Class D Technology

The black background many listeners can hear with Class D indeed suggests the heavy filtering is in some way affecting the audible sound.

Myself I would not describe it as a "black background".
But rather a "harmonic black hole".

Cheers George

Arc and Rogue have been on teh bandwagon for a number of years now knowing Class D is the ticket to get the sound their customers might like

It's called maximizing profits, as Class-D is many x cheaper to produce.

Cheers George 

Pass labs 250 INT - but while I am sure they are really great - are HUGE and serious $$$.

In Australia the Belcanto Ref600’s are $8k around the same as the Pass 250 int.
The new BC Ref600 monoblocks use the latest NC500 Hypex modules with moded from what I was told output filters (cascaded?) by BC. They sounded very good to me with a certain Raven ribbon tweeter that presented a very flat 8ohm load in the uppermids/highs. Read my post here.
https://forum.audiogon.com/discussions/class-d-technology/post?postid=1372318#1372318

Cheers George

I'm not sure what this "class A input stage" is.  Input stages are almost always class A (would be stupid not to)

+1
I've never seen anything but Class-A input stages, it BS advertising to con the gulible.

Cheers George

The day will come when Class D will compete and very well be better than any linear amps tube,s/s, class A, AB or whatever, BUT!!

 Class D needs much higher switching frequency (needs to be at least 5 x higher) technology isn't there yet but in the future it will come, only then will ClassD become a contender. Till then good for budget hifi and subwoofer/bass amps.

Technics has progress the Class D race and developed 2 x the present switching frequency with their own made components, in this amp but it’s very expensive $20-30k
https://forum.audiogon.com/posts/1334662?highlight=Technics

When the switching frequency is 3mhz or better, then it can be called hi-end, and will own it myself, then my linear heavy boat anchors will be sold or become door stops.



Cheers George

georgelofi you are correct about switching frequency being teh key to even better Class D amps in the future.

Have you listened to any good quality class D amps or are you judging solely on technical interpretation?

Yes the new Belcanto 600 monoblocks, they were the best of the Class D's I've heard so far, but still didn't convince me to go to the dark side yet.

In the future when the switching frequency is up around 3-5mhz then the filtering can do it's job properly without it's effects influencing the audio band.
The Belcanto 600's did a series of output filters to counter this, but it has it's own set of problems.

The Technics are up to 1.5mhz but you pay for this $$$$$

http://www.technics.com/us/products/r1/se-r1.html#overview

Cheers George

This small residue (about 1%) has no effect on the sound

Put your ear to a wide bandwidth tweeter, you will hear it’s poluting artifacts. If not the filter effects is set very low to cut way down to 10khz or even less, creating all sorts of other problems.

Cheers George

Just a couple of quotes from other Stereophile measurements personel.

I dislike measuring amplifiers with a class-D output stage. This is because such designs can throw out enough ultrasonic noise that you can never be quite sure that what you’re actually measuring is the input stage of your analyzer being driven into slew-rate limiting. What I do, therefore, is to insert, when appropriate, a sixth-order low-pass filter set to 20kHz or 30kHz between the output of the amplifier and the analyzer.
But you can see from this graph how the amplifier’s ultrasonic output rolls off rapidly, presumably due to the low-pass filter necessary to minimize the HF noise produced by the switching output stage

Cheers George

I agree with George that switching frequency should be increased, since 50-60kHz bandwidth limitation introduces around 20deg phase shift at 20kHz (causing wrong harmonics summing), but I’m not even sure I can hear such nuances. There are many highly praised amps that have similar bandwidth, I’m sure.

Switching frequencies are up around 600-800khz at the moment, except for that Technics above.
The problem is the switching noise output filter has to handle the full power of the amp and can only be low order, otherwise it will burn out. And being low order it has an effect down into the audio band. If the switching frequency is 3-5MHz then it can do it’s job well away from the audio band without having phase, fr, ect limitations effects .

