Class-D or switching amps, any opinions on??

Does anybody have experience on Class-d or switching amps vs either a/b or traditional amps?? I have heard people knock them for limited ability at the low frequencies. However, I listened to a Linn amp not long ago and could not hear it wanting for anything. I want to hear a Rotel switching amp to compare. Why buy a massive 90lb amp thats a space heater if you dont have to, right???
Bob,You are going to get all kinds of responses about what other people like or don't like.Only you can make the final decision on what sounds good to you.Enjoy the music.
I've been looking for reviews/feedback on the new class D technology, which is supposed to be far superior to the ICE-based technology. Does anyone have any experience, or general info....?
What is 'the new class D technology'? Who makes it? What makes it different?

Power supplies range from traditional to Switch mode stuff.

Class 'd' topologies (is that correct term?) are either full bridge or half bridge, from what I read.

Are you talking about say...International Rectifier modules? or Hypex?
Doesn't Rotel use ICE modules?

Except for pure 'A' amps, A/B IS traditional.

No LF problems as near as I can tell.

The only ALL NEW design I can think of is the new NAD Masters Series amp the M2.
Class D can offer as good phonics as A, A/B. Though, they are different beasts. Some like their signature, some dont. I have Rowland 201's and love them for what they can offer. I would look to purchase some second hand, and try them out.
>>10-26-09: Vandermeulen
Class D can offer as good phonics as A<<

Well that's an opinion and you're certainly entitled to it.

However, wrong it might be.
Well, I did mention "though, they are different beasts". We all know that class A is the cleanest amplification technology. But that doesnt necessarily mean anything in our world I venture to say.
Theres no wrong when it comes to our ears. They are the only determining factor that maters. Audiofeil its to bad that you are so biased when it comes to these fine, cool running, powerful, low operating cost, small, sweet sounding amps. The sweet sounding part is my opinion. The other descriptions are a fact.
Bobrock as more manufacturers inter the Class D market you will find different signatures of sound between them. Look for good buys used and manufacturers who offer a in home audition.
Good luck and enjoy the music.
As I said before I wad impressed with Linn, but Linn Does not come cheap. I want to hear cheaper alternatives to compare.

Funny, Linn refuses to even call it class-d.
I'd also look at Rowland and Bel Canto's latest. I had the older Bel Canto 1000's for a while and they were very enjoyable, though I prefer other topologies ultimately. I'd have to agree with Bill's general sentiment in pointing out the Class D really does nothing to help people learn to read by associating sounds with certain letters or groups of letters. Neither does class A for that matter. I also do not think class D amps that I've heard sound much like Class A amps. Class D sound has a certain coolness...squeeky clean and buck naked. Class A seems to come at you with more tenacity. If it were a meal it would stick to your ribs in a satisfying kind of way, whereas class D would be Sushi (which I love, btw)...both are enjoyable, but in different ways. You'll get all sorts of opinions as to which does better justice in creating an illusion that there's a musical performance going on in your home. There's certainly a stigma attached to new technologies in this hobby...just as there was when transistors were introduced as the "superior" antidote for tubes, or when CD's were introduced and gradually took shelf space away from LP's in most stores and homes. That's making no judgments regarding which of those technologies are actually better (I have an opinion but it's beside the point). Definitely listen with your own ears and make those decisions yourself, but I'm very confident in my statement regarding phonics.
Magfan - I don't know if Mosfet configuration alone can be considered topology. Icepower uses full bridge vs. half-bridge on Hypex. Some people claim that full bridge sounds more "tube like" but also places half of the supply voltage on speaker terminals and in addition cannot be bridged.

Bobrock - Bass is one of the stronger points of class D. The issue is not if class D is best sounding but how does it sound for the money and if YOU like it. If there would be something really wrong with it (as Audiofeil implies) Jeff Rowland would not switch whole production to Icepower. Class D sound is very clean and revealing - will show deficiencies in your system.

As for the amp being "switching" or using switching power supply - every linear supply is in fact switching supply operating at 120Hz.

