High end Class D amps?

OMG

'Now excuse me I’m going back to the workshop to finish off my 1973 Ducati 750 sport (round-case) engine main bearing replacement.'

so there is something to like about Gfi

noble,


as an X maggie 3.5R owner, I wish I was aware of this back then. Consider posting this in magnepan threads too

It's Fremer. If a dog looked like a turntable, he would claim its bark sounded like Pavarotti. I take anything he says with a bottle of salt.

I see a slight problem in Michael Fremer’s review of the PSA amps...he and Paul McGowan happen to be very good friends...so..for reality’s sake...I would take that review with a grain of salt.

It’s rare that someone will state so clearly that the don’t understand what they are arguing about. As a monument, I will place this here.

Hint for George, EPDR is NOT a measure of current loading. It is a measure of equivalent thermal loading. Unless the load is a resistive only, this will ALWAYS happens somewhere other than where the current is at a maximum.

georgehifi8,069 posts12-15-2020 6:09pm

George - You’ve brought up this notion of EPDR in several class D threads, but haven’t explained how it relates to class D.

It relates to any amplifier seeing the low EPDR loading which demands extra current to be delivered from the amp, which Class-D’s don’t do as well as good linear Bi-Polars can.

Is there a moderator in the house?

Hey moderator, this @georgehifi character pollutes every single Class-D thread with tons of messages making a claim that is totally wrong. This must be the 3rd of 4th thread just since I joined.

@georgehifi,

I am not going anywhere.

Your repeatedly attempts to use EPDR shows you have no idea what it means and how it relates to amplifiers, and I would say contrary to what Atmasphere said, it does not apply at all to Class-D as the FETS in Class-D do not operate in the linear region, hence the phase has no bearing on the thermal loading of a Class-D amplifier.


As well, Class-D amplifiers may not double in power intentionally, as they may intentionally current limit. That is not a bad thing and has no impact on sound quality if you are not driving into clipping and there is no stability issue. Your repeated attacks against something you clearly don’t understand really needs to stop.

About the IceEdge 1200 AS1 modules in the PS Audio and the amps I made last year: I measured them at 2 ohms of 1000 watts......200 watts below what it does into 4 ohms......yet Michael Fremer says it drives the Wilson’s very well? I have not read the review yet. OH NO, this cannot be. George will never talk to us again. Michael just destroyed his "class D cannot drive Wilsons" nonsense that he as been spouting for years.  He screams.....but it does not double its power into 2 ohms......it cannot possibly drive a Wilson......ha ha ha......So, i guess 1000 watts into 2 ohms is enough after all.

There are class A/B amps that have been designed to output very high current levels at the expense of cost and weight, and thus far, class D designers have chosen to focus more on the mainstream market where current demands are not as extreme. But this has nothing to do with EPDR.

I'll grant you that there may be limitations in the number of output devices that can be paralleled and still maintain appropriate switching speeds. With current output devices, this may limit the maximum current that class D amplifiers can deliver to less than is possible with a class A/B design. I have not tried to design a class D amplifier myself (other than using an off-the-shelf module), so I don't fully appreciate the limitations, But I think the potential is still quite high even with current devices. 

For most reasonable speaker loads, the current demands are well within the capabilities of mainstream class D amplifiers, such as those built using the Purifi, Hypex, and ICEpower modules. The Purifi module, for example, can output 25 amps before the current limiter will kick in. Obviously, this still requires that you have a power supply that can deliver this level of current, as it does with a class A/B amp. 

I’ll state once again as yet NO!! Class-D (and that also goes for my choice Class-D Technics SE-R1) will perform as good into a pair of Wilson Alexia and such, with their EPDR bass loadings like a hi current Gryphon Antillion etc etc can.

Interestingly enough, Michael Fremer reviewed the PS Audio Stellar M1200 amps in Stereophile this month. Class D Ice power amps. His exact quote in respect to bass performance when driving his Wilson Audio Alexx is "The M1200s ability to couple with, control, and drive the woofers of my Wilson Alexx loudspeakers matched that of any amplifier I’ve had here." Read that again, because he has had some pretty heavy hitters in that room driving those speakers. When he went to grade the individual aspects of the amplifiers performance he rated the bottom end as A+. When you read the review, you can tell he is pretty impressed with these $6000 a pair amps. The "whole product protection mode’’ thing is particularly interesting when the name of the product HE (George) builds is attached to every single post he makes here. Product promotion (or protection) at its finest more than 8000 times here.

