Class D is just Dandy!

Does anyone have compared the job 225 vs any class d amp? 

Little known factoid.

AES17 brick wall filters allow Class D Amps to report specifications IGNORING all the switching noise above 20KHz!!!! And there is a LOT of noise....

Shadorne,

That's not really a factoid so much as an operating principle.

You make it sound as if the specifications are illegitimate, they aren't. The filter removes the noise you are talking about, so that the noise is on the inside, but not the outside (mostly).

Sure, if you measure any random point inside the filter, you can find horrible looking signals with little resemblance to audio. True could be said of any DAC though. :)

Best,


E

shadorne6,590 posts01-28-2018 8:06amLittle known factoid.

AES17 brick wall filters allow Class D Amps to report specifications IGNORING all the switching noise above 20KHz!!!! And there is a LOT of noise....

Stereophile do similar now testing Class-D as not to upset readers with the noise on the graphs and to keep the manufacturers happy in case they may advertise. 

They use a very low power handling Audio Precision's auxiliary AUX-0025 passive low-pass filter between the Class-D's speaker output and the test equipment, which eliminates noise above 200kHz.

On figure 3 you can see the switching noise of the 1khz test sine wave, it will be far greater if they showed with a 10khz sine wave.

https://www.stereophile.com/images/218PSM700fig03.jpg
Fig.3 PS Audio Stellar M700, small-signal 1kHz waveform into 8 ohms without AP AUX-0025 low-pass filter.

If this noise was on test waves of the audio band like this on a linear amplifier, any tech would say it's faulty.


Cheers George   

I must say that for any amplifier, the PS Audio Stellar's measure poorly.

Most Class D amps I know of do considerably better. I'm more than a little surprised PS Audio put that out there.