Class D = Trash?

The best Class D I have heard does use an analog power supply (a large Toroidal trans with banks of power supply caps). In addition, if bass is of the utmost importance then an oversize analog power supply is a must. Don't get me wrong there are some very nice sounding Class D amps with a switching power supply but they seem to excel in the Mids and highs but lack bass to some degree or another.

....I can see a novel business opportunity here...a 'burn-in service' for D amps.

Send me your new D amps and I'll burn them in for you.  When I think they're ready, I'll send them on to you.  First come, first served, and be patient.

Don't gasp...either you can put up with it, or I will. ;)  Pennies a day....

I have a used D amp that needs to be re-broken in due to it being in storage for 1 year and 6 days. I would like updates at the following intervals - 600, 900, & 1500 hours...we can have listening sessions over Skype to monitor progress.

Look at Merrill Audio .they make Excellent amplifiers, and use Very good parts quality.I owned Mcintosh very dissapointmrnt wima caps donot belong in a $6k  amplifier I put Mundorf  supreme a Big improvement as well as resistors,wiring.
Class D  has nany variations, and   have their own implementations of class D.
Can compete with class A AB amplifier without exception. And a money back option I believe .I have them several times .I am going to purchase one myself.
I do recommend like myself a Very good custom Vacuum tube preamp 
Myself DHT  preamps are superior in Several ways 1 stage vs several in a conventional preamp.  The Russian 4P1L a fantastic most linear tube out there
As long as you have a veteran over 20 years in Vacuum tube design such 
as Radu Tarta, and the buyer chooses the quality of the parts choices. Far better 
Then most commercial average at best parts. 

I don't think there is a specified time for Class D to break-in. If there is and it would vary from one manufacturer to another should be mentioned in the manual. What we do know is that the longer they are powered up, the better they sound. The most important thing to keep in mind as they do require a lot of experimentation with different interconnects and power cables to sound their best and patience will prevail.

@phd that's interesting you find class D weak in the bass without an analog power supply. I've found class D to absolutely kick booty in the bass department with the normal switching power supplies. 

Is there anything consistent in audio?!

One of the amps that I own, I made from Abletec mono modules, put 2 in a single chassis..... It took and initial 400 or so hours to break in and still continued to improve beyond 1000 hours.  I don't listen to this amp much, but none the less, it is no slouch.  Good bass, smooth midrange through the top end,  good detail... I like a few others better, but this is an amp does nothing objectionable and most could easily live with. 

Toddverrone, ah yes you could be right but somehow wyred4sound has managed to engineer the bass out of their amps. What I can say with confidence is that an analog power supply in class D does give you that full sound that class a/b amps posses.

Oh my, I hope it's not trash. I've got a Class-D amp heading my. Good to read of the positive experiences here. Would be nice to add my own happy story  in a few weeks. Fingers crossed.

Cheers,

Scott

Have owned and sold hundreds of amps from entry to uber (I am an older audio+music-phile and one time business owner). Now retired, I enjoy refurbished and upgraded Aragon (A/AB), Goldmund (AB), bel canto (class D) and Virtue Audio Sensation (Class T) amps. With the right associated gear and setting, all are compelling performers. Cheers! 

Bass and amps is a funny, funny thing. Some speakers are hard to drive in the bass and sometimes that is malicious. A speaker that requires a particularly beefy amp is called "discerning" and sold at twice the price it would be otherwise. :) Some speakers are hard to drive in the treble. This is another area where some amps probably show significant audible differences. Personally I have lost all interest in hard to drive speakers because I find their total cost of ownership just too high for little value.

So while I think globally panning Class D amps as inferior to analog, there may be some truth to some amps performing better with some speakers, a problem shared by all amplifier classes.

Also, ICEPower among others, have optional input sections. This allows vendors to use their own secret sauce to the overall sound. From input transformers, tubes, whatever, so it’s quite possible for two vendors to use the same ICEPower or Hypex modules and get different results.



Best,

E

Erik, your reasonable manner is so refreshing after some of the epic thread battles of late.

Thanks for your input on ICEpower when I was in the market. I'm loving my ghentaudio monoblocks and was sceptical before I spoke with you.

"What I can say with confidence is that an analog power supply in class D does give you that full sound that class a/b amps posses."

phd,  I could'n agree more, but I would add AND THEN SOME...Or a lot more :-).