I’ll state once again as yet NO!! Class-D (and that also goes for my choice Class-D Technics SE-R1) will perform as good into a pair of Wilson Alexia and such, with their EPDR bass loadings like a hi current Gryphon Antillion etc etc can.

Just look up the 'on' resistance of any GaNFET. This will be the value of the output impedance of the amp unless it runs feedback- in which case it will be lower. So explain how an amp with an output impedance of 10 milliohms or less will care one bit about a 0.85ohm dip in a loudspeaker.

George - You’ve brought up this notion of EPDR in several class D threads, but haven’t explained how it relates to class D.

It relates to any amplifier seeing the low EPDR loading which demands extra current to be delivered from the amp, which Class-D’s don’t do as well as good linear Bi-Polars can.

Obviously, you can contrive a situation where a given class D amp does not have the current capability to drive a particular load

I don’t contrive anything, it’s fact Class-D can’t do current into low impedances like good linear bi-polars can, and if you don’t believe or have the knowledge to understand that, it’s your problem not mine.

Now excuse me I’m going back to the workshop to finish off my 1973 Ducati 750 sport (round-case) engine main bearing replacement.

And Ralph in the below post below, it’s just not the GaN transistor wrong yet again, you forget the output filter and feedback also.
Just leave it be Ralph, anyone can see your in "product protection mode" your not doing yourself any favours.

So explain how an amp with an output impedance of 10 milliohms

Just like a Technics Su-G700 Integrated GaN Class-D with it’s milliohm output impedance also can’t drive the Alexia load either!!! It’s got the so called wattage at 4ohms

Back to the Duke, more important than talking to shillers of their own yet to be released amps. 

George - You've brought up this notion of EPDR in several class D threads, but haven't explained how it relates to class D. This is a term that was made up by a Stereophile reviewer to try to explain why linear amplifiers had a hard time driving speakers with a reactive load. Specifically, speakers whose current demands are not linearly related to the voltage across the speaker terminals. 

In a linear amplifier, this will cause a higher than expected thermal load on the output transistors because the high current demand can exist even with a high percentage of the rail voltage across the output devices. 

In a class D amplifier, the output transistors don't care about the voltage across the speaker since the voltage output only affects the duty cycle, not the power dissipation. They are constantly switching on and off at their oscillation frequency regardless of the voltage across the speaker. As long as the amp can handle the current demands, the fact that the load is at all reactive is irrelevant. 

If you disagree with these statements, please explain why. (And don't just repeat your previous statements since so far you haven't described how EPDR relates to class D). 

Obviously, you can contrive a situation where a given class D amp does not have the current capability to drive a particular load at the desired voltage, but this true with a class A or A/B amp as well. And, in fact, the thermal challenges are much more difficult with a class A amp, and even a class A/B amp, to meet a specific desired current capability.

No you have no idea, or, as I said you are in "product protection mode" and need to say the opposite for your future release. Most probably the latter I would think.

I’ll state once again as yet NO!! Class-D (and that also goes for my choice Class-D Technics SE-R1) will perform as good into a pair of Wilson Alexia and such, with their EPDR bass loadings like a hi current Gryphon Antillion etc etc can.

Well this is an excellent example of how George has no idea what he's talking about. Sheesh.

George, perhaps you could come up with some evidence of your preposterous claim?? You know what they say- photos or it didn't happen.

This statement is blatantly false. Class D amps are limited in their ability to play low impedance (and severe phase angles) in the same manner as traditional solid state,

No it’s not, and you know it and are in denial, your just once again in "product protection mode for your yet to be released Class-D".
 Just try to get any Class-D to perform as well as an amp with bi-polar output like a big Gryphon's into a pair of Wilson Alexia’s, the Class-D will be shamed.

Combined, these two give’s you what’s called EPDR, (Equivalent Peak Dissipation Resistance) and that can give the amp a very nasty load impedance to look at.
Good big current bi-polar amps don’t mind seeing this
.
Class-D tends to quickly drop off it’s current starting under 4ohms down to 2ohms, look at any Class-D "independently measured" spec and you will see that, they never come close to doubling wattage from 4 to 2 to 1ohm, many even go backwards, showing severe current limitations into low EPDR impedances, this is limiting bass performance and becoming like a tone control, rolling off the bass instead of staying flat to 20hz.

This statement is blatantly false. Class D amps are limited in their ability to play low impedance (and severe phase angles) in the same manner as traditional solid state, although in practice a class D amp usually has a much lower output impedance than most traditional solid state amps.


Be-it class D or traditional solid state, if the output power is dropping into lower impedances, this is entirely due to the power supply and not the topology of the amp. At anything less than full power, any class D amp made in the last 5 years will act as a nearly perfect voltage source with any conventional speaker, with loads as low as 0.5 ohms no worries (since their output impedance is likely less than 100th of that). 

