"John Popelish" wrote in message
...
pil wrote:

"Joerg" wrote in message
...
Johan, I don't know these or many other audio books. Just one hint:
Nowadays I
would certainly try to learn about class D audio amps, the digital
kind.
That
seems to be where technology goes.

Regards, Joerg.



Good thing you mentioned that. I always wanted to know this: What is the
difference between digital and analog?

How can a digital signal be amplified???
How can a one become a louder one?
And most important to me: How can you drive a speaker with a digital
signal???

As far as I am concerned every "digital" hi-fi must still have an analog
amplifier somewhere in its design. The amplified speakers (which they
claim
to be digital speakers) has a DAC and a normal analog amplifier right?

I would greatly appreaciate answer on this

No. Digital audio (class D) treats the speaker current like the
output of a switching regulated supply that has AC capability. There
is nothing but two levels coming out of the speaker terminals, except
for the effect of filtering components.

A good intro to this kind of amplifier is the datasheet for one of the
integrated versions.

http://focus.ti.com/lit/ds/symlink/tpa3001d1.pdf
--
John Popelish

It's debatable whether class "D" is really digital. While it's true that
internally, the signal is switched, it isn't a digital signal. It's pulse
width modulation. The pulse width is continuously variable, making it an
analog quantity.

The amplifier you referenced is a pulse width modulator. The input is
analog, and the output is analog. Noise and distortion are not particularly
outstanding, either. It's primary claim to fame is extremely high
efficiency, approaching 90%. It might be acceptable for battery-powered
equipment or automotive audio. Conventional class A-B linear amplifiers are
still preferable for high fidelity.

Here's a web site that has some great practical designs and discussions:
http://sound.westhost.com/index2.html