Just look at the ringing artifacts in Stereophiles 1kzH square waves of Class D, they now test with a inline heavy filter to make this (ringing) disappear, that Audio Precission’s filter they use makes the test wave look clean, but it’s a con job as it’s done at very low power so it doesn’t burn out, in real use it would last a microsecond.
I have asked JA to include both unfiltered (normal) and filtered square waves, just so readers can see the real deal.
Read comments at the bottom of the page, no answer from him.
http://www.stereophile.com/content/bel-canto-eone-ref600m-power-amplifier#G7miwIhm5pj5EDlK.97

Cheers George

If you want to be eco friendly, and be a little compromised at the moment, then sure get a ClassD.
Or pay the bucks and get "maybe the new Technics SE-R1 Class D".
http://www.technics.com/us/products/r1/se-r1.html#overview
Cheers George

Here is just one of many that Stereophile tested, not using their test filter. It’s more than 1%.
And this Class D had a linear power supply as well, most use smd now which creates even more other noises as well.

http://www.stereophile.com/images/archivesart/805CIAfig2.jpg

Cheers George

You aren’t sold on class d yet.

Correct, and Technics are showing the way with the SE-R1, why strive for higher switching frequencies by deleloping their own components, if what we have off the shelf is "good enough". Technics knows and are doing something about it, they can see the forest through the trees.

And like I said when they do get the technology to make it much higher I will be the first to change over, till then I’ll stick with linear for hiend amplification.

Cheers George

Cymbals, for instance, sound more "brassy" and less "splashy".  To me it sounds more natural, but it might create false impression of limited extension.

If the switching noise output filter is set at a higher cutoff so to make the amp look to be flat to 20khz on test this will sound hard.
If it's set lower to try to rid most of the switching noise, this will already be rolling of at 10hkz and therefore rid any cymbal harmonics, this will sound more natural but not very extended.
So your compromised either way, the only solution is a much higher switching noise so it can be cut out totally with the output filter without effecting the audio band at all.

Cheers George  

So I get the obvious strengths of Class D. Efficiency, power output & running cool which allows for small form factors. I also understand the weaknesses somewhat. 1. Non-linear & lots of distortion that needs to be cleaned up with an output filter.
So my question is, if it weren't for efficiency & power, would there be any reason to own a Class D amp? Do they beat Class A in any other categories that count for sound quality?  

+1 seanheis1

Cheers George

sonicbeauty

Quite some years ago, I purchased a pair of Bel Canto REF-1000.

It ended up being my absolute worst purchase in my 30+ years in this hobby.

I understand of course that those class "D" designs have much improved since.

Still, I could not bring myself even today to even remotely give D another shot.

seanheis1 OP

Does anybody know what causes the dead silences in songs that is a characteristic of Class D? Is it the output filter or dead time? I really noticed this with my Ice Module and couldn’t figure out if the amp wasn’t allowing for the music to decay or if it was something else causing the inky blackness.

The BC 600 monoblocks we listened to were better than the Ref-1000’s when we a/b them, probably because of the 600’s multiple series up output filters.
But they still had a stripping of the harmonic structure of the upper/midrange and highs, leaving what seemed to be just the fundamental with no decay and an opaque sound with larger than usual "nothing" gaps in the music.

Like I said before the switching frequency needs to be several times higher so then these output filters can do their job properly well away from the audio band without their side effects coming down into the audio band.
A bit like those nasty "brick wall filters" used to do in the early days of CD
Cheers George

seanheis1 OP

It seems like some companies are aware of this and add tube input stages to try and add harmonics and meat back to the bone.  

Yep, agreed Sean, that's called microphonics, colorations, distortions or euphonics, and not the real harmonics of the instruments or voice that are supposed to be there, but hey some people like it, each to their own.

Cheers George 

No I’ve never heard one. How does Class "D" compare to SS? I’m a tube guy who has not heard the very best SS amps

We, most are all in agreement that Class D is great in the bass. To me where they differ mainly is in the upper mids and highs, some saying there’s hardness up there, and others saying there’s missing information that causes larger then usual gaps between notes creating the "illusion" of a blacker background. I call it an opaqueness.

The different sound of Class-D especially in the upper mids/highs, comes down to how close to the audio band the mandatory output filter on all Class-D’s is bought down to get rid of the class d’s massive amount of VHF switching noise.