I’ve noticed that they do tend to truncate the natural decay times on bass notes, which I believe is due to their very high damping factors.

For those that want to know, I believe "that experience" is more likely because many speakers have there lowest impedance in the bass and also their highest -phase angle.
Combined, these two give’s you what’s called EPDR, (Equivalent Peak Dissipation Resistance) and that can give the amp a very nasty load impedance to look at.
Good big current bi-polar amps don’t mind seeing this
.
Class-D tends to quickly drop off it’s current starting under 4ohms down to 2ohms, look at any Class-D "independently measured" spec and you will see that, they never come close to doubling wattage from 4 to 2 to 1ohm, many even go backwards, showing severe current limitations into low EPDR impedances, this is limiting bass performance and becoming like a tone control, rolling off the bass instead of staying flat to 20hz.
https://www.audiosciencereview.com/forum/index.php?threads/stereophile-has-started-calculating-epdr....

This link also on EPDR on the second page:
https://www.stereophile.com/reference/707heavy/index.html


Cheers George

Thank you for sharing your experience. And thank you for realizing that you are just guessing. You actually have no idea.....that your theory about damping factor and class D has any meaning. You would have to get every class A amp that exists and every class d amp that exists and drive your subs and also your main speakers and see what you hear. Then you MIGHT have some actual real information. Every class D amp sounds different....including in the bass (my direct experience). Maybe adding great subs to any system will always get you better decay.....everywhere. Just as adding a supertweeter can make the bass better. So, what are you hearing? Without doing extensive experiments we are just a bunch of guessers. There is very little real information shared anywhere about how audio actually works. It is basically every man for himself. There are SOOOOOOOOOOOO many things that change the sound. Unless you account for every variable.....you know very little. I have spent over 40 years doing listening tests......and I know some things.....but really what I know....is that I know NOTHING! It is infinite. In drag racing there are only 5 things that make for performance......horsepower, weight, drag, traction and gearing. And all this can be measured by the clock. This is why dragsters all look the same......like the same person built them all. Everything is known in drag racing. Audio is the opposite. Nothing is known. All brands of solder sound different.....you cannot measure it....you have to listen....every wire, every resistor brand, on and on into infinity. Most things that make a sonic difference cannot be measured.

I brought a proto of an amp I sold last year to someones house and A/Bed the amp versus his. Both his and my amps used IceEdge 1200as modules in mono blocks. Mine was modded....his was not. Both had the same damping factor and power as I did not change the feedback or output stage. His amp sounded "tubey" in the bass.....my amp sounded way faster, and cleaner and preferable by him and me. Damping factor is just one of tons of things that can affect bass performance.

I am not saying that we should not share our guesses.....it is fun. The trouble is, that most state things like what you said but leave out the part that you have limited knowledge and its a guess. So, it is stated as "class d amps have zero decay in the bass....they are overdamped".......Then the rest of us just repeat this on other forums till everyone thinks the same thing. The blind leading the blind. Words are very powerful. Thank you for your intelligent use of words.

The best words are those that uplift us. For we all want to be happy. Share uplifting words and deeds with everyone....we all win that way. May you all be happy and joyful this season and always.

     I'm a big fan of class D amps, however, I've noticed that they do tend to truncate the natural decay times on bass notes, which I believe is due to their very high damping factors.  I find this a bit ironic, since class D is often dismissed as only good enough for sub amplification.
     I'm wondering if others have noticed this because I've never read about this unnatural class D shortening of decay times here or anywhere else.  It's important to note that this class D bass note decay time truncation issue is not something that is easily and immediately discerned by listeners, mainly because it's more distinct on certain instruments, notes and types of music. 
      When I listened to my first class D amp, a Class D Audio SDS-440-CS with a rated damping factor of over 1,000, driving my former Magnepan 2.7QR speakers, for example, I distinctly recall perceiving the bass performance as the best I had ever heard on them since I bought them used about 6 years earlier.  I perceived the bass as clearly being more prominent, powerful and dynamic  as well as tauter and, at least initially, seemingly more detailed through my new class D amp than through my prior class AB Aragon and McCormack amps.
     It wasn't until about 6 months later, after installing an Audio Kinesis Debra 4-sub distributed bass array (DBA) system with all subs driven by a separate class AB 1K watt amp with a DF about 300-500, that I first became aware of this class D decay time truncation issue on bass notes. 
     I ran my Magnepan panel speakers full range knowing they only had a rated bass extension of 35 Hz.  My main purpose for installing the AK DBA system in my room was to provide full bass extension down to 20 Hz and provide the bass power and dynamics that my Magnepans lacked between 20 and about 40 Hz.  
     I clearly noticed the bass quality was much improved being reproduced through the AK DBA system. The bass was even more powerful and dynamic, as expected, but it was also smoother, faster and much more detailed.   I believe it was this added detail that enabled me to notice the stark difference between how the AK DBA reproduced the decay times of bass notes in much finer articulation, without any truncations and with more natural sounding durations than the class D amp was able to reproduce them through just my main speakers.
     Of course, I realize there's likely more factors involved in achieving high quality bass performance in a system and room than the type of amp used and its rated damping factor.  The truth is that, more than anything else, I was surprised by the truncation of bass notes through just the class D amp driving my mains and the vast improvement in their reproduction, along with other benefits, provided by the addition of multiple good quality subs driven by a class AB amp.  
     Currently, it's just my theory that the DF of the amp(s) utilized in a system is an important factor in determining the quality of a system's ability to accurately reproduce the decays of bass notes. This is all based on my personal experiences, however, and I understand that I'm no expert and that we typically don't know what we don't know. 
     Which suggests that there are likely other important factors involved.
Tim

