Class-D amps - a different re view

I recently heard the Onkyo A 9555 integrated amplifier. It is a Class D amplifier, and sounded excellent, and infact better than my SimAudio i-3. Its a steal for its price. I feel that it rightfully got good reviews from Stereophile and TAS.
Onkyo makes profits by volume and selling it at a profit low margin, unlike most hi-end audio manufacturers who try to make profits by selling less volume at high profit margins. Thats the reason many hi-end audio manufacturers go out of business.

Kijanki:

Your post mentioning jitter and PLL seems to be off-base, and probably ill-suited to this thread. Perhaps you would like to clarify it, but may I suggest in a different thread.

RF gumby:

Yes, I think I am in the right place. I am pretty sure I did not hit the bookmark for the Insane Asylum.

Or it might have something to do with my being an RF engineer, partially out-of-place in the role of front man for a minor high-end company. (It fell upon me by default. Long story.)

The "talking points" that were mentioned as proof that Class D amps are by design inferior seem to be a mix of technical points and sophistry. I could make a similar list for any number of other technologies. Equally convincing, equally misleading. If I didn't know better, I would come to the conclusion that someone had an agenda.

However...........some points do have a bit truth to them. Some Class D amp modules have an output frequency that does vary with speaker load. The maker(s) of these modules clearly show this in their data sheets. I would think that anyone who truly has a background in electronics design could understand how changing the impedance a second-order LPF operates into could have an effect on its damping ratio.

I believe the voltage on the output that he refers to is the Vcc/2 in the ICEpower-based units. They operate with only one polarity of power supply, and being a full bridge design, will have 1/2 of the rail voltage on BOTH output terminals.

Translation:

Don't grab your speaker cable in one hand, and ground in the other! Not a good idea. (Maybe that is why so many have shook-proof terminals.)

Also, there will be a certain amount of the carrier frequency on the output. Yes, it may be a few volts. Somehow, I don't know of many tweeters that will generate tons of IMD with that sort of voltage present.

As I said, some technical facts, seemingly massaged to possibly scare off the uninformed.

Ar_t

Icepower uses full H-Bridge of 4 Mosfets switching direction of the speaker between +VCC and GND. In spite of VCC/2 on the speaker terminals, voltage between terminals is zero. The only disadvantage of this scheme I know is that you cannot bridge amplifiers. My amp has 23.5V on speaker terminals - it won't zap you (voltage up to 60V is considered safe)

As to effect on the damping ratio - filter is within negative feedback and DF is very high. At higher frequencies it drops as I stated before to about 30 at 10kHz. What about DF of a tube amp at 10kHz?
What about zobel networks on traditional transistor amps.

It has about 1% of the carrier - not important (cannot radiate and the tweeter produces IMD only if it's membrane moves - not possible at 500kHz).

Talking about "scare" - the scarriest part of Mr. Colloms presentation is the fact that he believes that amplifiers like Icepower or Hypex (he tested Channel Island D100 - didn't he) are sampling systems and have AD/DA inside with limited resolution.

Sure anyone can find something wrong with any type of amps. The wrong think to do is to pick possible deficiencies of different amplifiers and make general statement about whole class of them. At the same time he did not mention any positives like very low THD, extremely low IMD+TIM etc.

I would advise everybody to listen to Icepower, Hypex, NuForce, Flying Mole and make up your own mind.

Kijanki:

"Simontju, Amp is close to 95% efficient and does not have to be large to do so."

1 - Even if efficiency would be 99.99% some heat would be generated and...dissipated somehow

2 - No heatsinks! I am talking NOT about chasses of the amp or whatever but inside the very small power module packed DENSLY with microscopic size electronics

3 - I can re-assure you that each responsible designer and manufacturer of class D module like Spectron, Bang & Olafsen, Philips did themselves or invited outside consultant(s) to make most comprehensive thermodynamic analyses.

4 - All The Best

Simon

Kijanki:

If you have a 1000ASP, then it will have much more than 22 V on the output terminals, so I would not advise touching them. (Rowlan uses that module in some of their amps.)

As for the output network, I was talking about the damping factor, or Q, of the filter. Not the damping factor of the amp.

If Colloms believes that they have sampling stages inside, then he is ignorant as to their operation, or else one can conclude that he has an agenda. Modern Class D amps of the self-oscillating style (like ICEpower and Hypex/UcD) are basically an amplifier that is unstable, and use that oscillation to generate a carrier wave. (Unlike clocked designs, which no one seemed to like.) They use some simple circuits, in some rather clever manners, to modulate that carrier with the audio signal. Over-simplified story on how they work.