Yes, because they are more likely to add distortion. That is why some people claim to like them. They call the distortion "warmth". I don't get the attraction.
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Let's stop calling Class D amplifiers "efficient" when they are not.
- Thread starter restorer-john
- Start date
Yes, because they are more likely to add distortion. That is why some people claim to like them. They call the distortion "warmth". I don't get the attraction.
He may not have even done that.
Jim Taylor
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True. I need to remember to state qualifiers, otherwise we'll be testing surfboards against battleships.
Jim
I handled a large Yamaha amp with the class A switch and like you experienced with your amp the difference was not there. Sounded exactly the same. I handled many class A JVC and Technics amps and they ran class A for the first little bit of power and they sounded the same as any other amp when on a switchbox and comparing them. Class A is a very broad brush stroke that encompasses many amps from many manufacturers and so the comment made by @A.wayne is too broad a stroke and makes little to no sense.
True. I need to remember to state qualifiers, otherwise we'll be testing surfboards against battleships.
Each of those is well suited to the job it is designed for and would be very bad at the other job so both are needed.
I don't see any use for class A amps when there are superior options at lower prices.
I believe the headphone amp in the Wiim Ultra is class D and it works very well.
Class D headphone amp? That might be a first.
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I'm going with 'yes' then. But no matter- you and I are on the same page.
Sy, you can take this post as a Citation
Class A used to be used to place the output devices in the most linear part of their range of operation. This is traditionally done because in the old days it was hard to put enough feedback on the circuit to prevent non-linearities raising their ugly heads. So every means possible to reduce the innate distortion of the circuit was used to allow feedback to better do its job; class A operation is one tool used for that.
These days class D allows the designer to use a considerably higher amount of feedback than is often practical in a class A or AB design as in those designs doing so without very careful design of the feedback network likely will result in stability problems.
In all amps you have something called 'Phase Margin' which describes the limits of bandwidth and feedback, which if exceeded, results in oscillation (due to phase shift at higher frequencies, usually ultrasonic). You are familiar with this problem as it has appeared a number of times in class A or AB amps over the years. Usually its something to do with the load such that frequencies which exceed the phase margin of the circuit pass through the feedback network (a well-designed feedback network can prevent this so is more than just a simple resistor). That is why I said 'without very careful design' earlier.
Examples are the Futterman OTL (in particular the New York Audio Labs versions) which could oscillate if the load was not ideal and especially if the amp was overloaded. Other examples showed up in the 1980s when a number of solid state amps would oscillate when used with a particular Polk Audio speaker cable. There are a good number of other examples. In the tube era, one of the lowest distortion amps made was the Khronhite UF101, which ran up to 80dB of feedback at some frequencies. But if you look at that design, two things are obvious- the first being that the designer was very good at feedback network design and the second that he recognized both the limits of tubes to have enough Gain Bandwidth Product and also that phase margin must not be exceeded. So the feedback varies in that design depending on the frequency.
Class D can solve the linearity problem and the oscillation problem with one stone, using a technique called 'self oscillation'. In this case, so much feedback is applied to the amp that it goes into oscillation as soon as the amp is powered up. The feedback network is carefully designed so that the amp can only find one frequency at which to oscillate, and that frequency is used as its switching frequency. This allows for a considerably higher amount of feedback than was previously possible in many cases, although there are some class AB amps available now that do have more sophisticated feedback network designs which allow for more feedback with them too.
The point of this is when you get that much feedback in an amp design (in excess of 30dB at all audio frequencies, not just in the bass or the like), the feedback allows the amp to reject a great deal more of that which is not the signal, such as distortion- so can correct for phase shift due to limited bandwidth or the effects of AC power line sag. This also means that class A no longer has a particular distortion advantage it might have had in the past. I should point out in case you are not aware that any class D amp which uses a choke in the output filter (which is all class D amps used in audio) is incapable of any kind of crossover or notch distortion associated with the zero crossing of the audio signal. For more information on this topic see Bruno Putzeys' paper on negative feedback.There you will see how many class A and AB designs had limited feedback owing to limited Gain Bandwidth Product, and he presents it all with the math, diagrams and engaging text if the math isn't your thing.
Nope, not all. There are some specially designed modulation schemes that make it possibly to (almost) omit the output filters. They are not particularly high-powered devices, but they do exist:
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I was thinking of the kind that use computer controlled output to negate the filter. There are also uses such as in subwoofers such as in this paper from the AES. But I was being too general...
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When I think of a Citation, I think of...
umm, I mean...
It's OK -- I'll see myself out. Thanks.
umm, I mean...
