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Class D Switching Power Amplifiers and Power D/A conversion

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Old 19th June 2011, 09:46 PM   #141
asbjbo is offline asbjbo  Norway
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Originally Posted by Bruno Putzeys View Post
@asbjbo, All our graphs are THD+N, so when the graph goes up towards the low end that really means you're looking at noise. It's just because THD+N is expressed relative to the signal level that you get a graph that slopes down. If you graphed absolute THD+N in volts instead of percents you'd just see it level out into the noise floor. Actual distortion keeps going down as signal levels drop, there's no optimum. Other than noise, THD at 50mW is completely off the scale. Actually, the higher the rated output power, the lower the THD at 50mW.
Thank you for the clarification! I'll just start saving up some $$, then.
Old 19th June 2011, 11:35 PM   #142
OllBoll is offline OllBoll  Sweden
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One small idea that might be worth considering:

Since it seems this module performs extremely well with sensitive speakers also, what about designing so that voltage gain can be adjusted to low/high through for example jumpers?

If it has 26 db gain as the UCD line, then 90+ db sensitive speakers with balanced input @ ~ 4V would require massive attenuation and wasted gain. Being able to lower gain by say 12 db ( or even more ) would come in handy.

// Olle
Old 20th June 2011, 01:59 AM   #143
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my speakers only have a 82.5 sensitivity; NEED MORE POWERRRR..

Bruno, when are you taking pre-orders?
Old 20th June 2011, 02:03 AM   #144
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What are they? LS3/5A?
The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello
Old 20th June 2011, 02:58 AM   #145
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Originally Posted by abraxalito View Post
What are they? LS3/5A?
They are Mark & Daniel's Mini+. I've recently purchased another pair of M&D's Monitor+ (with a slightly better efficiency of 85dB/2.83V/1m).
Old 20th June 2011, 03:37 AM   #146
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Ah, thanks That brand is new to me. They're good for 400W+ peaks then?
The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello
Old 20th June 2011, 10:40 AM   #147
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I´ve been looking for a good chance to dive into a UCD (now nCore) project for a while. The introduction of this second generation `UCD´ seems to be that very chance, so I´m also very interested in when pre-orders can be made

Regarding the needs for this future DIY oriented module, my feeling is that low impedance/high current abilities are the way to go. Most people won´t need more than 100W/8ohm if the amp can handle whatever load you through at it. To me the essence really is that one needs as little modulation as possible hence a rigid PS and an amplifier circuit that can pass some amps through without sweating.

If someone needs incredible amounts of outpower for their heavy speakers, the possibility to bridge two modules would bring exectly that, and the high current capability would be even more crucial yelding up to 4x the output power in an 8ohm load. If the price for one module can be kept within reasonable limits, the bridged solution will be aswell considdering the potential output

If this modular approach is possible, everybody should be glad, more modules should be dispatched, the power greedy can keep on building inefficient speakers, the high end manufatures should still feel that their modules are exclusive regarding high power specs, and Bruno can claim to be the best friend of the DIY community

Regarding the buffer, a world class discrete one would be most welcome! But how tough is the nCore actually to drive? the UCD in itself is a 1.8 kOhm as i recall? i could imagine that some DIY´ers may like the ability to fiddle with the buffer stage still, and if the module and the discrete buffer could be sold separately, one buffer may also be able to drive more than one nCore, making bridging and passive bi/tri -amping cheaper aswell as increasing the possibilities with the same components...
Also, the powersupply for the bufferstage may be a special area of interest. Will it be possible to drive it through the same supply as the output stage like in UCD180/400 and also beef it up by using dedicated and maybe externally regulated supplies for the buffer stage? BTW, how much gain will the nCore bring compared to the UCD´s? the same? or will the improved discrete buffer make it sensible to decrease the gain of the nCore if better sound can be reached through this appoach? Also what voltage is the buffer supposed to be run at? What I´m also fishing after, is whether there could be a chance to make the buffer for the nCore adaptabel for the UCD, esentially making them upgradable this way?

Concerning connectability, I have the feeling that most DIY´ers aren´t afraid to solder, so could it be possible to make easy and good solder-connections? The out put connection sounds clever, but wouldn´t a good solder still be better and more straight forward aswell? Another approach for the crucial loudspeaker connection could be the naim approach, which is made only for 4mm banana plugs. This could implemented as integrated directly into the module. this way the module could be placed in the back of the amp chassis with the banana connections directly accessibel from the back of the amp. No screws, no soldering, just plug it in

just my 2p

best regards,
Old 20th June 2011, 09:51 PM   #148
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As the lone high-power advocate and at some personal risk of offending or alienating the common sensitivity, I respectfully submit a plea for open-mindedness and real consideration and discussion of a much higher-power module or set. I bring my own prejudices and I'm admittedly not knowledgeable about the previous generation of devices, so much so that I perhaps should not be wasting this bandwidth. I'd just like to have more discussion and to understand what looks to me like un-lofty goals. And no, I'm not some kid with 100,000 watts in his car with his engine running a dozen alternators... I just don't understand this thread's mindset where power is a bad thing. Perhaps I need some questions answered.

