Class D amplifier module

A class-D amplifier or switching amplifier is an electronic amplifier where all power devices (usually MOSFETs) are operated as binary switches. They are either fully on or fully off. The term “class D” is sometimes misunderstood as meaning a “digital” amplifier. While some class D amps may indeed be controlled by digital circuits, the class D amplifier control circuit can be also implemented with analogue component. I would rather call class-D amplifier as a switching amplifier rather than “digital amplifier”.

Class D amplifiers work by generating a square wave of which the low-frequency portion of the spectrum is essentially the wanted output signal. In a simplest form he generated signal can be just pulse-width-modulated (PWM) square wave, but in many practical class D amplifiers the output signal is slightly more complicated. After the output driver stage a passive low-pass filter removes the unwanted high-frequency components, i.e., smoothes the pulses out and recovers the desired low-frequency signal. To maintain high efficiency, the filter is made with purely reactive components (inductors and capacitors). The switching frequency is typically chosen to be ten or more times the highest frequency of interest in the input signal. This eases the requirements placed on the output filter. In cost sensitive applications the output filter is sometimes omitted.

I bought some time ago Y148 Audio Amplifier Module so learn more than just the theory of the class D amplifiers. Hands on on some new technology gives better insight than just reading the theory. Here is the picture of the amplifier module ready to use on my desk.

classd1

To make connecting the wires easier I have added screw terminals to Y148 Audio Amplifier Module (the module came only with soldering holes for power and speaker connections). Speaker and power connections have large well spaced holes. I also added pin strip (L_in, GND, R_in) for audio input and audio cable to connect the audio source.

Here is some data of the amplifier:
- Model: Y148
- PCB board
- Adopts YDA148 high-efficiency digital audio power amplifier IC
- DC input voltage: 9~15V
- Current: 2~4.5A
- Power output at DC 15V input: 15W x 2 (8 ohm), 30W x 2 (4 ohm)
- Power output at DC 12V input: 10W x 2 (8 ohm), 20W x 2 (4 ohm)
- Needs heat sink at 4 ohm, doesn’t need heat sink at 8 ohm
- Frequency response: 10Hz~20KHz(+/-0.2dB @1KHz)
- Load speaker: 4 / 6 / 8 ohm
- SNR: at least 90dB
- Harmonic distortion: THD+NC no more than 0.1%P=0.1W

classd2

Y148 Audio Amplifier Module is cheap super small amplifier. It works great, and plays all right. No noticeable noise/distortion at reasonable audio levels. It runs nicely on 12V power. Great product, especially the price is really attractive.

The specifications are pretty good for such small device. The module drives 8 ohms speakers from 12V power source directly. The tiny IC in the center of the circuit board can handle 2x10W without any heatsink! If you try to run 4 ohm speakers or higher power the chip gets quite hot (you should be able to solve the problem with a suitable small heatsink added on top of that that little chip).

You can use it even on battery powered applications, because you can get quite a bit of audio output with about 100mA from the battery! Not the full power but useable volume levels. The high efficiency is the reason that class D amplifiers are popular in many battery powered electronics devices.

classd3

As I told earlier Class D amplifiers work by generating a square wave of which the low-frequency portion of the spectrum is essentially the wanted output signal. YDA148 high-efficiency digital audio power amplifier IC operates around 500 kHz frequency according to datasheet (I measured 508 kHz on my module). The IC generates pulses (starting from 0V and going up to +12V in level) to both + and – side of speaker output line at that frequency. The pulse length varies depending on the signal that needs to be sent to speaker. When there is no output signal, both pulses are short. When the amplifier needs to send positive voltage to speaker, the pulse at + line gets longer and longer depending how high voltage need to be set to speaker. The – side pulses stay at the same short length. In case of negative voltage needs to be sent to speaker, the – side pulses get longer and + side stays short. The picture below show the pulses that can be seen on speaker + output on IC output.

classd_scope

YDA148 high-efficiency digital audio power amplifier IC datasheet says that a low pass filter at corner frequency of 50 kHz normally needed (digital amplifier operates around 500 kHz).

yamaha_filter

The amplifier board has this kind of filter in it. Ther filter works pretty well in attenuating the high frequency signal. I measured around 50 mV (RMS) 508 kHz triangle wave on the speaker oputput after the filter. So the switching feququency is pretty well attenuated, and in taking account the fact that speaker elements can’t play back those high fequencies and will not hear them, I don’t think it could hurt the the sound quality at all.

classd4

The size of components is one that might in some applications drive to try to avoid the filters. As you can see on the board I have the filter components take much more board space than the actual IC. In the picture below you see the amplifier IC on the top and filter components for one channel on the bottom.