phd a trumpy democrat hater -- woohoo

and i thought red just stands for the uneducated pull wool over my eyes contingent...

Tsunami coming 

+1 phd, especially the vote counters

Raise your hand if you like Class D amps! I'll let someone else count the results, definately not the democrats.

@bullitt5094, Do you use RoomPerfect, and if you do is it a major factor in how good the 2170 sounds? 

I A/B tested LTA, Odyssey and Lyngdorf in my home. I auditioned them for my wife, with exceptional hearing as tested, and my Daughter, also excellent hearing, and neither having any idea about the technology. The Lyngdorf 2170 was the overwhelming choice for all three of us. I was very surprised. I've since constructed a Pass "First Watt" F5 power amp and B1 Korg preamp. The Lyngdorf sounds better than the Pass too. And that includes both digital and analog inputs. Just offering my personal experience.

Atmashpere, how would one ever test that variable independently outside of other amplifier qualities? Plenty of seasoned audiophiles and reviewers alike that would argue subtleties in how a woofer is damped is second only to an amps ability to provide current into load variance in determining the best match.

@petland  Actually its pretty easy to determine if a woofer or other driver is overdamped with a fairly simple circuit. An amplifier does not need to be involved. This was demonstrated by the chief engineer of Electro Voice back in the late 1950s (it was EV and MacIntosh that led the way using the voltage rules for driving speakers). The physics of course hasn't changed since then.


Here's D.J. Tomcik's article, in case you are interested:

https://pearl-hifi.com/06_Lit_Archive/07_Misc_Downloads/1385_Critical_LS_Damping.pdf

I have Martin Logan CLX's which are difficult to optimally drive due to their capacitive load  which produces very high impedance in the bass and extremely low impedance in the upper treble.  I have used a number of good amps to drive them ranging from Class A Pass amps, the Pass Labs 100.5's, the Coda 15.5, to class AB, Krell Evolution 402e and Rowland 625's, and a good tube amp, the ARC Ref 150.  All had good points but one could criticize each depending on your tastes.  I also used a single Benchmark AHB2 which could not handle this speaker; however, two AHB2's in mono are surprisingly excellent and give away nothing to the previously listed amps.  The AHB2 is an overperformer but not Class D.  

Of the Class D amps I have personally auditioned on the CLX's, clearly the best was the Merrill Element 116's which can clearly handle the CLX's  providing transparency and detailing equivalent to the AHB2's,  a neutral tonal balance,  images extremely well and has excellent dynamics l.  It does not sound like any of the Class D amps I have previously heard.  I have not auditioned the Technics amp nor the most recent Purifi based amps or every Class A or Class AB amp out there, but I suspect that the Merrill Element amps would compare well against any amp near their price range.  In the end it comes down to your own preferences.  It is a platitude, but each of us may prefer one flavor or the next and how each amp's idiosyncrasies will interact with your room.

When I first received my EVS1200, elements in my system were not worthy of it. In the last 9 months I have upgraded interconnects and speaker cables with WireWorld Eclipse Series 8, I also unplugged the 1200 from the CorePower 1800 PLC, now direct to my 20 amp dedicated line. Speakers updated from Emerald Physics KCIIs with Wire World and clarity cap upgrades to EP 3.4s with upgraded outboard XOs and WW jumpers, but I was still using my Oppo 105 with LPM and EIC mods direct to the amp so that I could flip between red book and SACD/DVDs on the fly. Redbook sounded detailed (but I now realize dry). A week ago I decided to reinstall my Audio Alchemy DDP -1 + PS 5: this was right after Peter Madnick left designing really high end kit (I forget whose), but the AA line was/is a mega-bargain.


