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Review and Measurements of Hypex NC400 DIY Amp

maty

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https://m.int.kef.com/products/ls50-wireless

Amplifier output power

LF: 200W HF: 30W
KEF LS50 Wireless by Phil Ward, January 2018

https://www.soundonsound.com/reviews/kef-ls50-wireless

Interestingly, while the bass/mid amps provide 200 Watts of Class-D power, the tweeter amps provide 30 Watts of Class A/B. The discrepancy between bass/mid and tweeter amplifier power ratings arises partly because the tweeter is more sensitive than the bass/mid driver (so needs less power), and partly because headroom is required on the bass/mid amplifier to enable LF equalisation to be applied. The decision to use Class A/B for the tweeter was taken on sound quality grounds.
 
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D700

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Great dead-on-balls-accurate fact based advice you all give out here. Thanks much! Maty, I looked at the LS50 wireless, its a wash price wise....unfortunately the wireless would have created some oddball wiring runs that didn't work in my office. I'll be running about 10' of Canare 4S11 to the LS50s.
 

maty

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Canare 4S11

http://www.canare.com/ProductItemDisplay.aspx?productItemID=65

Cables with star quad geometry is ALWAYS a very good choice, ant not only with speakers cable!

I have a thread in Audiocircle forums: Star quad, the best geometry to build audio and power cables

********* *********

Btw, just now I listen for the first time this fantastic recording in native DSD256.

Yuko Mabuchi Trio (2017), DSD256 (Native), Yarlung Records

https://www.diyaudio.com/forums/music/6958-playing-listening-post5667055.html

DR Peak RMS Duration Track
----------------------------------------------------------------------------------------------------------------
DR14 -0.37 dB -18.75 dB 7:32 01-What Is This Thing Called Love
DR16 -1.78 dB -23.84 dB 5:10 02-Valse Noire
DR16 -1.27 dB -21.91 dB 7:20 03-On Green Dolphin Street
DR17 -1.39 dB -22.73 dB 8:46 04-Seriously
DR16 -2.96 dB -23.35 dB 8:30 05-Medley: All the things you are, take the A train, satin doll
DR16 -1.97 dB -23.15 dB 11:17 06-Japanese medley: Hazy Moon, Cherry Blossom, Look at the sky
DR16 -3.31 dB -26.31 dB 4:19 07-Sona's Song
DR15 -1.02 dB -19.67 dB 6:16 08-St Thomas
----------------------------------------------------------------------------------------------------------------
Number of tracks: 8
Official DR value: DR16
 

svart-hvitt

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I think ATI (NCore, not HYpex, IIRC) and perhaps others have built class-D amplifiers using large conventional linear supplies. Since supply modulation can directly affect the output, subject to feedback (much better now than 10-20 years ago for class D amplifiers), I wonder if there's a market for that? (I could get rich in the 0.001% of the week I actually have free, eh? :) ) Ideally a SMPS is a much better choice but I wonder about reliability given comments here... For low-voltage use the SMPS used at work are very reliable, millions delivering 10~20 A at 1 V and 1.8 V in crowded high-temp/high-noise environments for years, and certainly wall warts seem to work OK as well as the +/-15 V etc. supplies for low-level gear, but I wonder if the high-voltage versions for audio amps are having growing problems? What is inside the Crown, maybe they and some of the other pro guys have it figured out after doing for many years whilst Hypex etc. are still learning? Or learning what corners can and cannot be cut (Google "Muntzing", R.I.P. Earl)... High voltage, high current, and high-slew(*) have always been a challenge.

Curious - Don

(*) Note that, unlike the discussion of the slew rate needed for audio signals, much higher slew rates are needed in class D switching outputs and SMPS (switch-mode power supplies). Switching rates can be in the MHz (though probably not for power amps) and the longer it takes to slew the lower the efficiency and the greater the heat in the output devices.
@DonH56 , you wrote:

«I wonder about reliability [of switching outputs] given comments here...»

You are probably a victim of FUD here. Genelec haven’t noticed any increase in repairs due to switching outputs. And Genelec take repairability,, reliability and sustainability pretty seriously.

Lower quality switching technology? Who knows?
 
