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Review and Measurements of Hypex NC400 DIY Amp

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Well done Amir. :)

So is there a situation where the NC400 on its recommended power supply can deliver [email protected] at 1% THD? From your tests, it appears not, as it took a mere <4 minutes to shut down at 84% of its rated peak power and there is no point on your AP plot where the Po hits the 400W graticule.

The 2ohm figure now also appears extremely suspect. I would expect a much shorter shutdown period.

The other point to note is the THD at [email protected] hovers around 0.3%, not exactly a fabulous number.
Sorry for spamming this thread but I am on vacation and have too much time on my hands. :)

I am not sure that this test disqualifies the NC400 from reaching 400W with 1% THD+N. I suspect that it is the SMPS600 that sets the limitations in this amp with regards to both long term power because of heat and short-term power because of the rail voltages dropping.
 

DonH56

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Does anyone ( else) test amps for four/five minute at max?
Keith
Virtually everyone who reports power numbers per the FTC. That would be most all manufacturers selling to the U.S.A. That is the requirement for stating max average power levels in a spec sheet. The FTC requires a 1/3 (or 1/8, now I am not sure) power level preconditioning for 1 hour followed by a five-minute full power test at the desired THD (etc.) rating.

I would think an amp pushed hard for a few hours would approach or exceed the limits of the five-minute full-power test so I am not sure it is all that unfair or unrealistic. Remember amplifiers (any class) are less efficient at lower power levels so there is a point at which lower power for longer term will cause more heating than a short full-power test. At least as I see it thinking off-the-cuff...
 
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I took another look at the current SMPS600 and NC400 datasheets and wanted to summarize because you unfortunately have to read both in order to determine what performance you should expect under any given condition. They definitely need to clarify a few things WRT power. It is also possible that I have older hardware revisions and a spec may have subtly changed.

Hypex claims:
  1. With single SMPS600, stereo NC400 can output 2x200W @1% THD+N into unspecified load for 5 minutes on 120VAC or 230VAC.
  2. With single SMPS600, mono NC400 can output 1x300W @1% THD+N into 4Ohms for unspecified time period on 120VAC. If you want the full 400W, you need 230VAC.
Without knowing more, 1&2 seems to be at odds with one another.

Amir's most recent testing revealed:
  1. With single SMPS600, mono NC400 can output 1x335W @0.3% THD+N into 4Ohms for 3:45 before some protection circuit is enabled. This is 35W above the rated output and below the rated distortion. This makes no sense to me without seeing the discrepancy between 1&2 above.
  2. With single SMPS600, mono NC400 can output 1x365W @1.2% THD+N into 4Ohms for "brief" time period. This is 65W above the rated output at 120VAC and above the rated distortion. Again, see #2 above.
  3. With single SMPS600, stereo NC400 can output 2x226W @0.004% THD+N into 4Ohms for "brief" time period. This is 2x26W above the rated output at any line voltage and below the rated distortion. Here is your Music Watt (TM) rating.
  4. With single SMPS600, mono NC400 can output 1x315W @0.007% THD+N into 4Ohms for "brief" time period. This is 15W above the rated output at 120VAC and exactly matches the rated distortion. Did Amir just validate a datasheet?
  5. The SMPS600 heatsinking is insufficient if you intend to drive the amp hard. Even if you use one SMPS600 per NC400, or switched to the SMS1200, we have no consensus on capacitor lifespan.
 

Purité Audio

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Virtually everyone who reports power numbers per the FTC. That would be most all manufacturers selling to the U.S.A. That is the requirement for stating max average power levels in a spec sheet. The FTC requires a 1/3 (or 1/8, now I am not sure) power level preconditioning for 1 hour followed by a five-minute full power test at the desired THD (etc.) rating.

I would think an amp pushed hard for a few hours would approach or exceed the limits of the five-minute full-power test so I am not sure it is all that unfair or unrealistic. Remember amplifiers (any class) are less efficient at lower power levels so there is a point at which lower power for longer term will cause more heating than a short full-power test. At least as I see it thinking off-the-cuff...
Thanks Don, are the results published?
Keith
 

DonH56

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Thanks Don, are the results published?
Keith
Hey Keith,

Disclaimer: This is NOT my day job and I am not an expert on U.S. consumer laws and regs. Others here may have more insight and better experience upon which to draw. Mine is from prior experience both from the retail sales and design/manufacturing sides of the biz but fairly long ago.

