Class D Technology

Tim,

If you can't hear the difference, stop! :) Unless you are a QA professional, learning to tell the difference in equipment you couldn't hear before doesn't lead to better enjoyment.

I traded in my class A/AB amps after evaluating class D and finding them inaudibly different. I could not tell blindfolded which I was listening to.  I DO see potential for tweeters with rising impedances or high capacitances being too much of a challenge but that's not how I make my speakers. :)

Best,

Erik

I've been living with ICEPower based amps for six months, I don't hear any of the issues being discussed, and my speakers have extension beyond 30kHz.

savdllc (can’t "at" you for some reason) you wrote:

What I did state is that Class D designs tend to sacrifice fidelity in favor of efficiency, which is true in most cases.

This is the bias I was trying to answer, my apologies I did not connect my statements more clearly to your writing. I am unable to support this statement based on any evidence at all.

I do believe that Class D is in a much wider quality range of products than Class A. By this I mean from cheap portable music players to high end.

Class D is, numerically, overwhelmingly dominant and across every market segment, while the ONLY place in audio I know of with Class A being produced today is high end, often mono-blocks. (There’s probably some Bugatti with Class A amps, but lets get real) This may lead us to make unfair apples to oranges comparisons which don’t actually tell us much about the overall potential of Class D.

At the high end, I see no sacrifices being made for Class D except to my carbon footprint. I DO hear differences in amplifiers. However to hear those differences and say "OH, well Class D is inferior, so the A/B amp must be better sounding" is an snobby prejudice.  There are even some strong benefits, as some have very high damping factors (output impedance) and therefore more consistent performance across speakers.

I think that the subjectivity of the "high-end" can be quite trendy, or go pretty far from neutrality. If that keeps a Class D from reaching top-tier status, then it's just a matter of time before a vendor creates the right input buffer for you. 

Again, to everyone, please please buy what you like to hear, but let’s not use cost as our golden calf of determining what’s best.



Best,


Erik

Inferiority... well, I don’t believe this is true either... but! :)

In Class A the transistors (or tube) never switches "off". It’s at least minimally on through the entire voltage swing. This is what causes all the heat. At 0 output volts, the + and - transistors are maximally conducting!!

To swing in the positive direction the negative transistor has to start reducing current, and vice-versa.

The result of all this is that a class A biased device never has "notch" distortion. This is caused by the transistors shutting off during part of the swing. To turn them back on the voltage has to exceed the diode voltage, when it suddenly "snaps" on. It’s not perfectly linear from 0 to 1 volts After the transistor is conducting it gets linear quickly. Whether this is audible.... well, that’s a whole other discussion. :) There's also a lot of debate and misinformation about feedback. This notch distortion is measurable, but reducible by increasing feedback, to the point where the distortion figures can become incredibly tiny, regardless of bias type.

There are also a number of interesting single-ended Class A designs of very low power, which use a single device. Look up some of the Pass Labs First Watt designs for lots of info on this.

Best,


Erik

@mapman 

I will not agree to any such prejudices. While I can say that class A lacks notch distortion, it is by no means the only type of distortion or non-linearity!

We can't on the one hand talk tech. theory on a subject like notch distortion while rejecting THD figures, which is (oddly) what a lot of audiophiles like to do.

The distortion and noise measurements between high end class A, A/B and D heavily overlap.

I'm also not sure that what audiophiles like to hear is always "better" if "better" = "more accurate."

I think audiophiles like sweetening (which is fine!) in which case trying to match an argument with notch distortion and sound quality blows up. The "sound quality" isn't found in the technology per se. If I had all the time, money and space in the world I would not mind having a pair of Conrad Johnson Premier 8 for instance, knowing full well they lie lie lie. :)

Best,

Erik

So the ICEPower and Hypex modules have a built-in buffer, but the configuration is such that manufacturers can bypass it and implement their own if they want to. Without the buffer the input impedance is very low for line level.

This allows manufacturers to add their own sweetener/secret sauce to the amps. Anything from a transformer input, to MOSFETS, op amp, whatever you want. The modules like ICEPower also conveniently provide a 12V source.

Other differentiation can be done in using the ICEPower modules without power supplies built in. This, again, let's manufacturers make their own linear supplies, or whatnot and claim further product differentiation.

Best,


E

@mapman

That's really good. My one exposure to Triangle was with high-end McIntosh gear in the early 2000s and bright and glaring is exactly what they sounded like.  It never occured to me to consider the amps.

I'm listening with very high end AMT tweeters and ICEPower amps and there's not a hint of glare or brightness. These tweets are flat to 20kHz, and have considerable output to 30kHz. Maybe -6 dB?

I also have a center channel with an equally exquisite ring-radiator used by many high-end manufacturers (Sonus Faber, Krell, etc.) and again, not a hint of glare or grain.

They sound just like the Parasound A23s I had before. Which, while you can argue not the best SS ever, are linear amps.

@mapman

Thanks for your observations. I've never been drawn to McIntosh, so I never end up listening to them for long. :)

Best,


E

I said this in another thread. :)

Anyone can make a switching amp. Making one that sounds good is a whole other thing. Any manufacturer who can bring that kind of engineering talent on board would be VERY VERY lucky indeed. 

The paper Dr. Marshall Leach wrote in the late 1970's transformed solid state design so much that every amp after almost had the exact same layout. (a little hyperbole). Digital is not yet that mature in my mind. Still ways to innovate.

NuForce and Yamaha with their hybrid / Carver / NAD like approaches to marrying linear to Class D amps is pretty cool. Technics with their auto-correcting technology is also something to look forward to.

Best,

E