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In Reply to: RE: Corrections posted by J. Phelan on March 16, 2017 at 15:55:11
These type of products amplify in the digital domain, not analog. "Digital amp" would be the correct term.
And the output filter is one part, not a stage.
Under 'digital amplifiers':
This from your linked review:
"however, they accept digital rather than analog input signals. These "digital" amplifiers take in the pulse-code modulation (PCM) signal from a music server or other source and convert those audio data to a pulse-width modulated signal. This PWM signal then drives the output transistors, just as in a Class D amplifier . "
While its input may be digital, its output is necessarily the same as an analog switcher.
It might be -but the point is that the amp removes all analog stages. Inc. D to A converter, current to voltage, DAC output-ramp, etc.
-but the point is that the amp removes all analog stages.
This statement is false.
PWM (pulse width modulation) and PCM (pulse code modulation) are both analog processes. There is no such thing as a true digital amplifier.
I've never heard anyone say PCM is analog.
As for the unit, even Robert Harley says it: *digital* amp.
PCM is for the encoding of analog signals to digital.
But we're not encoding. We're only dealing with digital signals.
You won't be doing PCM. Instead, you'll be using PWM, which is an analog process. It can be adapted very nicely for use with digital systems.
The specific forms of PWM used in the amps to which you referred is either Delta or Delta Sigma.
Read the Wiki article at the link.
Notice things like 'waveform', 'integration' and so on- all analog thingys.
The fact is the world is analog and true digital does not exist in it. That is why IBM developed the parity bit.
I looked it up in a few different dictionaries. The consensus is that in the context of signals and data, "digital" means representing a quantity as a series of numbers, presumably finite, usually but not necessarily binary numbers.
So in the case of pulse width modulation, if the pulse width is constrained to be one of a finite number of possible values, then it would be fair to call it a digital signal.
Once you low pass filter it after amplification by a high power switching output stage, the output at the binding posts is analog. Kind of like a R2R ladder DAC, which is why some people call this type of Class D amp a "power DAC".
J.Phelan has a point in that the amplifiers he mentioned are different from other Class D amplifiers having digital inputs (e.g. Tripath) which have a more conventional DAC followed by PWM formed in the analog domain.
Clearly the line between what is an analog process is what is considered 'not' is a bit dubious. Your point is well taken, and not germane to where this thread started, although once that got debunked it drifted pretty wildly afterwards...
I look at things from an engineering standpoint as that is my training. And having built class D amps, know that they are an entirely analog process. As I mentioned earlier on in this train wreck, class D lends itself nicely to hybridization with a DAC for a more direct-conversion process, but its wholly inaccurate to say that such an amplifier it truly digital when an obviously analog process is employed. The guy that started this was insisting that class D was digital all the way to the output, which really isn't true at all- otherwise dead time circuits and other aspects of class D operation simply would not be needed.
You never built a class D amp, therefore your comments (should be) ignored.
Look at the Harley piece. A sample-rate converter is used -that is NOT analog. These are digital all-the-way, as far as the amp is concerned.
Clearly you've not read my prior posts...
I have in fact built class D amps. We've been developing our own for some time and have a patent in the works. I also linked a simple class D amp for you to look at, easy to build, and had you read the simple article (with lots of photos) at that link, you would also know that all class D amps are an analog process.
From the Wikipedia page on Class D amps:
The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time. The smallest amount of noise, timing uncertainty, voltage ripple or any other non-ideality immediately results in an irreversible change of the output signal. The same errors in a digital system will only lead to incorrect results when they become so large that a signal representing a digit is distorted beyond recognition. Up to that point, non-idealities have no impact on the transmitted signal. Generally, digital signals are quantized in both amplitude and wavelength, while analog signals are quantized in one (e.g. PWM) or (usually) neither quantity.
emphasis added; after that follows why class D is in fact not digital.
Your company never sold a class D amp.
And you keep linking *outdated* information.
Besides Harley, here's another. Note the statements "digital input fed directly to the output stage", "keeps everything in the digital domain".
So how it works for you is that facts go out of date. Would it help if that Wiki page got refreshed recently??