If bought down low to erase most of the switching noise, this intrudes into the upper frequencies of the audio band. Which makes it very smooth but robs most of the harmonic structure of the mids and highs, this "could" be compared to tube or class A s/s smoothness.

If it’s not bought down to low it lets quite a bit of VHF switching noise through, this maintains the harmonic structure of the mids and highs but also adds a certain hardness to the sound of class-D

To me the only way to cure this comes in future semiconductor component development, which will allow the switch frequency to be set 5 x higher, so the the output filter can be set much higher as well so then do it’s job properly to get rid of all the switching noise without effecting any of the audio band at all. Then they’ll also be able to drive full current even down to 1ohm from 20hz to 20khz, instead of today falling off a cliff below 4ohms.

Technics have a >$30k amp the they developed with their own components to get the switch noise up 2 x as high as anyone one else, a step in the right direction, but it needs to be higher again 5 x the norm today. They still do not include a 2ohm wattage figure in their specs, as it would still show limitations.
http://www.technics.com/us/products/r1/se-r1.html
When that day comes we’ll all be using them and our heavy, hungry, hot tubes and SS, will become boat anchors.


Cheers George

My class D amp has 60kHz -3dB bandwidth. Georgelofi - you must be a bat?

What brand model? Maybe I can find some non affiliated bench tests

Even so with those figures do some homework at -3db at 60khz you will have phase shifts all the way down to 5khz,  because of the low order of the switching noise output filter.

Cheers George

There are many class A or AB amps that have similar bandwidth but nobody talks about phase shifts.

That’s because good ones are usually much faster, and they don’t freak out at low impedances like ClassD does in distortion and loading.

I like to see bench tests v reviewers subjective listening. As Stereophile does.

But here is what a reviewer from another mag said subjectively, without any bench test to back his listening.

" Here is what the amp doesn’t do. It isn’t airy and it isn’t laid back."

Good highs are airy, they float with harmonic structure.
Cheers George

The JR 102 uses the Ice 200asc modules as you are probably aware.

Look at the distortion figures for the highest their willing to put up in red which is just at 6.5khz. Look how fast the distortion rise is for the given wattage. And this is all at just 4ohms, I would love to see it at 2ohms.
If you can then visualize just what the 15khz one looks like, if they rise this rapidly from 100hz to 1khz to 6.5khz you have an idea of what’s going on the upper mids and highs.

Then you can imagine what happens if the’re driving an ESL speakers which can go to down 1ohm.
This is just one I found I'm sure there's more if I dig.
http://www.icepower.dk/images/200asc_700px.jpg

Cheers George

The output filter vs switching noises frequency is the bottleneck for Class-D HF distortion and low impedance drivability.

As I said when in the future when it is not a bottle neck, and the switching frequency is much higher, I too will dump the hot inefficient boat anchors and go Class-D.
But today it doesn't compete with good linear s/s or even tube (especially OTL tube) which has other limitations.

Cheers George 

randy-11
It sounds like a Class D amp would be best for a sub-woofer, based on a comment above
If the new MOSFET designs will be out (as products) soon, I would not want to sink too many $$ into an amp right now...

You are correct Randy, really good for bass
Technics have lead the way and developed a very expensive one
http://www.technics.com/us/products/r1/se-r1.html
with double the switching frequency as it is today @ 1.5mhz. This is a step in the right direction, but it really needs to get to around 5mhz before the right effective filtering can be done, and then able to get rid of todays Achilles heel that Class-D has.

So just go the cheaper not so glitzy ClassD’s if you want to dabble in it, or even do your own clone if you or a friend are able, and purchase the Icepower/Hypex?etc modules and the power supply modules they sell. They are very much a pluggable build to do, hardly maybe no soldering to do.


Cheers George

So it's come down to mud slinging. 
Not from you sunshine, I think everyone knew I meant megahertz as there's 1,500,000,000 difference between the two.

Cheers George  

One of our audiogon friends uses class D amp (H20) with Apogee Scintilla in 1 ohm mode with great results.

Then I feel sorry for this person as he has never heard his Scintilla’s at their best. It may work, but at their best?? FAR FROM IT!
As they are a great speaker and should be driven with the right amp and Class-D is definitely, absolutely, not one of them, not yet anyway, give it some time and in the future it will be.

