Power Output of Class "D" amps




I have noticed a lot of discussion about class D amps in the past weeks. One thing bothers me. The most of the amps are rated high outputs into 8 ohms. Upon looking at the power into 4 ohms, the power is less that the normal doubling of output we see in most class A/B, and class A amps. I have been told ( maybe incorrectly ), that class D amps do drop in power output as the impedance falls. I am not sure since I am not an engineer. What does seem to be a common thread is that, especially the Spectron’s, seem to sound better when run in the mono block config. I wonder if the power supply sections of the class D amp are not as stout as traditional amps, again one popular company offers several thousand dollars of factory mods ?? to a finished product, to improve the sound. In what section of the amp do most of these mods take place, the power supply. I for one hate to buy a product that needs to be made better the day I buy it. Could the quality of the power supply sections of class D amps not be meeting the demands of the designs ?? or are they just cutting cost ??

Class D amps are a confusing lot. Some call them digital, others do not. Yet, they do switch on and off, at fantastic rates. Some companies even tout the fact that they switch so fast that they are super, super fast, so they sound better. That is also a funny fact, since may people here have stated that increased sample rates in CD players, ( switching ), decreases sound quality.

Last time I checked, sound when created I real life, is a group of waves that are unbroken, until the sound ends, or is made to stop on purpose. I believe we call that analog sound. If the sound that is fed to our speakers is a product of the input being switched on and off, not matter how fast, then it is not analog, but what ??, even if the designers are claiming that it recombined, isn’t it always wanting to play catch up ??

Could the decrease in power output into decreasing ohm values, be a lack of true analog tracking ??, and could this be the reason why class D amps sound better when run as mono blocks. Maybe it’s because it’s only then that they have the capability handle complex loads, and meet the expectations of the owners. Is 600 watts of Class D actually only equal to 300 watts of class A/B or Class A

I’d really appreciate if some qualified technical people would reply, along with all the regulars.

Fire away.
brimmer5000
My Gilmore Raptor class D monoblocks are 250wpc at 8 ohms and 500wpc at 4 ohms. So much for that theory.

It all depends on the power supply.
My Bel canto M300 Monoblocks are 300W into 4 Ohms and 150 W into 8 Ohms. Power supply is important but I believe less so than with large tube amps. Even the AC in is less important and doesn't have to be "cleaned", at least for me. I don't think anyone knows why switching amps sound the way they do, they just do sound different, not tube, not solid state. You either like them or you don't. Some are better made than others. You won't know until you try. I'm keeping mine.
Yes they sure do sound different.
I have a Spectron MK2 with V-Cap and have hear them in my system mono-block and using one in stereo.

First off, there is plenty of power for 95% of the speakers made with just one amp. My B&W 803D mains are nominally rated at 8 ohm but can dip to between 2-3 ohms. The one amp has no problems driving the speakers into low or high volumes. To the contrary, this is one reason I like the amp. You don't loose anything at low volumes with the massive power reserves. My speakers recommend up to 500 watts of power an do indeed like power. Many 802D owners like the mono-block set-up as the power demands are higher with those speakers in reality.

The situation is just about the same with tradtion A/B amps like the Classe CAM 400 mono-blocks. They are going to sound better than the CA-2200 due to the higher power reserves and that they are balanced; the Spectron is balanced also in the mono mode.

The amp is also stable down to 0.1 ohms which may explain why the wattage doesn't quite double from 8 ohms to 4 ohm to 2 ohms. Not too many amps, class D or not, will produce specs for their amps at 2 ohms (1200 watts for the Spectron) since they are not continously stable there and/or the distortion increases too much to do so, imo.

High end electrostatic speakers like Apogees can dip below 1 ohm regularly and the Spectron does excel here and a mono-block set-up may be better depending on the manuafacturer's recommended power specs.

Spectron designs their own IECs rather than buying B&O's IEC so it can build it to any spec it wants rather than tweak the B&O IEC modules.

I also like the Bel Cantos especially the new REF1000 II that is an updated and modified version of the original REF1000.
I havent owned a class D amp so my comments are really invalid on that subject..My thoughts go to the statement about buying an amp that the maker offers instant upgrades before you take it out of the box i.e. Atma-sphere which I auditioned..Ive stated this before but its the same marketing as buying a Harley motorcycle which Ive done ..You get this basic/nothing special bike and personalize it the way you want it,of course the check book comes out big time.. Good marketing I guess but if my amp needs updates new right out of the crate Im not interested..Just my opinion but from what im reading here im not the only one with this mindset.Yes the amp I heard sounded great but not for me with that marketing..
>>Yes the amp I heard sounded great but not for me with that marketing.<<

It's a wise man who denies himself a great product because the marketing is unsatisfactory.

Yup, I really liked that BMW but their commercials suck.

LOL
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Start and end with Rowland. 500 watts into 8 ohms and 1,000 watts into 4 ohms in the 312, 501 monoblocks or Continuum 500 integrated. They're complete as delivered. It would be a sin to mod one.

Dave
Yup, I really liked that BMW but their commercials suck

Your real quick with sarcasm...Ill throw it righ back at ya..now theres "another great audio genious"
Boys, boys, bo-WAYS! Let me hold your coats while you wrestle on the playground at recess?
Feil: GOOD sarcasm Coon: lern 2 spe....ah....err....spA-ul?
I have the infamous 1 ohm Scintillas. The H2O ICE amp can run these babies to their output limit of 110 decibles without loosing composure, or change of sound.
Class D amps are a confusing lot. Some call them digital, others do not.

