang-olufsen.com/sw2093.asp

Each data sheet contains a very comprehensive set of measurements and graphs which are very informative.

Also, the design of any electronic circuit cannot be done without taking measurements. How else do you verify that your design performs according to your calculations?

Here's a very valuable quote from one of my control systems professors: "You cannot understand or control what you cannot measure". This is so true for many things in life and not just control systems or electronic systems, but it's absolutely true in the latter case.

[nuforce-casey]

The specification of class-D amplifiers and their AP plots inevitably use AES17 to remove switching noise, and further, the typical fast roll-off of THD with the little kink near 20Khz is characteristic of AP filter set at 20Khz BW.

One cannot reasonably take THD measurement at 10Khz or higher with a 20Khz filter, as the 10khz THD+N number will be artificially 'improved' by the 20Khz cut-off filter.

Look at the measurement with Icepower when the AP filter is NOT set at 20Khz.   Another way to look at it is to use a pencil to extrapolate the THD+N curve all the way to 20Khz, and it'll hit 1-3% THD+N.

If you have access to an audio analyzer, like HP, or AP, set the cut-off filter to 40Khz or higher, then do the measurement.  The result will be shocking.  Set the cut-off filter to 200Khz and the "other" mentioned switching amplifier will show 15-20% THD, while the NuForce Ref9 is still <0.2%

[rustydoglim]

I was referring to manufacturer's plot on their website. Yes, I know that Hypex and Icepower provide data on their website. Manufacturers that use these modules add their own tweaks and power supply, but I don't see any plot available on their websites. May be I missed it.
I created this topic mainly to discuss how to coorelate plot with listening experience or to answer your questions.  We'll try to avoid knocking other manufacturer's plots.
If you're a happy owner of a new non-nuforce amp, don't listen to a nuforce amp. You might regret your purchase  

[Rivendell61]

The specification of class-D amplifiers and their AP plots inevitably use AES17 to remove switching noise, and further, the typical fast roll-off of THD with the little kink near 20Khz is characteristic of AP filter set at 20Khz BW.

One cannot reasonably take THD measurement at 10Khz or higher with a 20Khz filter, as the 10khz THD+N number will be artificially 'improved' by the 20Khz cut-off filter

Hi Casey,
Regarding the UcD400 plot I linked:
I know the NuForce objection to setting the AES at 22Khz--and that they used 30khz--the UcD400 plot was done at 40khz.

Mark

[Rivendell61]

Jason,
OK!  Good idea.
I just could not resist when you asked  

I would be very interested if the thread could turn in that direction because the subject of measurement to listening correlation interests me.
The relationship is usually ignored or refuted in the modern popular audio press and audiophile perception.
And yet we know it is really descriptive--if you know what to look for.

Mark

[nuforce-casey]

Hi Jason,
Well, since you ask so forcefully....I'll respond!
As a D-100 owner I know CIAudio/Hypex stuff best.  There are AP generated plots for the Channel Islands Class D amps right here on Audiocircle (on CIA Circle)--mainly THD vs Power and Freq. resp. info.
But there are also many Hypex plots for all sorts of parameters out on the net.

I'll link you to a THD vs Freq graph of the Hypex/CIAudio Class D amp module (....since we are already showing other makers plots, e.g., ICE):
http://www.audiocir ...

If you refer to this specific link, it has the 20Khz filter, see the 20Khz extreme roll down and the classic 'kink'.

[rustydoglim]

This is a good article that discuss the importance of freq > 20khz
http://www.cco.caltech.edu/~boyk/spectra/spectra.htm

We know that by playing with the bandwidth, we can hear (or should we say sense) the sound stage changes. There are orobably other factors that affect how we perceived sound stage but we don't know.

It might not be important to persue THD < 0.1% but  go for higher bandwidth. Unfortunately THD+N meausres the cumulative distortion AND noise up to the cut off freq so for a switching amp with 100khz bandwidth, it's THD+N will not look so good but the listening experience could be better than that of a 50Khz bandwidth amp.

[Rivendell61]

Hi Jason,
Thanks for that bandwidth article--  It look like an interesting read.

Casey,
I think we would all (including me!) be happier moving along now....and picking on ICEpower
However....as you have disputed my post above I kinda gotta, reluctantly, re-state the facts to preserve accuracy:
It was done on an AP2 (SYS2322) with the AES17 set at 40kHz bandwidth--not 20kHz.
The downturn after 16kHz is when the 3rd harmonic shifts outside the 40kHz measurement bandwidth.
If you want some more info how about taking it to PMs.
Mark

[trekker]

Would it be possible to have the owners manual available on the NuForce website?

Thanks,

Arnold

[rustydoglim]

Would it be possible to have the owners manual available on the NuForce website?

Good point. I will do that next week. I am taking a weekend break in Vegas  

[trekker]

Cool    

Remember, what happens in Vegas, .....

[rustydoglim]

Just to be clear, we at NuForce patented (3 USPTO patents granted with many pending in US and PTC) and developed all our amplifier technology and do not use or license third parties technology.
We are not just a box maker .

Nphysics and NuForce are two of the same entities   .
Nphysics is the brand used for our power business and NuForce is the brand for consumer electronics.