Disclosure: I am a manufacturer using Icepower modules with Analog Power Supply.

Henry

Hi Henry,

     I respect your knowledge and experience as well as your H2O amps.

     I realize you utilize large analog power supplies in your Icepower based amps, rather than the more typical switching power supplies, and your amps are known for their excellent bass response.

     I own three class D amps that have all been used to drive my Magnepan 2.7QR speakers at separate times.  The first two were both stereo amps that have analog power supplies/toroidal transformers, a Class D Audio SDS-440CS and an Emerald Physics EP100.2.  My current class D amps are mono-blocks that have built-in switching power supplies in their Anaview/Abletec power modules, D-Sonic M3-600-M mono-blocks.   

     All three class D amps produce the best bass I've ever heard from my Magnepans but, IMO, the D-Sonic monos with the switching power supplies have significantly better bass response than my other class D amps with analog power supplies.

   My former class A/B  Aragon 4004 MKII amp also used an analog power supply that included 2 very large and heavy toroidal transformers. Both of my stereo class D amps, with much smaller toroidal transformers, and my class D monos, with small and lightweight switching power supplies, all have much better bass response than my former class A/B amp had even with its very large analog power supply.

    Of course I realize you don't want to give away any trade secrets, but I'm curious on your thoughts about whether there's a direct relationship between an analog power supply and good bass response in an amp.  My personal experience implies there is not a direct relationship but I sense the truth is likely more complex and think it is best heard from an amp designer such as yourself.

Thanks,
  Tim

Thanks for your kind words, Todd.

It's hard to be level when so many forces on this site want you to be extreme. :)

Best,

E

Tim, Thank you.

I think a bit more valid conclusion as to which type of power supply is better is to have the same amp with SMPS and then the same amp with analog power supply given EVERYTHING else is equal. I emphasize everything is because as you would agree a front end and/or a preamp or even speaker wire can influence the sound, for better or worse. First, let me clarify that there are two fundamental differences between the two type of power supplies we are discussing here.  One being the SMPS and the other is the traditional analog power supply and that is obvious. But another big difference which is also worth mentioning is the SMPS type is being regulated...Meaning that the output voltage is held constant as long as current draw from the load (the amp) is within the supply's design capability.  And that is very desirable in audio power amplifier design or anything electronic for that matter.   However, regulated analog power supply for high power amplifier is very expensive to design just from the standpoint of hardware involve.  This is the very reason why regulated analog power supply is mostly done in preamplifier circuit since power involve is not huge, compared to Power amplifier.  In fact, 99.9% of power amplifier out on the market have been designed using an unregulated analog power supply, at least for the output stage. A fewer design may have a regulated analog power supply for the input and maybe a driver stage, but power supply for the output stage still is unregulated.  Stable voltage supply rail is highly desirable since changing voltage supply rail can change biasing current in conventional discrete transistor design especially.  Also, change or reduced in voltage supply will also limit how far the signal can swing, after all the amplified signal can only swing as far as the available supply voltage rail, and as  a result power is reduced.  Though the first effect (changing voltage under dynamic condition) is much more detrimental than the secondary effect of reduced power IMHO.  Due to those effects mentioned the result will turn for the worst in the final sound through the system. This is the fundamental reason (not the only reason of course) why most power amplifier can sound quite good at low volume but falls apart when pushing hard at high listening level, and especially into a difficult speaker load, because an unregulated power supply will sag (drop in voltage level) under heavy current demand from the load. While the analog power supply we are discussing here is not regulated, though it can be.  From my experience, an regulated analog power supply is always better than an unregulated analog power supply, again given everything else is equal. Then again, there used to be a debate( isn't it always with audio :-)) that an unregulated analog power supply can actually sound better than a regulated one.  Note that so far I have made a differentiation between a regulated and an unregulated ANALOG power supplies and not SMPS.  SMPS by design is always regulated.  Please note also that so far I have only mentioned power supply topology but in regard only to conventional discrete transistor design as in typical Class A and Class A/B design and not with PWM switching amplifier.  As mentioned above I preferred a regulated analog power supply for conventional discrete transistors design, simply because in class A/B and especially class A, always draw current constant current, and can be lots of it if it is class A or a heavily biased class AB. The reason is simply that if the supply is not regulated, the voltage rails will sag significantly resulted in lots of ripple on the DC rails.  And the end results will end up with is noise, hiss and hum.  And this is only under static condition (no input signal so no amplification), and will get worse under heavy dynamic condition where heavy current demand is asked for.  And that is very true for class A/B power amplifier.  But what we are talking about here is switching amplifier.  There is no constant current being drawn here as in the case with conventional amplifier. Well, there is but very tiny amount of current being drawn. The amp only draws current when there is signal.  But more importantly when it does draw current, but unlike conventional design, the transistor does not spending so much time in the linear region because the output stage acts like a very (make it extreme) fast switch.  And therefore, there is not much power dissipation as heat is being generated.  So this is the very reason why it runs so cool and efficient as we all know about class D amps.  So for Class D I really think the important thing is to be able to deliver huge amount of current but FAST and as fast as you can and not so much of being regulated or unregulated.  Though I got to admit that my intuition tells me from experience that a regulated analog power supply (mind you) even for the output stage would give a better result. I don't know since I have not tried it neither with SMPS nor regulated analog power supply, with class D that is. I have tried it with conventional design and for sure regulated supply wins hand down. There is something about switch mode power supply which I need to investigate further.

