Class D at low volume


Hi,

How do class D amps behave at low volume levels?  My question is general rather than related to a particular amp.  I know there are exceptions, but as a rule, SET’s and class A SS excel at low volume.  What about class D?  Is low volume performance of class D predetermined, all else being equal? Do class D amps have a comfort zone?  Do they distort more at low volume or is it uniform throughout?  For the purpose of this question I am only referring to analog input amps and not the ones that take in PCM (e.g. NAD M2).

The second part of my question is as follows.  I’m interested in some higher end commercial class D amps from the likes of lab.gruppen, powersoft, mc2, XTA, etc. due to their network-ability as in, I can control them, DSP them, and stream digital, all via RJ45, at the same time dispensing with all the extra boxes and cables.  But, they are all of very high power from 100‘s to 1000‘s of watts.  Does this mean that in a domestic setting at low volume they operate much closer to their noise floor or is this different with class D?

Thanks
serge_s
Good question. Since I built my Class D Audio amp, I haven't really done any low volume level listening, as all my listening sessions tend to be at my comfort zone, or my systems' comfort zone, and at, or near, concert hall levels.

I can't help you in any technical manner, but I don't see why they wouldn't perform well at low volume level. I have been very impressed by the amount, and quality, of detail, and intensity of each note, the Class D amps provide.

There has been no noticeable "noise floor", just the much-cliched "black background", all good components seem to have.

Class D Audio offers high quality kits, or complete amps, at what are extrordinarily low prices, all made in the USA using high quality parts. If you are curious, try one of their amps out. At their low prices, you have very little to lose.

At this point, I'd better add the usual disclaimer, of "having no affiliation with Class D Audio" in any way.

Regards,
Dan
I cannot speak of very high power class D, but my Rowland 102 producing 150W with my 6 ohm speakers is wonderful at low volume. In spite of hearing curve I don't feel any lack of lows or highs, resolution is there and image is even better than one at higher volumes (that might be related to some echo in my room). It behaves much better at low volume than my 50W Cambridge integrated, I had before.

Also, I hear much less noise/hiss while bringing my ear to the tweeter, in spite of higher power.
Mine work great at lower volume.

They are so clean and effortless and totally non fatiguing. I often do not realize how high the volume is until someone speaks in the room.

They are playing at low volume currently as I type on my triangle speakers which themselves are fantastic lower volume speakers.

👍👍
I can report that with class D amps that I have loved, Rowland M925 and M312, Merrill Veritas, and Bel Canto REF1000M, low volume playing is as good as medium and high volume.... Clean, effortless, musical... Just like any good amp of any other topology.

Would this behavior apply to all class D amps? Who knows.... The induction step is one dangerous thing in logic.

G.
My peachtree 220 plays well at low volumes. I listen at very low volumes for long periods late at night. The bass is still there, good imaging, good detail...
I can echo what is said above by Mapman and Guido as relates to my Ncore NC1200 amps by Acoustic Imagery. Listening at low levels now as it is getting late in the EST zone.
i have wyred for sound 1000 watt class d amp , that i purchased due to price point . took out my wyetech ruby set 36 watts out of system ,the class d amps incredible , audiophiles here every day are stunned , as well as myself bass , resolution , detail , soundstage , truly amazing considering the $20000 price difference
Pavpet, happily replacing an expensive SET with a much more modest cost Class D amp is certainly saying a lot. I've heard both sounding their best and frankly Class D technology is a game changer for me when it comes to considering tube amplification. I just like good sound when I hear it no matter how it is made.
I caution against comparing tube, linear solid state, and switching amplifiers. Each has its own set of virtues that the others can't quite match and that class D is simply a third choice in amplification. On the other hand reading about the Bob Carver challenge gives one pause.