Main problem of class A/B is very high gain before feedback (up to 4000) that is about 10x higher than gain in class A amp (as low as 200). This high gain, in presence of limited bandwidth, is causing some overshooting on high slew rate pulses (TIM distortion). As a result of this amp produces/enhances higher order odd harmonics - that our ears are very sensitive to, making sound sharp/unpleasant. Tube amps on the other hand enhance even harmonics making sound wonderful on voice or guitar bad worse on instruments with complex harmonic structure like piano (sounds like out-of tune). Class D or A are likely neutral.
Love my Class D Gilmore Raptor monos. Clean and clear, with gobs of power and a sound that is smoother than I could have imagined. 93% efficient as well! They use huge toroidal power transformers and weigh 37lbs each, a lot of weight for class D amps. I've also owned the stereo model, the Raven -it has a similar sound to the raptors, but only half the power.

When I did the audition for the Raven, I compared it to Nuforce ref 9 V2 and an Atmasphere OTL tube amp. The Gilmore sounded more like the Atma than the Nuforce (which was harsh to my ears).

Gilmore Amps
Check out the Nuforce 9SE V2 amps. Great sound and good value.
I just sent mine for the V3 upgrade. Should be very interesting.
" ... they don't mimic the special quality of tubes -- a kind of creamy sweetness in the harmonic presentation. It is easy to understand the appeal of that tube sound; it has had a grip on me for years. But what the Spectrons do is, to my mind, ultimately even more impressive....[they] have a crystalline purity in the reproduction of every voice and instrument that sounds more to me like the essence of live, unamplified music -- which I attend, on average, more than once a week year-round-- than any other amplifier, at any price, based on any technology, that I have ever heard"

-Blue Note 2009 Award for Best Amplification by Enjoy The Music to Spectron Audio amplifier -

John Ulrick of Spectron is the inventor of class D audio amplifier in1976.

Check their awards and professional reviews on their web site and do Audiogon search for the owners comments/reviews.

All The Best In Your Search

Here are some interesting links:
The International Rectifier module has a fullbridge / halfbridge selector switch for those who can't decide!;jsessionid=74D07C3679B3902FCD3E847F05518E49?cmd=catSearchFrame&domSendTo=byID&domProductQueryName=IRAUDAMP7S

Here is another link with several articles on 'd' amps.

I have the IR reference board out in the garage, awaiting a power supply. I will be able to directly compare with an ICE moduled PS Audio GCC integrated, which I will probably be forced to use as a preamp! Awaiting funds to build a +-55volt ps.
Dob - Sinclair produces class D audio amplifier called X-10 in 1964 (Designer: Gordon Edge)
That is one of the best descriptions I've yet heard. Class A is more like meat and potatoes where as class D is more like sushi. Nice analogy Jax!
I have been using the Tact digital amps for sometime. The lower noise floor has allowed me to understand words in familiar songs which had been previously buried in the mix while using tubes and class a/b solid state. I interchanged the Tact with my CJ 2500A and my ARC vs55 for a few weeks, but finally I could no longer tolerate the additional noise in the analog amps. Nothing is perfect, but digital amps now offer lower noise and greater resolution than analog, and they can tailor their response curves and loudness contours to taste (and speaker demands) with no additional distortion penalty. It can only get better!
Probably not the only person here who has owned class A, A/B, D and tubes. Currently using two PS Audio Trio C-100 in full balabnced bi-amp configuration. The C-100s use the same ICE module as Bel Canto, Cary, Rotel and probably many other makers use. To my ears they are exceptional for the money.
I won't say they beat the others in every category. But for many reasons, including the low power requirements and small size, I'll stick with them. When the newer ICE versions hit the used market I'll probably move up in power, although in my small system, 100 watts bi-amped is probably sufficient.
As stated earlier, your ears are what matters. At used prices though, if you are really curios, give one a try.
I meant to say I'm using the PS Audio Trio A-100 amps, not C-100.
Wouldn't an edit function be nice here?
not to split hairs, but add PS Audio to your list of ICE users.
Have never owned tubes, for 3 main reasons. Panels, heat and Tubes.

