Talk:Class-D amplifier

The easiest way to explain how Class D works is to have an animated gif of a normal wave form next to a square wave with pulse modulation of the same sound. — Preceding unsigned comment added by 24.246.52.178 (talk) 20:10, 14 April 2023 (UTC)

Show the original waveform and then a PWM waveform and then a filtered output waveform. — Omegatron 04:17, 7 February 2007 (UTC)

Block Diagram Needs Updating
Not to nitpick, but the low-pass filter show in the block diagram figures shows the symbol of an inductor where a resistor should be used instead. Can this be fixed by whoever has the original .svg file?

Saket (talk) 17:34, 6 October 2009 (UTC)

The inclusion of the inductor is correct, and typical of the majority of class D output stages. —Preceding unsigned comment added by 205.175.225.22 (talk) 15:59, 15 July 2010 (UTC)

Hi, my read of the block diagram is a PMOS pull up and an NMOS pull down driving the output as indicated by arrows for the bodies. The PMOS appears to have its input (gate) tied to a non-inverting output of an amplifier. The NMOS appears to have its input tied to an inverting output of the amplifier, with inversion represented by a bubble. If this read is correct, when the PMOS is off, it is driven with a logic 1, which inverted is a logic 0 meaning the NMOS is also off. No current to the output. PMOS on is a logic 0, so the NMOS will have a logic 1 level signal, so both transistors are on? Maybe some current to the output depending on the strength of the transistors. I usually see the output stage of class D described as an NMOS for pull up and another NMOS for pull down. In this case the amplifier with inverting and non-inverting outputs is correct. Additionally effort is made to keep the duty cycle and phases of the inverting and non-inverting outputs of the amplifier adjusted so the two NMOS are not on simultaneously, I think this is called a non-overlapping clock? Thank you for your consideration. — Preceding unsigned comment added by Kennethlayintheroom (talk • contribs) 14:11, 7 November 2020 (UTC)

PWM amplifier is subclass of Class D Amplifier
i suggest renaming the article class D amplifier. the PWM method is only ONE of the possible methods to modulate the active device on/off. today there are more advanced methods which cannot be categorized as PWM, such as the sigma-delta modulator of the class-D amplifier chip mentioned in the article (Analog Devices AD1990 Class-D audio power amplifier).

i would also suggest defining new articles for class E/F (today it's the same class, in the past it was 2 classes until it was realized they are basically two variants of one common methodology).
 * I would suggest that instead of renaming it to "Class-D amplifier", it would be better to call it "Switching amplifier". P.S.: Please sign with ~ Rohitbd 08:53, 10 May 2006 (UTC)


 * But there are other types of switching amplifiers that are not PWM, no? — Omegatron 05:09, 12 May 2006 (UTC)


 * I can't think about any high frequency switching method that is not PWM: delta and sigma delta are different way to find out the value of the duty cycle, but we still end up with varying the duty cycle of a square wave to obtain a given average value. I think this is the definition of the PWM (and I edited the PWM article in that sense). So I think all switching amplifiers are PWM, though the PWM is computed using different methods. -- CyrilB 08:18, 12 May 2006 (UTC)


 * Yeah, I guess you're right. Even if there are other types, they probably don't deserve their own article.  A single switching amplifier article should be good.  I support the name change.
 * Make sure to be clear that the article is about amplifiers that switch the output stage to produce a waveform, and not analog amplifiers with switching power supplies. — Omegatron 13:25, 12 May 2006 (UTC)
 * Switching amplifier redirects to PWM amplifier...? So what's the final verdict? Rename to Switching amplifier or Class-D amplifier? Rohitbd 15:23, 13 May 2006 (UTC)


 * I like switching amplifier — Omegatron 04:40, 14 May 2006 (UTC)
 * Moved PWM amplifier to Switching amplifier. Rohitbd 07:58, 14 May 2006 (UTC)


 * I wrote the original comment at the top. agreed, switching amplifier is a good term. so, who wants to start a class E/F article (using the text located at electronic amplifier - class E/F as seed?


