Class D Technology

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?  

Showing 50 responses by georgehifi

Is the S500 made by Red Dragon?
It maybe assembled by them, but it sure looks like the modules come from here. As do the Rowland Continum S2

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

Cheers George
Try to find any of these module numbers on the TI website, especially the last one that drives the analogue speaker, I couldn't.
Someone once told me never ever get anything from these guys.

Cheers George
Bel-Canto Ref 600 mono’s as the newest and most complete.
They really respond to tuning with power cords! They are green, run cool, but perhaps as important they are much easer to move around. Are they the last word in amps? not yet.. but getting much better day by day.
+1 They have sounded the best Class-D to me so far, but they have modded the filters of the newest Hypex modules to do it.

As you said "are they the last word not yet", and I agree, as for me to have liked them, they had to be driving a very benign 6ohm load of a very expensive Raven Ribbon to get me to say this. Even then with long term listening they were still a bit too "cold/analytical" sounding in the upper range.

Cheers George
Mapman, I'm glad that you enjoy your Ice Modules. The KEF LS50 was just released in an active version. The woofer is powered by Class D and the tweeter is powered by Class AB. Does this mean that there is a problem with Class D higher frequencies to some ears...or is it just an issue with procurement budget and not being able to purchase the better Class D modules? I don't have those answers but it is food for thought.

Kef know what's better for the upper range with using an A/B amp for it, otherwise they would have used another smaller Class-D for it as well, instead of just for the bass, and it would have cost less to manufacture, and been "greener", then they could have called it Kef LS50"G" active.

Cheers George 
(reduced price,electricity consumption,heat, size and weight)

Take the "green" thing out of it  has nothing to do with sound quality.

Audiopiles have never been "green" let face it those that keep on about the "green thing"  are a bit hypocritical. It's a wonder we aren't dead just listening to our "non green" audio.
I bet the greenies that spruik the "class d green thing" ignore the rest of the toxic waste dump inside their other audio equipment.
the energy tube and s/s use
before vinyl it was bakalite
then vinyl
Boron cantilevers
Nickle inside tubes
Toxic fluid in capacitors
Beryllium dome drivers
ect ect  ect  

Cheers George
"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?"
That is the debate, my answer is no, not yet, (except in the bass & upper bass). And it’s not because of the power, but more the damping factor (low impedance output) which some say is aided by of gobs of feedback.

Cheers George
Kijanki, I don't think that anybody is doubting that your amplifier sounds brilliant to you. At the same time, I think it's okay for others to be less satisfied about what they hear. Don't get me wrong. Class D is the future and there are a lot of audiophiles sitting on the sidelines, waiting for the technology to mature.
+1, and the only way is to speak up and get it done. So far Technics is leading the way.

Cheers George 
You originated this thread pretending you want to learn about class D, while knowing you hate it.
I will remember your login and will be careful to answer your posts next time.
Maybe it's some that are so pro Class-D as it stands, and can't/refuse to see that it's maybe it's not become of age yet.
If they can concede that Technics with their SE-R1 are showing the way in the area of switching noise frequency development, maybe then there'll be an even faster development in that area by other class-d manufacturers demanding to have those components to make it happen. 

Cheers George  
That is trolling
Only in your mind, because you refuse to accept that the higher switching frequency has yet to be realized, and you can't hear anything wrong with it where it is at the present.
Even though companies like Technics are showing the way and striving for higher frequencies, with their very expensive SE-R1.

And as far as not giving any positive post go, I said they have a bass control that can't be equaled, and I'll be the first to get the newer generation of higher switching frequency ones, when they evolve which will fix the problems that many hear in the upper mid and highs, and you obviousely can't.

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
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
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

With Audio Precision’s auxiliary AUX-0025 passive low-pass filter

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
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
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
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.

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 
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
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

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.   

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
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
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 
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.

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
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.

Cheers George
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.

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
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.

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 
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
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.
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
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
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
I understand your just protecting your JR120 investment, that "if" you had the knowledge you could have built for 1/8th of the price.

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
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

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

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
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  

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
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
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 
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.

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
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

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.
When that day comes we’ll all be using them and our heavy, hungry, hot tubes and SS, will become boat anchors.

Cheers George
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
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 

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