So no longer able to play SACD/DVD-As without reconnecting the 105 direct to the 1200 BUT... DAMN my jaw drops, re-listening to disks like Jennifer Nettles Playing with Fire, some of the songs are very poorly mixed (3s), now sound like (8s). Is it that the AA is warm,a better impedance match, or just that the dac does a better job playing red book? Perhaps ricrevs will chime in


Obviously my 105 could benefit from additional mods (but I would need to send it out), or replaced with a better universal disc player, but in the mean time... I’m a happy camper playing red book


hth

I brought my first proto of the mono IceEdge amps over to a guys house last year and we A/Bed it with his mono IceEdge amps from Mivera Audio. When we were listening to his amp the sound of the bass was rather "tubey" and I told him so. He said he liked that sound. However, when we put my super modded monsters in (same module with the same output stage with the same damping factor).....the bass now was way tighter and better and he remarked as such....he liked it much better with my amps. There were so many things different about the amps.....not just all my mods but different platform and feet.

No one ever thought my super modded IceEdge amp was overdamped or dry sounding......espeically once I did the last 7 mods.......which is what I released and what Tweak 1 has. Not saying that it is as liquid as tubes or whatever.......just another perspective.

Here is a link to a review by Herb Reichert......about his experience with the Harbeth 30.2.....He found no dry overdamped sound from the Bel-Canto amps Ncore based amps......though he did like the liquidity of tubes best.

https://www.stereophile.com/content/harbeth-monitor-302-40th-anniversary-edition-loudspeaker-page-2

However, enter a zero feedback input stage Purifi amp and now Herb thinks the Bel-Canto is dry.

https://www.stereophile.com/content/lkv-veros-pwr-power-amplifier-page-2

By the way, the Bel-Canto amps he has are simply stock NC500s with the stock switching supply from Hypex and an op amp for a buffer on the input....very basic...and way overpriced. You can buy a pair of mono blocks from VTV with the same configuration for $1300 delivered......Bel-Canto Ref 600s were $6K!!!!!

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-purifi-1et400a...

Scroll down a little and you will see the insides of the ref 600s


Both the Bel Canto and the LKV use stock super low output impedance Ncore or Purifi modules. You should hear my modded Purifi modules with air core coils and super caps oriented correctly and modded Wima bypasses.....and with all the other mods too! So many ways to change things. Never ending fun! BTW, I can modifiy Purifi modules in your LKV or whatever amp.....and do other mods, as well.

Hey Ric, nice to see you around, 20 years ago I had one of your wonderful modded Dacs.

That was my point, how do you account for DF independently. My point too was more about lowish DF vs. the ridiculously high DF in most of the OEM modules, one of the keys to the bad sound of class D IMO, especially with my recent experience with the DS225. I get to this a matching issue, I listen mostly to easy to control 2 -ways.

I can say this with confidence, strap 20db of NFB on my DS225, gain match a test into a typical woofer with nothing but bass lines and I am going to be able to tell you when I am listening to to DF of 167 vs a significant multiple of that, and I would not need to hear the normal deterioration of the mids and highs. I would agree, amps sound different for a variety of reasons but extremely low output impedance class D amps share a house sound that to me is similar to way too much NFB in a class A/B design.

Take your Ncore amp and put a .1 ohm non inductive power resistor on the inside of the amp right at the binding post (in series with the post).  Now the output impedance of the amp is at least .1 ohm.......so, listen to it again.  Does it sound exactly like some other amp that has 80 damping factor?   Not likely......there are so many factors that are probably part of the sonic equation.  The measured damping factor of an amp could be realized by several things....including amount of feedback, amount of output devices, resistance of coils in series (if applicable), etc.  I bet every amp with the same measured damping factor will sound different in bass quality.  This game is way more complex than most people think.  You can bypass the power supply with serious film caps and the bass will tighten, faster electrolytic caps in the power suppy will tighten bass....fi you damp certain things you will tighten the bass....or dry it up (over dampen)....on and on and on into infinity.  Over simplification is usually done by those that do not do much actual hands on testing and A/Bing......mostly just guessing...and that includes manufactures, as well.  I mean, how much time does anyone have to really research something?  High end audio is mostly the blind leading the blind.....he he.  In drag racing everyone knows what works......this is why dragsters all look the same, as if one person makes them all.   This is because there are only 5 things to consider when making a dragster (performance wise).....horsepower, weight, drag, traction and gearing......and the performance can be measured by a clock.  No one really knows why a certain piece of wire put in a certain direction would make a sonic change......and that is just one if the infinite possibilities of sonic change.  This is why there are tons of amps, including class D and at every price point and they all sound different (and always will)......and sometimes the cheaper one is better.  However, one thing is for sure.  If you spend enough time doing serious listening tests than you can figure out a lot of ways to lower audible distortion.