So Norman Crowhurst (was writing 60 years ago) can be ignored? How about Shannon- I suppose he's pretty out of date too huh? and that Nyquist dude- he's so old he's dead? Sheesh!
The Wiki page is factual. If class D had somehow become true digital in the meantime, it would have been an article worth the front cover of every audio magazine in the world.
But apparently you only believe people who listen to stuff for magazines as the only possible experts in the world.
How about people that actually have an engineering degree or work on class D amps or anything like that?
Do you think that because we've only sold tube amps so far, that tube amps are somehow the only thing I know??
Is there any possibility that you simply don't me as a person? Any rational person would know the answer right away- you don't know me, don't know my qualifications, don't know what my job entails, etc. You just have made-up stories.
You've been taken in by advertising; hype, hook, line and sinker.
You have no proof you built a class D amp. I could say *I* built one !!
Now, it's not "marketing", it's "magazines". John Atkinson and Robert Harley were "taken" by advertising. I don't think so.
Digital amps are the future !!
Don't confuse the situation with facts huh?
I'm sure it does not matter how many awards I've gotten (about 35 or so) or how long I've been in business (over 40 years) or anything like that. You'll go with someone that writes instead of someone in the industry that actually makes amps for a living. Because you have to be right.
It'll be interesting when someone actually makes a digital amp.
From the link below:
Footnote 1: The D in class-D does not stand for digital, as some commentators have suggested. Rather, D was just the next available letter in the alphabet when amplifier circuit topologies were being classified. A class-D amplifier can be either digital or analog in operating principle.
The author, John Aitkinson, happens to be misleading in this comment, as there is no such thing as a digital amplifier. If you change the last sentence above to read " A Class-D amplifier is analog in operating principle" then the entire paragraph would be correct. How about I see if we can get JA to weigh in on this?
Mmmm...John Atkinson 'misleading', I hope he sees this.
You're the only person who says "no such thing as a digital amp". There is.
Now a schematic, which eschews analog stages. No wait, this is phony too !!
I've spent some time on that site in the past as it often comes up in Google searches. I would direct you to other portions of the site which refute your claims but since you've not read a lot of that sort of thing in the past there is no expectation that you would do so now.
JA would be welcome in the discussion. I'm sure he can clarify.
Can't refute the page I linked.
Atkinson and Harley have enough credibility, they don't have to 'clarify'.
By causing this thread to 'spiral', you pulled more attention to it. Thanks to you, they'll now be a buzz on (true) digital amps...
If you're claiming that the amp at that thread is a digital amp, well it uses analog process to do its job. Quite literally there is no way it can't.
This is true of any amplifier that can drive a loudspeaker.
If a reviewer that has never built an amplifier before wants to contest that, all that happens is he's wrong. In JA's case, I'm pretty sure he was using shorthand with his use of 'digital amplifier' and I'm also sure he would be happy to clarify that for you.
Did John tell you he would clarify ? These are digital amps, as the schematic shows...
And they're not easy to make. Noise-shaping is required, but I wonder if the Technics R1 system has a clock frequency high enough to avoid it.
The output stage has 1-part -analog. But this too looks different -it's now high-speed. Compared to the typical slow, losing-its-shape analog waveform.
The Technics is one of the few that has a clock speed approaching what is needed and so far looks like one of the better class D amps out there.
Your links don't prove anything, at least in this discussion.
Harley said digital amp and the signals are amplified in the digital domain.
Digital is everywhere inc cable-TV systems and satellites. For audio, DSP crossovers could be placed before a digital amp. (1) part in the output stage sends the signal to the speakers.
This technically is analog, but it's far different than the slow-speed circuits and gain stages we're all accustomed to.
So, faced with the rather obvious facts, you prefer to go with one person, who, if you were to ask him, would confirm everything I said?
Point him at this thread and see what he says!
Don't know what 'point him' means.
And it's more than one person -it's any co. making this type of product -inc. Classe. Plus AES papers explaining all this (which can't be linked).
That's because said papers don't exist :)
t might be -but the point is that the amp removes all analog stages.
Except of course for the output stage driving the speakers with an analog signal. :)
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