OMG, I can't believe I went this far and still have not answer Tim's question :-).... So without dwelling into too much of all of the technical jargon, the short answer is YES!!! at least what I have tried so far with class D.  I apologize for the post being too long, and in all honesty, this is the very reason why I decide not to anticipate with most of the discussions through the years as this took me hours to compose something like this as I am not a very good writer.  Though I found most of the discussion very interesting to say the least.

There is one confession which I need to make and that is coming from conventional strictly pure class A design through the years, I always chuckle and LMAO at time when I read debate where a piece of wire would make a difference in the final sound.  Well, I have stopped laughing ever since dealing with Class D.  Boy, talk about temper.  Just a simple bypass cap, which used to make tiny (if at all) difference in sound with conventional design, but with class D? It can sound heavenly or like trash.  The same goes for type of rectifier being used, and the wire and ....
 And for the record, the H2O has regulated analog power supply for the front end and unregulated power supply (and huge at that) for the output switching stage.  Also, I have finally manage to get a pair of the NCore 400 modules and have implemented them with a similar power supply which I have implemented for the H2O using Icepower module. I have been listening to the Ncore and have been rotate the Icepower in and out from time to time for comparison for the last month or so. Now what I need is to have is an NCore with switching mode power supply which design by hypex for real comparison.  Hopefully I would have a better insights on the difference in sound.

Henry

Henry, thank you. While I understand only half of what you're talking about, the detail and knowledge in your post is superb.

The points  @h2oaudio makes about regulated vs. unregulated are pretty much true. VERY few analog amps are regulated at all. Krell did this with the FPB I believe. Sanders's Magtech is what I would call semi-regulated. Brilliant compromise.

Doing linear for a carefully implemented input section also makes a great deal of sense if you want to get the best you possibly can out of it, without requiring a massive investment in hardware that a fully regulated amp would need.

Best,

E

One interesting experiment I read about I've wanted to try is to actually LISTEN to the amplifier power supply lines. The + and - supplies are, in theory, at fixed DC voltages but as the music plays, the current draw will cause the supplies to sag with each note. You can actually attach headphones (carefully, wth appropriate circuits) and hear just how much effect driving speakers has on the power supply.

This technique can be further expanded to analyze the actual frequencies that the supply is worst at isolating, and to add appropriate filtering. A fussy technique I don't know if anyone but one vendor (probably out of business) has ever done. Still, fun idea.

In stereo amps, this effect is probably one of the main reasons for increased cross-talk between channels.

Todd, Thank you.  But I admit my knowledge is very limited actually compared to some of the GODS of amplifier designers such as Nelson Pass, John Curl and quite a few other designers.  I am a rookie compare to these amplifier designers.  I just know enough to make the amp sounds halfway decent by lots of experimentation.

I sincerely hope I did not offend anyone with some of the statements I made.  Please remember that my opinion is just that...one opinion.  It is just happen that I am a manufacturer.  And more importantly, what I referred to as "BETTER"  is only in the context within my system and others system which I heard, and furthermore to my ears and my ears only.  I do believe lots of members on this board have been around long enough to know, that there was not, is not and will never be one absolute.  It will always depend on the system as whole and more importantly listener's preferences, type of music, room acoustic and the list goes on.  And to answer the OP's questions.  The answer is NO.  Far from trash actually.  Then again, just like what I just mentioned above.  It depend to whom are we asking?  So the correct answer I believe is YES AND NO :-).