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D700

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Canare 4S11
Cables with star quad geometry is ALWAYS a very good choice, ant not only with speakers cable!
Glad to see the quad cable is still popular, I researched it for a big home theater 20 years ago, loved the way it sounded, looked and felt in hand. I used to put a mesh sleeve on it and terminate with WBT, then heat shrink. Markertek is where I've always bought mine but I think Blue Jeans will terminate it now for you. Geez...now I'm getting that itch to build these NC400s and call it a day. I'm thinking a Marantz ND8006 to an NC400 amp, LS50s would sound pretty good.
 

rebbiputzmaker

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Glad to see the quad cable is still popular, I researched it for a big home theater 20 years ago, loved the way it sounded, looked and felt in hand. I used to put a mesh sleeve on it and terminate with WBT, then heat shrink. Markertek is where I've always bought mine but I think Blue Jeans will terminate it now for you. Geez...now I'm getting that itch to build these NC400s and call it a day. I'm thinking a Marantz ND8006 to an NC400 amp, LS50s would sound pretty good.
I drive LS50s with NC400s and they are excellent.
 

restorer-john

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You are probably a victim of FUD here. Genelec haven’t noticed any increase in repairs due to switching outputs. And Genelec take repairability, quality and sustainability pretty seriously.
These aren't the droids you are looking for.

Coming from a company that refuses to release schematics, service manuals or even sell spare parts directly to their own customers? How many people in far flung countries are effectively forced to landfill their gear due to those practices? Sustainable, I don't think so.
 

amirm

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Dumb question.

How do you adjust volume on power amps?
You have to use a DAC with volume control or use a pre-amp. The other way is to use software volume in whatever system it is connected to assuming you have a computer involved.
 

Roen

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You have to use a DAC with volume control or use a pre-amp. The other way is to use software volume in whatever system it is connected to assuming you have a computer involved.
How does a HT AV receiver or processor control volume?
 

restorer-john

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How does a HT AV receiver or processor control volume?
Multiple ganged pots like this:

1547695170407.png


Or these days, mostly done in silicon with VCAs or digital attenuation at 24/32 bit.

Lots of ways to skin a cat.
 

DonH56

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@DonH56 , you wrote:

«I wonder about reliability [of switching outputs] given comments here...»

You are probably a victim of FUD here. Genelec haven’t noticed any increase in repairs due to switching outputs. And Genelec take repairability,, reliability and sustainability pretty seriously.

Lower quality switching technology? Who knows?
Yeah, happens to me all the time, I just make stuff up. :rolleyes:

I do not know anything about Genelec, but looking at consumer repair stats and IEEE CE Journal articles apparently a few others have fallen victim to the same FUD regarding high-voltage (HV) SMPS' and amplifiers. For a number of applications from audio to automobiles to computer supplies to video cards to washing machines HV SMPS units have been the subject of a lot of scrutiny for poor reliability. That said, it appears to be capacitors and thermal management more than the output transistors. Too many don't get that high efficiency does not mean 100% so there is still a lot of heat in a high-power supply (or amp), and making it very compact means a lot of components are in close proximity to heat sources.

In my day job one of the things I have to deal with is making sure our board team keeps parts quality high and low-cost. There is intense pressure to do both despite their incompatibility by nature. They have been really great in helping me help them and going back and forth on the PI design. I am not a PI guy by trade, but get pulled in because, as one of my bosses used to say, "it's not your chip, but it is your ass!" SMPS require high-quality caps and inductors along with great attention to layout details. I do the analog filter designs but the board team does all the work to design and lay out those high-current switchers; I just put in my two cents now and then to keep them from messing up my analog paths. We have plenty of evidence of what poor components and design can cause, from noise mask spec violations to exploding caps and regulator chips.

The good news is that a lot of manufacturers and ODM/OEM companies are producing class D amplifiers these days. Compared to ten years ago, let alone the 1980's when they first started appearing commercially, their reliability has skyrocketed. Still no match for a decent conventional design, jury's still out on their reliability over decades, but my gut says the Hypex SMPS problems are more the exception than the norm. With the caveat that those low-ESR caps can cause problems over time, especially the electrolytics, and with an SMPS you don't usually get much warning in the way of hum like you do with a conventional supply. They just go boom.

As for analog'ish volume controls, there are a bunch of flavors these days, either digitally-controlled attenuators or VCAs, including stepped attenuators on a chip, to multiplying DACs, to conventional potentiometers or stepped attenuators using digitally-controlled motors to drive them, to optical units in various forms. Not something I deal with but there are articles in the trade rags and I tend to read them since I still have a little audio interest.
 

restorer-john

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With the caveat that those low-ESR caps can cause problems over time, especially the electrolytics, and with an SMPS you don't usually get much warning in the way of hum like you do with a conventional supply. They just go boom.
They do go boom, but increasingly I am seeing in SMPSs, completely shorted electrolytics (of good or respected capacitor brands) that take out the switching IC/MOSFETs and the primary and/or secondary rectifiers along with the MOVs/PTCs and non-resettable fuses. The 450V primary side electrolytics can go high in ESR as do the secondary low voltage caps. It is almost always accompanied by venting of electrolyte at that point.

