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  #1  
Old 11-09-2017, 11:33 PM
vivitern vivitern is offline
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Dose Class-D Amplifier Audio Perform Better than linear classes

The audio amplifier market is progressively growing while advances in semiconductor technology enable more applications to use class D amplifiers. But are metal-oxide-semiconductor field-effect transistors the only solution?
Class D audio amplifiers are able to fulfill the requirements for audio applications such as mobile handsets, Bluetooth/wireless speakers, and vehicles, to name a few. These amplifiers dissipate less heat, extend battery life in portable devices, and are much more efficient than linear audio amplifier classes, such as Class A, B, and AB. They are small in weight and size, which makes them suitable for applications like the ones mentioned earlier.


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Class D amplifiers also are extremely efficient (often up to 90% or higher) because the output transistors are fully turned ON or OFF during operation. Therefore, there are no power losses in the output device. Class D amplifiers use metal-oxide-semiconductor field-effect transistors (MOSFETs) as switching devices. Typically, they use a pulse-width-modulation (PWM) topology with a fixed-frequency to produce a PWM equivalent of the analog input signal. But they use lowpass LC filters to extract the amplified audio signal, thereby increasing cost and board space.

New filterless modulation techniques eliminate or minimize the use of external filters. Removing LC filters, however, invites the possibility of electromagnetic (EM) radiation caused by the amplifier switching at a frequency much higher than the highest audio frequency to be amplified. To deal with this problem, solutions from semiconductor vendors like Texas Instruments and Maxim Integrated offer filterless spread-spectrum modulation and feedback technique schemes with different output configurations (e.g., one-channel, two-channel, etc.). They mitigate EMI and improve poor Total Harmonic Distortion Plus Noise (THD+N) performance.


Developments in power semiconductor technology had created a new approach for handling higher efficiency with minimal audio distortion. For example, Class D amplifiers can also be developed using enhancement-mode GaN (eGaN) FETs. Efficient Power Conversion’s eGaN FET-based Class D amplifiers claim to switch many times faster than power MOSFETs and do not have any reverse recovery charge. As a result, the dead-time—typically 25 ns for silicon power MOSFETs—can reportedly be reduced by 80%, to 5 ns or less (Fig.1). This means that the turn-on and turn-off delay, as well as the rise and fall times for eGaN FETs, will be much faster and contribute less to signal distortion. Very low THD+N also can be achieved, while minimizing Transient Intermodulation Distortion (T-IMD) and the EMI emissions from the amplifier. The EPC9106 (http://www.kynix.com/Parts/3591380/EPC9106.html)reference design has demonstrated 96% efficiency at 150 W / 8 Ω, and 92% efficiency at 250 W / 4 Ω.


1. Shown is a comparison of MOSFET and eGaN FET switching waveforms. (Courtesy of EPC)



With advancements in class D amplifiers, they are now being used in more applications than linear amplifiers used to dominate such as home theaters and televisions. The new solution from Efficient Power Conversion (EPC) for Class D amplifiers, for instance, looks very promising and it might be widely adopted by audio manufacturers in the future. According to Research and Markets, the Class D audio amplifier market is expected to be worth $2.76 billion by 2022, growing at a CAGR of 17.4% between 2016 and 2022. The two-channel Class D audio amplifier currently holds the largest market share and is expected to grow at the highest rate during the forecast period, as it is commonly used in in-car audio and television sets.
  #2  
Old 11-10-2017, 12:46 AM
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Class D amplifiers are the natural continuity for a digital source audio chain. As the output signal can be very well modulated beggining from the digital word, not transforming it into analog signal on early stages. The transformation in analog signal will be done, at good quality D class amplifiers, only on output power stages, on integrator . In my oppinion, of course. About RF noises such power amplifier can produce, can be probably induced in the rest of audio chain, especially if sensitive analog amplifiers like head pre or MC/MM pre. Again, only if digital connection between components, where noise is not big issue, such amplifiers can perform very well, maybe better than many linear ones, IMO.
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Old 11-10-2017, 12:25 PM
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I've had good luck with class D amps. They are dirt cheap, efficient, compact, powerful, sound good, don't need dual rail power supplies....but they don't like being pushed into distortion, and some have RF noise problems.

