Class D at low volume

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

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

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

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