The Truth About Digital (Class D) Amplifiers

[mtrycrafts]

Most notably we have the objective fact. The ASP1000 drops almost a decibel at 20kHz. The ASP500 only drops a quarter of a decibel, and the ASP250 has an even more linear curve.

OK, but can you hear 20kHz in the first place? And, if one could, what is the smallest level difference one would differentiate at 20kHz?
Well, that small difference, JND, at 10kHz is 1dB spl and at 16kHz, it is 3 dB spl. I am sure the researchers couldn't find enough subject to test at 20kHz, but I would say it would be closer to 5 dB spl, with pure tones. Music much more.

So, I seriously doubt it is something to worry about.

 

[silversurfer]

There have also been subjective reports about the mid-range being better with the 1000ASP.

 

[mtrycrafts]

There have also been subjective reports about the mid-range being better with the 1000ASP.

It may be, but so far, from the indications anyhow, it is only a subjective opinion. It would be better if it could be made objective through bias controlled comparisons and specs???

 

[silversurfer]

It may be, but so far, from the indications anyhow, it is only a subjective opinion. It would be better if it could be made objective through bias controlled comparisons and specs???

I absolutely agree.

 

[Sleestack]

First, as a reminder, I do still use the TACT Boz 216/2200 combo in my 5.1 setup. I now use the Bel Canto OneRef.1000s in my 2.2 setup.

After several weeks of listening, I would say that the primary differences between the TACT and Bel/Canto amps are simply power and connectivity. The TACT amps only accept digital sources and the Bel Cantos only accept analog. In my 5.1 setup, I favor the digital chain because it allows me to apply room correction and crossovers, and keep the signal in the digital domain until the PWM conversion in the 2200s.

On the sonic front, both amps are completely transparent with dead silent noise floors. They can be driven to high volumes with absoultely no evidence of distortion. I would recommend either amp depending on power and connectivity needs. I bi-amp each of my speakers in the 5.1 setup, so 400wpc @ 4 ohms is more than enough. In my 2.2 setup, I wanted more power for my corner load subs, which the Bel Cantos definitely provide.

I honestly can't find a criticism for either amp. The versatitlity of the TACT amps and their seamless integration with the TACT preamps make them the perfect choice for a multichannel room-corrected setup, or a setup utilizing multiple external crossovers. I can't think of a better amps for those purposes. The Bel Cantos make a perfect amp for anybody looking for a ton of flawless power. IMO, the can replace any "audiophile" amp at any price and do so at a relatively modest cost.

I did listen to both amps in uncorrected mode. If I were to note any difference, I would say the Bel Cantos have a brighter sound I more typically associate with solid state, whereas the TACT amps may have a slightly smoother sound. Nevertheless, the differences may simply be attributable to level differences resulting from the power differences. Both amps handle their tasks effortlessly and partner perfectly with room correction.

 

[Peter Nielsen]

I did listen to both amps in uncorrected mode. If I were to note any difference, I would say the Bel Cantos have a brighter sound I more typically associate with solid state, whereas the TACT amps may have a slightly smoother sound. Nevertheless, the differences may simply be attributable to level differences resulting from the power differences. Both amps handle their tasks effortlessly and partner perfectly with room correction.

Thanks for the writeup. You confirm what I already guessed. Amps really don't sound that different.

If I understand it correctly, the ASP based amps have one big weakness: The voltage & frequency is hardwired by design. I noticed that 120 volt ASP modules are limited to a 55-65Hz range in mains frequency. This means that an amp bought in the US will be worthless in Europe (and vice versa, I assume). The voltage can be corrected with a transformer, but not the frequency.

Also, buying an ASP based amp today is like buying a high-end computer. In one or two years when a new improved ASP module comes out, the price will drop like when a new computer chip comes out. The old modules will literally drop in value overnight.

Personally, I think TacT amps will hold their value a little bit better, since the TacT technology is not available as a mainstream generic module.

Hypex-based amps is another cost-efficient way if one wants a digital amp that is not frequency-dependent and that can be reconfigured for 120/230V simply by replacing the transformer.

Peter

 

[Peter Nielsen]

Sleestack,

Have you driven either amp to clipping level?

I'm very curious to hear how the two amps compare soundwise when they clip. I bet there's a very noticable audible difference between the amps in this area...

Peter

 

[ar-t]

The response at 20 kHz does drop significantly whne used with low-Z speakers. Trust me: you can hear it. The other ICEpower modules have a similar effect, but to a much less degree.

As the ICEpower modules were created with powered loudspeaker systmes in mind, I am not sure that they intended this particular one for full-range applications. You will note that the stand-alone version of the 1000W module is only useful to 6 kHz (or so).

As for how it compares to the other modules............sonically:

We feel that it does have more "slam" in the bottom, but the midrange does not sound different from the others. We concluded that it is a strong candidate for (sub-) woofer applications, but we have reservations in making one available for full-range applications.

As for this claim:

If I understand it correctly, the ASP based amps have one big weakness: The voltage & frequency is hardwired by design. I noticed that 120 volt ASP modules are limited to a 55-65Hz range in mains frequency. This means that an amp bought in the US will be worthless in Europe (and vice versa, I assume). The voltage can be corrected with a transformer, but not the frequency.

You don't understand it correctly. That is what the design ratings are for 120V operation. The same module is rated for 45-55 Hz at 230 VAC operation.

If you had taken the time to actually look at the complete specs, instead of guessing, you would have seen that can run from anywhere between 90-132 VAC and 190-265 VAC simply by taking out the fuse, changing it to the proper rated one, and inserting it into the corresponding orientation on the PCB.

