Do Class D Amplifiers Deliver Rated Power?

[audioresearch]

I would like people's opinions who have owned and/or tested class D amplifiers.

In general, do they deliver their rated power at all sine wave frequencies from 20Hz to 20KHz, both channels driven, for an indefinitely long continuous period of time without clipping (lots of debate over how much distortion is audible, so I'll be easy on the amps and consider their max power to be what they output just below clipping) and deliver that into typical loudspeaker loads?

By the way, I do not refer to "rms power" because there is no such thing. The definition of RMS does not apply to power. I am asking about continuous long term power both channels driven over the entire range of frequencies generally considered to be audible to most humans.

 

[JSmith]

for an indefinitely long continuous period of time

Why would an audio amp need to be able to do this?

You may wish to read this mega thread;

Power amplifier tests with respect to FTC: 16 CFR Part 432 (July 5, 2024) requirements on output power claims

With derailing this discussion that is over my head, is class B really an embodiment of that size or at all? examples? That is a $4000 question! :D

www.audiosciencereview.com

JSmith

 

[BeeKay]

Why would an audio amp need to be able to do this?

Hardcore class-A (AB) fans cling to that as the final straw to discredit class-D, even if it means supporting test scenarios that have no practical application in real-life audio.

 

[Snoopy]

I mean you can easily get a 500 watt class D amp. But i wonder why some people need that .. there are still 20 watt class A amps that are plenty powerful enough. 100 watt used to be a „monster amp“ so there has to be a reason why most class D amps are so much more powerful to deliver the same results?

I don’t really have a preference but I think it’s interesting that a 40 watt Tube amp is driving most speakers .
20 watt luxman class A as well.

 

[Waxx]

Class D amps are mostly limited by their power supply and are rated in burst power. If you want continues RMS power in general you need to divide by 4. But RMS power on it's own says little as no music gives constant tones at max volume. You only need to watch out with music with long deep bass notes (use double power than needed and it's solved).

With class A, peak power is RMS power as the power is limited by the amplifier device (tube or transistor), and it's very limited in power (so you need high sensitive speakers to make it work). That it's limited by the amplifying device is also one of the reasons why distortion is higher. Class D is more versatile and today beyond the resoluton of our ears when done right. A class D and many class AB amps have a peak power rating that is double or 4x the RMS power and that is perfect in most cases, certainly for hifi.

And do you need 500w RMS for hifi, off course not for most cases. But the amp is rated for 500w so it can give you a clean 100W RMS Power, that is 5 to 10 x the power of most class A amps, and a lot cleaner in sound.

Btw, i have both, know the advantages and disadvantages of both and rate both for what they are.

 

[wwenze]

Then again today I don't even know what the definition of burst power is. The previous long debate threads here seem to suggest that, the industry or at least the vocal authorities seem to define the manufacturer power rating as maximum one-cycle that can be reproduced without distortion, and real music is much lower than that e.g. it is acceptable that a 200W-rated amp is only able to produce 100W RMS of music due to music having high crest factor and even if this same amp has the headroom (thermal, power etc) to reproduce a 200W single-tone sine wave it will produce much less in music since it does not have the higher output voltages required to produce a 200W RMS music.

Class A is class A and behaves like class A because the heat dissipation is highest with no load, and power consumption is constant. For the other classes they have to think about power supply and cooling, since a 2x power supply or a 2x heatsink can affect cost and size a lot. Consequently this 2x or greater difference between music vs stress test becomes the point of heated debates.

 

[MaxwellsEq]

I would like people's opinions who have owned and/or tested class D amplifiers.

In general, do they deliver their rated power at all sine wave frequencies from 20Hz to 20KHz, both channels driven, for an indefinitely long continuous period of time without clipping.. ...and deliver that into typical loudspeaker loads?

"In general" - generalization is always risky. There are many chip-based Class D amplifiers available for a few tens of dollars which make clearly unbelievable claims. So it's extremely easy to buy a cheap Class D amplifier that doesn't achieve it's "rated power" at any frequency, even in bursts. Given the sheer numbers of such amplifiers, one could mistakenly generalise that all Class D amplifiers are a fraud!

Also, there is no musical reproduction requirement for high power at all sine wave frequencies, is there?

 

[Grotti]

I own a class D amplifier from ELAC which is rated 325 watts in 4 Ohm. Do I care? Not a bit because in real life I never use more than a fraction of it. I own it for about 5 years now and it never remotely ran out of juice. So the question if it is capable of providing maximum power for a unlimited period of time is purely academic to me. Since class D in general seems to provide no headroom for short impulse signal, I would always choose a powerful amp to be on the safe side, though.

 

[audioresearch]

I listen to movies/tv, not just music, and there could always be cases where I might want a lot of power at any given frequency-depends what is in the sound track. Maybe aliens are killing people with sound in a movie soundtrack??

Does anyone own a class D amp that can output, say, around 300 watts per channel or more both channels driven continuously at 20Hz, at 1KHz, and at 20KHz for a very long period of time and that amplifier is lightweight?

 

[Waxx]

I listen to movies/tv, not just music, and there could always be cases where I might want a lot of power at any given frequency-depends what is in the sound track. Maybe aliens are killing people with sound in a movie soundtrack??

Does anyone own a class D amp that can output, say, around 300 watts per channel or more both channels driven continuously at 20Hz, at 1KHz, and at 20KHz for a very long period of time and that amplifier is lightweight?

The Hyoex NC1200 module or the Hypex NC2K module (and amps based on those) can do that i'm rather sure, just like most pro audio amps like from Powersoft or Lab Gruppen. But for hifi you don't need that in normal situations. Read the tread mentioned above for why.

