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

How can this be when the turning on and off of output transistors at a rapid rate in Class D amplifiers produces high frequency noise which must be filtered out? There is no such thing as instantaneous switching.

I tried a Class D amplifier the last time my Colosseum was in for repairs and I hated the thing. It sounded harsh and gritty to me. Granted, it was a $1-2k Class D amplifier. I sold the Glass D amplifier as soon as my Colosseum came back to me.

@larrykell I get that- there is tremendous variance in the sound and technology of class D amps- if you heard the wrong one it can be a big turn off!

How the amp can be immune to crossover distortion has to do with how the audio signal is extracted from the switching of the amp. The output devices turn on and off for differing amounts of time depending on the slope (how steep it is, whether its going up or down) of the incoming audio signal.

This type of analog encoding is called Pulse Width Modulation.

When the switching frequency is filtered out, the audio signal is what remains; there’s no way to generate crossover distortion, inherent in the design. This is a considerably different approach as opposed to traditional Push Pull amplifiers where the output devices have to follow the signal (which is why they can be prone to this problem) in order for it to be amplified.

(Apparently it is possible to build a class D amp that has no output filter; if such an amp were built it could have a problem with crossover distortion. But I know of no such commercially available amp- all I’ve ever seen use output filters.)

Regarding noise, if the class D is designed properly the amount of noise it makes on account of its switching can be less than many tube or solid state amplifiers. They can also have considerably less noise floor in the loudspeakers, making them suitable for driving horn speakers.

"if the class D is designed properly the amount of noise it makes on account of its switching can be less than many tube or solid state amplifiers."

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

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.