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Old 22nd September 2011, 07:39 PM   #391
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Quote:
Originally Posted by Bruno Putzeys View Post
...When some designers (I saw a name flash by just now) claim their amp is "best below 1W"...
I retract my Pass-ing fancy!
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Old 22nd September 2011, 08:56 PM   #392
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Good Lord, I finally got the measurements of Halcro's DM88 monoblocks for comparison. You have to twist your head a bit, but the ncore BEATS the Halcro in high-power THD *AND* IMD--the latter measurement was at 400W@2Ohms for ncore and 495W@4Ohms for Halcro! Caveat, Stereophile has a curious testing history.

EDIT: OK the Halcro is close to clipping there, no other IMD graph available for it, ncore is just at ~40% of clipping. Halcro seems to be a little better at THD at 8 ohms, hard to discern, but at 4 ohms and below is owned by ncore. Low level THD is outstanding for both.

I haven't studied these graphs for long so would appreciate another interpretation.

In any case ncore actually is rated for and measured at 2 Ohms, is perhaps 10% the finished price, <15% the weight, and many times greener.

See:

Halcro dm88 Reference monoblock power amplifier Measurements | Stereophile.com

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

I would have found this months ago, I just stopped short. Not that I was about to buy a pair of Halcro monoblocks at $40k...

Last edited by Sam Lord; 22nd September 2011 at 09:20 PM.
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Old 22nd September 2011, 09:33 PM   #393
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Good Lord, I finally got the measurements of Halcro's DM88 monoblocks for comparison. You have to twist your head a bit, but the ncore BEATS the Halcro in high-power THD *AND* IMD--the latter measurement was at 400W@2Ohms for ncore and 495W@4Ohms for Halcro! Caveat, Stereophile has a curious testing history. Halcro seems to be a little better at THD at 8 ohms, hard to discern, but at 4 ohms and below is owned by ncore. I haven't studied these graphs for long so would appreciate another interpretation.

See:

Halcro dm88 Reference monoblock power amplifier Measurements | Stereophile.com

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

I would have found this months ago, I just stopped short. Not that I was about to buy a pair of Halcro monoblocks at $40k...
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Old 22nd September 2011, 09:47 PM   #394
_Wim_ is offline _Wim_  Belgium
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Let’s hope some of the selected VARs are no-nonsense engineering companies that make an affordable design, so that this excellent performance becomes available for non-DIYers also…

If you look at the performance data of the Amplifier modules produced by Douglas Self (class-A design by another of the audio guru’s), you’ll will see that the ncore beats even their performance in many ways
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Old 22nd September 2011, 10:20 PM   #395
PHEONIX is offline PHEONIX  Australia
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Quote:
Originally Posted by Sam Lord View Post
Good Lord, I finally got the measurements of Halcro's DM88 monoblocks for comparison. You have to twist your head a bit, but the ncore BEATS the Halcro in high-power THD *AND* IMD--the latter measurement was at 400W@2Ohms for ncore and 495W@4Ohms for Halcro! Caveat, Stereophile has a curious testing history. Halcro seems to be a little better at THD at 8 ohms, hard to discern, but at 4 ohms and below is owned by ncore. I haven't studied these graphs for long so would appreciate another interpretation.

See:

Halcro dm88 Reference monoblock power amplifier Measurements | Stereophile.com

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

I would have found this months ago, I just stopped short. Not that I was about to buy a pair of Halcro monoblocks at $40k...
Hello Sam_Lord

Dont forget that the Ncore amplifier is measured with a AES17 Low Filter at the input of the Audio Precision which has a stop band attenuation >60 dB, 24.0 kHz–200 kHz (for the 20Khz setting) which of coarse improves the THD performance at the high frequencies.

AES17 Filter

If we look at a high frequency like 12Khz for example the second harmonic 24kHz is highly attenuated by the filter , hence lower THD . Using this filter the Halcro and for that matter any amplifier would also benefit in the high frequency THD performance stakes.

I dont mean to be an apologist for the Halcro.


Regards
Arthur.
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Old 23rd September 2011, 07:44 AM   #396
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That's why one should do the IMD test. Not just on class D amplifiers but on any amp. You want to find out if a given distortion mechanism can give rise to mix products inside the audio band or not. Two amps could show a similar rise in THD at >6kHz (as measured without low-pass filter), but they could do so for different reasons. If the cause is merely loop gain dropping off, this means any mix products inside the audio band will still be met with the full force of the in-band loop gain. If the cause is some nonlinear capacitance, in-band IMD will be quite high.