Atmashpere, how would one ever test that variable independently outside of other amplifier qualities? Plenty of seasoned audiophiles and reviewers alike that would argue subtleties in how a woofer is damped is second only to an amps ability to provide current into load variance in determining the best match.
I am listening right now to a pair of Harbeth 30.2 through the DS225 at DF of 167 at 8 ohm. I can swap in an Ncore amp I have on hand and the immediate complete unnatural over tightening of the lower register with a DF in the thousands has to at least be in part if not fully due to that difference.

Hello, somehow I am on similar situation.
what I can say after listening many class d is to don’t rely too much on latest chip and this works as well for Dac but is the implementation that make big difference. There are three or 4 main chip manufacturers on class D, but only two (Purify is basically a rebrand of Hypex) are giving the bases for the implementation. What I see is that the are some purist who calculate best class d in Sinad but this is math and doesn’t tell you how it sound. The sonic difference are given by op amp (extra board) and other tricks that add somehow signal distortion (sorry for defining as such) and this make a sonic difference. What sound better is up to you and your match. You can take the oem amply and rely only on chip then add the coloration you want by pre amp or you can play with big brand who customise the chip or oem assembler who give you possibility to add extra operational amps to change sonic features. Somehow technology is mature but I believe there will be other chip in the future who
will add maybe other tricks, maybe a built in Dac for instance?! Is big market out there and cheaper than producing SS or tube, many brands jump into it others not probably they don’t have the capability. try and listen then take your consideration

Bass which unlike most people I find typically to NOT be a strength of most class D because it is almost always over damped for the modern speaker, is stellar on the DS225, fast and articulate but with some body like bass actually sounds.

@petland any damping factor over about 20 or so is going to be too much for almost any speaker made. You won't be able to hear a difference between 100 or 1000 if that were the only variable....

Having owned the lot from Merrill to Nord to Rowland to every conceivable output board in multiple iterations, including Bruno's latest which to me sounded very similar to Ncore, tube input stages, transformer coupled input stages, etc etc..the best I achieved was with a Rogue Medusa with a ton of money thrown at it in part upgrades and it still could not quite match the best A/B amps and certainly not the best class A amps.  I concluded class D was very very good with attractive attributes when well implemented and for me best used as my summer amp or in an AV setup. I am still a fan but thought it to be limited.

Then out of curiosity this spring I grabbed an ARC DS225 from a few years back to use as a back-up in an office system backing up Valvet A4e monos at the time in the summer months. To my surprise, DS225 is easily the best class D amp I have owned and I would say on par with a top shelf A/B design of similar power. Not particularly sure why it should be other than perhaps a completely in house design by a company known for its tube products, ARC apparently spent 2 years designing its own output stage, a huge linear PS (which has also been a component of other class D designs I have owned and certainly all of the better ones). Where it differs from all others is having no global NFB and hence a more modest damping factor of 167. Sonically, its the first class D amp I have encountered that really suffers no dead zone, and is fully "on song" at the lowest of volumes. I would say its easily the most enjoyable amp I have ever owned listening to at low volumes, which I do a lot of at night. Bass which unlike most people I find typically to NOT be a strength of most class D because it is almost always over damped for the modern speaker, is stellar on the DS225, fast and articulate but with some body like bass actually sounds. The biggest difference though and where all others I have owned really fall short including the Rogue, it actually digs deep in the midrange to flesh out with some tone and grunge to acoustic and electric guitar for example, like good class A and even dare I say a good valve amp is know to do. My sense is the DS225 probably does not measure as "pristine" spec wise as say an off the shelf Ncore module, but that says more about the Ncore than anything. Grab one if you see one, somehow they fell through the audio crack into oblivion and no one really noticed. It happens. 

Would love to hear the AGD amps, any news on his active speaker collaboration? Cheers

Huge thread...can’t read it all.  Not sure if the AVM Evolution A5.2 was mentioned.  Incredible integrated with tube input stage for $6500 and has optional phono-stage and DAC cards.  185w of awesome power.

