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Archive 1

It has been suggested that Rf power amplifier be merged into this article or section. (Discuss)

(Um, I don't actually see this discussion, so I guess I will start it).

In my experience amplifiers are used for all kinds of things, from radio frequency applications (KHz-MHz-GHz) to audio (Hz-Khz) and even below (e.g. electric pedal-assist devices). RF specifically refers to applications in the higher frequencies and RF amplifiers have special problems.

So no, IMHO, RF and non-RF should have separate pages.

--Nil0lab 01:55, 9 March 2007 (UTC)

I agree, and for additional reasons. In my limited experience, RF transmitting (power) amplifiers seem to be discussed in conjunction with receiving amplifiers. As frequencies increase, receiving amplifiers (possibly transmitters as well), tend to employ materials other than silicon, which would seem better presented separately from lower frequency applications. It may also be appropriate to extend RF amplifier discussions toward higher frequencies, approaching the IR, and I believe that would be inappropriate in a general amplifier topic. My rationale for suggesting an extension into IR stems from the use of both RF and IR in collecting space based atmospheric data. I found it interesting to hear a comment a few years ago indicating that, if weather satellite RF capabilities could be extended a couple of orders beyond current limits, the IR satellites may no longer be necessary for this purpose. IMHO, this would push RF amplifiers into the edge of IR.

EngrAtPlay 04:44, 29 March 2007 (UTC)

Oppose. The RF thing is much more specialized. Dicklyon 23:28, 15 April 2007 (UTC)

Oppose, imho rf work is a large subsection of amplification needing its own article or more likely articles. Tabby 01:19, 2 December 2007 (UTC)

Oppose, AF and RF amplifiers, while sharing many similarities, are too specialized and differ in too many ways to merge into one article. —Preceding unsigned comment added by 24.218.178.56 (talk) 07:37, 27 February 2010 (UTC)

bad words

"power wastage" , wastage ? is that even a word ? why not just power waste or wasted power ? "Wastage" is a word, meaning "that which is wasted", so it seems the right word to use here. "but can suffer from the drawback that there is a small glitch at the "joins" between the two halves of the signal"

instead of joins , use zero-crossing that's more commonly encountered in electronics literature

Clipping

I'm not sure how much of the info on this page is correct.

I'm not sure that clipping is ever really a good idea, though some amplifiers have forms of "soft-clipping" to give high level output which doesn't sound too bad.

One form of amplifier effectively uses two amplifiers back to back - one for the positive going part of the wave, and one for the negative going wave. This can improve efficiency, but gives problems where the two amplifiers "merge" - gives a form of cross over distortion - the problem with this is that it happens at low levels, so can be very significant for quiet sounds.

Other more digital forms of amplification use various forms of pulse modulation. The article refers to sampling - and "conversion to numbers", but while this can be done using A to D converters, digital amplifiers using techniques such as PWM - pulse width modulation or other tricks (maybe delta modulation etc.) in order to smooth the output of essentially a switched signal. Often the switching is at a much higher frequency than the signal - much more than twice the highest frequency - perhaps 16 or 256 times higher. The advantage of switching is that theoretically a switch can be 100% efficient - in both on and off states, so amplification should give very high outputs for a given energy input.

Perhaps someone who is expert in this area could help?

I've rewritten chunks of the page so it addresses some of the things mentioned above - I also had issues with some of the statements on here. Personally I have designed many different amplifiers and I've never deliberately let them operate with any clipping at all. I think the author is getting confused between clipping off the top of a wave, and clipping off the negative portion, especially when discussing Class B - however, he may know something I don't so I'm not saying it's totally wrong. I've introduced mention of the Class B push-pull as the most common form for audio power amplifiers, and taken out the assertion that Class A is "most common" for these amplifiers. Another confusion in the article as a whole is that it tended to not discriminate between small signal and large signal (power) amplifiers - the former are usually Class A, the latter Class B. I also think trying to cover audio and radio frequencies in the same article is possibly unhelpful, since design techniques tend to change considerably as one gets into RF circuits. I'm thinking that a more complete rewrite is needed, with separate sections for small signal and power amplifiers, audio and RF frequencies. The only diffgiculty is that there is still quite a bit of overlap among these sections. Also some diagrams of of the results of differnt class designs might help clarify this a lot - I may go and prepare some... GRAHAMUK 00:01, 25 Sep 2003 (UTC)

I've now rewritten the page completely. I hope the previous authors will agree that it's a lot more logically presented. I cut out a few things, (but only a very few) so as to make the various discussions clearer. I don't think there is much to be gained by adding in mention of every possible form of amplifier - if tempted maybe you can craete new articles as needed and lionk them - this one's getting pretty long. GRAHAMUK 03:53, 25 Sep 2003 (UTC)

Class D

The author of the Class D section, imo, seems to be confusing Class D amplifiers with Digital to Analog converters (DACs) - the only reason that they are considered digital is that the output devices are only ever in one of two discrete states (saturation/cut off). There is never any conversion of the input into numbers, and most of the distortion is due to the modulation, not the quantisation of the signal.

That is only the opinion of an undergraduate EE student though, if anyone feels more qualified to respond, please do.

-Stuart (March 22, 2004)

I agree with Stuart, the section on Class D and E needs work. As well, I am quite sure that Class D and DAC's have been confused. I remember very distinctly that the first Class D I ever saw had one TO-5 output transistor with no heatsink and delivered 30 watts.

On the whole, I think the article up to that point is excellent though. I am sorry I do not have more time to work on this, but I do have a few suggestions based on my first impression.

I think it is unfortunate that the basic inverter circuit shown is simplified so much, even though the text says the bias circuit is omitted. As shown, it looks like any transistor switch. I think this may lead to later confusion. The graphical representation of the transfer function, showing the bias point and operation in the linear region might make the ideas clearer. If these are not added, the transistor might be better shown as a black box or a circuit theory abstraction like a controlled source. After all, most of the discussion is focussed on the different bias modes. You might try as a simplification using a separate bias supply and then showing how to eliminate it or just mentioning that it can be. If you show the bias supply you can make it clearer on the graph what the different modes of operation are all about.

The introductory sentence makes the point that the circuits under discussion are intended to reproduce the input, but perhaps more space in the later discussion should be given to discriminate it from similar circuits that are not intended to do this. In fact, perhaps the qualification should be more explicit, like saying faithfully reproduce or reproduce within specified distortion limits.

Perhaps the idea of clipping could be reintroduced in a discussion of the fact that any amplifier has a limited region of operation where it can meet the design specifications and that outside those limits it will saturate and depart from the idealization. Also it might be worthwhile to emphasize a bit more that a major goal in high power amplifier design has been to prevent amplifiers from self-destruction.

Negative feedback was originally introduced to make it easy to interchange tubes. Before this invention (roughly 1928), the gain of amplifier circuits had to be adjusted each time a tube was changed. Negative feedback makes the gain of the circuit mostly depend on the ratio of some resistor values. Transistors are specified with a range of β values, just as tube specs have a gm range, and negative feedback is needed with them too for that reason. I do not think this idea came across in the discussion of negative feedback.

