When someone tells you it's a $40,000 amp, does it sound better?

not really, please try to hookup the oscilloscope to the class-D amp output while driving speakers at moderate power, and check residual noise..

@westcoastaudiophile  Are you referring to the 'residual',  a sine wave that occurs at the switching frequency of a properly designed class D amplifier?

If not ('residual noise' can be interpreted several ways), when you connect the 'scope to our class D amp at least, its clearly quieter than any solid state or tube amp I've tested. Of course, there is the residual, but its of no consequence as soon as it encounters the inductance of a tweeter.

@larrykell there is a max current limit through the speaker.. I agree, there is advantage of having more output transistors  in parallel to extend output stage linear region and to dissipate heat, which reduces distortions at high power end, but unfortunately that could increase distortions at low power end, <100mW. Also, driving more output stage devices requires to upsize other amp stages..

max current at amp output calculation using total resistance of speaker line (let’s ignore inductive and capacitive Z):

Rtotal= Rprot+Rcable+Rspkrcross+Rspeaker-coil

where:

Rprot: amp speaker protection circuit resistance, relay or MOSFET

Rcable: loop resistance of speaker cable (x2 one wire)

Rspkrcross: speaker crossover resistance, such as inductor ESR, additional freq. EQ resistors - this may way at different speakers used in 2 or 3 way design

Rspeaker-coil: speaker moving coil DC resistance, typ 3/4/5/6 Ohms

all combined, at 40V peak output voltage, gives 10A max current at ~ 4Ohms load

@atmasphere I’ve seen any king of while spectrum noise in different D class amps.. never sine wave! higher freq. though! higher switching freq. amps theoretically should be easier to filter noise out, but again, switching frequency generator has the same reference clock generator issues as any DAC, such as phase noise etc., thus can be heard. 

I am not sure what bothers me more: that there are 40K amps or this thread

I’ve seen any king of while spectrum noise in different D class amps.. never sine wave! higher freq. though! higher switching freq. amps theoretically should be easier to filter noise out, but again, switching frequency generator has the same reference clock generator issues as any DAC, such as phase noise etc., thus can be heard. 

@westcoastaudiophile If the output filter is doing its job, all you'll see at the output of a class D in terms of noise will be the sine wave residual that is at the switching frequency of the amp. That typically might be from 500KHz (near the bottom of the AM radio band) up to about 800KHz.

Honestly no-one can hear that.

What one might be able to hear is knock-on effects from other equipment if the amplifier has spurious parasitics that are messing with that other equipment- RFI can do messy things with audio.

But to be fair, lots of tube amps can do this too, through the swept resonance that can occur between the power transformer and the rectifiers installed.

We spent a lot of time chasing parasitics in our design. When it was finally ready, when we did the testing of our amp it was the bridge rectifier in the power supply that was making the noise, which we fixed. That is why I said a class D amp can have less spurious noise than a tube amp- whether in the speaker on radiated from the amp through the air or thru the AC power.