Cheers George

I believe you won’t find one tech guru here on Audiogon that would recommend a Class-D amp over "big current" linear amps for these kinds of loads, sure they may work, but are you getting the best from them? I think not. 2nd graph
http://www.lippaudio.org/old/MySystems/Scintilla/impedance.html

BTW: Carver 120 and Kronzilla Mark II are NOT big current amps, sure they consume big current, but they won’t push it into speakers load like these Appogee’s

Cheers George

I understand your just protecting your JR120 investment, that "if" you had the knowledge you could have built for 1/8th of the price. http://www.usaudiomart.com/details/649188442-icepower-200asc-modules/

And I’ll bet you’ll be the first to sell it when the technology comes that get’s rid of the switching noises problems without effecting the amps sound.

Cheers George

Can’t "see the forest through the trees" even though they are presented to you.

The Apogee’s in 1ohm mode were never meant to be driven with tube amps, especially ones like you mentioned, they needed big s/s amps like Krells, Classe, Mark Levinson, yes and even the earlier big JR’s, ones that could pump current into most loads down to 1ohm. You should know this being an owner of a Krell FPB-600c and why didn’t you drive the Apogee’s in 1ohm mode with that, I’m sure you would have changed your mind about the classd-.

Only condescending to the posts that believe that Class-D can drive a speaker to "it’s full potential", when most of the load it represents is around 1ohm, and we’re not even mentioning -phase angles yet. Though I think they will be pretty benign being a planer speaker.

Cheers George

Please let me know if you want, I’ll post in Tech forums for guru’s to respond.

Tech advise needed, Apogee Scintilla in 1ohm mode which amp?

Krell FPB-600c or is there any Class-D you can recommend to equal the Krell?

And yes even any of the ones you just mentioned would be fine, why weren’t these mentioned instead of just the tube ones you tried before, as they had no chance, and you should have known that.
Cheers George

I used the DR-25 and Krell with my Apogees for years before trading for the equally-difficult-to-drive Thiel CS-5i’s.

I assume that you had the same seeing you compared them to your friends.

Why would I need opinions of "gurus" when I have actual real-life listening experiences regarding this exact subject?

Because the ones I would ask, you’d have difficulty in dismissing them as well. Just ask and it will be done.
Cheers George

@uberwaltz

Keep your Krell KAV250 (nice amp) for a while yet, read my reasons here.   
https://forum.audiogon.com/discussions/class-d-technology

Cheers George

Bel Canto Ref1000 Mk.II

The newer Bel Canto e.One Ref600M monoblocks (that had the newest Hypex modules) with Belcanto’s own designed "series" output filters, these so far have sounded the best Class-D to me, and I thought, yes I could live with this.
They were were driving a speaker that had a very benign 6-8ohm flat load tweeter with minimal -phase angle which was one of the Raven Ribbon tweeters, once we used another speaker, with not such a nice benign load in the top end my opinions of it were dashed somewhat.
http://loudspeakershop.eu/glosniki/images_dane_750/raven/linesource_imp.png
Cheers George

Just to ad to Ralph, why would Technics (SE-R1) strive to develop twice the current going switching frequency, if there was no point to it.
But you pay for this first off development $30k! But the price will come tumbling down when others adopt it. But it also still needs to be higher again.

Cheers George

noble100
Georgelofi acknowledges the benefits of class D but mentions its low cost in a manner that suggests it’s not a further benefit,

Now that’s twisting words.
I suggested that future technology in higher switching frequency will be of great benefit to class-d, so then the output filter can do it’s job properly without effecting the audio band.

We’re trying to band fix the switching noise problems with some innovative (ML below) (Belcanto my last post) but not completely successful filter ideas.

Just look for one at the $50k Mark Levinson No53 Class-d monos. 4 x massive inductors for the output filter probably cascaded to get rid of the switching noise. Speaker designers know that doing this with filters has it’s own set of interaction problems. Didn’t get a great Stereophile review/measured performace.

http://www.stereophile.com/content/mark-levinson-no53-reference-monoblock-power-amplifier#kXGk3Vi1RAApjFoi.97

Like I said before, I’ll be the first to get a Class-D once the switching frequency is around 3-5mHz so the filter can do it’s job properly, but at the moment nothing save for the very exclusive $30k Technics SE-R1 with a higher (double) but not high enough switching frequency, then my linear amps will become boat anchors.