I hope I do not appear to be too critical. I liked the discussion and I agree with most of the points. I am merely trying to help improve it. 66.92.234.253 17:57, 22 Mar 2004 (UTC)

I binned the class D/E section and started again. Please feel free to improve it. -- Heron 20:48, 22 Mar 2004 (UTC)
A great improvement Heron!
I wrote most of what currently exists in the class A, B and C sections, and the anon user (66.92...) above makes some valid and interesting points.
The problem with the bias circuits for all three classes are that they could all look exactly the same. There is no significant architectural difference between them, the difference is merely in the values chosen for the bias point, resistor values, etc. For an encyclopaedia article, I think adding these would add confusion, since unless one was prepared to work through and calculate the bias point, the differences wouldn't be obvious. Most readers are not electronics engineers - they would know all this already. I felt the key difference was in what the circuit does to the signal, which is why I (over)simplified the circuits and emphasised the signals. However the idea of showing the transfer curve and noting the bias point could well be worthwhile if the ideas it embodies can be conveyed easily.
Agree about clipping and avoiding self-destruction. However, one of my goals in rewriting this was to eliminate a lot of the tangential discussion that the original article had. Many WP articles lose focus after a while, because everyone throws in their own little piece of knowledge into an article, and what is important vs. what is relatively trivial tends to get lost. I think the mention of clipping is worthy of a footnote, but should not cloud the main points.
A fuller treatment of negative feedback is probably better placed in that article, rather than reproducing it here. NF is not essential to an amplifier, even though probably all modern designs use it. The historical note is interesting regarding the origin of the invention of NF - that could well be mentioned. Graham 02:09, 23 Mar 2004 (UTC)
Sorry, I was just clumsy, not purposely anonymous. I agree the stuff about class D and E is on track now.
I agree that it is good to edit down and stay on point. I did add some stuff, and feel free to work it over, but the point about a part being a specification, with only a range of gains, is an attempt to warn people that doing away with negative feedback entirely has very bad practical consequences. That point seems relevant to the discussion here about the good and bad effects of negative feedback.
By the way, the negative feedback link could use some work too. The story about the discovery is rather nice I think. What I remember is that a young engineer, Black I think, was trying to design practical repeater amplifiers for AT&T. His vision inspired theoreticians such as Bode and Nyquist to study and explain what he had discovered.
Clipping is only an incidental point, the real point is that an amplifier has a power limit, it only works in a limited range. This comes nicely off the transfer function graph, but the current link is inadequate. Saturation is an important concept though, which becomes highly relevant again when switching circuits are considered. Introducing saturation opens the opportunity to mention that saturation is a low power state for the switch, almost as good as off.
Certainly designing to avoid self destruction is an aside, but it might go well at the end of the practical section, where the discussion almost gets to this point. It is just that I was struck once, reviewing an old circuit, to think how we had learned not to make "those mistakes" anymore, and how nice it was that things did not fail so often now.
I am concerned about the circuit diagram because I was taught not to oversimplify. The criterion I was given was not to teach something that would have to be unlearned later. While I agree that the bias circuits all look alike, showing the bias point on the transfer graph, at least for me, is what made the whole thing make sense. The trouble with showing the transistor the way it is is that it looks just like a switch, a circuit intended to saturate, just what a linear amplifier is not supposed to do. This is what I think would have to be unlearned. You could just show a battery for the bias, and use it to make the point that the bias value relative to the cutoff point is what matters. You say as much, but I think it is easier to see if you show the cutoff point on a graph. The cutoff point is an important concept, like saturation, that should be emphasized. I really think that if you want this degree of abstraction you could better show a box for the amplifier. I am sorry I am not in a position to make the graph I have in mind for you. I will try to look for some references.
Anyway, I do like what you have done, I think you have made almost all the major points well, I am only trying to add a few points that I recall were important to me, and I hope you do not think I am too critical.

AJim 04:20, 23 Mar 2004 (UTC)

exotic non-transistor amplifiers

I added some stubs on more advanced designs and then saw this sentence: "Other more exotic forms of amplifier are also possible using different types of devices, but these will not be discussed in detail here to avoid complicating the picture too much." Oh well. Maybe we should just section them off? I will try to do that right now. - Omegatron 17:19, Mar 23, 2004 (UTC)

The amplifier article is a good place to dump exotic non-electronic amplifiers.
But what about non-transistor amplifiers, like RBAs ? --DavidCary 22:44, 15 July 2005 (UTC)
"Ribbon beam amplifiers (RBAs) are smaller, generate less heat, require smaller backup batteries,
are more electrically efficient and cost thousands of dollars less than solid-state amplifiers."
-- Lauren J. Clark, July 11, 2005, MIT

What about magnetic amplifiers? They are still used for massive current control in things like electric locomotives They are strictly ac amps. They use transformers with highly saturable cores, and a control coil on one section of the core, biased with DC, to control the gain of the transformer assembly. Anyone know more about them? 70.236.35.214 02:49, 17 February 2006 (UTC)

unusual classes: class F, G, H, I, ...

Regarding Class G and H, recently added. All amplifiers "modulate the power supply" - that's what an amplifier does - at least, I've yet to see an amplifier that doesn't require a power supply. While having variable rails is an interesting idea, all it's actually doing is moving the inefficiency elsewhere, or from another angle, sharing the power loss across more devices. True, those other devices can be switching and so incur minimal losses, but do these approaches really warrant their own class designations? While classes A - E appear to be something that most engineers can agree on due to fundamental architectural differences, beyond that it seems to be a designation that manufacturers invent to suit themselves. We need to be careful to avoid confusing the two. Graham 23:11, 23 Mar 2004 (UTC)

Classes A-H are "official" classes, from what I understand. F is some weird thing that uses different amplifiers for different harmonics or something, used in radio. I am not sure I understand why a tracking power supply is the same efficiency as a fixed rail power supply. I would have to think about that more than I am prepared to do right now, but it seems like it would be more efficient. By the same logic the Class G would not be more efficient, either, but I know for a fact that they are. Regardless, I am just reporting what I know are common classes of amplifiers. "Class T" and "Class I" seem to be marketing schemes pertaining only to one specific company's amp, but the other ones are pretty standard. We should definitely do some research on how the entire class designation came about in the first place, and then we can talk about which ones are "official" and which are not, according to whatever original specification they came from. - Omegatron 16:59, Mar 24, 2004 (UTC)
I didn't say it wouldn't be more efficient, just that it's not that innovative really - but if the powers that be have allowed the class designation then maybe I'm missing something. It's like having a fine and coarse adjustment between the power supply and the output terminal. The current that flows out of the output terminal has to have gone through two devices in series - and both will have dissipated some power. The fact that the actual amplifier output device (the "fine" adjustment) dissipates less power that it might have done doesn't automatically mean that the overall efficiency is improved, though the fact that the power dissipation is shared across multiple devices may well allow greater power delivery without self-destruction (just as having parallel output devices would). One thing does worry me about this design though, and that is its responsiveness to transients - the rail modulation has to be damned fast to keep up with a sharp transient so that the amplifier has enough headroom to deliver it to the load. To my mind, any standard circuit for doing this would never be fast enough, leading to momentary clipping on sharp signals. I suppose a (digital?) delay line on the signal through the main part of the amp would solve this, but add lots of issues of its own. It's getting very complicated! Seems to me that class D is the way forward - I'm a little surprised at the comment that its quality isn't up there with the best analogue designs, since I seem to recall that some very good hifi amps have gone this route in the past, and after all, most CD players use a 1-bit DAC these days, which operates on the same principle, albeit for small signals. Seems to me a digital input amp with a class D power stage would offer a very high quality system, at least for audio.Graham 23:40, 24 Mar 2004 (UTC)
I based that comment on the Usenet Audio FAQ, Part 4 (Amplifiers), 2004-01-14, which says that "Class D amplifier quality could catch up with Class A amplifiers. Some believe that it already has." An article by Philips [1] claims that Class D is suitable for high-end amplifiers. So perhaps my comment is now out of date. A final point: 1-bit DACs (delta-sigma converters) use noise-shaping, which I think makes them better than Class D amps, which use basic PWM. -- Heron 09:37, 25 Mar 2004 (UTC)

I found a Usenet post [2] that refers tantalisingly to the IEC, but I can't find any reference to "amplifier classes" on the IEC website. Someone out there might be able to track down a reference. -- Heron 17:31, 24 Mar 2004 (UTC)

I've done some editing of the class D section. It was quite good the way I found it - hope it's better still. As time allows I might put up some drawings (basic circuit, waveforms). Would it be a good idea to do this or would this carry the amount of detail too far? Opinions invited. I was wondering if the author of the excellent art work could add a schematic to the class C section actually showing a tank circuit in the collector instead of a resistor. --Bruno Putzeys 21:55, 22 Dec 2004 (UTC)

More details are always good, in my opinion. If it gets too detailed we can always move each amplifier to its own article and leave the simplification that other people seem to want here. - Omegatron July 9, 2005 19:16 (UTC)

Merged content

I merged the content from Class A amplifier and Class AB amplifier to this page. The coverage here seemed very good and more complete than the pages I merged. Osmodiar 17:03, 6 May 2005 (UTC)

class D

So class D is good because the transistors don't need to dissipate much power/heat because they are either off or on.

