Class "D" amp? I do not have a clue. Do you?

Psag,

Class D and SMPS operate on the same principle (PWM). Class D was invented when designers of SMPS showed that response to reference voltage is so fast it can play the music.

Class D refers to the output device, not the power supply. Class D amps can have traditional power supplies or switch-mode power supplies.

6550 - The problem here is that SMPS is small. It is hard to believe that something smaller can be better. It is line and load regulated and basically the same thing as class D amps that win Stereophile class A classification.

It is difficult to change traditional way of thinking (you being example of it) but some great companies (like Linn) used SMPS for class AB amplifiers for a long time. New $48k Rowland class AB amp uses SMPS. As for being better suitable for the car since it is always used there - you can make the same argument for transistors (tubes for home, transistors for cars). I'm pretty sure it was the case at the beginning of transistor amps in audio.

Why not to listen first and learn what is inside later?

The first class D amp I was aware of was made by Infinity way back when (before they made speakers). The idea is nothing new and has been around for awhile. I think most car amps are Class D. It makes allot of since in auto and mobil applications. However, a liner power supply is still the way to go for the best sound and all designers know this. It does cost allot more and wastes energy and maybe it is getting harder to source really great transformers?

It is also possible that new generation is just only a little bit better (like BC Ref1000M with extra power supply caps) and "new generation" allows some critics to reevalute (read: save face) since others scored them much higher. For instance REF1000 was evaluated bu Martin Colloms for 10.5 points while Krell got 130 - that's less than 1 of 10. Ref 1000M is Stereophile class A. Sound like two completely different amps but in reality both use exactly same Icepower module with built-in SMPS.

That goes both ways when it comes to power. A large improvement was made not only to my Nuforce amps but all else in my system when i invested in power regeneration for my systems power supplys.

Also trying out the latest from Nuforce there Ref 18 and i can say without hesitation King Crimson will not run you out of the room if fact you will want to get comfortable and hear the whole lp. IMO

"I'm convinced the better Class D amps are those that pay special attention to the power source on-board."

Mapman - That would explain better reviews for BC Ref1000mkII
vs. original Ref1000. Same Icepower module (1000ASP) with built-in SMPS but new version has additional supply module/board with bunch of electrolytic capacitors.

I'm convinced the better Class D amps are those that pay special attention to the power source on-board.

I don't know if many here address the electricity going to their gear as much as I do, but what I have found is that the D amps that I own need the best power you can give them to sound their best.

That means the less you do to clean up the power to your amps(and whole system)the worse they will sound.

I recently did some more upgrades(I am firmly in the Shunyata camp)and the improvement to the sound of my system only let the clarity of my D amps(Red Dragaon Leviathans)shine thru.
I was pleased before, but really impressed afterwards.

The Red's will sound nasty if you feed them nasty power and sources, they are revealing, and if other D amps have the same traits, then perhaps those who do nothing to clean their power(dedicated lines, power conditioning,power cords)have heard the nastiness and attribute it to the D amp .Thus a myth about the poor sound of D amps is taken as part and parcel of all D amps in all systems.

It would be interesting to hear from others who own D amps of their stories and findings concerning the power being fed to their amps.

And I am curious if those who have found D amps not to their liking use any type of power conditioning , dedicated lines or upgraded power cords.

My Reds use Shunyata Annaconda Helix into a Hydra 2, ,the hydra 2 is connected to a 20 amp wattgate which is wired at the panel with 10 guage Romex of about 10 feet in total length.
Front end gear is on another 20 amp line, into a Venom plug, then 20 amp Annaconda Helix to the Hydra 8.

As I mentioned, before I went this route I was happy with the sound of my gear/amps.
Now I am very pleased.

"King Crimson typically chases me out of the room"

Well, they certainly are not everyone's cup of tea. Most people either love them or hate them.

What I like about the act is that they have a well deserved reputation for musical innovation, perhaps more so and over a longer period of time (practically the whole duration of modern rock music) than almost any other widely known rock music act. They practically invested art rock back in teh late sixties and have managed to keep up with and often ahead of the pack in almost every decade since.