Assuming that everything in the chain contributes, in my experience low volume dynamics is more a function of the speaker design. Most of the contributors above have evolved with class D. For me beginning with the PS Audio HCA-2 a few others then the NuForce SE class D has been the most responsive to power and cabling. The nCore 400s are another step forward that I can only describe as more of everything which would make the NC1200 yet another level that is better described by Larry Greenhill in his Theta Prometheus review of the Hypex 1200s ability to handle high rail voltage.
You guys already know how I feel about Class D...you won't find another owner out there happier than me with the Peachtree Grand Integrated X-1. And for people who not only need to listen at lower volumes, but do so in smaller environments, the lower heat output of Class D sure is welcome when you're not sitting that far from the device. I'm in Arizona - last thing I need in July is to have the AC fighting my amplifier.
I've been into high end audio since 1970,and these class d amps wyred for sound and nuprime/nuforce are killing my very expensive WYETECH ruby
Serge,

I agree with the previous repliers that the class D amps I've used perform very well at low to high volumes. In fact, this was one of the characteristics I was pleasantly surprised with when I installed my first class D amp in my system, a ClassD Audio SDS440-CS amp; I quickly noticed that the full frequency range, from deepest bass to highest highs and all frequencies in between, was presented in proper perspective no matter what level I played back at. This was a revelation to me. My prior amp was a class A/B Aragon 4004 that outputted about the same power (400 w into 4ohm speakers) but was many times larger, heavier and hotter. I would typically play music at high volume, with the Aragon, to attain what I considered to be the proper frequency response from bass through treble. I quickly realized the class D amp was different; the frequency response was well balanced at low volumes up to extremely high volumes. My wife was actually the first to notice I was playing my music back at a somewhat lower volume with the new ClassD Audio amp.

This issue reminds me of the 'Loudness Controls' found on receivers back in the 1970's and 1980's, which boosted the bass and treble when listening at lower volume levels to compensate for their perceived absence at lower listening levels. In my opinion, the class D amps that I've heard have no need for loudness controls since they maintain a proper frequency range perspective no matter what volume level is chosen. I'm not suggesting these amps boost the bass and treble, just that they get it right somehow.

I am not an audio engineer but I have a theory why class D amps seem to have such good frequency response that maintains proper perspective at various volume levels:

It's my understanding that class D power conversion modules typically use high levels of global feedback. The input signal is constantly being compared to the output signal (thousands of times per second) prior to the output signal being amplified. The output signal is only sent to be amplified once it matches the input signal and any necessary adjustments have been made. This high level of global feedback, which designers of more traditional amp topologies typically try to avoid at all costs, is a mainstay of class D amp design. My theory is that this high reliance on high levels of global feedback is responsible for class D amps' astounding neutrality and their performing so close to the ideal of 'a straight wire with gain'. Also, my theory is that this design results in excellent frequency response at all volume levels.

As I've stated I have no technical training on amplifier design or electronics. The above is based on personal reading about class D amplification combined with any small amount of rational thought and common sense I may possess. I may have this entirely wrong, however, and would welcome comments and thoughts on my theory from those with more technical knowledge on class D amps than myself.

Regardless of my theory, I do own 3 class D amps (D-Sonic M600-M mono-blocs, a stereo ClassD audio SDS-440CS and a stereo Emerald Physics EP100.2SE operated in bridged mono configuration) and can confirm that all perform very well at all volume levels as unanimously reported from others thus far.

I would suggest you won't be disappointed, especially considering many class D amp sellers offer in-home trial periods to ensure your satisfaction.

Good luck,
Tim
Tim very well spoken , at low volumes is like having a loudness control , as they seem to fit in any situation there called for , i have very expensive monoblocks in the SET WYETECH LAB RUBIES ZERO FEEDBACK , 36 RMS , AND NOW PICKED UP A PAIR OF WYRED FOR SOUND 1000 WATT MONOBLOCKS , AND THE BASS AND DETAIL ON THE CLASS D AMPS GIVES THE SET AMPS OR PUSH PULL AMPS A HUGE RUN FOR THE MONEY , I WISH IT WERENT SO , BUT HEARING IS BELIEVING
Thanks to everyone who answered. It sounds like class D could be the way to go. I think I can answer the second part of my question: 1000-watt pro amps will be too noisy on Klipsch Forte II at low volume no matter the topology.
Thanks Noble100. Speaking of feedback, what do you think of Benchmark AHB2.
Thanks Pavpet,

"I've been into high end audio since 1970,and these class d amps wyred for sound and nuprime/nuforce are killing my very expensive WYETECH ruby"

How long have you been listening to wyred? Where do wyetechs fail in comparison?
Listening to wyred for the last month , difference between wyred and wytech ruby mono blocks , wyred $2995 , ruby $25000 , can't pick out the differences they are that close ,doing A B tests for 3 weeks nothing stands out in either one , will keep trying
Where /how does Bel Canto class d fit in the pecking order.
Efficiency done well is always a good thing for sound quality I would say, including at lower volumes. Class D amps are the modern way to introduce some efficiency into a system with out the size bulk and other idiosyncrasies that might go with full range high efficiency speakers


Schubert,

Bel Canto has been doing Class D for a number of years so there is significant variability there I would say with newer models capable of outperforming older in general.