 * The ΣΔ produces a special kind of pulse trains, named Pulse Density Modulation (PDM). The variablity of pulse width in this scheme is limited to two discrete values {0, T}. That is, the switch remains open or closed along the whole cycle length. But who assures the PDM frequency invariability, which is prerequisite for PWM? Anyway, there are bunch of modulation schemes not belonging to the PWM class and even some closed-loop scemes, which, like linears, do not exploit any modulation at all. The control circuit must be distinguished from the whole amplifier, which is an aggregate device. The PWM is only one of the control circuit architectures possible and is related to the switching amplifiers as the notion of Monarchy to the notion of State or the Orange relates to Juice. The fact that you cannot think of apple juice is a bad argument. This also means that the PWM, which is a control method, is not a subclass of any amplifier, which is a device class. The amplifier topic might have a control scheme topic reffering to popular modulation and closed-loop designs. --Javalenok 18:45, 8 July 2006 (UTC)


 * Today I renamed this article Class D amplifier as per other classes of amplifiers such as A, B AB, C as well as D class. Switching amplifier could well be applied to the Class C if we want to get technical. Cheers!--Read-write-services (talk) 05:53, 31 August 2009 (UTC)

Misc
Suggest that this article be merged with Electronic amplifier. Wasn't aware that this has been covered elsewhere at the time of creation. Rohitbd 12:56, 5 August 2005 (UTC)


 * See Talk:Electronic_amplifier - Rohitbd 09:10, August 8, 2005 (UTC)

Another application worth mentioning for the Class D amplifier, especially in context to handling digital signals, are home-theatre receivers or home theatre in box systems that are based on this technology. Typically, they would use analogue-digital circuitry (for analogue inputs including the AM/FM tuner), accept digital inputs directly and do the processing or decoding in the digital domain before putting the signal out to Class-D power-amplifier circuits (typically 5 or 6 in the units that are affordable for most people). This is usually to permit the design of compact affordable equipment. SimonMackay (talk) 14:14, 11 February 2008 (UTC)

Merge Class T
Class T amplifier should be merged here, and this is the appropriate article for other vendor-specific "classes", such as Class I, and whatever else people come up with. — Omegatron 18:53, 8 August 2006 (UTC)
 * Agreed. Class T are also switching amps. Rohitbd 15:07, 12 August 2006 (UTC)
 * Oppose. It has its own page because it's a notable product in its own right. (I created the original article, if that matters) --Dtcdthingy 02:22, 16 August 2006 (UTC)

'Class T' is a proprietary implementation of a class D amplifier it is not a class it its own right. Perhaps there should be a section separate of the real classes of other or proprietary amplifiers which includes all other classes such as Class I (BCA) Class TD and Class T


 * Oppose the merge w/ Class T amplifier. This term is a commercial one (nd would on that ground not justify a separare WP atricle) for some amplifiers which are distinct in some ways from other switchers. Among other things, they have found acceptance across the entire range of audio amplifier use, from Audio Research to very small and inexpensive battery powered amps from Sonic Impact. This is unique in the amplifier world, hence a separate article is justified after all..
 * On another point, the title of this article should not be Transistor amplifier, as there are many types other than switching amplifiers. And there several flavors of those. The curretn title has to go... ww 06:24, 20 March 2007 (UTC)


 * Is it a switching amplifier? — Omegatron 05:15, 26 July 2007 (UTC)

I oppose the merge with "Class T Amplifier" too. There are other commercial variants of the Class D too, and if we add them all as sections it would really clutter a Class D article. Esobocinski (talk) 19:57, 27 March 2008 (UTC)

I'd also oppose a complete merger. There's a level of detail that you would go to in the Class T article that doesn't belong in this type of overview article. It seems that the issue has been on the table for discussion for a long time, and that merger isn't appropriate, so it seems time to set that idea aside. Class D should be a subcategory of electronic amplifiers, and this article should be an overview that doesn't delve into the details of the may implementations (which will only grow over time). 141.154.19.152 (talk) 01:27, 5 June 2008 (UTC)