I hate to point out that the price of any amp drops like a rock once you buy it. Regardless of whatever technology it uses. I doubt anyone buys any current piece of electronics......amp, computer, whatever..........with an eye towards investment.

BTW.......if it makes anyone feel better, we also offer products using Hypex modules. Take your pick.

 

[Peter Nielsen]

If you had taken the time to actually look at the complete specs, instead of guessing, you would have seen that can run from anywhere between 90-132 VAC and 190-265 VAC simply by taking out the fuse, changing it to the proper rated one, and inserting it into the corresponding orientation on the PCB.

Ok, I am not a manufacturer, so I don't have access to the specs...

Why do the manufacturers (like PS Audio et al.) say that the Voltage CANNOT be changed. I have been told that if I buy an ASP-based amp in the US, the voltage CANNOT be changed. Is that just FUD?

Thanks,
Peter

 

[Peter Nielsen]

I hate to point out that the price of any amp drops like a rock once you buy it.

Maybe with digital amps. Solid state amps can keep their value unchanged for a year, and I can prove it:

I bought nine Parasound JC-1s more than a year ago. I have now sold 7 of them. They sell for the exact same amount I paid for them ($1950/each).

http://cgi.audiogon.com/cgi-bin/cl.pl?ampstran&1159791834

Of course this might be a bit exceptional, since Parasound upped the MSRP from $3000 to $3500...

Peter

 

[Sleestack]

Sleestack,

Have you driven either amp to clipping level?

I'm very curious to hear how the two amps compare soundwise when they clip. I bet there's a very noticable audible difference between the amps in this area...

Peter

No I have not. Both amps stay clean at whatever volume I play my system at, however, the Bel Cantos are capable of achieving louder volumes without any gain.

Personally, I much prefer either amp to any solid state or tube offering. I have no indication that the Cantos have any deficiencies and the extra power is very well suited to room correction.

 

[silversurfer]

Ok, I am not a manufacturer, so I don't have access to the specs...

Have you tried here?
http://www.icepower.bang-olufsen.com/sw2013.asp

 

[Peter Nielsen]

Have you tried here:
http://www.icepower.bang-olufsen.com/sw2013.asp

Thanks! That's very useful. I haven't seen that page before.

Peter

 

[silversurfer]

Just came across these relatively inexpensive ICEpower based amps:

http://www.audiocircle.com/circles/index.php?topic=30208.0

 

[Peter Nielsen]

Just came across these relatively inexpensive ICEpower based amps

Yep, that's why I'm very hesitant of buying any high priced ICEpower amps. There seem to be new offerings all the time and the prices come tumbling down...

Those agressively priced monos are going to make the PS Audio Trio a hard sell at $995... http://www.psaudio.com/products/trio_a100.asp

Peter

 

[ar-t]

Why do the manufacturers (like PS Audio et al.) say that the Voltage CANNOT be changed. I have been told that if I buy an ASP-based amp in the US, the voltage CANNOT be changed.

I can not answer for them. Does their perception inspire you to do business with them?

Solid state amps can keep their value unchanged for a year, and I can prove it:

Ever hear of an Orion Blue Book? One year does not a lifetime make.

 

[ar-t]

Just came across these relatively inexpensive ICEpower based amps:

Those obviously use the newer ASC series modules, which are only available in the 100 W (8 ohm rating). That series utilises the SMPS feature of the ASP and its short-circuit protection, but strips away the ability to power "hanger" modules. (Remember my comment about powered loudspeaker systems? The ASP was intended to supply DC power to additional modules, as you would have in a 2- or 3-way speaker.)

Our experience has been there is less of a market for the lower power modules. Much to our chagrin, since I decided that we should try to sell more of them than the higher power units. Low price does not promise more sales.

(Translation: We are overstocked on the 250 W versions, while the 500 W ones are darn near gone. Sounds like time for a factory blow-out sale.)

But in answer to the obvious question that is the back of everyone's mind:

Yes, you can sell an amp with those modules at that price, but not for long if you plan to be in business for the long run.

Or offer anything other than a module shoved in a chassis with the appropriate connectors, and shipped out the factory door.

 

[Peter Nielsen]

I can not answer for them. Does their perception inspire you to do business with them?

Well, PS Audio is very highly regarded...

Ever hear of an Orion Blue Book? One year does not a lifetime make.

No, I haven't heard about that. However, one year is a lifetime for a computer. Digital amps are evolving like computers... Hence, one year can be considered a lifetime for a digital amp (if you want to stay on the leading edge of technology).

Peter

 

[Sleestack]

No, I haven't heard about that. However, one year is a lifetime for a computer. Digital amps are evolving like computers... Hence, one year can be considered a lifetime for a digital amp (if you want to stay on the leading edge of technology).

Peter

I don't think that digital amps are quite like computers given their different goals. IMO, the ultimate goal of an amp is transparency, which has been achieved with current amps. They might become more efficient, more powerful, etc., but on a sonic level, they are as good as anything I have heard, if not better. I might upgrade in the future purely out of whim, but not because of any performance deficiencies.

 

[Peter Nielsen]

I don't think that digital amps are quite like computers given their different goals. IMO, the ultimate goal of an amp is transparency, which has been achieved with current amps. They might become more efficient, more powerful, etc., but on a sonic level, they are as good as anything I have heard, if not better. I might upgrade in the future purely out of whim, but not because of any performance deficiencies.

Ok, let me clarify: What I tried to convey is a metaphor.

Class-D amps are evolving at a rate comparable to computers at the 80286 stage... Clear enough? (Significant breakthroughs are yet to come, and the ASP modules of today will be fossiles of tomorrow -- just like a 286 or 386 computer is a fossile...)

Peter