Cheers George

What I’ve been trying to get across re the Class-D’s switch noise and it’s associated output filter, trying to eliminate that noise without effecting the audio band.
This is a page by the actual component manufacturer that allows the new mega expensive Technics SE-R1 to double the speed of it’s switching frequency, which in turn allows the filter to do a better job, and be less destructive to the audio band.
They still need to double it again before I’ll dip my feet into Class-D.
http://epc-co.com/epc/GaNTalk/Post/13752

Cheers George

Is there no need to advance in this direction in raising the switching frequency then?? Too many myself included think it is.

Quote from manufacturer of these new transitors, who btw invented the Mosfet power transistor.

" Higher PWM switching frequencies allow for a higher audio bandwidth, and hence higher-frequency output filters. As a side benefit, this higher-frequency output filter allows for smaller output filter components (especially, the Inductors) without compromising the sonic performance.

In addition to offering higher audio bandwidths (which is increasingly important for the new high-definition audio requirements), the increased PWM switching rates also allow for more moderate output filter slopes, which offer more linear performance without introducing higher levels of residual switching noise."

Cheers George

I cannot hear 500kHz

Nobody can hear 500khz, it the filter that has to deal with it and what's left over and the byproducts of it that is the problem.

Read the link and carefully try to absorb it.
http://epc-co.com/epc/GaNTalk/Post/13752

Cheers George

They have Ice modules in them minus the power section. The amps have huge analog toroidal power supplies. And massive caps for reserve power.

This is a huge step in the right direction getting rid of another point of noise (the smp), with the added lift of future higher switching frequency/filters and the benefits it brings, would spell the end of all linear amps. And Srajan's tubes below.

What Srajan Ebaen of 6 Moons said about the H2o M250's

In conclusion, I love these amps for different reasons than my tube amps.  The emotional connection is still stronger with the valves

 Cheers George 

Yes, top manufacturers still use linear power supplies, but main reason is demand from people who, mistakenly, believe that if it has to be heavy to be good.

Sez who???

Cheers George

THD numbers, while appearing to be unusually good, may be partly the result of using too much negative feedback. I’ve never heard this amp, but too much negative feedback and you can end up with a soulless amp.

You’ve got that right, anyone who’s had an amp that’s had feedback level control, knows that too much can lead to worse sound, minium is best if you can keep the bass tight extended. I put them on all my tube amps that I made, to do it on s/s can be dangerous.

Cheers George

3 of the main reasons manufactures choose use smp (switchmode) power supplies.
Size/weight, efficiency, and cost to manufacture.
 
Well designed linear power supplies, are still the supply of choice for performance/noise and reliability. But they are costly and inefficient.

If/when I go to Class-D amps, I would also prefer to have a well designed linear power supply powering it.

Just quickly two that I can think of that use linear supplies for the best result they believe to power their Class-D amps are. Mark Levinson and Rogue Audio, there are many more from the upper end of town.

http://www.stereophile.com/content/mark-levinson-no53-reference-monoblock-power-amplifier#OXQH9C1XSJuv27p5.97

http://www.rogueaudio.com/PDFs/Pharoah.pdf   

Cheers George  

You should do a study to see if class d amp sound quality correlates strongly to switching frequency alone.

I have, done numerous bench/listening tests, and tried to come up with my own cascaded output filters like Belcanto I believe did with their 600ref monos, but doing filters this way has a other set of problems (interactive ringing) if your familiar trying cascaded filters for speaker xovers.
Mark Levinson with their no53 also tried it but that fell a bit foul with a Stereophile review/measurements.

Cheers George

Noise needs to be heard to exist

Not correct, EG: take an opamp for instance, it can oscillate (if not implemented well) at VHF, too high to hear, but it will make a known opamp with smooth sound, sound hard/bright because of the oscillation that you can’t hear.
And if the noise is filtered out afterwards then the opamp is compromised and can sound too bland, better off not having the oscillation to start with in the first place.