Sam, repeat after me 'Class d is NOT digital'. repeat as necessary. read links I provided in earlier post.
Timrhu - when you move up in power the bandwidth gets lower. Your PS Audio amp's module has higher (65kHz) bandwidth than more powerful 1000ASP 1kW module. It is simply because stronger Mosfets are slower. New much faster Mosfets are introduced every year and bandwidth eventually will increase.
Sam, repeat after me 'Class d is NOT digital'. repeat as necessary. read links I provided in earlier post.

Actually, most or all of the TACT products Sam referred to accept digital inputs, and provide a d/a conversion function in conjunction with a Class D power amplification function. So I think that would legitimize the fact that Tact headlines them as "digital power amplifiers."

Unfortunately, though, that probably contributes to the widespread misconception that "Class D amp" = "digital amp," which it certainly does not in the case of a more conventional Class D amplifier that has only analog inputs.

-- Al
Al, I won't make an issue of whatever it is you opin Sam said. He could clear up his intent with an additional post.

The ONLY amp I know of which can claim the title 'Digital' is the new NAD M2.

It operates in the digital mode, which I expect to be the real definition of 'digital amp'.
I thought the question was "Does anybody have experience on Class-d or switching amps vs either a/b or traditional amps??" The question seemed general enough, not technical in nature. "true digital" seems to me as elusive as "true class A". Hard to get folks to agree on the term. Class D means "not an analog amp" to most of us. FWIW Tact amps can be digital input only, or may have an analog input in addition.
Hello Kijanki:
Many people participated in the development of class D technology. However, as journal Sound & Vision reported in "50 Greatest A/V Innovations", January 2008 issue:


Going back to the Infinity SWAMP-1 of the mid-1970s, digital amps have had a checkered history, but they seem finally to have turned the corner in terms of reliability and performance. Highly efficient and cool-running, they promise to play a bigger role in the future."

John Ulrick at that time was chief designer of Infinity and SWAMP is his amp. Moreover, he introduced SWAMP as the first commercially available class D amplifier into the (hi-fi) audio world at CES 1974.

So without taking a credit from anyone who worked in the filed of this technology, Spectron chief designer John Ulrick is generally recognized as the father of Hi-Fi class D audio amplifiers

All The Best,
Have a PS Audio Trio C-100 Cullen modded(stage III) hooked to a pair of Quad 11Ls. They have really brought the Quads to life. The amp makes them seem faster without diminishing the musicality.
Have Bel Canto Ref 1000s hooked up to Reference 3A Grand Veenas. I'm waiting for a pr of Wyred Reference amps(class D) to be built. Have both an analog and tube front end.
Dod - I just wondered why you call him "inventor" when class D is known from 50's and Sinclair X-10 was sold in stores both as a product and a kit in 1964 (12 year earlier). It was followed shortly by X-20.

Samujohn - class D does not mean "not analog" - it is purely analog in 99% cases. The fact that output stage switches between two voltage levels doesn't make it digital because time and not the voltage is analog quantity here. Word "digital" was used by uniformed people and became popular name for class D. I don't have anything against calling it "digital" as long as you realize it is not.

As for digital inputs making amplifier "digital" it would be true for any amp. Combining in one box DAC and tube amp would make it "digital amp" - nothing to do with a class of an amp.
Magfan: The new NAD M2 ... operates in the digital mode, which I expect to be the real definition of 'digital amp'.

Agreed 100%. My previous post was not worded as precisely as it should have been, to the extent that it implied anything different than your statement quoted above.

The signal path through a digital Class D amp will consist entirely of either digital signals or switched waveforms, from the amp's input to just before the low-pass reconstruction filter which reconstructs an analog waveform at the amp's output.

However, the literature at the Tact site appears to indicate that their amplifiers do exactly that. For instance, see the section on page 8 of the 2150X Manual entitled "How Does It Work."

I know of no other Class D amplifiers besides the Tact's and the NAD which you mentioned which can properly be called digital amplifiers, although there certainly may be a few isolated exceptions that I am not aware of.