"So when someone proposes that modern Class D amps just cannot cut it, I have to take that with a major grain of salt. In the right system, they are exactly what the doctor ordered IMHO."

I would whole heartedly agree with you on the first part of this statement on the simple premise that each individual's tastes and goals are addressed differently and would not discourage one from auditioning such amplifiers.

I know what I like! I know that does not correspond with what everybody else likes or that what I like is either best or right. Afterall, one of my favorite combos is Krell/Wilson - two companies that elicit pretty extreme positions.

Mapman, I have a lot of respect for your comments and recommendations and believe your statements are rarely made on emotions, but more on personal experiences - as they should be.

That being said, King Crimson typically chases me out of the room ;)

I've found the Class D's in my rig to be phenominal for modern pop/rock music, the best by far I have ever owned.

Only big, expensive, heavy, hot running, power gulping monster amps can compete with this kind of music IMHO.

I was listening to "Amputechture" by The Mars Volta last night, LOUD!

This record contains visceral, muscular prog metal that can rip you apart (in a good way) if well delivered, and also has some delicate, beautifully recorded parts. The BC ref amps deliver it all beautifully and you can listen to the whole album loud as intended without being chased from room (assuming this kind of music is your cu of tea to start with, which it may not be for many). Of course you also need speakers that can play the game as well.

Lower your refined audiophile/musical standards a bit and play Boom Boom Pow by the Black Eyed Peas. The electronic percussion should be both viscerally powerful but clean crisp and dynamic. That's what I hear with my Class D amps running either pair of my OHM Walsh speakers.

"Thrak" by the venerable "King Crimson" is a similar kind of listen that will either hold you enthralled if things are clicking or chase you out of the room if not.

They do similarly well on most any kind of music you throw at them.

So when someone proposes that modern Class D amps just cannot cut it, I have to take that with a major grain of salt. In the right system, they are exactly what the doctor ordered IMHO.

Ckoffend,

Very well written and interesting post.

I'm wondering if you heard the same issues with Spectron?

>>10-20-10: Mapman
Or they may have heard them in the wrong setup.<<

Agreed.

In my prior post there was an allusion to a "proper speaker match". This is critical.

No speaker or amplifier can be evaluated without a correctly chosen counterpart.

But it is disingenuous to knock Class D as a totality. Even the most discriminating ears can appreciate its' attributes.

IMO

"Those who claim Class D amps are aggressive and/or unbalanced either haven't heard the newest products or have poor listening skills."

Or they may have heard them in the wrong setup.

No amp or amp technology works best in all cases, including Class D, though I suspect it may be the most versatile amp technology around overall nonetheless.

A few years ago, Class D amps received a bad rap from both users and reviewers. Perhaps deservedly so.

However, the latest generation products from top manufacturers require a listen IMO. Given a proper speaker match, some of them challenge far more expensive solid state competition. They still may not be your cup of tea but the overall sonic quality has improved significantly.

Those who claim Class D amps are aggressive and/or unbalanced either haven't heard the newest products or have poor listening skills.

IMO

i have auditioned class d amps and they sound aggressive in the treble. that is the frequency response seems unbalanced.

there is a hybrid class d amp, virtue audio which incorporates gary dodd's tube buffer--a hybrid class d amp.

CK,

One thing with the BC refs is they have very high damping factor, which I could imagine might make speakers that do not require high damping sound somewhat tighter or leaner perhaps.

The OHMs in my system are renowned for drinking lots of power and current and also to sound best with high damping, so the BCs were a very good match on paper and have panned out equally well in practice luckily.

I run a pair of small Triangle Titus XS monitor speakers off my system also. These are more efficient and easy to drive, more tube friendly speakers. The high damping and current may be a bit of overkill with these in that sometimes I detect a touch of leanness with these perhaps compared to some other amps I have used.

I agree with Mfsoa on the digital amp company. I got one used on the gon and have had it for about two years now, it is the best amp I have ever had. It runs cool, has loads of power and has a tube like sound to it, never bright, the model is called the 4800

CK,

Can't say I'm experiencing any of those issues with the BC ref1000m monblocks in my rig these days.