I hope the Rogues were mentioned, Sphinx and Pharaoh integrated amps along with the Hydra and DragoN power amps.  

Actually, you do not want any conductive material at all for a transformer bolt.  Even a brass or non magnetic stainless steel bolt will degrade the sound compared to no bolt or plastic bolt.  You want nothing conductive above, below or in the middle of a toroid.  Again, mount the toroid off the chassis on wood and use glue and tie wraps or wooden plate on top with plastic nut and bolt.  Likewise shielding a toroid with copper, etc. will close down the sound.  If you want to shield then do it a couple of inches away from the toroid......let the toroid radiate its field.  I also do not generally like shielded wires.

i have Nuprime MCH-K38 and MCX-4 which use the same proprietary power boards, class A and D hybrid, the former can be bridged and in that mode has more control, detail and punch. Next week I will be comparing these family offerings to the Starke Sound AD.320, which can also be bridged and is starting to get great reviews but is new. The construction quality is excellent and it too uses proprietary power boards, again not ICEPower or Hypex Ncore, and is a class AB and D hybrid. All amps should be considered for muti channel high end class d systems.

Most toroid transformer manufacturers supply mounting hardware, and if you use it the transformer will run hotter than it should. This is because the mounting bolt is steel

A least that’s one you got right and we can agree on, this has been known btw forever since toroidal’s were first released, and especially when the bolt is in contact with the chassis earth, sorry but you did not discover it. (so no self back pats) My Hungarian EE boss (rip Steve De’Ratz) back it the 80’s told me about this, as his family tree had something to do with the first ones. And it also applies to any air core chokes, in speakers, amps, anything.

Dont forget the Dark Horse AGD PRODUCTION ... Class D certainly is in a higher level of performance than ever before. Many of the old issues with class D are gone. Something to realize is class D is the leading amplifier technology when compared to A and AB for HiFi.

Heres what makes AGD my top choice by a good amount when it comes to Class D. First off my personal opinion is Alberto Guerra is a better designer than Bruno Putzey. why ? well for one his products sound better to me. Next Alberto designs all the way down to the GaN device itself. Yes, that means not only does AGD not use someone elses class D module, it means AGD has thier own GaN device that is not available to anyone else. Why on earth ?  because the GaN devices on the market that are most plentiful and best from a supply standpoint and least expensive to spec into your amp design are made to be used in battery rechargers. If you are lucky you get the milspec devices used for LIDAR in the military. The AGD output device is the first and only GanFet to be designed ground up for HiFi. So when we start with that , we start at the Pinnacle of GanFet and Class D design. Forget all the others this one is different and its clear to hear. These amps are made in USA. The "Baby" of the family is a monoblock called "Audion" can be held in an outstretched hand is made from Gorgeous custom milled aluminum  with a mirror polish offered as an option. It has both RCA and XLR Inputs and WBT NextGen binding posts . Its output is 80W at 8 Ohms, but do not be deceived, it can deliver 32A of current . Thats right one reviewer powered Apogee Scintilla with this mighty mite. Why have you not heard of it ? Because it is a brand of attraction not a brand of promotion. The best brands in the world for anything are not on the fast track to push product. They steep in the market and people find out about them if they are the right buyer. Prime example Viola Labs. Most have never heard of it nor understand that it stems from the brand of HiFi considered by many to represent the most extreme example of sonic quality ever made in our industry, which was Cello, which came from the man Mark Levinson. Well AGD sounds better than Cello, Ive compared to Duet. My first buyers have been my S.E.T guys... the most hardcore of audiophiles. I have a return policy mind you and NOT ONE pair has come back. One of my guys in California has Berning 300B monos that are built to the hilt, Silver Would transformers and original Western Electric 300B tubes.. The tubes cost more then the pair of monos does. And AGD Took the cake. So I know that hearing is subjective , but if one of these amps is to be considered most innovative and most unique its the AGD for sure,  hands down,  no questions asked . Anyone want to challenge ? I am available to back my mouth up with proof in the form of shootout and recording . Do yourself a favor check out the AGD Audion , its only $7500 per pair and is 100% proprietary, sounds line no other, comes in a flght case with die cut internal foam and 2 5 foot audiophile power cables, no molded crap cord. The amp is guaranteed to overjoy you or your money back , no restock fees.  