Over here to be a legitimate (legal) datasheet the full-power numbers published must meet the FTC requirements or the company can be sued for false advertising. So, yes, anytime you see a full-power rating in a marketing blurb or datasheet they should have passed the FTC test. What you typically see is that one number then a whole bunch of other, often higher, power numbers under various other conditions. One of the biggest failings in the FTC spec is that it does not address multichannel systems thus you end up with a higher two-channel rating and (sometimes much) lower all-channels driven rating. People then constantly debate the value of having the all-channel rating match or be as near as possible the two-channel rating, with a lower all-channel rating being undesirable. In the real world, chances are the AVR (or whatever) would support the full two-channel rating for brief peaks, much of the time the surround/rear level is much lower (and don't usually have deep bass or the LFE track), and the times everything is max'd out tend to be things like explosions where a little distortion is really going to matter.

I look at the two- vs. all-channel ratings but unless they are far apart don't worry about them. I have one AVR in the house that had significantly lower all-channel rating and it struggled to drive my old Infinity system (not that bad a load); it was something like 125 W/ch for two and ~35 W/ch for all. Loud peaks would cause it to clip audibly. It really did not like the 4-ohm load of my Maggies and is now coasting along in the family room where it is rarely used and even rarer loudly...

HTH - Don
 

amirm

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Thank you for the test. From the thermal image it looks like the capacitors on the left channel is around 80 degrees. (red colour). But then again the capacitors on the SMPS are also red and the thermocouple measuring there showed 58 degrees. Also the thermocoupe on the large PS heatsink show 81 degrees while the thermal camera show 100 degrees. Which one should we trust do you think?
Thermocouple readings a more accurate than IR camera.
 

DDF

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This thread includes Bruno's approach to margining the cap temps on NC400. 90k hrs @60C
https://www.audiocircle.com/index.php?topic=106814.40
I assume he'd take same approach on SMPS. He probably assumed 1/8 power as normal. No mention of heat sink assumptions

Thread includes additional thermal measures but they aren't too applicable given the 3 min cooling time before measurement
 
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DDF

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Hypex claims:
  1. With single SMPS600, stereo NC400 can output 2x200W @1% THD+N into unspecified load for 5 minutes on 120VAC or 230VAC.
  2. With single SMPS600, mono NC400 can output 1x300W @1% THD+N into 4Ohms for unspecified time period on 120VAC. If you want the full 400W, you need 230VAC.
I went with SMPS1200 to help avoid possibility of current limiting:
- SMPS1200A400 specs qty 3 UCD4000 delivering 240W/ea into 8 ohms @ 1%/1kHz
- SMPS600 specs qty 1 NC400 delivering 240W into 8 ohms @ 1%/1kHz

The heatsinking is also night and day. SMPS1200 comes with a thick heatsink that I sink to a thick aluminum chassis faceplate, so it should prove cooler and more reliableble long term than the SMPS600. At the time, the SMPS1200A400 was also 30 euros less than a single SMPS600
SMPS600.JPG
SMPS1200.JPG
 
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[QUOTE="DDF, post: 135016, member: 5244"
The heatsinking is also night and day. SMPS1200 comes with a thick heatsink that I sink to a thick aluminum chassis faceplate, so it should prove cooler and more reliableble long term than the SMPS600. OTE]

What case are you using? I think I may need to add better heat sinking or a small fan to keep the system cooler.
 

DDF

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What case are you using? I think I may need to add better heat sinking or a small fan to keep the system cooler.
I used a different seller NLA but the same chassis as this:
https://www.ebay.ca/itm/JC2210-full...h=item4b01d5f3bd:g:F0kAAOSwuMFUcrmk:rk:1:pf:0

Price shown is $Can. Excellent quality, fit and finish. Easy to cut and work with, and a good looking, strong case.

There's a temptation to add a fan but to me it seems counter productive to spend time, cost and effort to purposely build an amp with exceptionally low electrical noise to then compromise it with fan noise.

A decently thick Al chasis (bottom plate is 3mm Al, faceplate is thick Al), a cheaper significantly over specified and heatsinked supply, and a $10 switched power bar to turn off the amp when out of use seemed to make allot more sense to maximize reliability.
 

svart-hvitt

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The safe temperature values depend upon the components used; for example, you can get capacitors in 65, 85, 105, 125, and 140 degC versions (among others). There are some defined temperature qualification ranges we could utilize: 0 - 70 degC for consumer, -40 to 85 degC for industrial, and -55 to 125 degC for military spec components. There are variations on each theme, natch, and these are component, not external case ratings. If your amplifier's case is at 70 degC (about 160 degF, too hot to touch) then internal components are probably 40 degC or so warmer (110 degC), too hot for comfort.