I have never compared to say W4S equivalent. From what I have heard and read and based on what I know about the designs and the price difference, I would expect there to be a noticeable difference.

Mapman, Initially upon listening and buying a couple of the class D amps I found that they did most things overall to acceptable levels and felt their performance in most cases was overall quite satisfying.

However, in my case, I found that they felt thinner (not necessarily thin, just thinner) in sound than what I like. Maybe I am using the wrong term here so I will try to explain it better. My experience over time was that it seemed like the sound wasn't as full (not flat, bloated, or overly warm sounding), just not as impactful or with as much weight behind it. I also found that the sound staging, while being wide enough, always seemed to lack the depth I was looking for and also that the focus was not always consistant. It seemed to me to change with volume levels in terms of the focus aspect. I also found that as the music became much more complex, that the focus and soundstage did not hold up as it did with more moderate "sized" recordings. Again, these are parameters that are important to me for my own satisfaction, not necessarily what is either "right" or what others may be seeking (hence my recommendation to audition for extended periods of time). Additionally, as I indicated, I certainly have a limited experience versus everything that is out there and have not auditioned some of the super high priced D amps.

My other equipment that was in/out of the system included the following:

Amps: Krell FPB 200, M. Levinson 331.5, BAT VK-60 X 2 running in Mono
Preamps: BAT 30i (?), Cary SLP (?), J Rowland Capri (I really liked this preamp), Aesthetix Calypso
Speakers: VS4jr, Watt/Puppy 5.1, Wilson Duettes, Thiel 2.2 (ebay buy for $200 that I couldn't pass up, a great deal for those speakers)
Sources: Resolution Audio Opus 21 w/ GNSC mods (good player at a good price), EMM Labs, Esoteric X-03se

So you can see that the sound that I like is more on the highly resolving level (except as referenced via the BAT and Cary stuff - which didn't last that long by the way in my system for my tastes).

So I certainly don't claim to be an expert on Class D amps and while I have listened to several, certainly not to all by a long shot. My experience has been and continues to be for my sound type, I have found that components that have the biggest and best power supplies have delivered the most satisfying results for ME. Not to say other should or will have the same goals as I.

However, this experience is the premise for my recommendation for long listening sessions so that one can discern their likes for the (lumping together here) Class D amp sound.

One other 'd' player I've NOT seen mentioned.

International Rectifier has several 'd' amps out there. I've got a reference sample for test. I need to build a power supply so I need a transformer / caps / rectifier for a basic one.

http://www.irf.com/technical-info/refdesigns/audiokits.html

Anyone try any of these?

Ive been using Nuforce analog switching amps since 05 and have not looked back. Clean clear powerful 3D sound. Easy and affordable upgrades and they also offer a 30 day in home audition.The best and only way to hear/listen to any piece of gear and know if its for you before you buy, in your own home and system.

Some digital amps have 'heroic' power supplies, for example, Spectron and H20.
Have you heard those? As with non-class D solid state amps, class D shouldn't be lumped together soundwise.

Ck,

Can you elaborate some on what you found lacking and include which amps specifically and the systems used in?

Thanks.

While I have certainly not tried them all, I have owned and/or listened to a few/several. Actually liked the initial sound, but over time I grew tired of them and was disappointed the more I listened to them. I think, or at least like to think that there is a great future with them. However, I am a bit suspicious of the wide pricing range and the super megabuck versions in terms of improvement over many of the more moderately priced ones.

So in the end, I am not currently/presently sold on their sound/performance and found them lacking for my expectations in too many areas.

Whether right or wrong, I have found that with virtually all components I have tried (quite a few), that the bigger and better the power supply side, the better the sound. So far, I have found this to be true with Class A and tubed amplifiers as well.

My suggestion for those considering the Class D amps is that very extensive (lots of time) listening be performed prior to purchasing, preferably in one's own system. I think they deliver a generally appealing sound initially, but I myself found the ones I have auditioned and owned lacking in the longer run. Perhaps my sound goal differs from others, but for my tastes this was/is my experience.

Anyone tried the Red Dragon M500 or M1000 monoblocks?