BUT

The extra harmonic power that they are generating is then filtered out, correct? So the filters are dissipating a lot of heat. Is it the same amount as would normally be dissipated in the transistors?

What makes the amplifier more efficient, if a lot of the power is dissipated in the filters? - Omegatron 19:40, July 9, 2005 (UTC)

An interesting point. The amount of unwanted heat (or the power) can be easily estimated by considering the Fourier breakdown of the resulting waveform. A square wave is described by the infinite series sin(f) + 1/3sin(3f) + 1/5(sin5f) + .. + 1/n(sinnf). (n = 7,9,11,13 etc) So all the unwanted parts are the rest of the series following the fundamental. This converges to a value of 1.0, so the harmonic power equals the wanted power, giving an apparent efficiency of 50% for the amplifier as a whole. Thus on the face of it a switching amplifier is no better than an analogue one, and for many designs worse. However this simple analysis ignores the fact that the switching is occurring at a very high frequency, and that the rise time of the switching waveform cannot be infinite - therefore in practice the amount of power in the harmonic is going to be considerably less than 1.0, and so the efficiency will rise accordingly. Also, the filtering itself does not necessarily dissipate this power - charge is stored in capacitors and rise times are limited by inductors, and phase shifts will put the voltage and current out of phase thus reducing the power factor. The net effect of what occurs is complex to analyse and in the end the best way is to simply measure power in versus power delivered - a switching design can realise 80-90% efficiencies and filters don't get noticably hot. A good designer will need to do the analysis however and make sure that all this unwanted noise is dealt with properly.Graham 01:52, 10 July 2005 (UTC)

It's not that complicated.

The extra harmonic power that they are generating is then filtered out, correct?

Yes.

So the filters are dissipating a lot of heat.

No. People design the output filters of class-D amplifiers so they don't dissipate heat.

Passive electronic filters are made from 3 types of components: resistors, capacitors, and inductors. In theory, capacitors and inductors do not dissipate *any* heat -- only the resistors dissipate heat.

So, people who design class-D output filters simply don't use any resistors. Only capacitors and inductors.

(In practice, real capacitors and inductors have some small amounts of "parasitic resistance", so class-D output filters do get slighly warmer than room temperature. Still, the total heat generated by a class-D amplifier and its filter is still far less than any linear amplifier with comparable output power.)

(So where does this "extra harmonic power" go, if it is not sent out to the speaker or dissipated in the output filter ? It is temporarily stored in the filter, in the capacitors and inductors. At some instants, energy flows *into* the filter, charging the capacitors and ___ing the inductors. At other instants, energy flows "backwards" from the filter, through the class-D amplifier, back into the power supply. This is why class-D amplifiers need a lot more/bigger capacitors on their power supply than other classes.)

--DavidCary 22:44, 15 July 2005 (UTC)

As I let the question stew in my mind (after writing the above) I started to think much more along these lines - there is no reason for the filter to "throw away" the unwanted harmonics, just store their energy. This energy can be used in useful ways which reconstruct the original signal at the output, and in reducing the workload of the amplifier itself. Both of which lead to better efficiencies. In other words, Davd Cary has put it much better than I did, and has got to the heart of the matter!Graham 02:40, 18 July 2005 (UTC)

Another article about class-d amp

There is another article about class-d amps PWM amplifier, which I created without knowing that something about it already exists here. Should that article be merged with this one? It has the block diagram of a class-d amp and some more info... Rohitbd 08:22, 6 August 2005 (UTC)

It's pretty substantial. Maybe copy the info from this article into that one and say "main article: PWM amplifier" - Omegatron 14:31, August 6, 2005 (UTC)
Should we proceed with this? Any second thoughts people...? Rohitbd 20:39, August 6, 2005 (UTC)
I'll go with Omegatron's suggestion, and perhaps we should add an HTML comment saying "please don't make this section any longer - put extra stuff in PWM amplifier instead". --Heron 16:49, 7 August 2005 (UTC)
After reading both, it seems the PWM amplifier article and this section have more or less the same information, except for different wording. What to do? Should I just replace the content here with a brief description and link to "Main article: PWM amplifier"?? Or is it best to keep it as it is with the "See also PWM amplifier" link? Rohitbd 09:18, August 8, 2005 (UTC)

digital Class-D amplifiers

What a pleasure it is to read a description of Class D that makes it clear this form of amplification is not inherently digital. Thank you! But I need to draw attention to the last sentence of this paragraph:

"The letter D used to designate this amplifier class is simply the next letter after C, and does not stand for digital. Class D and Class E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a Class D amplifier merely converts an input waveform into a continuously pulse-width modulated (square wave) analog signal. (A digital waveform would be pulse-code modulated.)"

PCM is not the only way to represent data digitally. PWM can also be digital, if the pulse width is quantized. There would be no reason for doing this in a Class D amplifier, as it would needlessly complicate the design. But one could have a Class D amplifier with an S/PDIF (or similar) input in which the pulse width was varied directly by the digital data, and thus quantized. Such an amplifier would be a digial amp (just as a regular PWM amp is analog).

WilliamSommerwerck (talk) 13:57, 20 December 2008 (UTC)

note to self

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part2/page1.html http://www.interq.or.jp/japan/se-inoue/e_dance26.htm http://www.tpub.com/neets/book7/0074.GIF

#Apparent Error in Efficiency of Class A stage

In the article it say that the maximum efficiency of a resistance loaded Class A stage is 50%. In my college notes we derived an expression for eff:

Eff =(useful ac power to load)/(Total dc power from supply) = Pcac/Pcc

Eff =(Icpk2*Rc/2)/VccIo (expression 1)

where :

Io is the standing collector current

Icpk is the peak value of the collector current (ac or signal)

Rc is the collector load resistor, and Vcc is the power supply voltage as usual

Max effy occurs when Icpk = Io (ie the output is just on the point of clipping) So, substituting for Icpk in expression 1, it is evident that the max eff is:

(Vcc2/8Rc)/(Vcc2/2Rc) = 0.25

However, (max ac load power)/ (max collector power) = (Vcc2/8Rc)/(Vcc2/4Rc)= 0.5

So is this what the article intended to say?? Perhaps you can comment on the above calcs. are my college notes right or wrong>?? Light current 20:54, 9 August 2005 (UTC)

They are probably right, but I don't think it's worth getting too worked up about it. This is an encyclopedia, not a text book. If there's a gross error we can correct it, but on the other hand if the reader comes away with the correct overall impression (Class A is less efficient that the other forms) then we've done our job. It's a simple matter to substitute 25% for 50% in the article (and yes, the efficiency implied is meant to be the overall efficiency, useful power delivered / dc input power. It's likely that when I wrote it I was confusing this with the load/collector power) Graham 22:54, 9 August 2005 (UTC)

Misc Issues with Class A Section

  • note that "class A preamplifier", although a well-used term, does not mean the preamp uses Class A in the circuitry (that pretty much can be taken for granted). Good and bad preamps use Class A... the term really means "it is a top quality amplifier (that can be matched with a top quality Class A power amplifier without embarrassment)".
  • quite a few advantages exist for Class A stages, not the least is simplicity (and better high frequency performance because Class AB and B makes the turned-off transistor go through a "who? Me?" type of delay before coming on.
  • the article as it was almost made it sound like people who advocate Class A automatically prefer valve/tube amplifiers; sometimes this is true, but it needs to qualify what it goes on to say, and also try to keep it related to Class A (tube stuff mostly belongs elsewhere)
  • Efficiency of class A - note the main problem is not so much that some current is drawn all the time (even Class AB does that, but it can be almost as efficient as Class B), but the two problems are that normally (not for square-law) that standing current is about HALF THE MAXIMUM output current, and (unlike Classes D and G etc) as it conducts part way through the cycle, all of the remaining power supply voltage is developed across the output device (same problem for Classes AB and B of course, but not normally much of an issue for class C).