 

[voodooless]

I listen to movies/tv, not just music, and there could always be cases where I might want a lot of power at any given frequency-depends what is in the sound track. Maybe aliens are killing people with sound in a movie soundtrack??

Movie soundtracks have a crest factor of 15 to 20 dB. You don’t need full power for the 2 hour duration of the movie. So you’ll need on average 25 to 100 times less than your 300W of max power.

 

[Old_School_Brad]

Movie soundtracks have a crest factor of 15 to 20 dB. You don’t need full power for the 2 hour duration of the movie. So you’ll need on average 25 to 100 times less than your 300W of max power.

While it’s true that many film soundtracks exhibit crest factors in the 15–20 dB range, not all content conforms to this pattern. Titles like Interstellar feature prolonged low-frequency sequences that significantly reduce crest factor and increase sustained power demand.

Similarly, certain genres of electronic music can present extended high level bass content. In these cases, continuous power output becomes a key metric and peak or burst specs alone may be insufficient.

 

[Scytales]

Then again today I don't even know what the definition of burst power is.

You may want to read Paul Miller's article entitled 'Power Bursting' in the #205 issue of Hi-Fi Choice (page 56) : https://www.worldradiohistory.com/UK/Hi-Fi-Choice/2000-2004/Hi-Fi-Choice-205.pdf

This article provides good insights that help to figure out how burst power should be defined.

 

[voodooless]

Titles like Interstellar feature prolonged low-frequency sequences that significantly reduce crest factor and increase sustained power demand.

There are always exceptions to the rule. But even the more compressed tracks will still have a crest factor of 6dB or so, so still factor 4 in power.

 

[Oddball]

While it’s true that many film soundtracks exhibit crest factors in the 15–20 dB range, not all content conforms to this pattern. Titles like Interstellar feature prolonged low-frequency sequences that significantly reduce crest factor and increase sustained power demand.

Similarly, certain genres of electronic music can present extended high level bass content. In these cases, continuous power output becomes a key metric and peak or burst specs alone may be insufficient.

Exactly. Just from the top of my head the regrettable Black Adam movie had extreme average and peak SPL and probably the loudest movie I have heard. My Parasound amps did end up much warmer than usually. Or the final battle scene in terrific Avengers Endgame lasts almost for 30 minutes and is really intense.

Discussion about continuous output in HT becomes even more relevant if one uses bed speakers as large, and/or sends LFE channel to the bed channel. This significantly increases power demands in low end, especially at levels near to reference.

Don't have experience with D class yet, but that will be a next step when my old AB class gives up.

 

[Old_School_Brad]

There are always exceptions to the rule. But even the more compressed tracks will still have a crest factor of 6dB or so, so still factor 4 in power.

The notion that tracks with a 6 dB crest factor need only a quarter of the power is an oversimplification an arbitrary. Compared to what -0 dB crest factor? While a lower crest factor does reduce the peak power requirements, it doesn't eliminate the need for an amplifier that can maintain high output over time. Content with deep, sustained bass -often found in certain electronic music and film soundtracks, still demands an amplifier for continuous performance regardless of what its crest factor is.

 

[Waxx]

Exactly. Just from the top of my head the regrettable Black Adam movie had extreme average and peak SPL and probably the loudest movie I have heard. My Parasound amps did end up much warmer than usually. Or the final battle scene in terrific Avengers Endgame lasts almost for 30 minutes and is really intense.

Discussion about continuous output in HT becomes even more relevant if one uses bed speakers as large, and/or sends LFE channel to the bed channel. This significantly increases power demands in low end, especially at levels near to reference.

Don't have experience with D class yet, but that will be a next step when my old AB class gives up.

RMS !continues) power is relevant if you use long deep bass notes, that can be some HT, but is mainly important with bass heavy music like dub and dubstep, where even powersoft can suffer from pumping when used over half power. That is why many modern dub soundsystems that use those amps install double peak power on the bass channels than the speaker is rated, just to avoid the pumping. And those who don't fall trough in a soundclash where systems are pushed to the limits... I've seen it happen more than once, and also with less expensive amps than those powersoft. And on that level, a standard plug is not enough, many need 3phase 400V industrial power to be able to run their systems and those amps are made to handle that (certainly with Powersoft).

But in hifi you will never go that loud, so a few hundred watt peak power should do it in most cases. Idem with HT in a normal (average) home setup. I never ran out of power with my 150w in total per side and 89dB/2.83v/1m sensitive home system with Ncore amps. playing at -20dB on the preamp is already loud enough to disturb all the neigbours and shake the windows in their frames...

 

[Old_School_Brad]

I believe one of the main sources of confusion when this topic arises is the wide range of musical tastes, varying perceptions of bass SPL, and of course, the different listening volumes. These factors are so diverse from person to person that they create a massive gap in common understanding, almost like a grand canyon of confusion...

 

[MaxwellsEq]

I feel that a source of confusion derives from a lack of experience of bench testing power amplifiers.

There are definitely corner cases for certain film tracks and electronic music with difficult crest factors or frequencies which are uncommon in normally recorded music. But none of them are actually similar to a pure sine wave full power test across a wide range of frequencies.

I've run sine wave full power and soak tests on power amplifiers and absolutely nothing in music comes close to the heat generated!

 

[Oddball]

Well said @Old_School_Brad - people should think of their own preferences and gear to size it up for the task. Sizing it just right does not leave much room for future upgrades or different use task (bigger room, change of taste, etc.), so another thing to consider. Amps can last for a long time and selling them usually generates a loss.

Some 15 years ago I oversized my AB amp setup for 5.1 system so significantly that I am still able to stretch the same amps to the 9.4.4 system with even greater low end requirements. Don't regret it as learned more about bridging and bi-amping in the early days so don't have to worry about that now, but still can run a much bigger system.