Henry

Erik,

I believe Krell FPB does not have a fully regulated power supply from front to back.  The KRS series does and maybe the Krell master reference as well.  Though to my belief that power supply is one fundamental aspect of amplifier design, but it is only one of the many aspects which make the amp sounds good such as topology and devices being used, implementation to name a few. But I digress since we are talking about class D so let us switch (pun intended) back to class D channel shall we?

@h2oaudio - Since I'm not that big a Krell fanboy, it is VERY likely I got the models/series wrong. :)

I only wanted to point interested parties to examples.

I am going to start another thread I think, for people who LIKE class D. :)

Best,

E

Well, again, not a big deal, but this from a review on the Krell FBP:

The output stage in all FPB amplifiers employs a free-floating feedback arrangement wherein ultra-fast regulators independently monitor the output stage and respond to the smallest drop in current or voltage with regulator response that is all but instantaneous.

Bit of useless marketing/design trivia for Krell fans. :) Of course, this is only the output section, but it would be VERY weird to regulate the output but not the inputs, since the latter is much cheaper to do.

Best,

E

Hi Henry,

     Thank you for taking the time to respond in such detail to my question and stating that you do think there's a direct relationship between an analog power supply and good bass response in an amp. Given your praises of regulated amp output voltage, which the switching mode has but which the analog power supplies typically lack due to expense,  I would have thought the relationship between an analog power supply and good bass response would be less direct. However, I'm fairly certain it's best to defer to your knowledge and experience on this matter.

     It's very interesting and encouraging to know that you're continuing to explore the potential of the somewhat newer class D power modules such as the Hypex NCore 400 modules along with corresponding Hypex switching mode power supplies.  I would be very interested to know if you discover varying performance levels between these modules paired with the various Hypex smps (NCore 1200 and 600 smps) and the NCore 400 modules paired with your own analog power supply.

     Strictly from my subjective viewpoint,  the most obvious differences I've noticed between using class D and various class A/B amps(Adcom, McCormack and Aragon) in my system are improved bass response, a reduced noise floor,  increased dynamics (especially on content recorded in hi-res 24/96 format), increased detail and a more neutral sonic character in general.  
     These benefits were clearly noticed on the first 2 class D amps I owned (Class D Audio SDS-440-CS and Emerald Physics EP-100.2) and these qualities are even more clearly noticed on my current class D amps (D-Sonic M3-660-M).
      Just to be clear, I was not offended with anything you said and agree that there is no absolute in this hobby.

Thanks Henry,
 Tim   

@guidocorona ,

1) Once a class D is broken in is it stable from then on; or will it need to be broken in again if it sits idle for an extended period? (Actually any well-informed reader’s input on that would be much appreciated.
2) I just bought a used Audiosource on eBay for $60. When do I get my 500 Valium? Can I get more if break-in takes longer than 1,500 hours? Is this an honor system?

The valium is inside the amp. The pills look a lot like resistors.. just pull them off the circuit board. It'll be fine

Todd, I could only find 12. I took them all at once. Nothing happened. My breath does smell like oregano, though.

Eric, 
" I am going to start another thread I think, for people who LIKE class D. :)"
Please do!

Well... a lot of techy discussion here... and... I don't really know why my "Class D Audio" SDS-470C sounds so incredible (e.g. Ice vs Hypex vs something else or switching vs linear, etc.) - I just know it does.  

And... it seems to sound as good or better than my other amps, which are very good.  

And... I've not tried any other class d amps... so... I have no basis for comparison - I'm not really sure I need any - it sounds so grand!    

Hi Tim, Thanks

I apologize for what I wrote was not very clear. So let me rephrase and make it a bit more clear. You’re right that there is not a direct relationship between good bass and an analog power supply, which makes sense, after all power supply is but one of the many fundamental aspects of any amplifier design. Great sounding power amplifiers requires many aspects of the design, and not just the power supply. What I can say from what I have implemented and heard is that an unregulated analog power supply seem to always sound better than those with SMPS. And this is strictly in the context of class D Icepower. As indicated, I have implemented and listened to the NCore 400 modules with an analog power supply of my own design, but cannot compare to any Ncore (400 or otherwise) modules implemented with SMPS and so therefore cannot make any evaluation as compare to the Ncore 400 modules with my own an analog power supply. I have requested to buy sample of Ncore 1200 from Hypex to test as I am a manufacturer and have been declined by Hypex. It seems as though Hypex wants to supply to only those manufacturers with reputable brand names, sort of exclusive club if you know what I mean, since H2O is a no body apparently, and that is my feeling. My goal is obviously to find the best technology which sounds good to high-end community. No matter though, from what I have implemented and heard, especially with Icepower, there is absolutely nothing to fear, at least from my point view.