Maitchy (talk) 05:16, 11 February 2010 (UTC)

RF modulation

A fairly large section about RF modulation schemes has been added under the Class C section. There is some interesting info here, and a few errors... there is definitely the start of a decent article there, but I don't think the right place for it is here, under Electronic Amplifier. It's too specific to the application of just one type of amplifier in one type of situation (amplitude modulation) so I think it should either be split out to a separate article, or placed in a more appropriate article, which might already exist. Comments? Graham 23:37, 22 December 2005 (UTC)

On further thought and re-reading, I decided to remove it for now. It's a tricky one - there is some worthwhile stuff here it just needs to be put elsewhere. Here's the text:

<quote>

Use of class C stages in radio transmitters

  • High level modulation.

One advantage of using class C amplifiers in a broadcast AM transmitter is that only the final stage needs to be modulated, and that all the earlier stages can be driven at a constant level. These class C stages will be able to generate the exciting drive for the final stage for a smaller DC power imput. One disadvantage is that for a given power output a class C stage will require a larger exciting drive. Another disadvantage is that a larger audio amplifer will be needed for the modulation stage.

  • Low level modulation.

One advantage of using linear ammlifiers in the chain of amplifers between the exciter and the final output stage is that the gain of the linear stages is larger than class C stages. Also one of the smaller early stages can be modulated, which only requires a smaller audio amplifer to drive the modulator. The great disadvantage of this system is that the amplifer chain is less efficent.

  • Key clicks

In morse (on off carrier keying) if the carrier is turned on or off rapidly the bandwidth will be very large, if the carrier turns on and off more slowly the bandwidth will be smaller. The problem of excessive bandwidth used by a morse transmitter which turns on/off too sharply is known as key clicks. If a perfectly made morse (CW) transmitter's output is feed into a series of cascaded class C stages then the output will be likely to suffer from key clicks becuase the power output of a class C stage increases greatly when the input power is increased slightly. </quote>

As a former designer of RF transmitters, (albeit a loooong time ago) there are some errors here - in practice the drive stages also need to see some modulation otherwise the output can be rather distorted. Class C gain versus Class A (linear) gain depends on the design - it's not a general rule that Class A will have higher gain. Class C can often be operated at higher gain because it is less prone to unwanted oscillation than Class A. If you are modulating the final stage of an AM transmitter, then the class of the amplifier has nothing to do with the audio modulation power required. It will always be equal to the peak power of the transmitter. However, I think what the author is trying to say is that you would only modulate a class C stage in this way, because if you have a Class A output, there is no point in modulating it, you might as well modulate a lower power drive stage with much less power, and the final linear stage will amplify it faithfully. So yes, Class C requires more power to modulate it, but that's not an inherent property of Class C, as implied, but of the overall design in which it's used, which is a different point. Low-level modulation doesn't always require a linear amplifier either - a very common type of design when I worked on them was to use a Class C lineup with low-level modulation applied to one or two of the drive stages. This modulation would not be completely eliminated by the final Class C stage, but could be detected at the output by a simple sniffer circuit and used in a feedback circuit to modify the modulation waveform to compensate for the distortion through the amplifier. The result was undistorted AM at the output, with low power modulation and efficient Class C amplification. Maybe this would be called feedforward now. Anyway, surely there's an article in this, somewhere...? I just don't think it's here. Graham 00:01, 23 December 2005 (UTC)

No 100% efficency for digitals?

> the amplifying process cannot be 100% efficient

This statement at the beginning of the article is not obvious for digital technology amplifiers and should be explained with reasoning. 195.70.32.136 13:46, 26 January 2006 (UTC)

Perhaps some explanation is required in the article; a moment's thought though will make it clear that even switching designs must waste some power - the saturation ON resistance of a device can never be zero, and switching times cannot be infinitely fast. But I agree, maybe this needs making explicit. Graham 10:23, 27 January 2006 (UTC)

how does it "make it clear"? don't assume anything... class D amplifiers based on supercondor junctions are 100% efficient. they're noisy (because the energy flow is quantized), have serious i/o interfacing problems, but these are other issues.

Perhaps that is so, but it's hardly a practical, buildable, obtainable, amplifier. With any generalisation there can be found exceptions; hence the expression " the exception that proves the rule". Graham 00:32, 15 April 2006 (UTC)

Class F

Class F amplifiers are used in radio frequency communications such as cell phones or data links. They have provisions designed into them that accommodate for the modulation (or decoding) of the output by both amplitude modulation (AM) and frequency modulation (FM). This gives the designer multiple multiplex paths, whereby different information channels can be encoded into the signal, not just the AM or the FM, but also secondary paths such as side bands, pilot signals, or data streams. This also allows for redundancy to be designed into the signal, to ensure the prevention of error, or loss of data. This type of amplifier often uses Pulse Frequency Modulation (PFM) techniques to provide this complex modulation.

I removed the above, as I believe it's not relevant or really correct. The amplifier itself does not care what form of signal it amplifies. The complex modulation is created by a modulator and then amplified - the amplifier doesn't need to be specially designed to handle the resulting signal (as long as it has the desired bandwidth, etc). Once you drag in all this extra complexity, you are no longer talking about an amplifier, but a chain of signal processing in which the amplifier is just one part. Graham 05:59, 20 April 2006 (UTC)

I wrote the above deleted section as an attempt to simplify a complex subject. The problem with the dismissal of this section is that the different types of modulation require different types of coupling, and different insertion points in the flow of information through the amplifier. The designers of the more advanced class "F" circuit components (Motorola, aka "ON Semiconductor", for example) are producing chips that have provisions for multiple types of modulation, and therefore multiple channels of possible information paths. These redundancies are intended to be used by the circuit designers to ensure robust communications, even when data loss occurs with noise, interference, of low signal strength. For example, if you examine the class "G" and "H" sections, you will find the modulation to the amplifier being applied at different points: the inputs and the power rails. Should we dismiss those sections also? 70.236.25.140 16:30, 15 February 2007 (UTC)

>is created by a modulator and then amplified

this is in contrast to what google says ... citation needed ... It may not be relevant, and the article should not be bloated, but linear amplifiers are suited for AM, amplifiers for 100% duty cycle can do FM. Arnero 10:29, 16 February 2007 (UTC)

Definition of amplifier

While the term 'amplifier' is loosely used to describe a device that increases the current or voltage, strictly speaking for a device to be an amplifier it *must* increase the power level. Otherwise a power supply is not required and a transformer or other passive device will do. That is, the product of voltage and current at the output must be larger than the product of voltage and current at the input.

Amplifiers are usually thought of as electronic, but mechanical, hydraulic and pneumatic amplifiers are possible.

Peter Hiscocks phiscock@ee.ryerson.ca

I tend to concur with this definition Peter. ie a transformer is not an amplifier; atuned circuit is not an amplifier although both increase the current or voltage. It would be nice to find a ref to this effect!. 8-)

BTW, could you please add any new posts at the bottom of the page and sign them with ~~~~. THanks! 8-)--Light current 04:26, 2 July 2006 (UTC)

Thanks for the guidance, as you might guess, I'm new to the wiki world. You might want to add something to the following effect

A particular amplifier may be referred to as a 'voltage amplifier', 'current amplifier', or 'power amplifier'. This is a reference to its intended purpose: for example, the primary purpose of a 'voltage amplifier' is to increase the amplitude of the signal voltage. The level of the signal current may increase or decrease as a side effect, but overall there is an increase in the signal power. Strictly speaking, then, every amplifier is a 'power amplifier'. However, this term is usually applied to an amplifier that is designed to produce significant power - for example, an audio power amplifier or servo motor amplifier.