Oh, no. Class T is just Class D with some refinements. I see no justification for giving it its own category, nor for doing this for any proprietary scheme. We are talking about a device whose output switches between the two supply rails at a very high rate, is pulse-width (or a variation) modulated by an audio signal, which escapes to the loudspeaker through a low-pass filter. In some cases, the loudspeaker itself is the inductive part of the filter. Somehow, that simple concept does not come through in the article; it reads like a disjointed mishmash of ideas and needs to be completely rewritten. Anybody up for this? I'm a little busy atm. Freddy011 (talk) 08:21, 4 September 2017 (UTC)

Disadvantages of Class D amplifiers
The article discusses their advantages but not their disadvantages. How come Class D amps aren't everywhere? &mdash; ciphergoth 08:43, 24 October 2007 (UTC)

Yes I agree, this should also be explained in this article. I personally know someone who have a bad experience by combining his LP-player with a digital amplifier. --Nabo0o (talk) 23:17, 12 March 2009 (UTC)


 * It seems to me, that with current technology, the extra work to design a good class-D amplifier is only worthwhile at higher power levels. Gah4 (talk) 01:07, 2 May 2019 (UTC)

Some absolute crap in the abstract (introduction)
(16:06, 22 October 2007):"Standard Class AB high-wattage power amplifiers are very heavy due to their bulky transformers and heat sinks. Class D amplifiers are lighter in weight and smaller than standard Class AB amplifiers, because they are more efficient. Class-D amplifiers use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) rather than BJT transistors and they generate a triangular pulse waveform which is filtered at the output stage with a low pass filter to remove the high frequencies."

In these two sentences I have tree things to disagree with:
 * The major distinguishing property of the switching is some lossless amplification. The elimination of weight of heat sink is a secondary, side, collateral, attribute of any non-dissipating device. (This is mainly an assent issue, but it is important to understand the principle rather than effects and applications, I believe)
 * I'm sure, nobody uses the transformers to amplify the power.
 * The transistors generate RECTANGULAR waveform rather triangular. The D-amplifier article authors even do not understand that the switches can generate nothing but the rectangular! The energy saving principle misunderstanding explains their misroute focusing on the wight. --Javalenok (talk) 17:01, 5 January 2008
 * I have corrected the edit today. --Javalenok (talk) 11:31, 6 March 2008 (UTC)

There's plenty of crap in the rest of it too. I tried to clean up a small part of it, but this article really needs a complete rewrite. Esobocinski 20:01, 27 March 2008 (UTC)

@Javalenok There are a lot of other dubious points you could be ranting about instead.
 * What is "lossless amplification"? The elimination of weight and bulk is not a trivial "side effect", it's part of the main event.
 * Nobody uses the transformers to amplify the power, but they do (less so nowadays) use them for power. A class AB amplifier wastes a lot of power, so a class D amplifier can use smaller power supply.  Almost all switchmode now; much cheaper to make than winding a transformer.
 * The third point makes no sense.

