Class D = Trash?

georgehifi,

I never set out to write long winded posts but I admit they tend to be overly verbose. I’m going to strive for more brevity starting now.

Your last post goes over information already discussed on this thread.and totally avoids answering both relevant questions concerning your theory asked of you in my admittedly long winded prior post:

1. Does any scientific evidence exist that in any way supports your theory that the current class D switching frequencies are too low and result in sonic anomalies that are audible?

2. Have you personally ever heard these sonic anomalies listening to good class D? If so, please explain what these theoretical sonic anomalies sound like. Apparently, you currently may be the lone known human believing in, and claiming the audibility of, these sonic gremlins.

Tim

Make of it what you will, something more for the OP to read, on the title of his thread.

"Switching Frequency" it’s mentioned a few times here.

This was an Absolute Sounds Round Table discussion with the industry top dogs on Class-D, the only one in favor is the one that manufactures them Jeff Rowland but had little to say amongst his peers.

Bob Carver
"I built many of them right here in my own laboratory with the thought they could and would fulfill that final promise.... I was never able to build a Class D amplifier that sounded as good as a linear one."

John Curl (Parasound, CTC, Vendetta Research, Constellation)
"Some version of hybrid Class A/D looks like the future in optimum audio design."

Cyrill Hammer (Souloution)
"if you want to have your product performing at the cutting edge it is not possible with today’s known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz."

Lew Johnson (Conrad Johnson)
"I tend to think that Class D circuit design is an approach best relegated to producing low-cost, physically manageable multichannel amplifiers—where one might accept some compromise in sound quality for the sake of squeezing five, six, or seven 100 watt channels into one moderate-sized package for a budget home-theater installation."

Vladimir Shushurin (Lamm)
"No, it is not. And I would like to respond to the second part of this question with an allegory. Any field of human activity defines a number of requirements which, when properly implemented, guarantee a positive outcome.
For example, the basic requirement in the army and sports is an able-bodied individual. So, it would be quite natural to concentrate on searching for such an individual (especially as we know where to find him).
However, out of the blue we decide to choose a feeble-bodied person who, on top of that, is encumbered by various diseases. Having made this decision (which is a priori improper) we start justifying it to ourselves and others by citing the great state of our medicine, which is capable of curing many ailments."

Fumio Ohashi (BAlabo)
"No. Class D can’t really be considered for super-high-end performance in its present stage of development, although it can be fine for mid-market products."

Nelson Pass (Threshold, Passlabs)
"Does a $10 bottle of wine compete with a $100 bottle? Of course it does, and it often wins based on price. Right at the moment Class D designers seem to be still focusing on the objectively measured performance of their amplifiers. I expect that at some point the economics of the marketplace will encourage them to pay more attention to the subjective qualities, and then they will probably play a greater role in the high end."

Jürgen Reiss (MBL)
"I have worked a lot lately with Class D. Ninety-nine percent of Class D circuits are not competitive with linear circuits.
Most Class D sounds sterile. It’s tricky to figure out what to do to compensate for that."

Jeff Rowland
"I consider Class D to be highly competitive in the present, and to offer an evolutionary pathway of audio design that may produce even more astonishing results in the future."

Thorsten Loesch

I have yet to hear a pure class D Amp I’d rate above "below average for solid state" (which is not very high performance).

In a little update of my classic "Valve Analogue Stages for DAC’s #" I wrote:
"Perhaps more crucially, so called Class D Amplifiers, which have in recent times sprouted up like mushrooms after a warm rain, continue to use the straight two or three level modulation scheme described above. And thus they still require the use of heavy handed noise shaping to attain anything like acceptable 16 Bit Audio performance.
The clock frequencies for these amplifiers are usually at 300 KHz to 1MHz in the best cases. That is 3,000 to 10,000 times lower than what is required to attain 16 Bit / 44.1 KHz performance without noise shaping and other forms of signal manipulation!
And again, one is baffled and perplexed by the rave reviews many Class D amplifiers receive, as baffled as one was about the late 90’s reviews of timeslicing dac’s. The best of breed I have auditioned were certainly not bad; however in direct comparison to the best available valve and solid state amplifiers they do not produce a very good sound. Well, at least they offer novelty and the reviewers something to write about other than another (however good sounding) 8 Watt valve amp.
Incidentally, the best sounding Class D amps tend to be really low power single chip devices (putting out little more than the 8 watt valve amps), presumably because they are faster AND because they always work near what one might call “full scaleâ€, if they would be dac’s. On second thought, they of COURSE are DA Converters and where a Class D amplifier accepts analogue input directly it is an A2D converter followed by a power D2A converter!
What an insight!?" Mark Levinsons Interleaving of multiple Class D Amplifiers is potentially a step in the right direction, but does not go far enough.Personally I think that the best option would be something that combines a Class D Amplifier for the heavy lifting with something Class A for fine detail. Probably implemented in the style I did for AMR’s AM-77 "Jikoda$" Style. In this case both of the circuits involved can operate fully open loop.
In many ways the problems in Class D Amplifiers are analogous (but not identical to) those in Class B Amplifiers (but without an option to implement Class AB or Class A) so similar solutions apply.
All Class D amplifiers are essentially delta-sigma DAC’s.
If the input is not digital PWM signals (aka "DSD") but analogue audio then it is also a Delta Sigma Analogue to digital converter...
Now DSD (aka SACD) which to my ears fails to come close, never mind equal true PCM CD Replay in most aspects of sound quality, operates at 2.8MHz switching, or around 10 times as fast as common Class D Amplifiers...
Why anyone would want to listen through an A2D followed by an D2A Converter that are around 10 times worse than single speed DSD is beyond me.
But with enough hype and snazzy naming it cannot help but sell high and wide.


Cheers George

WOW, savage!

Yes, and they are the industries top designers, nothing will change until that dreaded switching frequency is taken up much higher. So then the output filter can do it’s job properly without any effects down into the audio band.

Technics is leading the way with the SE-R1 with twice as high switching frequency, but it’s not mainstream yet, and really should be even higher, one can only hope.

Cheers George

wasn’t that roundtable a decade ago?

I’d listen to modern Class D amps - like the ones listed above. I’d compare using A/B and extended sessions, all double-blinded.

I’d also listen to the Benchmark amp (not Class D), then buy the best one in my price range. if looked ugly, I’d stick it in a maple cabinet and glue some tubes on top of it.

But they will have to pry my tubed pre-amp out of my cold, dead fingers.





Just like the National Righteous Amplification club sez...