Peter

Well yes I could add it, but so could you! Remember this is the encyclopedia that anyone can edit!--Light current 01:07, 4 July 2006 (UTC)

Proposal: Break out Guitar-dedicated articles

http://en.wikipedia.org/wiki/Talk:Distortion#Proposed_Article_Titles_and_Changes

The refactoring is in-progress. MichaelSHoffman 03:47, 8 August 2006 (UTC)

The refactoring is done. MichaelSHoffman 08:49, 8 August 2006 (UTC)

Best Sound

Does anybody know which is the best sounding amplifier? - 12:40, 2 September 2006 (UTC)

It depends on what you mean by "best sounding", and what you intend to use it with. But there are some studio monitor specific amplifiers that are particularly flat. No amplifier is 100% perfect, every design has it pros and cons. Also, if you intend to have a perfect system, the amplifier and speaker must be matched. So this is not a question with a simple answer.--Lenilucho 16:34, 2 September 2006 (UTC)
Its the one that sounds the best to you!--Light current 20:23, 2 September 2006 (UTC)

Inverting & non-Inverting section

Arg! 180 degrees out of phase is not the same thing as an inverse relationship! —Preceding unsigned comment added by 81.105.21.22 (talk • contribs)

See Talk:Phase_(waves)#Phase_vs_polarity and Talk:Active_noise_control#Phase_vs._polarity. — Omegatron 13:28, 5 September 2006 (UTC)

Class B and AB issue

I think there is a problem with the section "Class B and AB". The schematic for class B push-pull system shows the wave-forms incorrectly. The particular schematic represents a "class B push-pull emitter follower" and hence the output wave-form must be in phase with the input. Rohitbd 12:26, 5 August 2005 (UTC)

Well spotted. I have uploaded a new version of the diagram. --Heron 19:35, 5 August 2005 (UTC)
Thanks...another small issue, the o/p waveform must be of same amplitude (slightly less actually, but of no consequence) as the i/p - it's a unity voltage gain stage. It may also help to indicate what the waveforms represent - voltages or currents. This may be applicable to all the schematics... Rohitbd 08:15, 6 August 2005 (UTC)
The Class A section implies that class A amps are always single-ended (esp. the comment comparing the sound of class A to the sound of push-pull). I think it should be amended to point out that a push-pull amp can also be class A, and to clarify that operatin class is a matter of device conduction, and is distinct from topology. Anyone disagree? 64.171.68.130 17:42, 13 November 2006 (UTC)

Class numerical suffix

"Sometimes a figure is added (e.g., AB1 or AB2) with higher figures implying a higher quiescent current and therefore more of the properties of Class A."

This is incorrect. The suffix 1 or 2 means that grid current is not (AB1), or is (AB2), drawn (the latter implies *power* rather than just voltage drive).

Both class AB1 and AB2 stages may well operate at the *same* quiescent current, but if anything a class-AB2 stage would tend to be biassed *away* from class A to limit anode dissipation.

This numeral suffix designation is also used to sub-divide Class-B into B1 (no grid current) and B2 (grid current).

"to clarify that operatin class is a matter of device conduction, and is distinct from topology"

I think this is an important point (given the misleading marketing hype around "Class-A"). BUT, while it's true that a push-pull stage *can* be Class-A, the idea is absurd in practice - push-pull topology is used to *avoid* the problems of Class-A.

ref: any valve era ARRL or RSGB Handbooks, Radiotron Designers Handbook, &c, &c. 210.9.180.221 (talk) 08:12, 22 March 2009 (UTC) -Rolls (tech, musician, Wikinewby)

I agree AB1/AB2 (or A1/A2) refers to whether (appreciable) grid current is drawn. I thought I corrected that error ages ago; I see it was wrong in March 2009 and still not corrected by Feb 2010, so I decided to correct it again but also leave a "some say" type of clause with what I think is an incorrect interpretation as an alternative for a while (in case anyone comes back and backs up the claim... I don't want a revolving door series of changes).

Still Needed in Class B/AB

  • mention of square-law (should not imply all Class A is based on a straight line).
  • "since much of the time the music is quiet enough that the signal stays in the "class A" region" is wrong for most transistor amps - typical quiescent currents being 20mA (used to be more like 70mA) and I think Douglas Self recommends much lower, so hardly likely to stay in Class A. But valve/tube amps tend to have quiescent AB currents of around 88mA (when the full-signal current might be 140mA,for 6L6's in the RCA manual as an example), so then that statement is correct.
  • great lack of references (should at least include ARRL or RCA, JLH, D.Self). —Preceding unsigned comment added by Maitchy (talk • contribs) 12:14, 11 February 2010 (UTC)

Negative feedback

The article said:
"Feedback was originally invented so that replacing a burnt-out vacuum tube would not change an amplifier's performance (manufacturing realities require that tubes and transistors with the same part number will have close but not identical gain)"
Did someone have an reference for this affirmation? because in

  • Ronald Kline: “Harold Black and the negative-feedback amplifier” IEEE Control Systems Magazine, Volume: 13(4), pages: 82-85, August 1993
  • Ron Mancini, Op Amps for Everyone, second edition, page: 1-1, ISBN 0750677015 (Available on TI website (PDF))

It's told that the first negative feedback amplifier was invented by Harold Stephen Black for the Bell Labs when he was working on reduction of the carier amplifier distortion. Yves-Laurent 23:34, 11 December 2006 (UTC)

So, nobody care about an mistaque in an featured article.Yves-Laurent 16:34, 1 February 2007 (UTC)

Disputed

There are numerous problems with the tagged section on negative feedback. More details to follow... Alfred Centauri 03:28, 15 April 2007 (UTC)

I agree. There are seeds of truth in there, but the long essay on what "many believe" with no attribution needs to be flushed and replaced by level-headed statement backed up by a reference. Probably the best thing would be to blank it and start over with more sensible content. Dicklyon 17:37, 15 April 2007 (UTC)
A few time ago, the french article was a traduction of the english one. But since he was rejected as FA, i had to rewrite it and add a lot of references. I think he is NPOV now. I haven't got the time to translate my work into english but you can use the references: most of them are in english.Yves-Laurent 12:36, 16 April 2007 (UTC)

Since adding the tag, I've followed some wikilinks around and there are already articles on feedback and negative feedback (although there are some glaring problems there too). I'm thinking that there should only be a mention of negative feedback here with a 'main article' link to the negative feedback article. Alfred Centauri 20:27, 15 April 2007 (UTC)

Sounds right to me. Shouldn't need to work on fixing multiple places. Dicklyon 20:30, 15 April 2007 (UTC)

Removed the following disputed section from the main article:

Negative feedback

Feedback was originally invented so that replacing a burnt-out vacuum tube would not change an amplifier's performance (manufacturing realities require that tubes and transistors with the same part number will have close but not identical gain). While amplifying devices can be treated as linear over some portion of their characteristic curve, they are inherently non-linear; their physics dictates that they operate using a square law. The result of non-linearity is distortion.

Feedback feeds the difference of the input and part of the output back to the input in a way that cancels out part of the input. The main effect is to reduce the overall gain of the system. However, the unwanted signals introduced by the amplifier are also fed back. Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. In this way, NFB acts as a technique to reduce errors (at the expense of gain). Large amounts of NFB can reduce errors to the point that the response of the amplifier itself becomes almost irrelevant as long as it has a large gain, and the output performance of the system (the "closed loop performance") is defined entirely by the components in the feedback loop.

Careful design of each stage of an open loop (non-feedback) amplifier can achieve about 1% distortion. With negative feedback, 0.001% is typical. Noise, even crossover distortion, can be practically eliminated. Negative feedback also compensates for changing temperatures, and degrading or non-linear components in the gain stage, but any change or non-linearity in the components in the feedback loop will affect the output. Indeed, the ability of the feedback loop to define the output is utilised to form active filter circuits. The concept of feedback is used in operational amplifiers to precisely define gain, bandwidth and other parameters entirely based on the components in the feedback loop.

The application dictates how much distortion a design can tolerate. For hi-fi audio applications, instrumentation amplifiers and the like, distortion must be minimal, often better than 1%.