Henry

Tim,

I wanted to add that though I have not have a chance to listen to one yet! But I believe the D-sonic amp is an great amp from what I have read.  And ice on the cake is the price especially.

Henry

Personally I have lost all interest in hard to drive speakers because I find their total cost of ownership just too high for little value.

+1 on that!

When you can connect headphones to the power supply of any amplifier and hear the audio signal, you may count on the fact that the power supply is contributing to IMD. This is a very audible form of distortion! It is for this reason that we have a separate power supply for our driver circuits as opposed to our output circuits.

IMO this should be the case in a class D amp too, and I think that should pan out as the input circuitry usually has very different requirements as opposed to the output section.

@atmasphere

Hah!

A recent phrase has made it into the news, I'd like to co-opt as a statement I never want to make:

I am being dominated by my loudspeakers

Speakers, like friends and family, should be easy to get along with for me. Not the secret Mistress whose every whim should be catered to. That's what secret mistresses are for.

About headphones and power supplies:  True, I also think it's a way of checking for checking the effectiveness of power supply filtering. For instance, if you get a lot more HF in your supply, may mean you need less inductive filter/shunt caps. It is also a way of knowing when you have done enough, so if I ever worked in the field again, it is a technique I'd try to apply to see if I could learn about any power supplies I worked on.

Best,


E

I guess what I'm saying is:

When I worked in circuit design we just threw a bunch of bypass caps of different types into the power supply without ever measuring their effectiveness or cost/benefits.

If I did this again, I'd take a more rigorous approach to every single power supply bypass cap. Spend money where needed as opposed to a shotgun approach.

Ahhhh, good times back then. :)

Best,


E

Laugh if you want.  You can Spend $10,000 or you can spend a few thousand.  The Crown International Drive core 2 amps are cheap and have many turning in their esoteric amps. Lexicon uses Crown Drive Core technology.   Was compared against Emotiva and it did not come close to the power and sound.  These are going in home theaters. Google it yourself.  
I still run a Crown D150 Series II and it still sounds great.  Over 40 yrs old.   No, Not like a Levinson, but close to a MAC. which is good.  The Drive Core II are supposed to be better.

Was compared against Emotiva and it did not come close to the power and sound.

Emotiva is a brand I had really high hopes for.

Best,

E

Hi Henry, 

     Thank you for clarifying your findings: "from what I have implemented and heard is that an unregulated analog power supply seem to always sound better than those with SMPS. And this is strictly in the context of class D Icepower."  I understand you're in the midst of experimenting to determine if the same holds true for Hypex NCore 400 modules.

     I'm not really surprised that Hypex didn't allow you access to their top NCore 1200 module. I've read that Hypex had a predetermined sales strategy to  reserve the NCore 1200 module for the larger OEM market while offering the NCore 400 module for sale to the DIY market and amp assembly market.  I believe Hypex is considering H2O a segment of the amp assembly market even though we, and likely many others, realize H2O  actually more closely resembles an OEM than an amp assembler.   
     
     I assume you're aware of the newest Hypex module, the NCore 500, which supposedly is very similar to the sound quality of the NCore 1200 but not quite as powerful.  There is even a U.K. company somewhat similar to H2O, Nord, that offers stereo and mono-block amps based on the NCore 500 module that use Hypex smps but have discrete class A input buffer boards that allow a choice of op amps (Sparkos SS3602 or Sonic Imagery 994).  Maybe this will be the future of class D, with op amp rolling rather than tube rolling.

     There are also many very good alternative class D power modules such as the Anaview/Abletech ALC-1000-1300 (used in the D-Sonic M3-600-M mono-blocks) that utilize Phase Shifting Modulation (PSM) rather than the Pulse Width Modulation (PWM) that Hypex NCore modules utilize and the Pascal modules (used in the D-Sonic M3-1500-M and M3-800-S, Red Dragon S500, Jeff Rowland Continuum S2 integrated and 525 stereo amps) that feature their proprietary and patented UMAC  technology.  I believe these modules would be available to you and could possibly be enhanced with your custom analog power supplies.

