So what do you think of Class D amp for subwoofers

Bingo Kijanki, I have heard marvellous amplifiers of every class under the Sun. . . and a few more not so marvellous ones as well. I do so adore the open, linear, and harmonically textured sound of my system for the long run, but readily admit that I have been occasionally enraptured listening to sound that is radically different from my more typical target. The task of audio engineers is a daunting one: they are dealing with the complexities of electronic engineering, the vagueries of psycho-acoustics, and the imponderables of human emotions. . . my hat's off to all of them for managing to come up occasionally with something that even vaguely resembles music. Guido

I have H2O monos. I have had them for 7 years. First I had them upgraded to Signature level. The second upgrade came from the ICE people themselves when they improved their ICE 500 A module. The third upgrade, and the most significant, was the add on of Sonicap Platinum bypass caps. Now, these amps are ready for anything.

During those 7 years, I had what some may call a foolhardy belief I could get close to perfection with these amps. No preamp was a decent match. H2O solved that problem by creating the Fire preamp, a perfect match to the H2O, and a big bonus to any amp.

Through trial and error, I learned the amps need fully shielded power cords, and naked speaker cables. Spelz cables proved to be wonderful for these amps. I did a lot better, though, when I replaced them with very thin copper ribbons.

I also learned only non oversampling DACs are appropriate to the class D on the whole, but especially for the H2O. My amp builder took AN DACs and created a full spectrum DAC. The depth is phenomenal. Macro dynamics are tremendous, while micro dynamics add life to players and singers. Bass is fully controlled, but that is a well known attribute. Mids are life-like, highs are fully spread out evenly over the spectrum. This gives a marvelous naturalness to the music. There are no hot spots. No frequency is spotlighted. Every musical instrument is tone correct and I mean all.

Finally, the speaker is of importance. If you have a hot speaker, this system will show your ears no mercy. That is what happened when I had one of my two pairs of Apogee Scintillas fixed with import ribbons of a different design. The sound was unacceptable. The frequency curve reached all over the place. The highs were piercing. Luckily I still had my stock Scintillas.

My point of all this is to let class D owners not to give up trying to better their sound. Persevering paid huge dividends to my amp's over all sound.

Kijanki, I sure don't know where you get your ideas on distortion but Class D amplifiers are not immune to any of the distortions that also affect Class AB or Class A. Unfortunately, using a Class D approach does not design any of them out. Shortchange a little output current during a dynamic burst of music and you will hear a lot of TIM, Class D or not.

Your analysis of 20 KHz, 16 bit resolution, and Class D is wrong. You are confused between the number of bits and the sampling frequency. The number of bits, which is exactly the same thing as the number of possible codes, dictates the maximum dynamic range available in the system while the sampling frequency dictates the maximum bandwidth. The analog equivalents of this is amplifier bandwidth equates to sampling frequency and the maximum voltage out equates to the number of bits in a system. How large in voltage each of those bits represent is dictated by the magnitude of the LSB. The entire reason for using a high frequency clock in the PWM is to include all the bandwidth of audio and reduce the quantization error.

Class D amplifiers can achieve the equivalent of 16 bit resolution if you can reduce the noise level to below 98 dBv on the output within the entire bandwidth of the amplifier. I sure don't see any reason why any well designed Class D amplifier can't do this. That of course doesn't mean they all do it but it certainly is very realistic and possible. This signal to noise ratio means it is measured on the output without the benefit of any external measurement filters. Unfortunately, most of the time Class D amplifiers are not measured in this manner so only the deign engineer knows what it is really capable of producing..

Here is another way to look at it: The human ear has the equivalent dynamic range of around 21 to 22 bits. Within that dynamic range, it can slide a window of 60 dB or approximately 8 to 10 bits or resolution. If a Class D amplifier was incapable of producing the equivalent of 16 bit performance then it is incapable of EVER achieving what the ear can hear. This is simply untrue.

That is a pretty amazing result regarding your little am radio. How close did you have it? Are we talking less than an inch or several feet? Did you try moving it in all three dimensions? Did you have the amplifier playing loud music at the time? Did you try setting the radio next to the speaker cables? If you did all this and you didn’t hear a peep on the radio then I would sure love to see that!

Measuring the signal to noise ratio, or SNR, within a bandpass of 20 Hz to 20 KHz means the signal to noise figure is realistic to what noise you can hear; it is not realistic to what damage the noise can do to the music. Measuring SNR wideband can indicate how much noise intermodulation distortion an amplifier can have and you will hear the effects of that even though the SNR within the audio bandwidth is very good. I guarantee that the 140 db SNR you quoted above was measured with a measurement filter in front of the analyzer. Where did you see this spec? Is it published somewhere? I like to see under what conditions they measured it. I suspect it is measured with an aggressive filter and is probably relative to something other than 1 V out.