Most of what's here is from 6 or 7 years ago. I have in front of me an amplifier that measures about 3 by 4 inches, consists of two TI TPA3116 amplifier chips, 4 3.3uH inductors, 4 680nf capacitors and little else, apart from a token heatsink. This thing is rated to put out 100 watts x 2 channels, 200 watts total, with 21 volt supply into 4 ohm speakers. This would have been science fiction just a few short years ago. And it cost less than ten dollars. Most discussions about this topic are hopelessly out of date, because the things that can now be done on silicon didn't exist until just recently. The degree of rigid control necessary to implement this function in this form factor without splattering EMI everywhere is only possible because all the work is done inside this tiny chip, which only measures about 6 by 8 millimetres. And you can pull 100 watts out of it. There are a lot of things now, just as staggering. For $3 you can buy a single tiny chip that contains a complete 802.11b/g/n WiFi radio, complete with TCP/IP stack, balun, LNA, power amplifier and matching network; built-in low-power 32-bit CPU; lots more. This is just to illustrate what can be done nowadays, that wasn't even dreamt of in 2007. As I said elsewhere, this whole article should be rewritten, and, yes, it should include history of how Class D came about; it was first proposed in 1958, but the existing technology couldn't implement it. Freddy011 (talk) 12:39, 4 September 2017 (UTC)
 * Your modern amp is a Class T though, not merely a Class D. We have to be careful with these articles as to what goes where. I still favour keeping them separate, and expanding each accordingly, even if that involves duplicating content between both. Clarity for readers is an issue, communicating the whole story is an issue, pasting some content is not an issue. Andy Dingley (talk) 13:59, 4 September 2017 (UTC)

Make "Switching Amplifier" an overview and reference separate articles about classes
I really think that this article should be split such that "Switching Amplifier" would be an overview article with an explanation of switching and only brief descriptions of the different classes. Details belong in separate articles that get referenced hierarchically. Much of this article would end up as "Class D Amplifier" or somesuch, and "Class T Amplifier" would either become a section of that or would get hierarchically referenced below "Class D Amplifier". My preference is the latter. Esobocinski (talk) 19:59, 27 March 2008 (UTC)


 * Yes, that's the way to go - an overview article that makes it clear what they have in common that makes them a class or category, and some discussion of key differences (how they use feedback?); with separate articles (and categories) for specific topics and implementations. There are going to be more and more implementations of switching amplifiers, both because (1) the technology has now reached a level where full frequency range (and not just subwoofer) applications are used in the mass market and for audiophiles; and because (2) the low energy consumption / "green" aspect is becoming more valued.  141.154.19.152 (talk) 01:31, 5 June 2008 (UTC)

I'd conjecture that 99% of the content is the same between articles, differing only in minor details, and we should cover it all here. I think a list of other technologies would be helpful for deciding this, though. I'll start it. — Omegatron (talk) 03:09, 5 June 2008 (UTC)

Types of switching amplifiers that have articles:
 * Class T amplifier

"Fully" Digital
Is this paragraph accurate?

"The term "Class-D" is sometimes misunderstood as meaning a "digital" amplifier. The quantization of the output signal at the power stage can be controlled by either an analog signal or a digital signal. Only in the latter case would an amplifier be using fully digital amplification."

Seems to me this is a confusing use of the term "digital." Aren't all amps essentially analog devices at their output stage? I understand that the circuit can be driven by a quantized "digital" signal. I don't see how this makes the amp "fully digital." A class A/B being driven by a quantized signal wouldn't be considered digital just because it was being fed a quantized signal.

75.71.201.190 (talk) 05:07, 15 August 2008 (UTC)

- Basically every digital device uses analog methods to accomplish 'digitality'


 * I'm not sure what's confusing about that sentence. I think it's point is that even though the SMPS switches amongst a discrete set of values, it should not be said to have a "digital" output. A traditional SMPS amplifier has an output that assumes two states (e.g., on/off, high/low). These two values certainly come from a discrete set, but the switching times can occur at any time. That is, the switching times are not necessarily quantized in any particular way. So the switching times are themselves an analog signal. When an SMPS device is driven by a PWM signal (as opposed to, say, sliding mode methods), if the duty cycle can take any value from the continuum [0,100]%, then the output is analog. However, if the PWM signal is generated by a digital source (e.g., a counter that turns off after a certain number of counts), then the duty cycle will be quantized. &mdash;TedPavlic (talk) 20:17, 26 June 2009 (UTC)

Hey, Ted, the rest of us know, and the article already states, that there's no such thing as a SMPS amplifier. This demonstrates a basic failure to grasp the principle of what we are discussing. There is, anyway, no such thing as a digital amplifier except that the output stage can be seen as swinging between "0" and "1". But there are no binary numbers involved, and the audio leaks out the end as a decidedly analog signal. Freddy011 (talk) 08:32, 4 September 2017 (UTC)

inaccurate "Terminology" section
This is a follow-up to the Talk section immediately preceding. Mr Pavlic is basically correct, and everything else is, to a greater or lesser degree, wrong. The article needs to be edited to bring it in line with what Mr Pavlic says.

