Class D FAQ

[Holmz]

… Nowadays class D amps are limited in BW, quite miserably, even the Purify. To me, power amp must have BW > 100 kHz and I do not care what anyone thinks about…

I have a couple of Hypex 502s, and I am not sure one needs 100 kHz on a subwoofer, or on a woofer. How fast does it need to slew?

I also of the opinion that there is also no dishonour in mixing Class-D with Class-AB or Class-A… but it is difficult to do that with passive XOs.

In any case, how do the Class-D do feedback? What is the circuit layout?

 

[Andykay]

Actually the best measuring amplifier known is the Benchmark AHB2, which is class AB with switching power supply. But the majority of amplifiers in the blue portion of the ASR chart are class D.

Does it really matter what measures best? It's the sound you hear with your own ears that matters, that is why a 1% distortion AMP can still sound best. Charts and measurements only tell a small part of the story. ASR reviews need to take many other factors, including Class of Amp, build Quality, sound signature etc... into consideration before measurements influence any buying decision.

 

[SIY]

Does it really matter what measures best? It's the sound you hear with your own ears that matters, that is why a 1% distortion AMP can still sound best. Charts and measurements only tell a small part of the story. ASR reviews need to take many other factors, including Class of Amp, build Quality, sound signature etc... into consideration before measurements influence any buying decision.

Uh huh.

 

[audio2design]

I was rather thinking about something like B., fast switching at power level and filter at high level. Nowadays class D amps are limited in BW, quite miserably, even the Purify. To me, power amp must have BW > 100 kHz and I do not care what anyone thinks about.

Your justification based on audible impact is?

 

[audio2design]

Uh huh.

You are too kind.

 

[rdenney]

In any case, how do the Class-D do feedback? What is the circuit layout?

Start here:

Hypex support downloads

Hypex downloads is the place where we publish our application notes and white papers.

www.hypex.nl

The white papers will help you understand how it works.

Rick "too long for a post, and too clear to need paraphrasing" Denney

 

[audio2design]

I would like to know the cradle to cradle cost (how many are just disposed because people can't fix them or it is just cheaper to buy another & throw the old one into a landfill in some other country. What is the true cost in wasted time (that you cannot get back, stereo down time, time away from your family or normal activities because you have to dispose the CLASS D when you could repair a class AB (G or H) that has been around for three decades. I don't thing the minor efficiencies over class A/B/G/H make up for the overall cost when you get to 3 generations of audio equipment that did not have to be disposed of (landfills, perhaps across the ocean, in the land of other countries). Consider the people there & their environment..

Refining all that heatsink aluminum comes with a cost. So does shipment. Then there is the reduced energy cost plus also the cost of reduced generation (it all adds up). Really no need to leave Class D on all time time and achieving a 20-50000hr+ operating life is viable. Then you have consider is the ClassD even an added failure or is it the optional switching supply. Lower heat also means less AC and AC for heating is generally inefficient.

 

[Kijanki]

One comment about the bandwidth. My older generation Icepower class D amp has 60kHz@-3dB. If this limitation is audible then what to say about Lamm ML3 Signature monoblocks that have bandwidth of only 32kHz@-3dB. It got all sorts of awards and glowing review from Stereophile that states:

"The ML3's standout features were its natural re-creation of instrumental attacks, generous sustain, and lifelike decay—all as close to live as I've heard, if nowhere near the real thing. It was quiet, fast, detailed, dynamic without reservation, transparent, airy, and extended on top."

"...airy, and extended on top" - perhaps 1.5dB drop at 20kHz is not that audible.

My AHB2 sounds cleaner and a little more extended at both ends, but newer class D amps likely improved.

 

[Evgeniy]

thanks for this FAQ.

But many D-amp's truly produce some high-frequency buzzing, probably at 15...20 kHz, at pauses.

 

[dc655321]

thanks for this FAQ.

But many D-amp's truly produce some high-frequency buzzing, probably at 15...20 kHz, at pauses.

Which amps specifically?

 

[Evgeniy]

Which amps specifically?

D amp's in many active speakers, for example Hedd 07 (it's not cheap).

 

[AdamG]

D amp's in many active speakers, for example Hedd 07 (it's not cheap).

I have 8 class D Amps in operation and dead silent when paused and when the music has silent passages. Strange that?

 

[Everett T]

thanks for this FAQ.

But many D-amp's truly produce some high-frequency buzzing, probably at 15...20 kHz, at pauses.

Probably?

 

[dc655321]

D amp's in many active speakers, for example Hedd 07 (it's not cheap).

In that case, sure. But then I would expect electrical noise (Johnson), which has peak power nowhere near 15-20kHz. Divide those by 100 maybe?

So if it’s high frequency noise you hear, there may be other causes than “it’s a class D amp”.

 

[Evgeniy]

But then I would expect electrical noise (Johnson), which has peak power nowhere near 15-20kHz.

may be.
But, on practice, noise from psu of D-amp is noise from D-amp.
Some other active speakers (with price $500...1300) also has same problem.

 

[Everett T]

may be.
But, on practice, noise from psu of D-amp is noise from D-amp.
Some other active speakers (with price $500...1300) also has same problem.

You're making generalizations. You seem to be referring to an article you read once, care to share?

 

[antcollinet]

may be.
But, on practice, noise from psu of D-amp is noise from D-amp.
Some other active speakers (with price $500...1300) also has same problem.

It you are hearing noise it is almost certainly coming from the source. And is most likely the result of a ground loop. You’d hear the same with any amp in that setup.

if it is coming from the amp then the amp is broken. It has nothing to do with class d

 

[Matias]

Ground loops, noisy gain structure, source, all kinds of possibilities. Can it be the amp in an active speaker? Yes it can, but then there are all sorts of designs out there, good ones and bad ones. Generalization is the issue here.

 

[avanti1960]

I'm not asking anyone to throw away their perfectly working Class A or Class A/B amp and go buy a Class D amp.

But if you're not buying Class D you're effectively a science denier, people here shun 'cables make a difference' people so hard, and want the best and most efficient equipment at all time. But when it comes to class D they become really stingy about it (Thus the thread).

unfortunately the science of evaluating amplifiers strictly from measurements and what my ears tell me are often two different things.
many things come into play by the time an amplified audio signal reaches one's ears, not the least of which is the electrical interaction with the loudspeaker's impedance curve and the resulting performance of the speaker.

 

[SIY]

unfortunately the science of evaluating amplifiers strictly from measurements and what my ears tell me are often two different things.

That's the reason for doing evaluations ears-only.