Just out of curiosity, what model Class D amplifiers to you have? And what did they cost?

Guidocorona: Your Socrates logic is missing a few logic equations. You can say that and you can say you used logic to achieve it but you would be wrong.

I never said Class D couldn’t sound good or even sound great. All I have been trying to do is explain to some folks why Class D amplifiers have a steeper curve to achieve good sound than Class AB or Class A. But it seems that anyone who owns a Class D amplifier is oblivious to the concept that their amplifier can produce, heaven forbid, unmusical distortions or any distortions that Class AB amplifiers also produce. Furthermore, it seems on this board that anyone who speaks in the least unfavorable manner of Class D is automatically considered hysterical. I have to wonder if these folks are in emotional denial or something.

Short of winning the lottery, I have no real interest in purchasing another amplifier. For now and for the next few years, this Class D amplifier I have will have to suit the purpose of providing power for the subwoofers. When it comes time to upgrade it, I will try a few amplifiers but in my system, not listening to it in some unknown stereo I have never heard before.

I would try a few more audio stores but how can one audition a given amplifier when the entire system is new to my ears? Is what I hear the amplifier or something else? Is the system masking some of the distortion mechanisms in the amplifier so it sounds great? This is why when I walk into an audio store, it is more to discuss what is new in the audio world, see what the store has available, and perhaps gather a few opinions on what I should audition. If the music is playing and it sounds great then I get a bonus, too. Unfortunately, about half the time the sound is worse than I have at home and that can be pretty depressing given I am in the market to upgrade.

Remember, I am a design engineer, so I look at things differently than most audiophiles. I am far more interested in who the designer is, what his/her opinion is on how to achieve good sound, what they did to get there, and how they got there. I try to find out where they put their design emphasis. When I meet someone who is blowing smoke in my face from an out of control ego and trying to sell me something which is obviously a lie, I know none of his/her products are worthy of my listening time. Frankly, I rarely let them know I have a degree in engineering much less that I actually design audio gear. I can learn so much more just playing dumb and letting them talk. There are a lot of honest design engineers out there, please don’t get me wrong. Actually, I believe the proper term is “most”; they are quite honest and deliver what they believe to be an honest product. But there are a few whoppers out there, that is for sure.

Also, to say there is no single test that describes the sound of an amplifier is correct. But it is incorrect to say there are no tests that tell you anything about the sound of an amplifier is completely wrong. It seems that there is a belief that measurements do not tell you how an amplifier can sound but that is not entirely true. One can learn a lot about how an amplifier will sound before you even hook up speakers with nothing more than a good audio analyzer. It is only a matter of knowing where to look, what to test, and how to test it.

Muralman1: I am intrigued by your comments. When you say you “non oversampling DACs are only appropriate” do you mean that oversampling DACs actually make the sound worse? That is, you have an oversampling DAC in front of the Class D power amplifier and the sound is worse than if you used a DAC which did not oversample? If so, I find that very interesting. Also, what do you mean by a “full spectrum DAC”? Spectrum usually implies bandwidth related characteristic -was the bandwidth changed in someway?

As far as I know class D ice power modual was developed by B&O for subwoofer use. I use ice power in a few bass systems where it works great. I have not enjoyed class D running full frequincy but YMMV. Since most all class D use B&O modual which wasent even designed for full range use. They do have problems higher up in frequincy but all amps have some - aspect and if this isnt a problem for owners then its not a problem;)

Thank you Spatialking for agreeing that my quasi classic example of an Aristotelian syllogism contained an intended flaw. In more modern terms, it illustrates a common problem in inductive reasoning.

As for class D 'hysteria', the term being normally associated with excessive and unnatural fears, I have definitely observed such hysteria in these pages. Yet, I suspect you really meant class D zelotry, which instead I still have to notice. having attended this particular audiophilic watering hold for the past 4 or 5 years, I am rather noticing an abating of the aforementioned anti class D hysteria, while the likes of Kijanki, Muralman, and a growing number of others seem to be suggesting that class D amplifiers need be treated individually, like devices of any other class, which inevitably is made of the good, the bad, and the ugly.

The only difference is perhaps that while other types of devices have reached a state of maturity a while ago, and designs seem to be now evolving at a stately rate, some class D designers seem to be on a steep learning curve and are making rapid strides. Case in point is the Bel canto Ref 1000 Mk.2 which I have just reviewed for Positive Feedback. For one thing, it definitely does not yield a stilted bass. See:
http://www.positive-feedback.com/Issue43/bel_canto_ref1000.htm
In case you were asking, no I do not use instruments to perform my admittedly subjective evaluations. . . my ears serve me relatively well and mostly do suffice. G.