Re: Class/type of amp ?

The Web is wrong. Most switching amps are analog. That is,
everything varies continuously, rather than in quantized steps.

That is a confusing and not particularly true statement.

It might be confusing if you've been brainwashed into thinking "pulses" =
"digital", but it is nevertheless true.


By the way, Arfa, you're doing something intellectually invalid -- you're
"appealing to authority", rather than thinking for yourself, or
explaining
what's going on.

I am not.

Then why did you post Web references as examples of what other people think?
Majority opinion is proof of nothing.


Because on average, in the real world, if "millions of people" believe
something, and one does not, it is not the millions who actually *are*
wrong.

On average. But there are exceptions. The world is not 6000 years old. Yet
millions of people believe that. The majority is not the "authority".


I'm not really quite sure exactly what you're saying here about the class
D
amplifier. The analogue input signal is not converted directly to any kind
of 'value' represented by a binary number, such as might be the case if
you ran it through a traditional A-D converter. Instead, it is run through
a
comparator, with a triangle wave as the reference input. This results in
direct conversion to a PWM signal. I accept that this does not represent
'quantization' as such, so is not producing a "truly digital" signal, but
I
also do not believe that once the signal is in PWM form, it can either be
considered to be analogue any more.

Ah! Here's the problem. It's the confusion between /waveform/ and /data/.

A pulse is just a pulse. In and of itself it means nothing. It is neither
"digital" nor "analog" -- it's just a waveform.

The issue here is how we modify a waveform to transmit data.

Suppose we sampled a signal at or above the Nyquist rate and transmitted
each sampled value as a pulse of that value. (This is easily done with a
sample-and-hold circuit.)

How is the /data/ in that series of pulses represented? Well, it varies
/continuously/, just as the original signal did. It has not been quantized,
so it cannot be represented as one of a /finite/ group of numbers. That's
analog -- continuous variation.

On the other hand, if we quantized the level of the sample data, it would
now be in digital form.

"Pulses" have nothing to do with digital. "Numbers" have nothing to do with
digital -- PCM is only one form of digital; there are others. Any time you
represent data samples with a quantized value (which can be represented by
one of a finite group of numbers, but doesn't have to be), it's digital. And
it doesn't matter a whit what the waveform looks like. Ever heard of ECL?
It used sine waves, but it was digital?

You really need to think this though, rather than reacting with a mental
knee-jerk.

I am slightly embarrassed at giving Web references on this topic, which is
what I object to -- appealing to authority. But "you" -- meaning the people
in this group -- should have a sufficient /understanding/ of math and
electronics so that the light bulb goes on when you hear a correct
explanation. "Ah! That's right! I hadn't understood it before! Now I do."

I have to apologize a bit, because I certainly don't understand everything
new the first time I'm exposed to it. But I make an effort to understand
it -- not blindly accept or reject it. I generally don't believe things I
don't understand.


The term "digital" may not be a strictly true one for this class of
amplifier, and in truth, there is no such thing as a fully digital
amplifier
in the sense that you are advocating, but in the way that most people
would
understand the term "analogue", it's not that, either. The reason that it
gets called digital, is because all of the power amplification is done
with
devices that have only two states - on and off. And before you say that
those devices are linear ones in that they are transistors of one
persuasion
or another, they are not used in that way in this type of output stage.

So, if you are amplifying a signal that has only two levels, using devices
driven to have only the two conditions of on or off, then I think that you
are stretching the imagination more by calling it an analogue process,
than
you are by calling it a digital one.

Again, you misunderstand. A PWM signal /does not/ have two levels. If it's
analog, it has an infinite number of levels (widths). If it's digital, it
has a finite number of levels (widths). The data (signal) IS NOT conveyed by
the signal level (which remains constant), but by the pulse width, which can
vary continuously (analog) or in steps (digital).


I don't believe that there is a true term for what the process is, but I
also think that "digital" provides for a better understanding of what is
fundamentally going on, than calling it an analogue process as you would.

And for the record, I am perfectly capable of thinking for myself, thank
you, and I am quite happy that I understand the principles of the class D
amplifier, enough to be able to make valid contributions to any
discussions
about it. For you to suggest that the entire web, including respected
manufacturers, has got it wrong, seems a little opinionated to me, and
based
once again on dancing around terminology and semantics, as popularly
understood by the electronic engineering world at large.

Are you interested in actually understanding things, or in simply parrotting
the majority belief? Does truth = what the majority believe? Really?

About 30 years ago, Pioneer introduced an FM tuner with a pulse-counting
detector. (Pioneer wasn't the first; Fisher had one about 15 years earlier.)
This was billed as digital, when it was wholly analog.

"Truth is truth. You can't have opinions about truth." -- Friendly Professor
Peter Schickele

This is not a pissing contest. This is my attempt to get other people to
THINK.


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