You may want to check out the Digital Amplifier Company's products. Many users have commented about the superiority of the DAC amps relative to ICE and UcD amps from Channel Islands, Wyred, etc. Massive linear pwr supplies.
While I am friends w/ the owner, feel free to take my comments w/ a grain of salt but there are many happy customers who have moved on from ICE/UcD much like the Spectron users have.
I'm still waiting to do a direct Spectron vs. DAC comparison.
"Tube pre before Class D" is a good mantra!

-Mike

Another very good brand of class D amplifiers is H2O Audio. They use ICE moduals but are powered by a very beefy torroidal transformer based power supply.

I've recently tried the H2O mono amps driving the Magico V2 speakers. They mate very well together. Better I think, from a synnergistic standpoint, than the Pass XA100.5 mono amps because of the extra bass control and frequency balance. In general I don't think that the H2O amps neccessarily sound better than the Pass XA100.5, but in the case of the Magico speaker wanting power and control, the match with the H2O amps was very, very nice.

"The ASP1000 module is worst in this respect being what....about 1/2 db down at 20khz w/4 ohm load?"

Magfan - you're right (just checked datasheet graphs) but 8 ohms have too much down and up by 1/4dB starting in less than 10kHz. My Rowlands 200ASC is a little better - it dives down about 1/4dB but comes back to 0dB at 35-40kHz. Phase shift over 20kHz is also smaller - effect of higher carrier frequency.

Mapman - I was turning everything OFF but now I have Furman Elite 20 PFI conditioner with non-sacrificial over and undervoltage protection and keep everything ON all the time. It clamps at much lower voltage than traditional MOV protection.

I leave my Class Ds on 24X7 also with little concern, except if I am away for more than a day or so I will turn them off.

I have been an audiophile for over 30 years and after owning tube amps from Conrad Johnson, to Michaelson Austin TV10,VTL,Grant Lumley,AtmaSphere OTL and SET from Cary and a host of good solid state amps, I now enjoy the Red Dragon Leviathan mono blocks-which if you haven't a clue about class D then you wouldn't know anything about my amps either.

All I can report is that I find much to admire about them, little to fault, and that they have been on 24/7 for over a year and no problems.

If they have a "sound" it is something of a cross between a good tube amp and a good solid state amp.
They are smooth, detailed,non fatiguing and have as much power as you are ever likely to need.

They sounded great on Merlin TSMMX,high eff. Tanoy Arden(dc)and on Ref 3a Grand Veena.
They emit no hiss, hum, or any snap crackle or pop.

Noises that most of my tube and solid state amps had.

Th

Kij,
I gave up listening to sine waves sometime soon after I survived the '70s.
Zobel limit on long term power is therefore pretty much a non-starter.

One other MINOR issue, I don't think yet mentioned, of 'd' /ICE is that the frequency response changes as a function of speaker impedance. Lower impedance starts rolloff earlier. The ASP1000 module is worst in this respect being what....about 1/2 db down at 20khz w/4 ohm load?
Give up, at least for now, the idea of flat, wide band response out to X-ray.

Channel Islands D-200 user here. They sound just as good as my previous amp, run WAY cooler and weigh a lot less. My previous amp was a Pass Labs X250.5

Mapman - you're right about low input impedance. My Rowland has extra board (with THAT1200 intrumentation amp) to increase impedance to 40k.

Coxhous,

ref1000 (10K icepower stock module input impedance) may not be an optimal mach in terms of input impedance for your tube pre-amp. That might be a factor in weak/poor bass.

ref100m has 100K input impedance specifically to perform better with tube pre-amps.

I seem to recall that newer Spectrons may have higher input impedance for use with tube pre-amps as well, more like ref1000m than ref1000.

Also damping factor could be a factor as well. Not sure about Spectron DF but BC 100m is >1000, which is very high and might produce lean sounding bass with speakers that do not benefit. Or it is possible that this particular flavor of highly damped bass may not be to everyone's particular liking. Then again, what is?

The OHM Walsh speakers in my system do benefit from high damping. The bass is more dynamic, cleaner and articulate than with the 120 w/ch amp I used prior with lower damping. The change was pronounced when I switched amps and sounded relatively lean at first, but that was a temporary illusion.