They can function to the point where the ripple gets so high that all sorts of strange behaviour is manifested in digital circuitry. Random resets, refusal to start, corruption of signals, etc. People don't blame the SMPS, they figure their device is dying. Your flat screen starts glitching and pixellating more than it used to? SMPS caps.

Who hasn't had a flat panel TV die prematurely? Almost always SMPS or backlight inverter failures. Who hasn't had a laptop supply fail? Zero ventilation, packed electronics in a 65+ watt SMPS. Who hasn't had an inverter microwave oven, a phone charger, LCD monitor, DVD player, or a modern 'fast' drill battery charger fail? All SMPSs. Incidentally, the best laptop SMPS supplies are made by Dell in my experience.

The little bastards are here to stay, purely because of size and cost, but personally I wouldn't own any piece of serious HiFi powered by an SMPS.
 

maty

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And more about SMPS, the invasion of cheap Asian SMPS that breach the strict EU RF/EMI regulations, with which they dirty the electrical grid and not only their environment.

Just thinking about mobile phone chargers, light dimmers,... or the DC that adds cheap air conditioners and other devices with electrical motors, home or commercial.

The electricity grid is getting dirtier every day, with the authorities looking the other way.
 
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DonH56

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All good points by @restorer-john A few years ago we had a rash of bad video boards in our test labs (hundreds of PCs) and it was all bad caps. The manufacturer replaced them but taking down all those test systems was... vexing. It was a combination of a bad cap (with subpar specs for the application) too close to a heat sink in a tight environment. We replaced a couple thinking it was an isolated event before the magnitude of the problem was apparent; we probably lost 50 in the space of a month or (bought together, failed together).

And that does remind me that we also had a run of bad caps on an eval board a few years ago that took out the regulators. Imagine our joy as, under intense schedule pressure, a two-week test died. Those shorted as John said so we had exploding caps and literally had holes in some of the regulator chips. That is when the regulator company discovered the over-current protection in their latest chips was shall we say "inadequate".

And I recently replaced a few caps in our built-in oven at home because SMPS caps failed and killed the display.

Audio -wise I have little experience since most of my gear does not use SMPS'. I have had a couple of inexpensive amps fail, both due to blown caps, and a few dead wall warts (I usually just toss those but should have kept one for fun -- the side was blown out and little bits of paper and Al foil spewed out).

SMPS also cause problems on the power inlet (wall outlet) side that utility companies have been highlighting. The two main issues IIRC are the power factor can be pretty bad, i.e. they present a very reactive load to the incoming AC line. Power factor correction (PFC) is commonly used but I know (based on recent experience with computer supplies) not everybody is implementing it. The second issue, somewhat related to the first, is that they can inject HF noise into the incoming power line. This is not radiated RFI/EMI (though as @maty said that is also a problem) but rather noise injected into the wall outlet that is then free to radiate or just travel to whatever else it can reach along the wire. Normal component power input RFI/EMI filters usually take care of it but it is one more noise source in the house.

The one or two audio class D amps I built (years ago) used linear supplies. Reliability is certainly better now for HV SMPS but I have no idea the actual failure rate compared to conventional supplies in say audio amplifiers. Crown and the pro world must be doing OK so again I suspect it somewhat learning curve and somewhat cost-cutting causing grief in the consumer arena. They'll use the cheapest they can until warranty repairs and hit in reputation costs more than the cheap caps. (The Ford Pinto gas tank fiasco, when engineering was ignored in favor of accounting, was discussed in the "elite deviance" section of my college class in social deviance -- one of the highlights of my pre-med days. Memorizing all the parts inside a fetal pig or 27 steps of the Krebs cycle with all the reactants' formulae, not so much...)
 

rebbiputzmaker

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Who hasn't had a flat panel TV die prematurely? Almost always SMPS or backlight inverter failures.
Samsung was notorious for under spec LCD TV ps caps A few years back a friends tv was serviced twice under contract, then twice out of contract for free, for the known issue of under spec caps. The last time instead of just swapping the board, the tech soldered in new higher voltage caps.
 
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