I have noticed that during recent Stereophile testing there have been several amplifiers that shut down during preconditioning and/or would not reach their full power ratings at low impedance without protection circuitry being engaged. (I have about six months of back issues and am slowly catching up whilst I have some time off.)

Rather than music, how about using pink or other colored noise or some other signal with a defined crest factor for power tests? That has been proposed before but I think shot down because it was too stringent (too hard on amplifiers). Foggy memory again back to the 1970/1980 decades when power wars were on-going and various standards bodies were trying to develop something reasonable. These days, we could create all sorts of fancy test signals. How about a multitone test with 10 or more tones across the 20 - 20 kHz bandwidth? That could provide a good crest factor for testing. Or a number of tones weighted to follow the Fletcher-Munson loudness curve (but at what level)? For me the problem is more what test conditions are reasonable and realistic than our ability to create and run them.

What I have done in the primordial past back when I worked "in the biz" and had audio test equipment and all the gear to play with:
  1. Standard frequency response at 1 W into resistive dummy load;
  2. SINAD (THD+N) sweeps to full power (typically low duty cycle);
  3. IMD sweeps or spot checks (e.g. 100 Hz, 1 kHz, 10 kHz);
  4. A few square-wave signals;
  5. Full-power test (FTC, including pre-conditioning);
  6. IHF burst test;
  7. Overload test -- pulsed signal at 3 dB over max output to assess clipping and recovery behavior; and,
  8. Pink noise at -20 dB and -10 dB (latter would usually cause some clipping).
Pretty sure my original list had ten things on it but I don't have the list anymore (at least anywhere I would be able to find it). I did run the slew/TIM test that was (I think) a 100 Hz square wave with a 10 kHz sine wave riding on it, or something like that, and some other burst tests like five full-power cycles at some frequency so I could see how quickly the amplifier recovered. At lower power (usually) it was interesting to see what happend with such a test signal when driving speakers. I did make up some speaker dummy loads with a couple of resonators to add a peak and valley at LF (100 Hz) and HF (10 kHz). Not a Power Cube, just a home-brew reactance network I added to my dummy loads that emulated some of the gnarlier speaker impedance plots I measured at the time. And I have said before my dummy loads were big gold-finned power resistors stuck in gallon paint cans filled with transformer oil. I had 4- and 8-ohm and could create other values by combining those.

Steady-state responses were (and are) typically well-defined and well-measured by manufacturers so, while I measured those when repairing or checking amplifiers, I got caught up in transient time-domain response of amplifiers to various "burst" conditions in my long-ago search for what differentiated amplifiers. Sometimes it was very revealing, sometimes not. Remember back then there were no, or at least I did not have, all the nice digital analysis gear we have now. (I had Nak and HP audio analyzers plus all the usual test gear like analog 'scopes and meters, including my big HP rms voltmeter, and a bunch of commercial and DIY filters for testing.) I could grab frequency sweeps on a spectrum analyzer and take a screen shot using a Polaroid camera pack, hand-record the THD numbers and graphs, etc. (HP made a chart recorder but it was pricey and the places I worked did not have one, though the local college did so I got to play with it some.) Burst response and recovery I could see on a 'scope with persistence (phosphor, not digital memory like today) and again grabbed the Polaroid to capture what I saw.

I could easily spend a day or two testing an amplifier, and had a blast doing it. Sometimes literally... :)

And at the end of the day, I found that pretty high levels of distortion (1% ~ 10% or more depending upon frequency and the type of distortion) was essentially undetectable when music was playing. I added distortion before the amplifier to emulate high nonlinearity and in blind tests it was rarely detected. Music is often complex and includes so many harmonic- and non-harmonic signal components that distortion added by the amps was in the mud.

Oops, this got long, sorry! This is why I should not take days off.

FWIWFM - Don
@DonH56 , you wrote:

«There are some defined temperature qualification ranges we could utilize: 0 - 70 degC for consumer, -40 to 85 degC for industrial, and -55 to 125 degC for military spec components».

Why don’t «high-end» producers use military spec components?

Price shouldn’t be an obstacle in benchmark products, right?
 
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I used a different seller NLA but the same chassis as this:
https://www.ebay.ca/itm/JC2210-full...h=item4b01d5f3bd:g:F0kAAOSwuMFUcrmk:rk:1:pf:0

Price shown is $Can. Excellent quality, fit and finish. Easy to cut and work with, and a good looking, strong case.