It's OK -- I'll see myself out. Thanks.
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Yup! Brute force. That was an amp for laboratory work so efficiency wasn't a concern.
Hard to beat (Beats? ha ha) Apple's AirPods Pro 2, they're quite effective. A friend who has tested them all-he loves toys-said some others might sound a bit better but the ANC not quite as good. Over the ear, that Sony whatever model is damn amazing, I literally could not hear the salesperson talking next to me!
Note that in low priced stuff the "ANC" is only for the microphone, it does not reduce ambient noise. I tried various buds and eventually gave up and went Apple.
I have over 70 years listening experience, have designed and built quite a lot of equipment in the professional arena, and in my experience to date quality of design and implementation is the primary differentiator of audio amplifiers. To the extent that, given adequate design and implementation, it is impossible to differentiate between high quality amplifiers in a true blind test within their power ratings. It is a lasting source of regret that the letter "A" was chosen for the first of the series of descriptions of output device conduction angle. If they had started with "Z" things might now be different. I sit here surrounded by 2000W of Class D (and some 500W AB) audio power devices in my little studio, while most of the heat comes from Class A microphone and line amplifiers and valve/tube-based equalisers. I doubly emphasise the requirement for competent design and implementation, having suffered Clive SInclair's early attempts at Class D back in the '60s (and his class AB, come to that). And I say this having owned examples of many of the best valve/tube amps in my various studios, all of which I refurbished and sold at a good profit to otherSo in your 8 years as a member here, you haven't read or learned anything? Maybe start with this thread.
So, are Class A power amplifiers actually any good?
As per the title, despite their inefficient design, heat output, cost and weight, class A power amplifiers are often upheld as a kind of 'gold standard' on many forums with out objective justification. I note that very few, (I can't recall one), have been tested on this very illustrious site...
But I say again, they all sounded just as good as each other, but 15/25W with modern (non-horn) exclosures and driver efficiencies just doesn't cut it.I'm trying to think: why would my amps (tri-amped system) be idling? If they are, it would only be for the length of time that it takes to get music going.
I'm pretty sure that is not an issue in substantially raising the average.
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If at any given moment, one of the amplifiers is supplying, say, 50 mW to a driver (e.g., a tweeter), it's virtually at idle.
That's why.
My guess is that such is the case far more often than onewould EDIT (might) expect!
(and, yes, it's quite testable, if one is suitably curious)
That's why.
My guess is that such is the case far more often than one
(and, yes, it's quite testable, if one is suitably curious)
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I -- ahem -- still think it would be absolutely fascinating to:
Plug an arbitrary Class AB amplifier with linear P/S into a Kill-a-Watt meter. Hook it to a source and loudspeakers ad lib. (as it were).
Play an arbitrary recording of (e.g.) Holst's The Planets* at a pleasant SPL (say 80 dB-ish average-ish SPL at listening position; or a bit less if desired) via an arbitrary pair of loudspeakers.
Record energy consumption (kW-hr) of the amplifier via the Kill-a-Watt from start to finish of the piece.
Swap in an arbitrary Class D amplifier with SMPS for the AB amp.
Repeat, measuring energy consumption of the amplifier via the Kill-a-Watt.
Report results.
Yes. I would do it myself -- but I have no Class D amplifier here**, so I cannot do it.
______________
* Might as well make it interesting!
** I used to have a Lepai 2020 amp (the one with, ostensibly, the old Tripath chip) here, but I gave it to my son for his desktop music system.
He's 500 miles away, so not a trivial matter to borrow it back.
edit: note the smilin' EQ.
Plug an arbitrary Class AB amplifier with linear P/S
into a Kill-a-Watt meter. Hook it to a source and loudspeakers ad lib. (as it were).Play an arbitrary recording of (e.g.) Holst's The Planets* at a pleasant SPL (say 80 dB-ish average-ish SPL at listening position; or a bit less if desired) via an arbitrary pair of loudspeakers.
Record energy consumption (kW-hr) of the amplifier via the Kill-a-Watt from start to finish of the piece.
Swap in an arbitrary Class D amplifier with SMPS
for the AB amp.Repeat, measuring energy consumption of the amplifier via the Kill-a-Watt.
Report results.
Yes. I would do it myself -- but I have no Class D amplifier here**, so I cannot do it.
______________
* Might as well make it interesting!
** I used to have a Lepai 2020 amp (the one with, ostensibly, the old Tripath chip) here, but I gave it to my son for his desktop music system.
He's 500 miles away, so not a trivial matter to borrow it back.
edit: note the smilin' EQ.
Ah, Motor Trend's car of the year in 1980