The earlier generation Bel Canto Class Ds ref500k, ref1000, not later m models, were stock older generation Icepower modules in a nice box. Prices reflect that.

ref1000m and ref500m added custom power and input sections to improve performance and match better to tube pre-amps.

ref500m uses a newer gen Icepower than 1000m last I checked so there could be some sonic differences there as reported.

latest BEl Canto products probably use newer IcePower mocules and I would assume implement design enhancements learned over time as well. I would expect top notch performance and that is what I read.

So Bel Canto crossed the threshold of top notch performance out of their Class D amps a few years back already I would say based on my experience with the hard to fault ref1000m however I have no doubt the technology is relative new still (compared to the others) and continues to improve technically in regards to bandwidth, noise level controls, etc., to whatever extent it may matter practically. The sky is the limit with this technology over time I believe and may already have crossed the threshold needed for top notch performance in "high end" systems practically. All signs seem to point to that.

I'm considering going to a compact integrated amp on my second system and the BC Class D based integrateds are on my shortlist there currently along with Wyred and Rogue. I am pretty sure I will go Class D only for an integrated as well at this point. It does not make sense to me to do otherwise at this point. Tube amps and monster sized Class A/B amps are becoming increasingly unnecessary to me as a result of the performance and value proposition with Class D.

Although you live in Minnesota right? You might want to go with an amp that wastes power and throws off some heat especially in winter. Kill two birds with one stone. I'm only half joking. Portable heaters are not expensive though I suppose.
Thanks for all the Info map, I'm bone tried of tube amps with their endless problems.
Mentioned Bel Canto amps are the best at any volume level.
My only caveat in recommending Class D amps over others currently might be in regards to the very highest frequencies, tne ones over 12Khz or so that we perceive as "air" in teh sound. I am 50+ and used to hear fine up to 20khz but now I am more limted, as are most people as they age. So I am not a good one to be able to compare how various amps might perform at the highest frwequencies. If one looks at Class D amp measurements, the highest audible frequencies is the final frontier for the technology to conquer on paper. In practice though I do not hear anything to be audibly deficient or missing though I suspect the latest and greatest Class D technology to have the technical edge from a pure bandwidth perspective. Noise control as well as mentioned. To the extent either might matter in practice that is. I have never done a focused A/B comparison on say how well teh best Class D reproduces things like cymbals and air for example compared to others, but I would expect it to be a reasonable competition as best I can tell.

When I was young and heard clearly up to 20khz, I also tended to be very sensitive to anything that was not going on well at teh higher frequencies.

It would be interesting to do a study of amp preferences based on age factor.
It's my understanding that class D power conversion modules typically use high levels of global feedback. The input signal is constantly being compared to the output signal (thousands of times per second) prior to the output signal being amplified. The output signal is only sent to be amplified once it matches the input signal and any necessary adjustments have been made. This high level of global feedback, which designers of more traditional amp topologies typically try to avoid at all costs, is a mainstay of class D amp design. My theory is that this high reliance on high levels of global feedback is responsible for class D amps' astounding neutrality and their performing so close to the ideal of 'a straight wire with gain'. Also, my theory is that this design results in excellent frequency response at all volume levels.

As I've stated I have no technical training on amplifier design or electronics. The above is based on personal reading about class D amplification combined with any small amount of rational thought and common sense I may possess. I may have this entirely wrong, however, and would welcome comments and thoughts on my theory from those with more technical knowledge on class D amps than myself.
while it is true that class-D amps use feedback to make them work & while you are right in stating that without global negative feedback a class-D power would not work, I don't think it is correct to correlate the use of global negative feedback to a class-D power amp's sonic quality.
The way class-D architecture was invented/designed/formulated, global negative feedback is part of its entity. So, just because you read global negative feedback you shouldn't relate it in the same way as you would to GNFB in a class-A, AB power amp. The class-D architecture needs GNFB while class-A, AB architectures have topologies that can do with little or no GNFB.
The class-D power amp is a continuous-time, discrete-voltage pulse width modulated system. The 1st gen of class-D power amps used (& still use) analog/linear power supplies (like the type you see in class-A, AB amps). And, now I'm observing that the next gen of class-D power amps are using switch-mode power supplies (which are themselves class-D power supplies). I think the audio SMPS has finally developed to a point where it is has a low enough noise floor & can handle large currents in a compact size.