I find it amazing that the overwhelming majority of engineers and technicians do not understand the difference between analog and digital. Simply stated, a class D amplifier can be digital or analog, depending on whether the samples "driving" the output are quantized or vary continuously. Yet when you point out this obvious and easily understood distinction, most people become violently offended, generating gallons of technical bilge of what "digital" really is, or how a signal can be both digital and analog at the same time. Mr Pavlic is that extremely rare exception; he understands. WilliamSommerwerck (talk) 22:03, 13 June 2012 (UTC)

d-amplifier term
I have an Electro Voice powered PA sub, on which back (where the built-in amp is) it says Class-D Digital Amplifier. —Preceding unsigned comment added by 77.35.41.134 (talk) 09:58, 28 February 2009 (UTC)

Drift
Question - for the non-feedback type wouldn't voltage drift be a problem - no two components are exactly identical. Maybe in practice this is inconsequential? since typical loads are not purely capacitive.

Is this an acknowledged factor - if so could drift be mentioned.77.86.67.245 (talk) 21:50, 23 April 2009 (UTC)
 * Of all performance issues that non-feedback amplifiers suffer, DC offset and associated thermal drift is the least serious one. A power stage would contribute a DC error if the FETs turn on/off at unequal times, but since non-feedback designs invariably use very fast switching you're unlikely to find more than a few tens of mV at the output. This is neither unusually large nor problematic. Classedhaie (talk) 06:45, 19 May 2010 (UTC)

Feedback is mainly to address distortion and, to a lesser extent, SNR. The type and quality of the encoder has the biggest bearing on performance. Freddy011 (talk) 11:52, 4 September 2017 (UTC)

Class D vs Digital
"Digital" amplification is something I've been hearing a LOT about lately, and much if not all of it is not related at all to traditional Class D pulse wave modulation concepts in all of its analog glory. After reading about NAD's new M2 Direct Digital Amplifier, it seems to me that the redirect from 'digital amplification' to this Class D article is now unwarranted (which is how I arrived here in the first place), because there IS newer technology that is derived from silicon-based "amplification" that is claimed to be "true digital" and that the Class D connection is not the case anymore--at least not in the traditional sense--regardless of any misnomers or mix-ups made in the past with the "genotype".

http://nadelectronics.com/img/datasheets/M2-white-paper-EU-Web.pdf  Monoblocks (talk) 06:39, 19 September 2009 (UTC)
 * The NAD amp (Zetex) is actually remarkably analogue. First, a "clean" small-signal PWM signal is made using a fast logic gate, a low-jitter clock and a very stable reference supply. The output voltage of the power stage is compared (using an analogue difference amp) with the "clean PWM reference" and the error integrated using an analogue integrator. The integrated error is then digitized so the controller chip can correct the PWM control of the output stage. This is effectively Karsten Nielsen's PEDEC circuit, except that there's an extra AD conversion in the "local loop". Since the output voltage is compared to the "clean PWM reference" and any differences reduced by feedback, the reference is actually the signal that is getting amplified. You can easily show this by injecting an analogue audio signal into the error amp along with the reference while no digital input is present. You will get a high-quality amplified version of the analogue signal at the speaker terminals. A better way of describing the Zetex design is an analogue PWM amp with additional digital processing inside the control loop, and with a ripple precompensator at the input. In absolute terms, the performance of the NAD amp is good (and it sounds the part), but the control structure is more complicated and contains more digital processing than needed to get to this level of performance. But however you slice it, an enjoyable listen. Classedhaie (talk) 06:57, 19 May 2010 (UTC)

