Digital amp

Why would you wish to do this?

A digital-input amplifier is basically a power DAC. Given the current state of technology it provides higher performance and lower cost if you implement the DAC as a low-voltage device, and then feed the analog signal to a class-D amplifier. This allows to to use a simple technique like 'UCD' which provides a proper NFB loop around the whole of the analog amplifier section. If you look at the few digital-input amplifier designs that enclose the amplifier in an NFB loop, you will find that they are dreadfully complex. (Look at the latest TI or Zetex designs for example). It seems a bizarre example of progress if you need a full DSP to do something that a UCD amplifier does with two resistors and two capacitors!
1. the volume control is the problem,
you can control it digi-> dsp->digital-input amplifier .
and use the dsp to control the volume.
this will make the noise floor very high when it was running at a low power output .

someone(perhaps sharp) control the power supply voltage to control the volume , strange way, but low noise.

2. the thd from the current (output) will be very high,
this is same like open loop vs close loop style,
some one like open loop even bad performance,
but most of open loop class-d amp have no very good performance at this time.




2007-02-06 12:43 am
1. the volume control is the problem,
Yes Texas Instruments have published a vol control circuit using variable PS here:
and Panasonic use this in their SA-XR* pure digital no feedback amps

2. the thd from the current (output) will be very high,
again TI have achieved low open loop THD and Panasonic have implemented this in their amp range. Agreed the PS quality is the critical factor in achieving low THD - a good, stiff, low impedance, regulated PS is hard to do