Thanks,
  Tim

 input buffer boards that allow a choice of op amps
  Maybe this will be the future of class D, with op amp rolling

Can they get any cheaper, in manufacturing with opamps instead of discrete transistors.

Any hi-end linear poweramp that used opamps as the input stage for their amps wouldn't be recognized for very long and die a slow painful death.

Cheers George  

georgehifi,

      Yes, Nord does cut costs and prices to customers by selecting op amps for their input boards that they like the sound of rather than the much more expensive method of designing and building their own.
       Class D power module manufacturers typically utilize the more expensive but high quality discrete MOSFET transistors in their output stages.  I've read that there's recently been a lot of effort in the transistor industry going into developing even faster switching MOSFET transistors expressly for use in class D switching amps.  Are class D amps becoming so popular and mainstream that their manufacturers' needs are now influencing the direction of transistor r&d?  I believe the future of class D certainly looks very promising.

Tim

Modern Op amps are very good implemented correctly. Most music is produced with tens of them in the signal chain at least. There's no way to avoid them entirely.

Almost all DAC's rely on them, if not external, then implemented in the filter chips themselves.

Power supply and supporting part quality matters.

Best,

E

georgehifi,

     Here's a link to what I was referring to in my last post about reading of faster switching mosfets:

http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html

      This transistor technology is called Gallium Nitride (GaN) and is poised to uproot the high-end audio world.  There's even mention of your favorite subject, higher PWM switching frequency, and how these new GaN FETS will enable it.

Tim

@pcrhkr - I had a crown xls 1500, which was the first gen if they're more tech. It was a great amp, especially considering it can be had new for not much more than $300. 

I recently bought a used pair of class d monoblocks by Ghent audio.. they are noticeably better than the crown. Just putting that out there.

Hi Tim,

Thank you very much for your understanding the tip on the Abletec power amp modules.  Unfortunately, I think all modules being offered by Abletec has built-in SMPS and there is not really a way to bypass/separate the SMPS from the amp section.  Even if that is possible, it would not be practical and/or economical.  This is the very reason I have gravitated toward icepower and Ncore so far, as these can be used with power supply of my own design.

I am aware of products being offered by Nord from England.  I believe, and I maybe wrong on this, that there is a misconception about the input buffer in most instances, in that it is choice rather than a necessity.  In reality, I believe it is a necessity first and foremost since most of these amp modules, may have a very low input impedance, in fact even lower than in the case of icepower 8 kohms in most modules, which is very low compared to the industry's standard.  One example would be in the Abletec's case, where if the module is being implement as is, its intrinsic input impedance is less than 2 kohms which is so tough drive properly for any preamp, except a very few preamps, and one being my Fire Preamp.

From what I have heard with the Ncore400, realizing that it is not the Ncore1200 which may sound completely different, Still, I believe that the Ncore technology is most appropriated to be mated with a tube preamp, and maybe preferably, a non-negative feedback design for best result, at least to my ears and in my system.  Thanks

Henry

Hi Henry,

       You know, if I said "Hi" and used your last name after, I'd be saying:"Hi-Ho".  Mind if I say it twice and add: "it's off to work we go"?
      True story from my college days:
       I worked at a Chinese restaurant and a new guy was hired.  He was a Chinese exchange student whose 1st name was "Ho".  When he came to work the next day, I instinctively said: "Hi Ho".  After I realized how goofy that sounded, I told him his  new American name would be "Henry".  Honest.

       Okay, sorry for my side track.

      You're correct, the Abletec modules have a built-in smps, auto European/North American power sensing circuit and a regulated input power circuit.  D-Sonic also uses a custom input buffer to raise the low input impedance to 60K ohms so it's compatible with almost any preamp; so my former tube VTL preamp (output impedance of 200 ohms) matched very well with the D-Sonic M3-600 monos.

     I believe the Pascal modules also incorporate the smps and other circuits on the same board, so these are likely ruled out for your purposes as well.  At least the Hypex NCore 400 and 500 modules remain as good candidates.  

     So, please knock our socks off with that thing that you do with your analog power supplies!