While feedback seems like a universal fix for all the problems of an amplifier, many believe that negative feedback is a bad thing. Since it uses a loop, it takes a finite time to react to an input signal, and for this short period the amplifier is "out of control", and worse, an echo of the signal will be fed back after the signal transient has passed, corrupting the signal that follows (which will in turn be fed back again, ad infinitum). In this way the signal is "smeared in the time domain". A musical transient whose timing is of the same order as this period will be distorted, even though the amplifier will show extremely good distortion performance on steady-state signals. This, essentially, is the rationale for the existence of "transient intermodulation distortion" in amplifiers which was exhaustively discussed and debated from the late 1970s through much of the 1980s.[1] Proponents of feedback deny this, saying that the feedback "delay" is of such a short order that it represents a frequency vastly outside the bandwidth of the system, and such effects are not only inaudible, but not even present.

This argument remains controversial, and at times quasi-religious and very intense, and is related to an equally long-running debate between an "objectivist" school backed by theory and measurement and a "subjectivist" school who claim to be able to clearly hear differences that the objectivists say cannot be there. As one small example, it is sometimes said that as distortion below 0.1% cannot be heard and amplifiers can easily be constructed that have measured distortion less than this figure, all such amplifiers are for practical purposes identical and "perfect". But if we look deeper,

  • the main source of distortion in many amplifiers is the "crossover glitch" of a class B or class AB amplifier, which might represent only a couple of percent of a full-power sine wave. The average distortion level measured might be low, but the distortion during the crossover glitch itself might be 50 times larger than the average - well above the hypothetical "level of inaudibility"
  • real-world music often contains quiet passages where the entire signal is down in the crossover distortion region.

It is thus seen that a "simple" statement of x% (averaged) THD at full power gives a misleading statement of distortion when listening to music with a class AB amplifier, since real-world performance will be much worse. Subjectivists propose similar arguments against many of the other measurements that objectivists cite as evidence. The debate continues.

Whatever the merits of these arguments about its effect on waveform distortion, feedback also affects the output impedance of the amplifier and therefore its damping factor. Roughly speaking, the damping factor is a measure of the ability of the amplifier to control the speaker. All other things being equal, the greater the amount of feedback, the lower its output impedance and the higher its damping factor. This improves the low-frequency performance of many speaker systems where low damping factors lead to irregular bass response. The majority of modern amplifiers use considerable amounts of feedback, though many of the high-end audiophile designs seek to minimise this.

NFB cannot be used in very high-frequency amplifiers where the propagation delay through the amplifier is much longer than the period of the signal being amplified, and other techniques have to be used to linearise the circuit, including feedforward amplifiers (e.g. digital signals on many cell-site base-station transmitters are precompensated for the radio amplifier's distortion).

Doherty amplifier

The article says:

The Doherty amplifier […] fell into disuse with the advent of FM radio.

Not so. Not only was the Doherty design contemporaneous with the invention of FM radio in the mid-1930s, but many long-, medium-, and shortwave transmitters based on Doherty amplifiers are still in use today, particularly in high-power applications. Western Electric was the assignee of Doherty's patent, which was granted in 1940; Continental Electronics was building broadcast AM transmitters based on this design into the 1990s. There were other, competing designs throughout the 1960s and 1970s from companies like RCA, Collins, and Gates. What eclipsed the Doherty amplifier in broadcasting was not FM (although FM does not require linearity) but rather, the development of practical modular transmitter designs, which use a large array FET-based low-power amplifiers and a combining network to achieve high power output, as exemplified by the Harris DX-50 et seq. 121a0012 19:39, 27 May 2007 (UTC)

Please do fix the article then. If you have sources to back up the details, that would be much appreciated, too. Dicklyon 19:43, 27 May 2007 (UTC)
I've done so to the best of my ability (not being an E.E.), including a citation to the Doherty patent (which this article seems rather weak on). I don't know what the legal status of patent drawings is, but figures 9 through 12 of the patent show some fairly typical embodiments of the Doherty design. Perhaps someone might care to redraw one of these using modern symbology to illustrate this section. 121a0012 02:20, 1 June 2007 (UTC)
US patent drawings are generally public domain, so if you'd like to include some of those, go ahead. There's an image rights tag for it, but I forget what it's called. Dicklyon 02:31, 1 June 2007 (UTC)
I would not like to do so. I suggested that someone who has the ability to draw schematics (not me) with modern symbology (not me) redraw one of them. 121a0012 05:20, 14 June 2007 (UTC)
Still would be good to upload the original patent drawings. — Omegatron 05:40, 12 July 2007 (UTC)

Class G and H not well-defined?

Are class G and H officially defined anywhere? I've seen them used interchangeably and used to mean entirely different things.

  • This BASH amplifier looks like our definition of class H, yet the terms "class G' and "class H" don't appear anywhere on their site. We should also point out the use of a single switching power supply used for multiple channels of audio.
  • NXP calls their amplifiers Class H, but they look more like a variant of our definition of class G to me, generating a temporary second rail at twice the supply voltage for playing high crest factor music waveforms. — Omegatron 05:38, 12 July 2007 (UTC)
  • QSC's RMX amps (schematics here) are a better example, in that they are clearly of the rail-switching variety, but are called "class H" by QSC:

    Class G: This high-efficiency technique uses cascaded Class AB output stages; each connected to a different power supply voltage, with the magnitude of the input signal determining the transistors to be used. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs. [Historical note: Hitachi is credited with pioneering Class G designs with their 1977 Dynaharmony HMA 8300 power amplifier.]

    Class H: An amplifier output circuit design, which involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single Class AB output stage that is connected to two sets of power supply rails by diodes or transistor switches. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks [thus the nickname railswitcher]. Another approach is Class G. QSC's lowest-powered amplifiers use Class AB, while the higher-powered models use Class H. Class H circuitry adds cost and complexity, but can drastically improve the electrical efficiency over that of a class AB output section of the same power rating.

  • ProSoundWeb's definition:

    Class H: A variation of Class AB. Changes the power supply voltage to the amplifier depending on the signal level. Improved dynamic efficiency. Requires complex power supply. Single tone efficiency up to 65 percent Sounds excellent—if well-designed

  • According to Rane Corp (and Stanley of Crown):
    • Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this...
    • Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices [thus the nickname rail-tracker or tracking power amplifier]...

An etymology search and look through AES literature might help clear up the discrepancy. — Omegatron 05:14, 20 July 2007 (UTC)


Rane/Gerald R. Stanley credits Hitachi with popularizing the class G design in 1977, and Hitachi's paper from 1978

  • Tohru Sampei (1978). "Highest efficiency and super quality audio amplifier using MOS power FETs in class G operation". IEEE Transactions on Consumer Electronics. CE-24 (3). {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

says:

As one of the approaches to this generally incompatible requirement for higher efficiency and improved quality in an audio power amplifier, we developed a special power output circuit consisting of stacked 2 Class B system in 1976. This system was referred to as Class "G" operation.

But Rane/GRS also say that it was mentioned in 1965:

  • Thornton, Richard Douglas (1966). Handbook of Basic Transistor Circuits and Measurements. Wiley. p. 156.

A Google Book search doesn't find the phrase "Class G" in this book, though this isn't conclusive. — Omegatron 03:25, 25 July 2007 (UTC)

Hitachi, the makers of the MOSFET output devices used in many audio power amplifiers, created such a marriage when they developed what they called the class G type of output circuit. What is class G? Basically, it is a push-pull output stage that looks like a class AB output stage, but with an extra output device added in a series ladder to each class AB output device on each side of the push-pull circuit.

— International Audio/Video Review

Rane/GRS credit Soundcraftsmen with popularizing Class H, with some schematics available at http://www.soundcraftsmen.info — Omegatron 04:02, 25 July 2007 (UTC)

Ronan van der Zee (1999). High Efficiency Audio Power Amplifiers; design and practical use. ISBN 90-36512875. lists:

  • Class G
    • Series type - with two output devices connected in series for push and pull, with either switching on and off to make the higher rail accessible and the other acting as the output device
    • Parallel type - with two parallel push-pull stages connected to the two rails - more efficient but more expensive for more than 4 devices.
  • Class H

This book has definitions of class G and class H, as extensions of class B. This one agrees, as do others. Dicklyon 03:58, 25 July 2007 (UTC)

Those two conflict on their definition of class H, don't they? — Omegatron 04:14, 25 July 2007 (UTC)
They sound the same to me. Both say they use a bootstrap circuit to vary the supply voltage dynamically. Dicklyon 05:40, 25 July 2007 (UTC)
Well, the Douglas Self one says "a method of dynamically boosting the single supply rail (as opposed to switching to another one)", which means the switching lift capacitor to me.
The Slone one is more ambiguous:

instead of switching between two sets of power supply rails, class H architectures dynamically adjust the power supply levels to accommodate the power output requirements. In principle, this amounts to increasing the power supply voltage when higher output power is desired.