I have owned several amps over the years. Mostly mid fi until the last ten years I owned the Krell Chorus, Theta Dreadnaught D nc1200 based and the ATI Nc500 based amps. I kept seeing Cherry Amps mentioned in these class D amp threads. So I figured I would give it a try. Well to say I fell in love would be an understatement. I have 11 channels of Cherry Amps. But I can honestly say they don’t all sound the same. They all sound good but the best I have heard are the mono maraschino’s with the biggest 60 volt power supply with tripple capacitance. These little amps have bested some high end amps. The amps were Musical Fidelity M8 700m’s. The Cherry Maraschinos just sounded so much smoother and real. I know I won’t choose anything else ever. It is the perfect amp for me.

By the way, if you are using a toroidal transformer and you use metal plates or bolts to secure it to the chassis....you are closing down the sound. You want your toroidal transformer off the chassis on a piece of wood an mounted using tie wraps and glue or a wooden plate on top and teflon screws......way better sound.

Just a FWIW: the problem you are addressing here is the mounting. Most toroid transformer manufacturers supply mounting hardware, and if you use it the transformer will run hotter than it should. This is because the mounting bolt is steel, its magnetic and while a toroid is supposed to contain its magnetic field very effectively, in practice it does not, so that bolt becomes a magnetic short. If you install one just for fun, you'll see that the bolt is running hotter than the transformer. The solution is really very simple: just use a stainless non-magnetic bolt and no worries. And does this sound better? Yes it does- we discovered this phenomena about 25 years ago and its a nice tweak to any amplifier- the sound will 'open up' a little and of course the transformer will run cooler and make slightly more voltage- both audible and measurable!

Yes, but none yet "so far" that have taken the full major advantage of the 1.5mhz switching speed on offer when GaN Technology is used

Actually GaNFETs and MOSFETs are both capable of switch far faster than the switching speeds seen in all class D amps including Technics. The problem isn't how fast the devices are! Its how much noise is created (or not) by the switching at power; how much RFI is created, how much of this noise is then affecting other parts of the amplifier circuit, and then there is the issue of the 'body diode', which is where GaNFETs actually have the advantage over MOSFETs. This gets a bit technical, but has a lot to do with the coil in the output filter, which stores energy and then has to release it. Essentially its what is called a 'flyback' voltage (named after flyback transformers in old analog TVs), working in a manner similar to that of a spark coil in a car. In a nutshell, the output device can behave oddly- you tell it to turn off and it won't, partially due to capacitance effects on the gate of the device and partially due to the body diode of the device, which is a primitive diode formed in the passive layers of the device when its made (and I am vastly over-simplifying in this regard!!).  The filter coil flyback voltage can be effectively used to kick the GaNFET into its off state. That's a more important reason to use them than their speed, since MOSFETs have made so many gains in the last few years.


An important reason to keep the switching speed a bit lower is dead time. Dead time is invariant with frequency- no matter how fast you switch or how slow, the minimum amount of dead time you will need stays the same. So as you switch faster and faster, the output device is waiting for a greater and greater percentage of its ON time. This causes distortion to go up. Its true that Technics has a faster switching time, but it does not seem to be doing them any good IMO as they are paying the price in several different ways- increased cost without increased performance due to the associated issues with speed.

I think the Weiss op amps could be worth a try. From what I've read, these are the best discrete op amps available and have the ability to bias the output stage fairly high (adjustable with a small trim pot). I plan to use these on one of the input board designs I will build for my DIY amps. 

My experience with the Sparkos op amps is that they dulled the sound a bit to much, although did add a bit of welcome body (this was on a hypex amp). The Sonic imagery op amps were very clean sounding but sounded a bit thin and sterile in my system. 

Can't loose then with 30 day trial, just like getting any Schiit product 14 day trial.
Be nice if Technics did it with the SE-R1, but to even buy one of those is very hard.

Cheers George  

So....I think I'll buy a VTV Purifi. I suspect I'm heading for disappointment again, but there's a 30-day trial so why not? Maybe I'll be wrong this time and I can convert over to class D. I have an all-tube preamp currently. I assume the tube buffer option isn't worth it but what about those op-amps? If all they do is impart color than I can rely on my pre. Is the custom input board worth it?

What about Techics GaN based class D amps, are there others who use GaN?

Yes, but none yet "so far" that have taken the full major advantage of the 1.5mhz switching speed on offer when GaN Technology is used, that Technics does with the 188lb SE-R1 that also uses linear power supplies, input ones are regulated.

https://ibb.co/S6CFz5y

https://ibb.co/wwH0vNr

Here’s a little to read on the GaN transistor and it’s higher switching speed ability, that Technics have used.

https://www.psemi.com/newsroom/pres...fastest-switching-speeds-to-gan-class-d-audio

Cheers George

Marantz uses class D in all of their highest end amplifiers now. One for instance would me the Ruby integrated, another would be the PM10, etc...