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Views On Class D Amps?
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XTRProf View Drop Down
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    Posted: 04 Apr 2008 at 1:49pm
Shoot! LOL
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Graham Slee View Drop Down
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A class D amp is more correctly known as a pulse width modulated amplifier. A fast triangular wave from an oscillator is applied to a comparator and so is the input signal. The output is buffered by a pair of fast switching output transistors, and these are followed by an inductor/capacitor network that tries very hard to remove the high frequency artifacts of the triangular wave. It has to come in low enough to get the output down enough at the offending frequency to prevent RFI (radio frequency interference).

They may sound a bit challenged from a harmonic structure angle.

My view is that they should be perfectly alright for a digital system, but could interfere with a vinyl front end. In fact I hope my neighbors never buy one because it could interfere with my vinyl front end.
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Darren/Audio Elevati View Drop Down
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Points: 144 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Darren/Audio Elevati Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2008 at 9:05pm
What about Class N, Graham.  Any better?   This from the Nuforce site...
 
"In order to suppress RF noise, speaker lead-out wires serving as high-frequency common-mode chokes are added to the circuit board. When a NuForce amp’s damping factor is taken at a speaker’s terminals, the number is 160, reflecting the wiring’s impedance and that of the output chokes."
 
Is there an English translation?  If not, a Yorkshire one?
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Originally posted by Graham Slee Graham Slee wrote:

... My view is that they should be perfectly alright for a digital system, but could interfere with a vinyl front end. In fact I hope my neighbors never buy one because it could interfere with my vinyl front end.
 
That's because you probably never connected a class D amp to a 'scope. By all means, do that when you the spare time which you never have, but make sure you are at least in a semi-stupor from alcohol, drugs, or best yet, a combination of both. Else your heart might fail.
 
Graham, some friends from USA connected a Technics/Panasonic commercial receiver working in class D. What they saw above 10 kHz is essentially a helluva lot of swirtching noise. NOISE, not sound, because that coulad be called sound only using a very large stretch of imagination.
 
Since they are elecrtical engineers, hard bitten audio buffs AND actually manufacture or used to manufacture audio products of their own, at first they thought they got a freak dud product. Three same receivers down the line, they realized they had the real deal. And that is being flogged to the unsuspecting public out there!
 
My own experience with them is rather limited, but what I have heard, including the TacT Millenium, is awesome bass, so-so midrange and Broken%20Heart highs. Highs as those from the dark days of audio I thought we got over way back in 1970. In a nutshell - highs sound unnatural, somehow all broken up and screaming at you.
 
In my view, I think we have another case of maths saying it's all right and our ears saying baby, that's anything but all right. In my view, despite stunning data sheets, with switch on times of MOSFETs quoted as "Ton 10 nS or less", we have EXACTLY THE SAME PROBLEM as you and I discussed on the subject of AD op amps, if you will remember. I told you then, and i think this is exactly the same case here - tremendous slew rates and short Ton times are in fact misleading, because for truth we need symmetry, we need out Toff times to be as close as possible to the Ton times.
 
Said MOSFETs have Toff as 450 nS, merely 45 TIMES (sic!) slower than Ton times. Symmetry indeed, in a pig's eye.
 
That technology has a looooooong way to develop yet.
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2008 at 1:39am
Well XTRProf did say "shoot LOL"

@dvv: That's why you are an adviser here my friend - WELL SAID!

@darren: "Is there an English translation?  If not, a Yorkshire one?"

Yes there is a Yorkshire translation but the "conditions of use (all forums)" prevent it being given here!

So what about "class T" (class Tangent actually) (note to self: Must claim "class S" (class Slee) by putting a flag on it...LOL)

..."class T" varies the triangular wave up and down in frequency to make the HF distortion more palatable - a kind of phasing or flanging effect, and dvv, did you know a friend of ours actually thinks it sounds good!
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Darren/Audio Elevati View Drop Down
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Points: 144 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Darren/Audio Elevati Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2008 at 1:15pm

Order me one of your "Class S" integrateds when you get chance, Graham.  How long will it be - a week or so?...  Do you do it in a metallic bronze finish to match my decor?...Confused

 
 
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2008 at 1:54pm
Sorry Darren, it'll be a power amp not an integrated. But we are considering offering it with different wallpaper coatings: woodchip and anaglypta blown vinyls (ready to emulsion) have so far been the clear winners in a recent poll of two 93 year old ladies...LOL
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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