I guess this could also refer to the lift capacitor type, though it sounded like a signal-tracking type at first. — Omegatron 00:57, 26 July 2007 (UTC)

In fact, I think there's enough material here to separate these designs to their own article. I don't know what it would be called. High-efficiency analog audio amplifiers or something? — Omegatron 04:11, 25 July 2007 (UTC)

I doubt there's much there. The refs indicate that the efficiency advantages are not worth the trouble. I think these are basically theoretical classes that nobody has ever done much with. Dicklyon 05:40, 25 July 2007 (UTC)
I'm not sure what you're referring to, but the rail switchers are quite common in audio applications, especially large power amplifiers, the lift capacitor switcher is used for relatively low-voltage car audio, and I've seen at least one example of the tracking power supply. If you built a 2000 W audio amplifier with no rail switching, it would be much more expensive. You need the higher efficiency to save all that money and rack space that would otherwise be spent on heatsinks, transformer copper, and extra output devices. — Omegatron 00:57, 26 July 2007 (UTC)
OK by me. I was just going by what the books seemed to suggest. Dicklyon 01:06, 26 July 2007 (UTC)
Class G and H are used in DSL line drivers, see "Driving the DSL Highway" by Sevenhans et al, in Proceedings of the 28th European Solid-State Circuits Conference, 2002. According to this paper, Class G switches the supply of the main amplifier whereas class H modulates the supply of the main amplifier. Saxm12 21:44, 30 July 2007 (UTC)

They also list a "class K" audio amplifier. Reference:

— Omegatron 03:01, 31 July 2007 (UTC)

I made a schematic of an class G amplifier. This schematic based on the schematic gave in "Douglas Self, Audio Power Amplifier Design Handbook, Newnes, 2006 (ISBN 0750680725)" and "Michel Girard, Amplificateurs de puissance, Ediscience International, 1993, 435 p. (ISBN 2840740419 et ISBN 978-2840740414)." and, for me, confirmed by the description of the class G in "G. Randy Slone, High-Power Audio Amplifier Construction Manual, Mcgraw-Hill, 1999 (ISBN 0071341196 et ISBN 978-0071341196).". Yves-Laurent 23:53, 13 November 2007 (UTC)

Featured Article Review

Shouldn't someone start by telling us why the FAR nomination? Is there some issue we should looking at or fixing? Dicklyon 01:45, 18 July 2007 (UTC)

Discrepancy with definition of electronic amplifier

The article currently defines an electronic amplifier as "a device for increasing the power of a signal", but section 1.4 states "Amplifiers can be designed to increase only the signal voltage (voltage amp), only the current (buffer amp), or both (power amp), of an electronic signal".

I don't agree with the current definition, but at least it should be consistent with the rest of the article and the gain article. Any objections to changing it to "power or amplitude of a signal"? -Roger 00:29, 3 November 2007 (UTC)

It's not inconsistent, since increasing only the voltage or only the current will also increase the power, if the other is fixed. But I wouldn't object to adding "or amplitude", as that does broaden the definition a bit. Dicklyon 04:44, 3 November 2007 (UTC)
Yeah, but it doesn't say the other is fixed. A transformer, for example, could increase only the voltage and be considered a voltage amplifier (by the second statement, but not the first). -Roger 04:57, 3 November 2007 (UTC)
I understand. However, the modified definition should not be interpreted that way. It's not saying that every device for increasing the amplitude of a signal is an amplifier, just that an amplifier is a device for increasing the amplitude of a signal. Sometimes the power level is quite irrelevant in amplifiers used to process signals, and a power increase may not exist at every amplifier circuit, even if the circuit is capable of providing an output signal of more power than the input signal. Dicklyon 06:12, 3 November 2007 (UTC)

Purpose of this article is not followed consistently

This article is intended as an overview of the term "Electronic amplifier"; as such, the massive detail on Class A, Class B etc, power amplifiers is misplaced and should be moved to an article on power amplifiers per se. Another similar discussion can be found in the article "Amplifiers", which article title seems not clearly differentiated from "electronic amplifiers", although "Amplifiers" should be higher on the hierarchy than "Electronic Amplifiers", being a more general designation. The topic of Power Amplifiers needs consolidation, as it seems to have become dominant to the exclusion of all else. Brews ohare (talk) 17:50, 9 January 2008 (UTC)

I have combined the Power Amp Classes from "Amplifier" with the more extensive discussion in this Article, which avoids elaborate digression in "Amplifier". However, a Power Amp article would be a better place for all this. Brews ohare (talk) 18:41, 9 January 2008 (UTC)
Moved classification scheme from "Amplifier" to this Article; rearranged a bit to get all the Class A, Class B stuff into the power amp subsections Brews ohare (talk) 19:11, 9 January 2008 (UTC)
I agree: This article is intended as an overview of the term "Electronic amplifier"; as such, the massive detail on Class A, Class B etc, power amplifiers is misplaced and should be moved to an article on power amplifiers... and there is duplication between the "Amplifier" and "Electronic amplifier" articles (I prefer the wording and structure, by and large, of the "Amplifier" article). There are h-u-g-e chunks of "Electronic amplifier" devoted to power output stages and classes (yet still has omissions - e.g. Square-law, and mistakes - e.g. AB2 used to be defined by the output valves drawing grid current - a lot different to the presented definition). There could be devised some graphic that clarifies subsets in the amplifier "taxonomy" tree (should I try doing one??). The big question I have is: should we have ONE article for amplifiers (that has a section on "Electronic Amplifiers") plus another article on all the technical stuff associated with power output stages (classes of amplifier, push-pull, even an overview of famous historical amplifier designs!)? I think the way forward is to ask questions like: "I am thinking of buying a sound system, and all these terms like distortion baffle me... what do I need to know?" or questions a mid-level techie might want to know before/during a google search for options, like "what types of amplifier circuit are good for efficient battery operation?"). Maitchy (talk) 09:38, 18 June 2009 (UTC)

It should be "increases the amplitude" of a given signal in some way, that is the only one that covers everything. Even if one is measuring a definition (power= volts x amps) or a value (voltage or current). After the act of amplifying, we can talk about the quality of the output: if it has more current, then it is a buffer: if it has more voltage, is is a multiplier. Since power is a definition created for use by multiplying the 2 values, the present entry is not better than the general "power increase" definition. —Preceding unsigned comment added by Ketchupman 9 (talk • contribs) 19:50, 15 February 2008 (UTC)

note that some amplifiers don't end up increasing the amplitude in every case - take a preamplifier with tone controls, and volume wound down. One definition of "amplifier" would take just the amplifier block without controls that are attenuating, but "amplifier" can also be used of the whole box. Also, an op-amp with a gain of -5dB is still an amplifier (we tend to say "gain" when we mean voltage gain... it probably has current gain even if the voltage gain is less than unity, but it might not). I think it makes sense to define an amplifier as something that has power gain (to distinguish it from transformers and attenuators, for example), but then go on to say there are exceptions... amplifiers can actually reduce the power, deliberately, even though the components are capable of increasing it. Maitchy (talk) 09:38, 18 June 2009 (UTC)

Diagrams

I made a lot of diagram for the french article fr:Classes de fonctionnement d'un amplificateur électronique (amplifier classes). Including some animations :

  • Class-AB
    Class-AB
  • Class-C
    Class-C
  • Class-D
    Class-D

I think some of them can help you to illustrate this article. Yves-Laurent (talk) 00:22, 5 February 2008 (UTC)

Those are good, hopefully someone will add them. -Roger (talk) 18:00, 24 February 2008 (UTC)

article split proposal

This electronic amplifier article is full of good information -- good job!