The difference in the bass with my Dynaudio monitors was significantly less noticeable yet also clearly present.

Bottom line is things sound more real and natural to me compared to live now with the BC ref1000ms in my system than ever before.

Also I do not feel that performance is lacking in any significant area now compared to the best reference systems I have heard recently.

I am always actively listening to establish new reference standards that I can target though, so we'll see....

Then I suspect that you Icepower having huge damping factor at low frequencies (about 4000) overdamped your speakers making very lean bass?

The problem with my speakers are they are 8 ohm not low ohms. My speakers suck down as much power as you can feed them. Most amps don't make power until you get into the low ohms.

I do not know the technical details of class D but I have owned the Bel Canto Ref1000. The Ref1000 could not drive my Eggleston Savoy speakers. The bass was lacking and the music was flat. My wife called it 1 dimension. My speakers, I agree are very hard to drive, but I now have the Spectron mono blocks and they quite fine.

Coxhaus - I'm surprised since I know audiogoner who drives with Icepower speakers with nominal impedance of 1 ohm.
Isn't Spectron a class D amp as well? There is probably more to it than just impedance alone.

I don't know much about class D but I have owned the Bel Canto Ref1000 and they could not drive the bass section of my speakers. I am not saying it is an easy job for any amplifier but I currently have the Spectron mono blocks and they do a fine job. There is no comparison between these amps with my speakers. They are not in the same league period.

Mike - Problem with switching power supplies is that most of them are designed to save money and space and not to improve performance. REF1000 for instance in improved version REF1000m has additional power supply with a lot of capacitors on separate board. I believe that with the same resources (cost and space) better PS can be achieved in switching than linear technologies.

I remember that there was an argument that high frequency can modulate audible frequencies on nonlinear (at this range) transducer - tweeter. Argument is valid under condition that tweeter membrane can move at 500kHz - not likely.

Larger Icepowers have a little lower carrier frequency than small ones and therefore lower -3dB frequency (50kHz vs. 60kHz). It is because stronger Mosfets are slower. Wide frequency range is necessary to provide smallest phase shift in audible range. Even with 60kHz amplifier shows about 30deg phase shift over 5Hz-20kHz.

This is first avalanche of class D amps (remember first SS amps?). Next generations will have faster Mosfets, higher frequency range, better power supplies and better noise filtering. I see it as technology of the future.

Magfan - this Zobel, can be improved as well. In Icepower it is simply common mode choke two filtering capacitors and one resistor. This Zobel network is responsible for time/power limitations and available power at higher frequencies. In practice musical power is only few percent of peak power (unless one listens to sine-waves)and high frequency energy is minimal. Should I pay for larger Zobel toroid to allow high frequency power that would make me deaf? Thanks for the link to IRF primer. I read opinion that full bridge sounds like very good tube amp while half bridge sounds more like high quality class AB amp (less tubey).

"QUESTION: how do the 2 different kilowatt Bel Canto amps differ? Don't they both use the B+O ASP module? Is there only a difference in input circuitry or the Zobel?"

ref1000 is stock Icepower module in a nice box.

ref1000m has additional input buffer and power supply circuits. If you open up the box, the 3 separate circuit boards/modules are clearly visible. It is dead quiet and most nonfatiguing.

I have read that ref1000m effectively addresses RF noise concerns in comparison to ref1000.

I have never owned or heard any other Bel Canto amp so I cannot offer an assessment of sound differences. From what I read however, others sem to concur that there are differences.

"Switching power supplies generate high frequency noise that is easy to filter out and non audible. For this reason Rowland uses switching supply in Capri preamp and he is very noise conscious guy (he used batteries in preamps). "

Hello Kijanki. By chance I owned Capri before I got my "heavenly" full tube Joule-Electra LA-300ME preamp. As strange as it may sound, this tube amp is more silent then Capri.

Next, I spoke with Simon from Spectron yesterday regarding asserion that high-frequency noise (or signal) is inaudible.
He says that then you emit hi-freq test signal it is indeed inaudible. However, then this hi-freq signal is a part of the mixture with other signals i.e. real music then due to the non-linearity it effects human perception of the music and effect listener fatigue.