There's a temptation to add a fan but to me it seems counter productive to spend time, cost and effort to purposely build an amp with exceptionally low electrical noise to then compromise it with fan noise.

A decently thick Al chasis (bottom plate is 3mm Al, faceplate is thick Al), a cheaper significantly over specified and heatsinked supply, and a $10 switched power bar to turn off the amp when out of use seemed to make allot more sense to maximize reliability.
Thanks - now the question is do I want to take my amp (with the same power supply) out of my cheap but fully connected and running steel box and move it to a new one that needs to have holes drilled for the offsets and inputs/outputs, etc.
 

trl

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Here is the square wave 10 watts before someone (John?) asks. :)

View attachment 19472

It is at 90 kHz bandwidth, with frequency of 1 kHz.
If John asks (only) about 1KHz squares, then I will always love to see, when testing amps:
- Squares at: 20Hz, 100Hz, 1KHz, 10KHz and 20KHz, showing both input-generator vs. output signals on the same graph, to compare amplitude, corners-rounding and phase-shift. Power should be anywhere between 1/8 to 1/2 of max. non-clipped power (for safety reasons).
- Crosstalk at: 20Hz, 100Hz, 1KHz, 10KHz and 20KHz. This will show us how good will be the soundstage due to channel separation. Sines could be used here for testing.

Sources:
- http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Tektronix Cookbook of Standard Audio Tests.pdf
- http://www.r-type.org/articles/art-125.htm
 

Frank Dernie

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If John asks (only) about 1KHz squares, then I will always love to see, when testing amps:
- Squares at: 20Hz, 100Hz, 1KHz, 10KHz and 20KHz, showing both input-generator vs. output signals on the same graph, to compare amplitude, corners-rounding and phase-shift. Power should be anywhere between 1/8 to 1/2 of max. non-clipped power (for safety reasons).
- Crosstalk at: 20Hz, 100Hz, 1KHz, 10KHz and 20KHz. This will show us how good will be the soundstage due to channel separation. Sines could be used here for testing.

Sources:
- http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Tektronix Cookbook of Standard Audio Tests.pdf
- http://www.r-type.org/articles/art-125.htm
I used to like the tests done on 40Hz square waves here many years ago. We have 50 Hz mains and this checked power supply capability. Only see 1kHz and, useless IMHO, 10kHz these days.
Maybe 40Hz unmasked too many amps?
 

trl

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Roll-off and phase-shift only matters on 20...100Hz and 10...20KHz. At 1KHz all amps are great.
 
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Other than wanting to see the square wave as square as possible, I don't know what I am supposed to be looking for e.g. overshoot, excessive jitter without the AP LPF, etc.
 

BYRTT

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Other than wanting to see the square wave as square as possible, I don't know what I am supposed to be looking for e.g. overshoot, excessive jitter without the AP LPF, etc.
Agree mostly and especially after @amirm post 220 think we should relax on that one, also if we think about how square waves will look passing the first recording device and the last device in reproduce chain then guess we should be covered here, those two devises have not much bandtwidth to get a real square wave going above say up to 6kHz area, mega huge bandwidth can sound nice to have but then what about rejection for modern RF pollution and also DACs do their limiting stuff for square waves.
 
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FWIW, I'm not too concerned about having full power for more than a minute. No way my tweeters would survive that, and I suspect the mids as well. The Ncore's low noise & distortion from 0-50W seem much more desirable for normal use, and there's always the ATI Monolith option.

But temperature, longevity & efficiency definitely matter, especially if we're trying to avoid wasting money. So, @amirm, how about measuring power consumption from the wall? Simply reporting Kill-a-watt numbers at idle, ~10W & full power would work for me. And I don't recall seeing such information from other sources.
 

trl

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Roll-off and phase-shift only matters on 20...100Hz and 10...20KHz. At 1KHz all amps are great.
Rolloff, phase shift, pre/post ringing, start of oscillation a.s.o.

With squares you can check if low/high pass filter are well done, if input/output caps are having the right values etc.

A scope is exactly for amp testing, the AP is for measurements (excellent FFT etc.).
 
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Other than wanting to see the square wave as square as possible, I don't know what I am supposed to be looking for e.g. overshoot, excessive jitter without the AP LPF, etc.
Not everyone agrees a "perfect" square wave is important. It is possible that the circuity added to make a "perfect" square wave actually hurts sound quality such as transient response. Here is a link to an article that recommends bandwidth limited square waves for amp testing and gives some illustrations on how to interpret them http://sound.whsites.net/articles/squarewave.htm
 
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