However, there seems to be some content that is duplicated in other articles, and I think it is about long enough to consider splitting into smaller articles.

I suggest moving the appropriate sections into:

leaving behind only a brief wp: summary style. What other articles would be a good place to move content out of this article? --68.0.124.33 (talk) 01:04, 13 October 2008 (UTC)

question on diagram

The schematic diagram is very nice, but (1) no reference is given as to where it came from (is it based on an expired patent? Did a Wikipedia editor/engineer make it up on the spot? is this the very first Class AB amplifier schematic?); (2) no component values are given; (3) no specs are given for THD, maximum wattage, speaker impedance (4 ohm, 8 ohm, 16 ohm). A beginner searching for a good, simple first amplifier to build will be confused. Mrdarrett (talk) 21:16, 7 May 2009 (UTC)

Witch diagram ?
This one ?
Yves-Laurent (talk) 07:42, 24 December 2009 (UTC)
The diagram looks fine to me as it is, its purpose is to illuminate the main features of amplifier design. Wikipedia should not be a "how to" guide and instructions for home electronic projects are not appropriate. If the OP wishes to discover the original creator of the diagram they can do this by clicking the diagram and then clicking the links to its predecessors (of which there are two). SpinningSpark 14:01, 24 December 2009 (UTC)
The user Glenn just made this edit to this schematic's caption, and looking at it, I think he has a point. The biasing of Q2's base seems oddly asymmetric with Q1's base. Why would one use a voltage divider but not the other? It would be nice to have citation for schematics; otherwise we can't tell if it's really a well-known design or something a Wikipedian made up using "common sense". I think a schematic is a factual statement as much as anything written in prose, and thus deserves the same treatment for factual correctness. CosineKitty (talk) 14:57, 24 January 2010 (UTC)
I believe that the diagram is correct as illustrated: if this amplifier were built with reasonable-value components, I expect that it would work. (Although it might need a compensation capacitor for stability). At first glance, the biasing of the differential pair looks wrong. But R8 and R7 form a feedback circuit and DC voltage divider which will keep Q2 properly biased, and also set the gain of the amplifier. R7 will tend to pull Q2's base down toward ground. When this occurs, Q2 will conduct less and Q1 will conduct more. Q1 will then pull Q3 on more, which will in turn pull Q4 on more, driving the output DC voltage higher. This higher output DC voltage will feed back through the R8/R7 divider, bringing the Q1/Q2 differential pair back into balance. If I'm wrong on any of this, feel free to say so.  :-) Wildbear (talk) 03:39, 25 January 2010 (UTC)
Very interesting, Wildbear. I majored in EE but ended up writing software for a living. My practical experience with electronics is mostly weekend-hobbyist stuff. So I feel better about the diagram based on your commentary. I still think it would be nice to seek citations for the schematics. CosineKitty (talk) 16:53, 25 January 2010 (UTC)
Follow-up: Should we remove the phrase added to the caption? It seems wrong to have "... that needs a capacitor in series with R7 or connected to Vsupply/2 to work" because we should either fix the schematic if there is something wrong with it, or remove the claim that there is something wrong with it. CosineKitty (talk) 17:01, 25 January 2010 (UTC)
The circuit should be able to work as illustrated; suitability just depends on the application. It's good enough for illustrating amplifier theory, so I have removed the claim that the circuit is wrong. User Glenn's observation may be partially correct, depending on how the circuit is intended to be applied. The R8/R7 divider sets the voltage gain, and also affects the DC biasing of the circuit. Higher voltage gain requires that the R8/R7 ratio be higher, which in turn requires that the Q2 base voltage be set lower, and/or the Q4/Q5 emitter voltage be set higher. Because of this, the available voltage gain may be quite limited before the biasing would take the circuit into nonlinearity or clipping. Adding a capacitor in series with R7 would disassociate the AC voltage gain from the DC biasing, allowing for higher values of voltage gain. There would be tradeoffs — if the circuit is on an integrated circuit, it would likely require an additional external component (the capacitor), and the frequency response of the circuit would be affected (less flat). I agree that source citations for the schematics is desirable. Wildbear (talk) 22:43, 25 January 2010 (UTC)

Class D and Electric Bass Amps

It should be mentioned that Class D Electric Bass Amps have become extremely popular due to their light weight and low cost. Mark Bass, Genz-Benz and David Eden each have popular models. —Preceding unsigned comment added by 151.203.41.51 (talk) 01:02, 24 May 2009 (UTC)

Class D amps 80-95% efficiency

It says this in the article. I thought that Rohm amp with 90% efficiency was reveled for it's record-maybe- efficiency? http://www.eetasia.com/ART_8800464222_499501_NP_c0bbb082.HTM Daniel Christensen (talk) 13:54, 29 September 2009 (UTC)

Class E mistake

Note: the above diagram contains a mistake. The capacitor should connect between L and L0, and not across the switch T1. A better diagram would be appreciated. Comment by User:130.113.100.19 Made in the article. Moved by SpinningSpark 03:30, 23 December 2009 (UTC)

I'll check the diagram this week-end but after a quick search on the internet, i don't think there's a mistake. Yves-Laurent (talk) 07:38, 24 December 2009 (UTC)

Class B schematic in article is really class C

the schematic diagram in the article representing class B push-pull is incorrect. there is no bias voltage applied between the bases of the complementary output devices, resulting in cutoff of the top (npn) device at 0V+Vbe and no turnon of the bottom (pnp) device until 0V-Vbe when continuous signal is applied. this results in class C operation, with significant crossover distortion and associated harmonic distortion due to the stairstep (discrete) response in the range +Vbe > 0 > -Vbe. this diagram, imo, should be modified such that a voltage source (roughly) equal to Vbe sits above the input to the npn and below the input to the pnp, resulting in a smoother transition from the top output device(s) to the bottom output device(s). the diagram however accurately represents class C operation, but not class B. —Preceding unsigned comment added by 24.218.178.56 (talk) 07:30, 27 February 2010 (UTC)

Yes, however none of the schematic diagrams show any biasing, so they are all incorrect as far as that detail is concerned. This is the first time I've seen this article, but it seems there is an unstated assumption that the schematic is showing only the vague arrangement and the relationship of the output to the input, which is probably all that should be attempted here. Johnuniq (talk) 07:45, 27 February 2010 (UTC)

Changes and corrections

I corrected several things, mostly hyphenation and punctuation. However, I notice that this article needs much more than that. I believe it needs to be fixed and reworked.

1. I changed "special classes" to "additional classes". E, F, G and H are "additional classes" of amplifiers and "special classes" are used for the trademarked spinoffs of regular classes.

2. The sentence "Also, Class E and Class F amplifiers are commonly described in literature for radio frequencies applications where efficiency of the traditional classes in are important, yet several aspects not covered elsewhere (e.g.: amplifiers often simply said to have a gain of x dB - so what power gain?) deviate substantially from their ideal values." is very messy and needs to be reworked, possibly without parentheses and questions marks. A few separate sentences are probably preferrable.

3. The section "4.3 Class B and AB" should be split in two just like in the summary under "4 Power amplifier classes".

4. I moved 3 paragraphs from "Class F" into "Class E" since they are primarily about Class E (I don't understand why there were under the wrong class).

5. Starting from "4.6 Additional classes", the text starts to be very hard to read, either because it's not very clear or because it's too technical.

6. Section "4.7 Amplifier circuit" shouldn't be at the end but a little earlier.

7. A simple circuit schematic for each class would be nice to see. Pictures do not really point out the differences between classes. A table summarizing efficiencies for each class would also be nice.

ICE77 (talk) 05:37, 3 July 2010 (UTC)

  1. ^ Otala, M., and E. Leinonen: “The Theory of Transient Intermodulation Distortion,” IEEE Trans. Acoust. Speech Signal Process., ASSP-25(1), February 1977.
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