Best regards,
-- Al
Hello Kijanki,

May be word "inventor" in not the most accurate - however, as I have illustated with the quote from "50 Greatest A/V Innovations" over last 50 years - John ULrick is attributed for bringing class D into HIGH FIDELITY audio, specifically in conjunction with his Infinity speakers which I believe were considered one of the best in 1970's. I believe that Spectron amplfiiers today are also one of the best among powerful amplifiers but this is besides the point.

All The Best
Rafael - Absolutely agree.

Al - I'm not sure what they do to obtain decent resolution. In order to get 16 bit resolution and 20kHz bandwidth with traditional PWM clock has to be 65536x20e3=1.3GHz. It is way to fast and no room to filter out carrier. They might play games with modulating power supply at the same time or creating more states (more Mosfets and more voltages). It is getting very complicated to get real digital amp. Pure digital might be not bad - just look at HDTV.
Pure digital might not be bad? It's not that good- yet. As for HDTV- I saw a demonstration of Sony's analog HDTV at the Chicago CES in 1989. It was amazing. Today's digital HDTV has a ways to go yet. Just look at the lack of low level detail in dark scenes. I also see pixelation in fast moving scenes in HDTV broadcasts, but not in 1080p blu-ray material.
Al - I'm not sure what they do to obtain decent resolution. In order to get 16 bit resolution and 20kHz bandwidth with traditional PWM clock has to be 65536x20e3=1.3GHz. It is way to fast and no room to filter out carrier. They might play games with modulating power supply at the same time or creating more states (more Mosfets and more voltages). It is getting very complicated to get real digital amp. Pure digital might be not bad - just look at HDTV.
That's an excellent question, Kijanki. I'm not particularly knowledgeable in that area, but I believe that what is done to provide adequate resolution is oversampling + noise shaping, conceptually similar to what is done in the so-called 1-bit cd players. I found the following paragraph here:
The PWM resolution is typically much more coarse (than that of the incoming pcm), in order to keep switching frequency above maximum audio sample rates of 192 kHz, whilst limiting MCK frequency. Typical ratios are between 32 (5 bits) and 256 (8 bits), giving a best dynamic range of 50 dB. Clearly, this means that other techniques are required to provide sufficient dynamic range, and the answer is oversampling with noise shaping. This technique essentially allows a time averaging of the PWM pulse widths to be applied, to deliver fractional resolution in the amplitude of the output signal.
The theory behind that is esoteric and also somewhat counter-intuitive, and I'm not sufficiently familiar with it to be able to explain it well, but I believe that is basically the answer. Note that the Tact manual I referenced indicates an 8-bit pwm resolution, within each pulse period (corresponding approximately to the 50db dynamic range mentioned in the quote above); a pulse rate of 384kHz; and a master clock rate of 98MHz.

Best regards,
-- Al
Here is a pretty good Wikipedia article on noise shaping. Very basically, oversampling + noise shaping allows the quantization noise resulting from the limited resolution to be mostly shifted up to frequencies that are higher than the audio information, allowing it to be digitally filtered without significantly affecting the audio.

-- Al
Al - Thank you for the link. My problem is with resolution. As you said TACT stated resolution from PWM is 8 bit. Where do they get required extra resolution (possibly by adjusting power supply?). 384kHz carrier sounds about right (Icepower is 400-500kHz).

Class D is here to stay. Some people don't like the concept of switching in audio but delta-sigma converters, SACD and DDS recordings are exactly that (PWM).
My problem is with resolution. As you said TACT stated resolution from PWM is 8 bit. Where do they get required extra resolution?
Kijanki, though it may seem counter-intuitive, reducing the quantization noise that results from limited resolution is mathematically the SAME as increasing the resolution, apart from any possible side-effects of the digital filtering processes. So they get the required extra resolution by the oversampling + noise shaping + dither processes that I referred to.

Keep in mind that limitation of resolution to a finite number of bits is mathematically identical to summing a noise component ("quantization noise") into the signal. If I recall correctly, assuming random error distribution (which is pretty much assured by applying proper dither), the rms quantization noise amplitude is equal to the lsb increment (in volts) divided by the square root of 12.