I don't see them completely displacing linear amplifiers though, there will always be an audiophile niche for 'em. (I still run class A tube amps lol)
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Old 11-10-2017, 01:46 PM
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Class D amps are definitely more efficient no doubt about it, but when it comes to sound quality they still lag behind by a long shot. Even the best ones by Bang & Olufsen (Icepower) are still a long way behind.

For me all that counts is sound quality. I use to have a very good well regarded amp by loads of people the NuForce 9SE V2 monoblocks but next to my Spectral Audio Class A/B it was like childs play, no way would I go back to Class D amps.

By the way a Class D amp are not digital, a mistake a lot of people make. D is just the next letter available in the series, We have A, B, A/B, C and now D.
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Old 11-10-2017, 10:38 PM
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Quote:
Originally Posted by TooCool4 View Post
Class D amps are definitely more efficient no doubt about it, but when it comes to sound quality they still lag behind by a long shot. Even the best ones by Bang & Olufsen (Icepower) are still a long way behind.

For me all that counts is sound quality. I use to have a very good well regarded amp by loads of people the NuForce 9SE V2 monoblocks but next to my Spectral Audio Class A/B it was like childs play, no way would I go back to Class D amps.


By the way a Class D amp are not digital, a mistake a lot of people make. D is just the next letter available in the series, We have A, B, A/B, C and now D.
I did not say class D is digital, I just said that is better adapted for digital , as the priciple permits that signal can be treated based on digital word up to the final stage , on integrator. This due to PWM modulation used on this amplifiers. The PWM can be directly controlled by the digital signal, in the most intimate mode, resulting awsome results , for the best creation of this kind. Signal will not be treated as analog, but converted from digital into PWM, amplified as PWM then integrated into analog using special filters. This is why this amplifiers will work on its best when fed with digital signal. If you want to use analog signal for this amplifiers, you have to use double conversion, very bad for quality, also low level analog will not be treated well due to rf noises and some other noises resulted from double conversion
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Old 11-10-2017, 11:23 PM
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Since the control signal for the FET-pair is square, or ON/OFF, the "digital" misnomer caught up, being not really far from reality.
Plus that "digital" sounded back then very fashion.... like "blue" today (bluetec, bluemotion, adblue, the blue light of the LED on audiophile gear etc...).

All types/classes of amplifiers suffer from one or more defects... there is always a trade off.
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Old 11-11-2017, 12:39 AM
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The trade offs are many but what people think is a good amplifier in D class may really be buying junk form China that will not last long nor do they care about any artifacts or high frequency noise. In other words they are not high quality products. Making something cheap only means that you will have to replace it more often than in the olden days.

One example are flat panel displays I bet there have been people that replaced their flat panel TV 6-10 times in the time my Sony XBR monitor has worked and I am still using it. Newer technology is not always a better product, it is just that they have figured a new way to sell you some new junk they thought up. Digital amps are no different. I am sure McIntosh would have gone out of business already if all you need is one of the garbage Chinese amps some with goofy names. For me I will stick with my regular stuff but I did like the Sony V Fet amps when I saw them they were just too much money back then, The TAE type product.

Any engineer can tell you that just because they cane make a square wave is no reason to think they are good sounding as audio is never square waves. Well maybe some Metal music is but there is no quality in that.
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Old 11-11-2017, 01:15 AM
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Quote:
Originally Posted by Skywavebe View Post
I am sure McIntosh would have gone out of business already if all you need is one of the garbage Chinese amps some with goofy names.
Luxury products share a different target people.
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Old 11-11-2017, 02:42 AM
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Quote:
Originally Posted by MagneticBlood View Post
I did not say class D is digital, I just said that is better adapted for digital
I did not say you said it was digital, I said “a mistake a lot of people make”
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  #10  
Old 11-22-2017, 12:55 PM
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In a controlled blind listening test, I doubt very much that one can discern differences in sound among the different amplifier classifications of similar build quality.
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Old 11-22-2017, 02:57 PM
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Give me a big-ass room heating, watt guzzling Krell KSA-250 (or similar) any day of the week over those PC class D amps.
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Old 11-22-2017, 09:53 PM
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The class D amps are , as principle, very good idea and if some small problems solved remain only the surprise of perfect dynamic sound, no negative feedback problems, amazing fast sound and so on. And do not forget please that this class D are also analog amplifiers.
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