Whether or not a class D amp is referred to as digital or analog is not related to its class D power output stage. What would properly be called a digital class D amp is one that can accept a digital input, and which puts that digital signal through some dsp (digital signal processing) to generate the modulation waveform that ultimately controls the switching of the class D power output stage. An analog class D amp would differ in that it would utilize an analog input and have an analog front-end signal path.

Some companies even tout the fact that they switch so fast that they are super, super fast, so they sound better. That is also a funny fact, since may people here have stated that increased sample rates in CD players, ( switching ), decreases sound quality.

My philosophy is to take claims of sonic superiority that are based on references to design parameters with several large grains of salt. At best the truth in them should be qualified with the phrase "everything else being equal." But everything else is almost never equal, because of the enormous number of tradeoffs, architectural decisions, parts selections, detailed design considerations, etc., etc. that go into designing and developing a product.

Not to mention that most such claims conveniently don't address the relation of those parameters to sonic performance in a quantitative way, that would provide some perspective on the degree of importance of the parameter.

Also, keep in mind that class D power stage switching rates have nothing to do with the sample rates of sampled data systems, such as the cd medium. In the latter, information is stored that directly corresponds to the amplitude of the audio waveform at specified intervals. In the case of a class D power stage, the instantaneous amplitude of the audio is implicit in the timing, not the amplitude, of the high-to-low or low-to-high transitions of its output. Those transitions are always the same (large) amplitude; it is WHEN they occur that defines the audio information. That waveform is then put through a passive low pass filter, which removes the spectral components associated with the switching, leaving (ideally) only the spectral components associated with the audio.

High switching frequencies conceivably could relax the sharpness with which that filter must roll off, potentially requiring a filter which is simpler, cheaper, and less likely to have anomalies in the audio passband (such as frequency response ripple or phase problems). For similar reasons, higher sample rates in a sampled data system may be advantageous, EVERYTHING ELSE BEING EQUAL. On the other hand, the presence of faster signals, particularly if the edge rates of those signals are correspondingly faster, raises the possibility of other problems such as crosstalk, emi, digital noise, etc., if the design is not done carefully and expertly. As is usually the case, the quality of the design and the skill of the designer tend to be more important than the particular approach that is chosen.

If the sound that is fed to our speakers is a product of the input being switched on and off, not matter how fast, then it is not analog, but what ??, even if the designers are claiming that it recombined, isn’t it always wanting to play catch up ??

Absolutely not, assuming good implementation. The switched waveform, when considered in the frequency domain, contains spectral components corresponding to the switching, which are at high frequencies, and spectral components corresponding to the desired audio waveform, which are at lower frequencies. In principle, there is no reason whatsoever that the audio cannot be perfectly recovered, by using a filter that separates the desired spectral components from the unwanted ones.

Upon looking at the power into 4 ohms, the power is less that the normal doubling of output we see in most class A/B, and class A amps.

I can't shed any light on that; sorry!

I’d really appreciate if some qualified technical people would reply, along with all the regulars.

So that you can properly calibrate my responses, I am a long-time audiophile, who has had no exposure to class D amps, and who has two degrees in electrical engineering, and several decades of experience as an electronics design engineer and manager (not in audio).

My bottom-line instinct with respect to Class D would be to approach it with caution. Its fundamental advantages are non-sonic (reduced size, weight, heat, and cost). It's application to high-end audio is recent and limited, and it is very conceivable to me that there could be many subtle aspects of good design, that would have subtle but significant sonic effects, that may not yet be commonly recognized by the designers or users of this type of equipment.

Hope that is helpful,
-- Al
It appears to me that perhaps, the only real "digital" amps are the TacTs. Then again they might not be amps at all. Or..., I just don't understand them all that well.
The BMW is SWEEET, and I like the commercials. It's the maintenance cost after warranty that gets me.

Oops- I think I'm off topic again.
ICEpower based amps like JRDG, Bel Canto, WiredforSound, and Gilmore, double in power when speaker impedance is halved. . . just have a look at actual specs on respective manufacturer sites.
Like with most amps I know of, of any technology, taking 2 otherwise identical class D stereo amps and operating them in monoblock configuration will most inevitably increase headroom, authority, staging, and so forth. . . no surprise nor dark plot there. . . just motherhood common to most technologies.
Like with amps of other technologies. . . some class D amps sound great, some sound good, and some are. . . struggling stragglers.
Some of us have adopted switching amps because of their compact size.
Others have been intrigued by their often attractive price/performance ratio.
Some of the more environmentally conscious audiophiles have gone 'switching' because of their operating efficiency.
Many of us have fallen in love with the sound of a particular amp regardless of its 'switchingness' . . . and are just glad of the fringe benefits outlined above that go with it.

I know that I, Muralman, DCSTEP, Rafael Dobs and many others have listened to many amps before falling in love with the sound of the particular class D devices that we so frequently wax poetic on these pages. Of course, our True Loves won't be everyone's choice. . . yet, do not worry about the aledgedly 'analog' nature of physical reality vs the supposed artificiality of digital sonic reproduction. . . just listen to a lot of amps. . . be patient. . . keep an open mind. . . and you'll never know what you may end up with.
Guido, you're so diplomatic...
>>Your real quick with sarcasm<<

Only with dummies.