Class D or AB

[agedhorse]

In other words, how much digital is required for it to be a digital amplifier?

Or looking at it another way... how much analog is required for it to be an analog amplifier?

 

[onosson]

Or looking at it another way... how much analog is required for it to be an analog amplifier?

Exactly!

 

[beans-on-toast]

All this digital stuff. Long before a chopper was a sub-circuit in a switched mode power supply, it was a type of motorcycle. SMPS and PCM circuits and those of a similar ilk are light and efficient, but I like the classic deep low growl of big mechanical motor with all tubes firing. Same holds for the tone of the old tube amps.

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[warnergt]

From the Wikipedia article: "By contrast, non-digital (or analog) systems represent information using a continuous function." The input voltage, modulation duty cycle, and output voltage of a switchmode amplifier are all continuous functions.

No, they aren't.

Let's look at that wikipedia entry on
"continuous functions" as you suggested and see what it says:
"In mathematics, a continuous function is a function for which,
intuitively, "small" changes in the input result in "small"
changes in the output."

The output of the comparator circuit (what you call the
"modulation duty cycle") defies this description. There is
a threshold on the input that results in a large jump (a step
function) on the output.

Look at the example provided by wikipedia:
"By contrast, if M(t) denotes the amount of money in a bank
account at time t, then the function jumps whenever money
is deposited or withdrawn, so the function M(t) is
discontinuous.

Hmm. Sounds very much like modulation duty cycle which
jumps up and down.

 

[warnergt]

In other words, how much digital is required for it to be a digital amplifier?

Exactly. Calling a class D amplifier analog is like calling a
hybrid car a gas vehicle (and possibly insisting that it is not
electric). Yes, a hybrid car runs on gas but there is a clear
distinction between it and a regular gas vehicle.

 

[majortoby]

And round and round we go

 

[Bob Lee (QSC)]

From the Wikipedia article: "By contrast, non-digital (or analog) systems represent information using a continuous function." The input voltage, modulation duty cycle, and output voltage of a switchmode amplifier are all continuous functions.

No, they aren't.

???

 

[4andnomore]

Wow this thread is really interesting and informative.

As a consumer who only understands the rudimentary concepts of analog and digital, when I hear digital I assume it means the audio signal i.e. "the sound" is at some point in the signal chain represented in its entirety by 1s and 0s. Just like a digital synth. Conversely (or is it inversely?) I would not define an analog synth that uses digital controls to be "digital". You can argue the finer points of the engineering all, but I believe the nearly all consumers would apply this logic. So, for practical purposes (and technical IMHO) class D does not equal digital.

By the way, the wikipedia definition states that digital is "a system that uses discreet values...". It doesn't state that the use of discreet values necessarily makes something digital.

 

[JimmyM]

I agree with 4and. That is exactly how I feel about it. Having one or two small functions in the amp acting digitally does not make it digital in my eyes unless the SOUND is digitally produced a la TC and Line 6.

 

[Bob Lee (QSC)]

By the way, the wikipedia definition states that digital is "a system that uses discreet values...". It doesn't state that the use of discreet values necessarily makes something digital.

+1

 

[Musicman20]

TC amps are digital and don't sound digital at all. Makes no difference to me.

 

[majortoby]

They sound digital to me, honestly. Well-executed digital , yes, but still not quite "right". BTW, I LOVE digital sound processing, but I do prefer that my "base tone" be derived from analogue equipment. Just my $.002

 

[seamonkey]

TC amps are digital and don't sound digital at all. Makes no difference to me.

TC is a great bit of technology. TC knows how to work in the digital domain.
TC bass amps are really analog on both ends.
It has a class-d power amp that is analog.

The TC amps convert the incoming bass to digital and then processes it in the digital domain in the "pre-amp" section. It sends this to the amp - but it has to go through D to A before the amp can actually amplify it.

Amplification is about increasing the amplitude of a signal.
A digital amp would make no sense.
Changing 1010 to 10100 makes no sense in the analog domain. Nothing in a class D amp understands or computes on 10100.

There really isn't any digital amps, but were stuck with marketing of digital amps.

 

[agedhorse]

Exactly. Calling a class D amplifier analog is like calling a
hybrid car a gas vehicle (and possibly insisting that it is not
electric). Yes, a hybrid car runs on gas but there is a clear
distinction between it and a regular gas vehicle.

There is also a distinction between a hybrid and a pure electric vehicle as well.

This opens up a great opportunity to explain why this analogy falls apart... on a "typical" hybrid vehicle, one that has both an IC engine as well as an electric motor, both power sources feed a planetary gearset, this means thet either the IC engine OR the electric motor can be the exclusive power source. In addition, BOTH can be the power source as the planetary gearset acts as a mechanical "or gate" (except that in the analog world with the way they are designed they are more accurately described as a summing node).

An IC vehicle is powered exclusively by an IC engine
An electric vehicle is powered exclusively by an electric motor
A hybrid is powered both, either together or independantly.

 

[PrairieDogma]

Thanks for finally pulling the discussion back to how they sound. Digital/analogue/something-in-between is pretty much a potato/potahto discussion to anyone who isn't an EE, but I truly appreciate the opportunity to understand (or try, anyway) how these things work.
I think everyone gets that there is a very clear audible difference between tube amps and solid state amps, especially as volume levels go up. As well, there's pretty much a direct relationship in an all tube amp between power and weight.
What I'm reading here, and in my admittedly limited experience, is that any tone difference between a Class A/B and Class D amp is so subtle as to be totally over-ridden by voicing, protection circuits and other design decisions taken by the manufacturer.
As to tube reliability, my only experience of amp failure during a gig was with a bar tube amp, but I also have my own tube amp that has worked reliably for over 45 years. Anyone as old as I am, that grew up when tube radios and tube TV's were the norm, will remember that just about any town of size would have a radio/TV repair shop and the TV repair guy would come to your house. That's all I need say about tube reliability. The youth of today don't understand how rough we had it. It was before remotes, and we actually had to get out of our chairs to change the channel!
I get it that solid state amps break,too. I admit I don't know the statistics, but I'm guessing it's 1 to 2 orders of magnitude less often than tube equipment. Solid state reliability boils down to design choices and quality of parts, as mentioned earlier. That said, probably any amp can be broken of one puts their mind to it (or maybe doesn't put their mind to it).
To each your own, choose your tone.
Have I pretty much got this right?

 

[B-string]

This has gotten me curious, what "class" output was Bob Carver's "Magnetic Field" power amps?

 

[Bob Lee (QSC)]

AB, as I recall.

 

[seamonkey]

...
The youth of today don't understand how rough we had it. It was before remotes, and we actually had to get out of our chairs to change the channel!

"Durn kids these days with all their remotes. Even their phones work as remotes. Why in my day I was never too lazy to tell my wife to get up and change the channel."

 

[majortoby]

Am I the only one who HATES car analogies?

 

[B-string]

AB, as I recall.

You sure? It used stepped transformer taps smoothed at the final filter. Odd design.