Thanks for your participation,
              Tim 

noble100658 posts04-13-2017 2:15amgeorgehifi,

Here’s a link to what I was referring to in my last post about reading of faster switching mosfets:

Yes I posted about these before, same guy invented the Mosfet.

https://forum.audiogon.com/posts/1414493

And yes it’s on the way, but this is just a small company able to supply Technics, not the world "yet"
Companies like Motorola will copy it and then the ball will be rolling, but with this transistor the Switching Noise Frequency has been doubled to 1.5mHz but I would like to see it to get to 3-5mHz.
This way the low order filter that has to be used on the output of all class-d amps can do it’s job well away from the audio band, without it’s effects (phase shift) or left over switching noise getting down into the audio band.

Cheers George

Hi George,

    So, you're saying it may be a year or two before you buy your first class D amp?
     If you're going to wait until class D is absolutely perfect, the good news is that it'll probably be the last amp you'll ever need to buy.  
Good strategy.

Later,
 Tim

So, you’re saying it may be a year or two before you buy your first class D amp?
If you’re going to wait until class D is absolutely perfect, the good news is that it’ll probably be the last amp you’ll ever need to buy.
Good strategy.

Yes, I’m waiting till it gets to what I believe will be time for me to turn to the dark side, with a 3-5mHz switching frequency, then it will address the problems I think it has "trying to filter out ALL of it" without effecting the audio bandwidth, and then my linear amps WILL become boat anchors.

One of the tell tale test will be to see in mags an almost square 10khz square wave without any buzz saw ringing across the top "without the use of test AP0025 (Audio Precision) inline filters" that are now being used by mags to hide it when measurements are being done, as I queried here on Stereophile.
http://www.stereophile.com/comment/565267#comment-565267
This then will show good audio bandwidth with total filtering out of the switching frequency.

This is what an unfiltered (by test equipment) square wave looks like on Class-D. If this was a linear s/s or tube amp a tech would say not to use it it has a major problem.
https://www.google.com.au/search?q=Class-D+square+wave&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj_g9zOsaDTAhWMnZQKHax5C8kQ_AUIBigB&biw=1255&bih=782#imgrc=OFuO9FVLq5xJeM:

Cheers George

Tim,

"Hi Ho".  After I realized how goofy that sounded, I told him his  new American name would be "Henry" .  LOL! That is very funny. 

Speaking of which there are a pair of the Nord monoblocks NC500 for sale right now on Agon. Fund is very limited right now, otherwise I would pull the trigger on this just to find out how it sounds compare to the NC400 that I have. Thanks again for reading all of my rambling.

Henry

georgehifi,

     From the comments of your fellow mates on www.stereonet.au,
it seems you've been posting about the need for an increase in the switching frequency of class D amps to the 3-5mHz range for years to the point of their apparent consternation.  

     I'm not certain, but I'm fairly sure you've been stalking threads concerning class D, and posting similar messages about the dire need for class D amps to raise its switching frequency to 3-5mHz, for years here on Audiogon.  If it hasn't been years, then I apologize, but it sure seems like years to me and I'd hazard to guess to other frequent readers of class D related Audiogon threads.

     Please excuse me while I flash my 'Literary License Badge' and briefly pontificate: Georgehifi is like a stealthy panther, desperately hungry for the definitive answer to the eternal delicious question of the optimal switching frequency for class D amplification that, due to his being a magnificent beast of nature possessing extraordinary feline aural senses,  he alone having the capacity to ever so faintly detect when that frequency is set a few kHz too low.  
     He persistently lurks and stalks through the wild plains of the audio forum hunting grounds until he spots a class D thread and then he suddenly pounces with an uncontrolled fury upon his allegorical prey and maliciously metes out his vengeance by predictably, mundanely, and rather annoyingly, launching into another repetitive attack/statement concerning his bloodthirsty quest for the elusive optimal class D switching frequency.  

     Okay, I think we've all had our fill of whatever that was.  

      I'm apparently to the point of consternation myself.  Unfortunately, I  must admit I lack the complete expertise of  mathematics, electrical engineering and class D amp circuitry and design that I believe may be required to definitively determine whether your claims of the necessity of a higher switching frequency utilization in class D amps is justified.