Because outband harmonics are in themselves inaudible (you can hardly hear musical content above 20kHz, let alone distortion) whilst mix products inside the audio band are not, it is OK to cut the THD measurement above 20kHz provided a HF IMD plot is supplied. This is more relevant to sound than a THD plot with a wide analyser bandwidth. Of course, if an amp has low THD with a wide measurement bandwidth, you can dispense with the IMD plot. In the case of the Self amp linked earlier it's hard to say whether the distortion rise indicates in-band IMD problems or not. My guess is not.

I'm a bit confused about the measurements in Stereophile. First there's the description of the test condition. They're saying 453W *peak* (not average or "rms"). That's 42.5V peak. This means each test tone alone has a 21.3V peak value (56.5W/4ohm). The average ("rms") power output during this test was 113W/4ohm.
That is of course unless the reviewer meant something like "peak average" power in which case the figures are 60.2V, 30.1V, 113.25W and 226W. This seems reasonable and entirely possible except that it's hard to believe that this is how the phrase "peak" should be read.

Luckily we can still work out how big the uncertainty is that results from this ambiguity. The THD plot shows onset of clipping at 500W/4ohm or 63V. Depending on how we read the above, the IMD test either excercises the amp to 67% or 95% (in voltage terms!) of clip. I guess we'll never know. On the other hand, we do know that THD rises monotonically with power right until the thing clips hard. In that case we can use the simple polynomial rule to extrapolate. According to the IMD plots, the strongest IMD product is the 3rd, which rises 2dB for every 1dB of signal level (indeed this is what the THD plot does). So if we interpret the test conditions incorrectly, the maximum error we can make is 6dB. So we err on the side of caution and presume that the Halcro was indeed tested at 95% output swing. The 3rd IMD product reads around -87dB

In the case of the Ncore measurement the 4ohm test was done at 200W average, being 100W per tone. Peak voltage of 56.6V. Because of the gradual clipping nature of self-oscillating amps (I mean THD starts rising sharply before actual clip) it's hard to say which is the clipping point. If we take 0.05% THD it's about 600W (69.3V). The IMD test stressed the amp to 81.6% (in voltage terms) of clip, where IMD was around -103dB.

Scaling the Halcro measurement down to the same ratio we get about -90dB. In the high power IMD stakes Ncore wins by a margin of at least 13dB (or 19dB if we take the other interpretation). Note however that Ncore's distortion does not drop off monotonically so it's quite likely that at some lower power the two will meet.

At least that's how I read the Stereophile plots.

And here's my second issue. I just find it difficult to believe that Bruce would claim <120dB THD if his own lab sample measured as in the Stereophile test. I won't speculate on the cause and it's more a human judgment than a technical one, but I'd like to measure a Halcro first before fully believing the Stereophile test data.
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Last edited by Bruno Putzeys; 23rd September 2011 at 07:56 AM.
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Old 23rd September 2011, 01:22 PM   #397
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Just a quick update to say things are still moving on the NC400 front. The whole discrete shebang (regulators, op amps) is working OK, the power stage seems to do its job as well. Modulator (unloaded) linearity took some tweaking. Attached pic is the THD vs power at +/-65V (Apologies for the colour).
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Old 23rd September 2011, 01:29 PM   #398
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Had to edit it to see it on my monitor. Thought I'd upload in case it benefits someone ...

I also apologize for the color
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Old 23rd September 2011, 02:11 PM   #399
jmbulg is offline jmbulg  Belgium
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Quote:
Originally Posted by Bruno Putzeys View Post
Just a quick update to say things are still moving on the NC400 front. The whole discrete shebang (regulators, op amps) is working OK, the power stage seems to do its job as well. Modulator (unloaded) linearity took some tweaking. Attached pic is the THD vs power at +/-65V (Apologies for the colour).
Is this plot directly comparable to the one of the datasheets of the UCD400HG etc ?
If so, very impressive !
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Old 23rd September 2011, 02:19 PM   #400
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Bruno, just a quick question : Will there be NCore-based plate amps, like a new version of the AS2.400 ? Sorry if this has been asked before...
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