Sonic qualities of a class-D power amp have to do with
* power supply design
* noise attenuation at the final output (the amp binding posts) - correct choice of filter
* managing the switching noise in the power output transistors i.e. reducing the switching noise impact on the analog circuits that form the overall class-D power amp
* routing of noisy & quiet signals

just to name a few items.
Class D (PWM) can be easily constructed without negative feedback at all. NGF improves linearity, bandwidth and output impedance like in any other class of amplification.

While global negative feedback in class A, AB is going over many stages of amplification, that create delay (thus producing TIM distortions), class D amplifiers have only one stage - a modulator that drive output switches (Mosfets). This modulator converts voltage to duty cycle of the output frequency. In simplest case it can be created using ramp generator and comparator but current modules resemble more of Delta-Sigma A/D converters. In short one analog quantity (voltage) is converted to another analog quantity (duty cycle) to end up with voltage again by obtaining average value of duty cycle. It is usually done by common mode choke and capacitors (Zobel Network), leaving about 1% of switching noise on the speaker wires. Amount of output power is controlled simply by setting amplitude of switched DC voltage. Frequency of this remaining noise is too low for the speaker cables to become antenna for electromagnetic coupling, but direct capacitive coupling is still possible.

As for the type of power supply - first generations of class D amp also has SMPS power supplies REF1000 being one example and my Rowland 102 being another. Ice power modules were available from the start in two different varieties - with or without SMPS. These switching supplies used to operate around 50-100kHz to preserve efficiency, but newer designed by Rowland run at 1MHz to make filtering easier (very difficult to design). I would say that good efficiency, very quiet SMPS operating at 1MHz able to deliver close to 1kW is a masterpiece.

One advantage of SMPS powered amplifier is often ability to operate at universal voltage and to tolerate any amount of DC. In fact my amplifier can be supplied by DC only up to 400V. Another advantage is regulation. SMPS have line and load regulation. Amplifier with SMPS keeps composure during power peaks since voltage does not sag, like it often happens in linear power supplies.
I think the audio SMPS has finally developed to a point where it is has a low enough noise floor & can handle large currents in a compact size.
The Acoustic Imagery Atsahs use the Hypex/Ncore SMPS 1200 switch mode power supply and in my system they sound at least as good as similar powered, high quality solid state, Class A and Class A/B amps I have owned. They are dead nuts quiet and I notice absolutely no listener fatigue. When I listen, I sometimes wonder why some are trying to use linear supplies with the NC1200 amp module, when it sounds this good with the stock SMPS.
Kijanki your right on the money,the Tim distortions can be very can be very fatiguing without noticing it
03-03-15: Kijanki
Class D (PWM) can be easily constructed without negative feedback at all.
I wasn't aware of this. how does the PWM system know that it's tracking the input if there is no feedback? Can you please point me to some references?
but current modules resemble more of Delta-Sigma A/D converters.
so, in current class-D modules, they noise shape the input music signal to move the noise out of band & the resulting pulse train from the delta-sigma block is used to drive the power switches? I suppose that delta-sigma technology makes sense for audio because the ear is very sensitive to distortion & noise? what frequency is the delta-sigma clocked at - also 1MHz like the new gen SMPSs? thanks.
03-04-15: Mitch2
I think the audio SMPS has finally developed to a point where it is has a low enough noise floor & can handle large currents in a compact size.
The Acoustic Imagery Atsahs use the Hypex/Ncore SMPS 1200 switch mode power supply and in my system they sound at least as good as similar powered, high quality solid state, Class A and Class A/B amps I have owned. They are dead nuts quiet and I notice absolutely no listener fatigue. When I listen, I sometimes wonder why some are trying to use linear supplies with the NC1200 amp module, when it sounds this good with the stock SMPS.
Someone i talked to last year about class-D amps & this someone I have some respect for informed me that the best part of the Hypex/NCore modules was their SMPS.... ;-)
SMPS have line and load regulation. Amplifier with SMPS keeps composure during power peaks since voltage does not sag, like it often happens in linear power supplies.
linear power supplies have line & load regulation as well, don't they? one could argue that it might be easier to design better line & load reg for SMPS compared to linear power supplies but i believe that a good linear power supply can also have very good line & load reg. I think a few such supplies are available for Empirical Audio gear from a Paul XXX (I'm forgetting his name) & I also see a good linear power supply in Sanders Magtech & ESL power amps.
Yes, traditionally the manuf of class-A, AB amps have not bothered to put regulated supplies hence the poor line & load reg.
Bombaywalla, Linear power supplies have regulation in preamps, DACs etc. but MOST of power amps are unregulated because of the amount of heat dissipated in power supply (and loss of efficiency).