A bit of history would be nice
When were these things invented? When did they become practical and popular? Dbagnall (talk) 10:20, 10 February 2012 (UTC)

Switching amplifiers go back at least as far as 1976, when Infinity introduced its switching amplifier, amusingly dubbed the SWAMP. WilliamSommerwerck (talk) 22:05, 13 June 2012 (UTC)
 * Indeed, some history would be nice. There is absolutely none at all in the article! Who developed the first one, what products they were first used in and why, when and why they made it to various levels of the audio markets... Huw Powell (talk) 13:44, 20 December 2014 (UTC)

Redirected from "Transistor Amplifier"
Why does "Transistor Amplifier" redirect to "Class-D amplifier"? There are other classes too. — Preceding unsigned comment added by 220.244.96.30 (talk) 08:28, 17 March 2012 (UTC)
 * Hm you're right, this redirect is not helpful. Actually I'm not sure if it's a good idea to have an entry called "transistor amplifier" at all. The only place the term is ever used is in audiophile circles to make the contrast with "valve amplifier". Ontologically this is not an effective way of understanding the world. Imagine wikipedia having separate entries for control theory depending on whether we're talking mechanics, hydraulics or electronics, let alone using valves or transistors. I'd vote for the removal of the "transistor amplifier" redirect altogether, but I'm not sure how to go about this.Classedhaie (talk) 13:46, 8 May 2012 (UTC)
 * Redirect it to valve amplifier, and have a section in there describing the (alleged!) "transistor sound". Andy Dingley (talk) 13:56, 8 May 2012 (UTC)

Removed duplicate explanation
User 96.224.66.232 had added this inside the section intended for terminology: "A purely digital amplifier with no feedback would have zero power supply rejection.[1] Real class D amplifiers use analog input stages as part of the rejection circuit, while amplifiers with digital inputs must emulate this feedback loop in software. True digital Class D amplifiers are rare." This relates to technical execution, not so much terminology. Also, the point is already made in clearer terms under the error control section. A term like "true digital amplifier" is unclear, especially considering the fact that anything able to drive a speaker must be analogue, however implemented. For future edits relating to the species "true digital amplifier", consider using the term "open-loop digitally controlled amplifier" instead. The only new point the bit I removed makes that wasn't in the article is that an open loop controller can be improved by measuring the supply voltage in order to cancel supply ripple. So I'll add that to error control. Classedhaie (talk) 13:25, 8 May 2012 (UTC)

Bus pumping
The section about supply bus pumping conflates a number of things. On half bridge amps, excess power is always drawn from one rail (depending on the sign of the output current) and dumped into the other. This will happen equally with purely resistive loads. Full bridge amps return energy whenever the sign of the output voltage and output current are opposite, which means that it only happens with reactive loads. It might improve clarity to fix this item.Classedhaie (talk) 07:09, 12 June 2012 (UTC)

Distortion
There is really no discussion of distortion except to mention it "in passing" in a few places. How can an article on an amplifier class not talk in detail about the kinds and effects of distortion? Intermodulation, total harmonic etc. Are there inherient limits or types with this class? How are the design challenges met? What can the user expect from this topology? ... — Preceding unsigned comment added by 97.86.249.149 (talk) 13:03, 24 June 2012 (UTC)
 * The article discusses distortion in greater detail than you'd think at first perusal. It mentions the dominant error sources (dead time, power supply ripple, the LC filter) and the main method of combating it (adding negative feedback, for instance a PID controller, around the amp). Harmonic distortion and IMD are not 2 different kinds of distortions but two different manifestations of the same nonlinearity. What is worth adding at some point though is a section on distortion arising in the modulator, and that dead time distortion manifests itself as a non-linear output resistance in series with an idealised version of the amp. Spelling out the gory bits would become a bit redundant I guess. The article is more in need of a structure than of further details.Classedhaie (talk) 10:43, 3 August 2012 (UTC)