He agreed with you, however, that future audio equipment will have only (perfected) switching power supplies even in class A ss amps - which will not have a weight of huge transformers and somewhat less of the heatsinks; the same with high power tube amplifiers.

fascinating topic !

Mike

Kij, How DID you know my speaker wires were 197 feet long? Just kidding!

As for the PS switching noise at the output, that is removed with the low pass Zobel. However, there are special filters used by the measurement crowd which test equipment. Some problems occur when measuring 'd' amps.

Kij has it correct. The RDon is very low for MOSFETs. Resistance Device on.
This is a big selling point for discrete power devices. less resistance is less power lost, or rather delivered to the load.....whichever you prefer.

Now, on to the full /half bridge argument.
http://www.irf.com/product-info/audio/classdtutorial.pdf

Above is the Internation Rectifier article on 'd' amps. Very good read. But, this is only part 1 of 2.
The full/half bridge configurations are well covered as are some of the rf issues.

QUESTION: how do the 2 different kilowatt Bel Canto amps differ? Don't they both use the B+O ASP module? Is there only a difference in input circuitry or the Zobel?

Here is a link to the B+O ASP site.
http://www.icepower.bang-olufsen.com/files/solutions/icepower500asp.pdf

Looking at the technical specs you will see the power output is specified for 60 seconds.....not FTC continuous. The ASP1000 module has only a 30 second time limit.

I like my 'd' amp. No question about it getting the job done.

"With medium efficiency speakers the MEASURED peak voltage is above 100v."

- I don't understand it. What speaker efficiency has to do with the voltage. Icepower 1000ASP voltage is regulated always 80V and since it is bidirectional it becomes +/-80V.

Switching power supplies generate high frequency noise that is easy to filter out and non audible. For this reason Rowland uses switching supply in Capri preamp and he is very noise conscious guy (he used batteries in preamps).
Linear power supply is also switching - current comes in narrow spikes of very high amplitude producing high frequency noise in addition to 120Hz noise (difficult to filter out).

Now - In order to become 1/4 wave antenna for 100kHz SMPS frequency wire/cable has to be 2460ft. Below 1/10 of the wave (984ft) antenna practically doesn't work. Small amount of the amp's carrier frequency (1%) appears on the speaker wires but at 500kHz it needs 197ft of wire to become 1/10 wave antenna.

"Ref1000 can drive 2ohm delivering 40A "
That means that its peak voltage is 40x2 = 80 volts. Its not bery good!
With medium efficiency speakers the MEASURED peak voltage is above 100v. This why Spectron amps have peak voltage of 240 volts (to cover poor efficiency speakers too). As I understand switching power supplies also generate high frequency noise. I believe these are two the main reasons why high caliber class D amplifiers like Spectron and Mark levinson (No 53) use traditional transformers.
The single exception is Jeff Rowland 312 which uses switching power supplies with PFC (power factor correction) and for its $15k price provide very good sound.

DC Offset: any semi-decent amplifier ( e.g. Spectron I own and enjoy!) has protection circuitry. Richard Vandersteen may have some bad experience with either old design or new "cheap" class D amp. Today its not a problem (if done right)

Mike

Spectron: DC offset can harm your tweeter, depending on the tweeter design and degree of DC Offset

Simon, can you clarify why that would be? I would expect any reasonable amount of dc offset to be blocked from reaching the tweeter by the capacitor(s) in the speaker's crossover network. Aside perhaps from transients during turn-on and turn-off, or during times when the amount of dc offset might be changing, and in each of those cases I would expect the resulting transients to be minor and brief.

Thanks!
-- Al

Pugstub - It might be related to fact that Icepower's full bridge places half of supply voltage (30-40V) on both speaker terminals. Non-powered speaker sees only voltage between terminals (difference) but ground referenced powered speaker might not tolerate such common mode voltage. They also mentioned in Stereophile that some electrostats don't work with Icepower for the same reason. Half bridge schemes like Hypex don't have this problem and can be even bridged while Icepower cannot be (already is).