AFAIK older REF1000 and newer REF1000M use the same module, but REF1000M has additional separate power factor correction module.

Look at fig. 2 showing how PWM signal can be obtained by just using linear ramp. Icepower modulator uses sinewave, has two feedbacks etc. - but only for improvements.
http://en.wikipedia.org/wiki/Pulse-width_modulation

One limiting factor in class D is bandwidth. Latest Rowland class AB amps have bandwidth of 350kHz while newest class D model 925 50kHz. My small 102 extends to 60kHz. It is limited by the speed of Mosfets currently available especially high current devices, but it is improving every single year. We definitely cannot hear 350kHz but wide bandwidth prevents phase shift thus preserving harmonics within audible band. My amplifier with bandwidth of 60kHz shifts phase of the 20kHz signal by 20 degree.

The difference in sound, with class D, I observed is that sound is more immediate, faster but at the same time there is less of brightness in high frequencies. Cymbals sound less "splashy" but more brassy with more body. Perhaps it is related to lower TIM distortions or it is just the nature of the beast. It is definitely different but I like it.
Serge,

You asked:

"Thanks Noble100. Speaking of feedback, what do you think of Benchmark AHB2."

Sorry, I've never listened to the Benchmark AHB2 or read any reviews on it yet. I've read very positive reviews on Benchmark DACs, however, and knew they recently came out with a couple of new class D amp products. If I were to venture a guess, I'd bet that the obvious care and attention to detail they devote to their high quality DACs is likely to also be devoted to their amps.

Mapman,

I've read your comments about class D, on this thread and several others, and typically find your impressions on this evolving technology closely mirror my own. I think that 2 independent users of class D amps having such similar impressions of their high quality performance, among other benefits, speaks volumes about the excellent high-end bargains these amps actually are. It seems like we're both now drinking the class D Kool-Aid.... but only because it's delicious.

Bombaywalla and Kijanki,

Thank you both for explaining things in more detail.

Bombaywalla, you stated:

"The way class-D architecture was invented/designed/formulated, global negative feedback is part of its entity. So, just because you read global negative feedback you shouldn't relate it in the same way as you would to GNFB in a class-A, AB power amp. The class-D architecture needs GNFB while class-A, AB architectures have topologies that can do with little or no GNFB."

I realize that many traditional amp designers have considered the use of GNFB in their amps to be something to be avoided since the early tube designs, believing having zero feedback improved sound quality. Solid-state amp designers seemingly just adopted this low/or no GNFB principle in their next generation class A and A/B amps.

I also realize class D amp designers have taken a radically different approach, embracing GNFB and making it an integral circuit within the amp to lower noise and distortion levels as well as to ensure the input signal faithfully matches the outputted signal.

In my visits to various hi-end audio shops over the years, I've listened to many systems powered by tube, class A and A/B amps (with zero and low GNFB design) that sounded excellent. However, most of these amps exceeded my budget by a large amount.

From my layman's perspective, good class D amps that utilize high levels of GNFB represent a great alternative that is more cost effective and energy efficient means of achieving excellent sound.

I'm not technically savy enough to know what the main reason is for my class D amps' excellent performance. I just know they are lightweight, small in size, sip electricity, run cool and sound great.

But I think Paypet's comment probably drives the point home the best:

"Listening to wyred for the last month , difference between wyred and wytech ruby mono blocks , wyred $2995 , ruby $25000 , can't pick out the differences they are that close ,doing A B tests for 3 weeks nothing stands out in either one , will keep trying."

That is a very honest and powerful testimonial.

I apologize for getting a bit off topic from Serge's original post question and am now stepping off my class D soapbox.