     Therefore, the only current recourse that came to mind is to directly quote the acknowledged guru of modern class D amplification as well as the inventor of class D UcD and Hypex NCore technology, Bruno Putzeys.  The quote below is a relevant portion of an interview conducted by Peter Roth (PR) of Bruno Putzeys (BP) done on March 1st,2014 and posted on www.sounstage!ultra.com (I'll link the entire interview at the end of my post):

"PR: At Hypex, obviously, you continued development and implementation of the UcD modules for OEM clients -- but tell me about the much newer NCore class-D devices. Is NCore a further extension of what you’ve been doing with UcD, or is it an entirely different class-D scheme?

"BP: I think it would be fair to say that it builds on from UcD. Certainly the fundamental math is the same. The really crucial part of NCore was to figure out how to improve the loop gain even further from what we had -- UcD had substantial loop gain up to 20kHz of 35dB or something -- and I wanted to go beyond that. As I said, there is no such thing as too much feedback, so I was looking for a way to add 20 more dB. That’s actually a very hard problem to crack, because once you start doing that, you have to remember that a class-D amplifier has a limited bandwidth. A reasonable switching frequency for a class-D amplifier is just under 500kHz or so. If you go much above that, you run into efficiency and headroom problems. That, in turn, implies that you have no more than some 200kHz of bandwidth to play with -- actually, less than that. And if you want to cram 50 or 60dB of audioband loop gain into that bandwidth, you have to think completely differently from the way that linear amplifiers are usually designed.

Linear amplifiers typically have what we call single-pole compensation; some of them have two-pole compensation, but nothing much beyond that. UcD has four-pole compensation, and NCore has five. Once you reach into the four- and five-pole compensation, you have this problem that the amplifier can be operating in perfect stability until you clip it, and then it will suddenly start oscillating at a frequency that will immediately damage the amplifier and the loudspeaker -- so you want to avoid it like the plague. And not just that, but you actually want to return the amplifier, once it comes out of clip, to its normal operating regime so quickly that you don’t hear any glitches. The whole NCore patent revolves around the practical solution to that stability problem, the way that it actually catches the feedback loop at the moment that it’s thinking of going unstable, and then lets it go when it is safe to do so.

Apart from that, of course, I did learn some more tricks as concerns driving the output stage. If you have 50dB of feedback, and you are aiming for -100dB of distortion, you’ll still need to manage to get -50dB of open-loop distortion. In that respect, you are right in your previous question: You have to start out with something that’s good, because there is always a trade-off. If you’ve got yourself 50 or 60dB of negative feedback, but if you can also get 10dB improvement in open-loop distortion, why not do so? So the actual power circuit has also changed between UcD and NCore, and obviously, then, the later UcD modules actually use an improved power stage that was borrowed from NCore. The core of NCore is the feedback circuit, but the actual product contains some more improvements that are now trickling back into the UcD range."

     georgehifi, Putzeys states that a switching frequency of 500kHz or so is reasonable and you're claiming 3-5mHz is necessary for optimal class D performance.
      I'm not actually claiming that he's right and you're wrong.  For all I know, he may believe 500kHz or so is reasonable but may agree with you that 3-5mHz is optimal.  I just don't know if my class D monos would sound better with a higher switching frequency since there's no method to currently compare unless I compare my amps to the $30K Technics amp with the new eGaN FETS.  It's honestly hard for me to imagine how my amps could sound better but I'll be keeping an open mind until I can try a more reasonably priced alternative to the Technics.
      I'm thoroughly pleased with my experiences with class D amps so far and likely a permanent member of the class D Fan Club;I've already got my official club card, big club ring with the diamond studded 'D', club jacket, beanie, "Class D Stands for Delicious" t-shirt, "Class D or Die" bumper stickers , matching underpants and, due to years of practice, now have the unbelievably elaborate secret member handshake down pat.  

     Anyway, my main point is that I know Bruno is a friendly and accessible guy via email and will answer your email inquiries on class D switching frequencies.  Wouldn't you rather receive answers straight from the horse's mouth than constantly raise the subject on Audiogon Forums?  Speaking for myself, I know I'd sincerely enjoy not hearing about this subject again until you, hopefully, post on what you discovered in your discussion with Bruno.  


Complete Putzey Soundstage interview:
http://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/455-searchin...


Thank you,
   Tim  

 Here's a link to what I was referring to in my last post about reading of faster switching mosfets:

http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html

Hmm. I'm a fan of class D amps (really expect them to bring home the bacon someday and am working on one myself) but not the 'digital' amps to which this article refers, because they don't exist. I expect the author really meant 'class D' or 'switching' when he must have accidentally used 'digital amps'... ya think?