The oversampling allows most of the quantization noise to be shifted to higher frequencies than the audio information, where it can be filtered out with minimal impact on the audio. Dither randomizes the process to eliminate "deterministic errors," as the article indicates.

I believe that the other pwm applications you mentioned, delta-sigma converters, sacd, and dds, do the same thing.

-- Al
Al - they do, but carrier frequency is almost 10x higher and resolution is 16-bit. SACD pulse width modulates at 2.8MHz - said to be equivalent to 20-bit on non-oversampling system. My analog class D amp (Icepower 200ASC) runs at about 500kHz with unlimited resolution. There is no quantization noise since it is not a sampled system.
I have been enjoying the Red Dragon Leviathan mono blocks.
They replaced Classe DR 8 monos, and Cary 300sei.

I have used them with Tanoy Arden,Merlin TSM MMX, and Ref 3A Grand Veena.

I have experienced all of the pros and none of the cons when people describe D amps.

Very satisfied and trouble free.
First amp I have ever left on 24/7.
10-25-09: Magfan
What is 'the new class D technology'? Who makes it? What makes it different?

If you go here you'll know as much as I do - except that I have heard about this elsewhere (an online discussion at one of "the' various sites).

I would like to know more...
Sigh, one more time. I have used SS (mosfets) and "Class D" amps (Tripath and Hypex), Class D is better. I have used a tube pre with both technologies. I would rather have a tube pre with a SS amp than a SS pre with a Class D. My old ears (61) say CD to SS pre to SS power just doesn't deliver. If you want a warm, more natural, musical sound; you are going to have a tube in the equipment chain, at least a tube DAC. Really good tube power amps are Really Expensive. The damping, power, clarity and tonal balance of power switching amps is within financial reach. They will faithfully amplify what they are fed; quality of input=quality of output. I believe Class D or power switching or whatever you want to call it is a better amplifying technology than Mosfets or Jfets. Are there SS amps superior to Class D? Yes, but the cost difference is, at least, a factor of 10 ($400=$4000).
This topic has been kicked around so many times, so I guess one more time can't hurt. Good listening for everyone.
Bought my first 'trinatron' 19" w/mechanical tuner for my parents when first available. before that, we had one of the miniature, 'belly top' b/w Sonys'.

As for HDTV detail, coming thru small dish, quality depends on amount of compression. more=worse picture. In worst case on my 60" SXRD, the HD picture only looks marginally better than the sd on the next channel over. Sometimes, I'd prefer the picture from my OPPO '981 thru HDMI !!

However, sports and live news always has a stunning picture. I think they use those shows as a 'hook'. One day maybe I'll be able to do the BR compar-o.
Found this awhile ago on AVSForum. Tangentially related to the Class D AMp discussion.

Warning to REL owners with Class "D" amps and/or receivers of damage due to improper ground.

The following situation can cause damage to your audio equipment. If you use regular "High Level" cables connected to any of the main outputs on a Class "D" amp or receiver, there is risk of damage due to improper grounding. However there is no risk of damage if your using the RCA type connection while hooked up to the low level connection.

If your using a newer REL sub bass system that's designed for both music (high level input) AND movie sound (.1 LFE Channel low level RCA type connection) while connected to both connections at the same time, AND your using a class "D" amp or receiver, you risk damage to your audio equipment with only the High Level Input connection.

Again, the issue being proper grounding. Hooking the black wire of the "High Level" cable to a phono ground will not help. Hooking up a RCA type connection to the black wire and attaching it to any of the unused RCA connections on the back of your amp/receiver will also not help.

The way to properly hook up your REL to a class "D" amp/receiver (while using the high level connection) is to use a "High Level Digital Cable" available through your local REL dealer. This is a "new" situation and the "High Level Digital Cables" are only being manufactured on a case by case basis. The word "Digital" is not to be confused with the type of signal being sent through it, it only describes the type of cable to be manufactured. Many local REL dealers may not be aware of this and will have to contact Sumiko for further information.
I use a Digital Amplifier Company "Cherry" amp. Check the web site for details. It has powered my Ohm mk5 IIs and my Apogee Caliper Sigs. Very powerful, clear and no lack of lows. I highly recommend it.