Tim
03-04-15: Kijanki
Bombaywalla, Linear power supplies have regulation in preamps, DACs etc. but MOST of power amps are unregulated because of the amount of heat dissipated in power supply (and loss of efficiency).
agree. There might a small change happening here - Sanders Sound Systems Magtech amps have a regulated power supply (& I believe Roger Sanders has applied for a patent for that?).

Look at fig. 2 showing how PWM signal can be obtained by just using linear ramp. Icepower modulator uses sinewave, has two feedbacks etc. - but only for improvements.
http://en.wikipedia.org/wiki/Pulse-width_modulation
thanks for this reference, Kijanki I'm quite familiar with class-D PWM using a ramp waveform.
My question was using delta-sigma instead. There might be some info on that same page you sent the link for. I'll read up.

Also had a question re. how class-D PWM can be designed without feedback like you wrote in your initial post. Got any references that I can read?

My amplifier with bandwidth of 60kHz shifts phase of the 20kHz signal by 20 degree.
agree! The "funny" thing here is that I wrote something very similar in another thread but had Almarg state a contrary view stating that it wouldn't be such a big deal given that the hi freq energy is much less at these frequencies. Perhaps that is true - it's true that the there is generally less energy at the high frequencies. So, even tho' your amp produces a 20 deg phase shift at 20KHz, it might matter very little(?).
What I wrote in that thread specifically was
....This also means that since the ARC Ref 150 bandwidth is just 3X (rather than 8X or 10X) the music bandwidth (of 20KHz) one can expect to hear the amp impart its own phase shift onto the higher frequencies of the music. This can manifest itself in a few ways - the highs could sound rolled-off or they could sound warmer or there could be less sparkle/shimmer compared to an amp of higher bandwidth.
.
Almarg's comments to my post:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1423113432&openflup&50&4#50
Went to class D 12 years ago when replaced my Bryston 3B-ST with Sunfire 300(class T which is same as D) and never looked back.
Bombaywalla, fig. 2 shows exactly how it can be done. For
any input voltage corresponding duty cycle is created.
Feedback would only improve performance. Modulator itself
might be not 100% linear but most likely linearity error is
created by the Mosfet switches. Their positive and negative
slew rates are different and vary a bit with the load
(creating timing errors). Negative feedback improves timing
but also lowers output impedance increased by the presence
of common mode choke. Early D class amps (tripath) had this
choke outside of the feedback and had loading problems with
many speakers. Icepower uses two different feedbacks. One
is from the output of modulator (improving timing), the
other from the speaker output. At least that's what I
remember from Karsten Nielsen doctorate.

Icepower uses single supply. Speaker (thru Zobel network)
is placed in the bridge made of 4 N-channel Mosfets. Bridge
is connected to GND and +Vs. At any given moment speaker is
always connected between +Vs and GND only direction changes.
Mosfets are turned on in pairs diagonally. At 50% duty
cycle average, filtered voltage on the speaker is zero. Half
of supply voltage is always present on the speaker's
terminals and the output cannot be bridged. Hypex used only
two Mosfets switching speaker between GND and +Vs or -Vs.
This allows output to be bridged.

As for the phase shift - 20 deg is a substantial phase shift
but I have no idea how much it (summing of harmonics) is
audible. Obviously Jeff Rowland wants no phase shift,
extending bandwidth to 350kHz.

I've read few times people saying "I know that class D
requires a lot of negative feedback" Now I hear that it
cannot even operate without feedback. How do they know
that??? If anything, class D requires less feedback since
voltage-duty cycle conversion seems to be more linear than
nonlinear bipolar transistors in class AB output stage.

SACD is an example of class D without any feedback.
Incoming 2.8MHz train of pulses is averaged and becomes a
sound.
Tim, GNFB serves the same role in class D as it does in class AB - reduces distortions, widens bandwidth, reduces output impedance. It is not necessary for operation in general but particular circuit can be designed to depend on it.

Since even shallow 20dB of GNFB will improve everything tenfold it is very tempting to use it. It can be done without negative effect if certain rules are obeyed but then GNFB will be shallow. Designer has to start with good design and quality components to start with and not to fix everything with GNFB.