Cheers George

no human has ever claimed to hear these affects or even describe what these affects would sound like.

Plenty have with saying, hard sound, soft sound, lacking in harmonic structure, dead gaps between notes (no harmonics) like the amp has been turned off.
There are many that hear these effects, myself also, but like I said before I "could" live with the Belcanto Ref600's, with their in house special filter for the switching frequency, but they were driving an expensive two way with a very benign 8ohm Raven ribbon tweeter load.

Cheers George 

modules and device designs have evolved enormously in the land of class D amplification

I say more of a gradual upwards evolvement, with tweaks and band aid filtering, no real technical breakthroughs.

The only one I know who is stretching out for real progression is Technics with their SE-R1, with the supply finally of newest technology to double the switching frequency, with this latest device from EPC Corporation Inc. Who invented the Mosfet Power Transistor years back.
This is where the real evolvement for Class-D will come from the manufactures of the components, not the manufacturers of the amps.

In a way it’s up to the audiophiles to get them to use this new technology then the price will come down for something like the $30k Technics through demand of those components and other device manufactures copying them.

http://epc-co.com/epc/GaNTalk/Post/13752

http://www.technics.com/us/products/r1/se-r1.html

Cheers George

Theta Prometheus... I believe it is an NCore NC500

Ncore NC1200 class-D module with a linear power supply created by Theta's David Reich.

Cheers George

I read a tip that a portable am/fm radio could be used as a crude detector for any RF radiation emitted by a component.

Yes for smps leakage, should also work not that I tied it for Class-D switching frequency leakage.
Tune down low and try at different frequencies between 500-800khz on the am/band, so it’s off station not getting a station signal just white noise (some portables mute these are no good to use), then switch on the smps/class-d, and go close to it with the radio, and see if you get a change in sound or level.

Cheers George

NCore1200, not on the lower end NC500 module... My bad!!!!

The NC500 is their newest most advanced module not mentioned anywhere on their site, avalible only to selected few, and is in the BelCanto Ref 600 monos, but BelCanto used their own filters instead of what comes with it.

Cheers George

There is about 1% of switching voltage noise on the speaker cable

You need to rethink this.
Look at the switching noise ringing on the test square waves Stereophile show when they don’t use their special Audio Precision’s auxiliary AUX-0025 passive low-pass filter to hide the switching noise ringing from view.

This is what’s on the speaker cable on the $7K Anthem Statement M1 monoblocks, and it more like 20% of the wave form.

Without Audio Precision’s auxiliary AUX-0025 passive low-pass filter
http://www.stereophile.com/images/1212AM1fig02.jpg

With Audio Precision’s auxiliary AUX-0025 passive low-pass filter
http://www.stereophile.com/images/1212AM1fig03.jpg

Cheers George

Sorry your wrong kijanki, the switching frequency to signal ratio follows the signal level in a proportional manner. and that 20% pod SF noise in the links I provided above, the SF noise does not disappear at certain levels of playing, it stays proportional to the level your playing.

And I didn’t ask you about tweeters playing 500kHz, but seeing you mentioned it, ask the poor sod I had to replace both the Wilson 8’s tweeter diaphragms on, because they were blu’ed with heat abuse from this 500kHz noise. They still worked but never sounded quite right, but they did when I replaced them. BTW he won't use a Class-D again, until he's convinced that the SF noise won't harm his tweeters again. 

Cheers George

I’ve seen it on the scope, with Nuforce 9se V3, you need to see it for yourself.
Lower or raise the signal level at the same frequency, then increase or decrease the scopes sensitivity to the same visual appearance, and you’ll see the SF noise remains the same. Forest and trees sunshine.

BTW it was this amp that gradually cooked the WP8’s tweeter voice coils, and the owner (a reviewer) was never abusive with high level, if anything he was anal about playing too loud, he now ones Gryphon Antillions, and has not looked back at Class-D.
Maybe in the future when they can rid this SF noise demon totally without any effects down into the audio band, even he concedes to this after what he went through.

Cheers George