Computer amplifier ?

[James D]

Nick,

I assume they mean a digital power amplifer without the ADC on the front end. Thats what I had in mind anyway. So the 16 or 20 or 24 bit datastream or whatever it is, is then digitally filtered to provide a digital datastream suitable for drving a big switcher that providea a high amplitute (power) digital stream that can then be filtered back to its analogue analogue if you see what I mean!

Present digital amps use 1 bit datastreams and filter to get back to analogue. In theory one could use a parallel power DAC but it would likely drift all over the place at a few LSBs rate :-)

James

[NickG]

James, thats what I assumed you were talking about, simpley put, converting the parallel data into some form of PWM, and then filtering, I can see so many places where this would cause problems. I just can';t see what it gains (other than efficiency of course). Still has the same problems of a DAC, jitter, and filter problems, butthis time its worse, as its at power.

But I was wondering what the OP were meaning, as it almost sounded like the idea was to multiply the number by another number and assume that would drive the speaker.

[petercom]

Sorry, I thought that there had been enough discussion of PWM that we all knew what we were talking about.

Basically you convert from the 16-bit, 24-bit or whatever data to a PWM bitstream where the width of the pulse defines the power. At the output you put the bitstream through a low pass filter and, hey presto, you are left with the analogue waveform.

There is an interesting history and explanation here:

http://www.psaudio.com/articles/sdat.asp

Of course everybody has a new and patented version of the one 'true' path to perfect PWM. Don't believe a word of any of them. I've tried them and they all fail a simple listening test in one way or another.