As for new Benchmark amp - it is class AB with SMPS supply.
http://www.enjoythemusic.com/magazine/equipment/1214/Benchmark_Media_AHB2_Stereo_Power_Amplifier_Review.htm

Pavpet, yes TIM distortion can be fatiguing. It is basically an overshoot, in time domain, of the rapidly changing signal. It won't show with any THD or IMD measuring. In freqeuncy domain it translates to very audible odd order harmonics that our hearing is sensitive to. It makes sound bright. In extreme cases (perhaps some SS amps in 70s) overshoot was so big that it could choke output transistors that remained choked for a while (charge trapped at the junction) creating short gaps in music. These gaps were not audible, since our brain compensates for that, but made listeners very tired.
lots of great thought in this forum discussing class d amplifiers, being an audiophile since 1970 , and owning very expensive gear , its nice to purchase a product at a very very resonable price , and make magic , the wyetech ruby monoblocks list for approx $25000, plus ive installed 1942 rca 211 radiotron tubes , ( took out stock tubes as well as input tubes)AT an additional $3300 , plus upgraded power cords , but thats the audiophile journey , this i know , but now and then its nice to get a breath of fresh air ,without getting a second mortgage. guys thanks for all your input very much appreciated
Tim: thanks for getting off topic. This thread is educational for me and hopefully for many others as well.

Thanks for your comments folks! Please keep the discussion going.
Serge,

I was looking at your initial thread posting again and you stated you're considering Lab.gruppen, Powersoft, XTL and others. These are pro amps used for large venues and not intended for home audio.

I apologize that I didn't read your original post closely enough. However, all of my replies, as well as most replies from others, were based on the assumption you were looking for an amp for your home audio system.

I've never used pro amps and have no useful knowledge about them. The info and impressions about class D amps was based solely on my experiences and knowledge of home audio class D amps and may not be applicable to the pro audio class D amps you mentioned.

I think you need to clarify exactly what purpose these amps are intended for.

Audiogon is a site devoted to home audio, not pro audio environments that are used in clubs, concert halls and auditoriums.

If you are interested in pro audio amps, I would suggest posting your question on a forum devoted to such.

All of my replies, and I think most if not all of the other replies on this thread, were given from the perspective of home audio and therefore should be disregarded.

Sorry for the confusion,
Tim

When I want a nice listening session, the gear is warmed up already but not my ears.
I like to listen at a lower level for a little while as my ears get acclimated (warmed up too I suppose :) )

I`ve been noticing that I`m listening much longer at the lower level before I actually come to realize it...and the remote is sitting right next to me ! This Class D Audio 470 sounds great across the board no matter what volume and that`s a first for me !!
Been traveling w/o computer. Upon return I have found this to be a very interesting and educational thread! Thanks to everyone.
Performance at low volume is more determined by the sensitivity of the speakers than the design of the amplifier. Having said that, class-D performs fine at low volume, no better or worse on average than other types of solid state amplification.
I have tried many solid state and tube amps and was never able to achieve good low level dynamics until I got a class d sds 470c. In fact I find that I do not listen nearly as loud as I used to.
Tim, my comment on getting off topic was tongue-in-cheek in reply to your comment. This thread is educational and I appreciate yours and others contribution.

Re my looking into pro amps: It is for home use. The ones I listed are of interest to me due to their ability to accept digital input from PC via RJ45. Since I started the tread I came to conclusion that at low volume a thousand watt amp will operate too close to its noise floor and will be unfit for my purposes.

Thanks
Serge,

Okay, thanks for clarifying.

I also agree with Chrshanl37 that class D amps seem to perform better at low volumes than other types of amps. My first class D amp was from the same company as his, ClassD Audio, but mine was an SDS-440-CS model. My current D-Sonic M3-600M mono-block and Emerald Physics EP100.2SE stereo class D amps both also posses this same quality at low volumes.

My previous amp was an Aragon 4004 class A/B amp that was very large and weighed 85 lbs. The much smaller and lighter ClassD Audio 440 was much better at low volumes while still delivering 440 watts (the Aragon was 400watts) into my 4 ohm speakers. I tended to play the Aragon at a much higher volume than the 440 to achieve what I considered a proper frequency response over the total audible range.

Good luck with your search,
Tim
at low listening levels CLASS D AMPS , sound so good , as the s/n is very very very good , compared to class A/B AMPS , SO YOU PICK UP TONS OF MICRO DETAIL THAT GIVES YOU GOOSEBUMPS

LOW NOISE FLOOR NOW VERY VERY BIG, AND HAS BEEN FOR ALONG TIME , NOW ITS BEING REDISCOVERED AS AMPS ARE BECOMMING REAL REAL GOOD