Digital input amp


I see a few coming on market.  Previous threads were quite old.

They take a USB or other input. No DAC on the front end. Just the DSP engine to do volume, eq, etc, then whatever conversion to PCM to feed the class D output. So the only "DAC" is the output stage.   This makes sense as it further reduces the functions in the chain.  I have not seen objective testing or any reliable subjective testing. The ones I have seen are Infineon processer based. No idea if the output filtering or feedback implementation is up to the Purify quality.   I guess the next innovation is the GaNFET output.  One has a DAC to feed a sub out. Easy as any old $5 DAC will wo there. 

I was browsing and came across the Sajab A30a. ( quite inexpensive)  Peachtree has the old Gan-1 but coax PCM only.  That would be fine if it managed buffering and clocks internally. Unfortunately my all-in-one only has USB out. 

I suspect there is a lot to be learned here but it makes sense to me for the future. 

tvrgeek

They take a USB or other input. No DAC on the front end. Just the DSP engine to do volume, eq, etc, then whatever conversion to PCM to feed the class D output. So the only "DAC" is the output stage. 

@tvrgeek To be clear, the DAC is at the input of the amp, not the output. Class D is not digital since the switching of the amp does not have meaning whereas the switching of a digital word does. So you have to convert from the latter to the former.

Not these designs.  They take a bitstream , do DSP, do the digital conversion to PWM and feed the output. So the actual integrator and filter is the output.  There is no DAC on their input. 

Not these designs.  They take a bitstream , do DSP, do the digital conversion to PWM and feed the output. So the actual integrator and filter is the output.  There is no DAC on their input. 

@tvrgeek What you are describing above means that the DAC is at the input of the class D amp portion of the product. Put another way, the PWM portion of the circuit is at the input of a class D amp, not its output.

Digital at its fastest might be 192KHz sampling frequency. Class D amps often switch at 500KHz or higher. You can design a DAC that can produce a PWM output, but it really does have to be at the input of the class D amp in order to work. I know a lot of companies say they have a 'digital amp' but if they also say its class D then the DAC is always at the input to the class D circuitry.

Maybe you should look at the block diagram of these products.  They take digital in. Process within a DCP chip which produces the PWM signal to feed the output.  

I know a lot of companies say they have a 'digital amp' but if they also say its class D then the DAC is always at the input to the class D circuitry.

That's what I always thought. Thanks for confirming, Ralph.