The definition
Class-D amplifier is an electronic circuit that has the ability of gain, but it's not the analogue-acting amplifier, and this is why so simple linking to amplifier is risky. This is switching amplifier or pulsating amplifier – very close to the principle of switched mode power supply. I suggest to fix the definition. --Robsuper (talk) 12:36, 11 April 2013 (UTC)


 * Yes, Class D amplifiers exhibit analogue gain. Looking at their internals, they use PWM. However, from the outside, they also make use of a low-pass filter. The result of this (c.f. Fourier, I hope I don't have to spell this out) is that their overall behaviour is indistinguisable from an analogue amplifier. Andy Dingley (talk) 13:58, 11 April 2013 (UTC)


 * If you treat such amplifier as a "black box" then yes: an analog signal at the input and at the output. However way for a particular purpose, and I am thinking of booster effect, is quite different - variable filled short pulses. The amplifier can not give energy without using properly selected low-pass filter attached between its output and the receiver (load). In applications the problem is the high level of noise from output transistors acting here as controlled switches - this disadvantage is the distinguishing feature of this type of signal amplification method. Thank you for kind response. --Robsuper (talk) 11:23, 16 April 2013 (UTC)


 * I think the second paragraph makes abundantly clear that "amplifier" need not imply "linear gain block". Class D audio amplifiers are particularly curious in that respect in that they behave (as much as their designer can make them) like a linear gain block even though the actual power stage is decidedly nonlinear. That does not detract from the fact that said power stage is still an amplifier for the relevant intents and purposes. It turns a small PWM signal into a big one. That's what it's asked to do and it does it well. The fact that on its own it'd be hopeless when called upon to amplify a sinewave is irrelevant. Its task is to amplify PWM, not sinewaves. That's the task of the overall circuit that beyond the switching stage includes modulation, error control and output filtering. Engineers define amplifiers operationally, not mathematically or abstractly. If a given contraption makes the signal bigger in the context that I'm using it in and with sufficient precision that I can use it, it's an amplifier.Classedhaie (talk) 09:16, 25 April 2013 (UTC)

Clarification
I just removed the addition "in digital amplifiers" from "The same errors will only lead to incorrect results in digital amplifiers when they become so large". Those three words were out of context. The sentence refers to transmitting digital signals (e.g. computer data) and recovering them exactly from their physical representation. No audio in sight.Classedhaie (talk) 09:20, 25 April 2013 (UTC)

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SMPS and amplifiers?
The article mentions the difference between class D amplifiers and switch-mode power supplies. I believe I have known amplifiers with non switch mode outputs that adjust the SMPS to keep power dissipation down. At lower power levels, the power supply generates a lower output voltage, and appropriate negative feedback allows appropriate output. This would mix up the meaning difference between class-D and other classes. (I don't remember which amplifiers I thought I knew that did this, though.) Gah4 (talk) 01:14, 2 May 2019 (UTC)

Early Vacuum Tube Patent 1930's by Bedford, GE
First invented by Burnice D Bedford General Electric Co in 1930 Although this predates the "Class-D" label it does utilize the same modulation methods.

Kgynkisd (talk) 21:30, 4 May 2020 (UTC)
 * From the patent -- "by properly varying the ratio of the time during which current flows in the respective valves the average current-over a complete cycle maybe Varied from approximately zero to maximum in either direction." Sounds very similar.  The invention by Alec Reeves isn't ref'd --- Is this acceptable?
 * https://bassmusicianmagazine.com/2020/11/history-of-the-rise-of-smaller-more-lightweight-bass-gear/ Alanf777 (talk) 20:55, 28 December 2022 (UTC)


 * Patents are WP:PRIMARY sources and, perhaps counterintuitively, are not great sources to use to support a claim of first invention. I don't particularly trust Bass Musician to have the facts right for the history of Class-D amplifiers. To get this right, we need to have a look at several reliable sources and see if there is a consensus about this. ~Kvng (talk) 15:33, 31 December 2022 (UTC)