My first use would be for powering the incredibly efficient Danley DTS-10 sub kits, not for low-efficiency speakers. 1000 watts is pretty much the minimum per-channel rating necessary for realistic reproduction down to 10 hz, even with these, the highest efficiency low-frequency speakers available, and I'd double that if using switching-mode power supplies or amps. Low-impedance load capability is a great idea (especially for bridging) but would have to be exceptional to work bridged into the Danley's complex low impedance or most of my other speakers unless I rewired their internal drivers in an undesirable series config. I'd really need to power each internal driver seperately with two bridged modules, so for two DT-10s I'd need 8 modules and they'd still be WAY underpowered, giving 200 watts where 1000 is more optimal and more if switched-mode is involved. In the 1950's 10 watts was the new 5 watts, in the 1960's 60 watts was the new 10 watts, in the 1970's 100 watts was the new 60 watts, in the 1980's 400 watts was the new 100 watts. Then in the 1990's and 2000's high-accuracy 5, 10, 20, and even 100 watt amps brought enthusiast hi-fi full-ciricle to speaker efficiency while the 50-100 watt mass market went to mid-fi modules and amp chips embedded in various home appliances or low=-power multi-channel surround-sound. Now in the 2010's for the first time we might experience cheaper efficient amps with high power and improved accuracy, and 1000 watts can be the new 5 watts if we express some ambition. Economical high-power capability is really what high-efficiency modules offer that's new. "Most people won't need more than 100 watts" should really read "most people don't know they really need more than 100 watts." High power should not be your first requirement, but it should be on the wish list, and rising on the list if home theater or other real emotive reaction is involved. I see people in high-end showrooms actually straining to appreciate the experience, working hard to overlook the obvious deficiencies and not mention the "elephant in the room" to find the hidden gold. The fact is that you cannot reproduce a broad bandwidth down to 15 HZ including peaks at high levels from a 100 watt amp. And if you can't satisfy even that minimal requirement you don't really have high fidelity in my book. That low a power capability is an obvious compromise. I was really hoping to minimize this discussion because my opinions are strong and unpopular on some tweeky threads, but IMHO low-power hi-fi is interesting, revealing, and educational but usually sacrificing more than it's gaining. Get an economical efficient amp with 1000 watts a channel with the same distortion figures as your favorite low-power amp and you'll never ever go back if the price is reasonable. How many would say no to a gift of the top of the line high-powered Pass Labs amps? The problem is there hasn't been any such thing as affordable accurate high-power. We've been trained to psychologically favor low power thru efficient speakers by designs that operate in class A only at low levels or operate single-ended only at low levels. Affordable high accuracy has only been available at low power. I have the opposite psychological problem from similar experiences but with bigger amps. I have been conditioned to appreciate the accuracy of high-power amps running at low average power. So I know my own prejudices, based on my own limited experiences. I always had very high-power commercial amps on-hand from PA use. Even in the 1970's in college I'd put 900 watts or more on each of my Wharfedale bookshelf speakers where my dad would put his 60-watt/channel Citation II on his identical W60Es, and sure enough both always sounded better the quieter you played, the Citation sounded great in class-A, but mine sounded better than his at "realistic" levels. It made me lust for a higher-output class a tube amp and settle for a much higher power transistor amp. Admittedly they were not efficient speakers. And I'm digressing off-subject and could take the discussion into unscientific statiscically-irrelevant isolated experiences. But despite years in pro sound and hi-fi involvement, unscientific statiscically-irrelevant isolated experiences form some of the limited knowledge most of us think we have but are really prejudices.

IMHO any amp with a switching-mode power supply or switching mode amplification section needs to have its continuous rating at least doubled (or more) to compare properly to conventional "analog" amps when evaluating their performance handling dynamic music including peaks. 1000 watts from a digital amp is comparable to only 400 watts analog for real music that's not over-compressed, since a good 400-watt amp will put out 1000 for a few milliseconds. And that's not too much power for any typical home speakers IMHO. If you don't have kids, there's really little risk of turning it up to driver-destructive levels. Yes, my amps are often capable of frying my speakers to a smoky crisp. No, it has never happened (except rarely at live PA shows). Well, I did have a voice coil de-laminate once, and I did burn up a crossover coil years ago before I went to tri-amping. But I again digress into private war stories. Do I really need that much resrve power? Well, it does sound better.

IMHO perhaps the problem is that there has never been any affordable highly-efficient high-power economical amp that has anywhere near the low distortion and high fidelity of the very best low-power designs. Now we are being offered what may be the first and not saying "yes PLEASE" mostly because we have no experience with such an item. The high-end market is pleased with the experience of sacrificing power for accuracy in an environment where you can't have both in a reasonable package for a reasonable price. Now and over the next decade we might "have it all" for the first time. A manufacturer is asking what we really want, and we're telling them we want the 100-watt toy available for DIY and the high-power product only available for licensed mfgrs. with overpriced products. This could and should be a game-changing event and we're asking for more of the same-old same-old minimum power specs that can easily be bested in accuracy now by other less-efficient means for a little more money. Who cares if a 100-watt amp is efficient; add a heat-sink and turn off a light bulb in the house and you can have class-a for a price! The electric bill or the waste heat just isn't a significant problem in low-power amps. Creative people can imagine what they have not experienced, and other people just can't until they have it, live with it, and experience it for extended periods and intimately. I'd really expected more DIYers to have imagination and the judgment to make the best of the real advantages this technology offers. Even Pass gets DIYers interested in quality sound with single-ended kits, then once addicted pays his bills selling "the good stuff" X1000.5s that deliver the 1000 watts per channel really required to do the job properly.

The low-impedance idea for bridging is a nice crumb to throw, but I'd prefer the real thing. Oherwise what's the real advantage of these things? That they're better than the previous generation (which didn't impress me much)? That they're small? Convenient? If it's a cost advantage or efficiency advantage or size advantage, scale it up to make that advantage meaningful.

In mainframe computing there's a concept called "latent demand" which makes it difficult to right-size the performance of a system. It's easy to look at an existing installation and calculate the exact effect of various system changes on the existing workload. Unfortunately, in the real world, those system changes in supplied capability also change the workload demand. There are applications that are only thought of and only become possible with the additional computing power being available. The previously "latent" demand is only really appreciated and accurately quantified after the abundant supply is made available and quickly consumed. At one time I remember it was common belief within the industry (IBM) that the world would only ever need perhaps a dozen computers with 16 meg / 10-mhZ performance. I believe many hi-fi systems would in fact benefit from a 100-times or even a 1000-times increase in amplifier power, even with efficient speaker systems. What's the penalty of too much power capability, that you have to be careful with the volume control? No, it's usually a cost issue. But in mass-produced modules and chips the power/cost relationship is often just a marketing artifact. Computer chip mfgr's expend extra effort to disable portions of chips in order to sell them to the economy market and maintain prices at the high-end. There's often little or no (or even reverse) relationship between the cost and the performance. So I'm asking what the real manufacturing cost to power output curve looks like for these new modules, something most mfgrs never reveal even to stockholders. Would a high-power module cost much more than to manufacture than a low-power module?

Of course, if the low-power distortion specs of a high-power module are terrible, then we'd need more than one module, or we would need it configurable for lower-power use. I'd really like to know how bad the low-power performance of a high-power module would be. And could a high-power module be configured for lower power use?

Also, I would like to know how a high-power module would perform with an under-powered power supply. Are the associated other high-power component an absolute requirement?

But please, don't just go after producing drop-in alternatives for integrating in existing systems for the current mass market. Do that if it pays the bills and keeps the company afloat while the market changes. Please realize where this can really be a game-changing innovation by radiacally increasing the power output for a reasonable price and in a reasonable package. Do what Carver never could.

Target perhaps the much-beloved now-obsolete Crown K2 which was so easy to live with for bass subs in home or commercial use. Better that accuracy and performance in a cheaper more compact even more efficient high-power package that doesn't require fans and me and my friends will beat a path to your door. That's 500 watts a channel at 8 ohms, 2500 watts bridged mono into 4 ohms. Give me a spec-by-spec comparison as a frame of reference.

Last edited by cyclecamper; 20th June 2011 at 10:05 PM.
Old 20th June 2011, 10:11 PM   #149
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A favorite quote from my high-school friend Tom Danley, applied to both speakers and amps:

You can hear "effortless" even if you can't point to it on a measurement.

So my first question is whether this is true for the characteristics of these modules, and how their distortion relates to their power output.
Old 20th June 2011, 10:45 PM   #150
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Man, do you guys arc weld when not listening to music?! I guess it's my tube amp background, that a good 20-60 watts seems as much as I ever need.

I've been playing with tripath and icepower amps, and I just ordered a pair of the UCD180 modules (and switching supply) to see how they compare to the very cheesy looking Ice-Ice-Amp-Baby amp.


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