Direct connection from IC to speaker element is also possible according to YDA148 datasheet when speaker has element is suitable (inductance 20 microhenries or more), wires are short and speaker is present always. I think that direct connection method would be feasible only in active speaker applications where amplifier and speaker elements are inside same cabinet. In all other applications that filter is needed, because EMC reasons (feeding a strong 500 kHz signal to unshielded speaker cable generates easily lots of interference).

YDA148 datasheet also says that this IC supports differential input. Using differential interfaces is a good idea in many audio applications. Unfortunately this amplifier module board does not support using differential input. The module I have has only traditional unbalanced line level input option. That is useable, but I would have preferred to have differential interface as an option.

Y148 Audio Amplifier Module seems to be a good small audio amplifier. It was cheap, performed well and provided a good platform to lears about class D amplifiers. Class D amplifier technilogy is nowdays mature and ready to be taken into use.

44 Comments

  1. Tomi Engdahl says:

    Tips & Tricks: Avoid Harmonic-Balance and SPICE software flaws for time-domain simulation
    http://www.eetimes.com/design/communications-design/4392093/Tips—Tricks–Avoid-harmonic-balance-and-SPICE-software-flaws-for-time-domain-simulation?Ecosystem=communications-design

    There are severe flaws within the Harmonic-Balance and SPICE programs now widely used. Mentioned as far back as within an abstract of Session WSO at the 2008 IEEE International Microwave Symposium

    Engineers using SPICE time-domain software to find the steady-state periodic response, also have difficulties: they run the program for 100 to 1000 periods, depending on the Q (Quality Factor) of the resonant circuit at the operating frequency. That takes a long computing time, and it suffers from increasing errors, the longer the running time

    In the case of switching-mode power amplifiers, now a very popular application, those problems can be avoided completely, by using, instead of Harmonic Balance or SPICE, a mathematical algorithm for a direct computation of an exact solution for the steady-state periodic response [2] and subsequently improved [3]. This “Liou-Sokal” algorithm works for two reasons: (a) the algorithm is an exact analysis, and (b) the computations are executed in double precision, which gives correct results, even in nearly unstable cases.

    Reply
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  3. Tomi Engdahl says:

    This seems to be a lot like Y148 module packed to metal box:

    YDA148 Aluminum Alloy Digital Amplifier – Silver (DC 9~16V / 3A)
    http://www.dealextreme.com/p/yda148-aluminum-alloy-digital-amplifier-silver-dc-9-16v-3a-153343

    Reply
  4. Tomi Engdahl says:

    Digital-Input Class D amplifiers expand the benefits of traditional Class D and simplify system design
    http://www.edn.com/design/analog/4400490/Digital-Input-Class-D-amplifiers-expand-the-benefits-of-traditional-Class-D-and-simplify-system-design-?cid=EDNToday

    A new generation of digital-input Class D audio amplifiers achieves high PSRR performance that is comparable to traditional analog Class D amplifiers. More importantly, digital-input Class D amplifiers provide additional benefits of reduced power, complexity, noise, and system cost.

    Electronics vendors commonly use high-efficiency, filterless, analog-input Class D amplifiers to manage the power requirements of portable audio speakers found in cell phones, tablet computers, and personal navigation devices. These Class D amplifiers allow direct connection to a battery which minimizes losses and reduces component count. The amplifiers also achieve >70dB PSRR performance which is important to avoid audible buzzing with 217Hz demodulated GSM signals.

    Reply
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  6. Tomi Engdahl says:

    New approaches to switched-mode audio power amplifiers (Part 1)
    http://www.edn.com/design/consumer/4408451/New-approaches-to-switched-mode-audio-power-amplifiers–Part-1-

    The Class D amplifier has been the usual switched-mode answer to linear amplifiers for three decades. Class D amps have a clear efficiency advantage over their linear alternatives, which, over the years, has led to much effort being invested in improving the linearity of switched-mode designs.

    Even so, the harmonic distortion of switched-mode amps remains inferior to that of linear power amplifiers.

    The time ratio of the ON time of the two switches determines the average output voltage.

    There are three main sources of distortion in Class D Amps.

    First, the best FET switches, driven optimally, still spend a significant time in the linear region when switching. That means dead time must be inserted to avoid upper and lower FETs conducting at the same time (shoot-through). Dead time causes non-linearity in the output which is difficult to correct for. The brief period of linear switch operation is a source of asymmetry

    Second, Class D amplifiers do not provide power supply rejection. Audio frequency noise on the supplies will appear only slightly attenuated at the output.

    Third, the switched inductor in a Class D amp interacts with the speaker’s inductance (or capacitance) in non-linear fashion. Care must be taken to avoid resonances and beat frequencies that can be heard in the audio range.

    One answer is to use Sigma-Delta modulation instead of Pulse Width Modulation. With Sigma-Delta modulation, periods of ON or OFF are integer multiples of the clock period. Linearity can then be improved, but at the expense of a higher clock rate. Sigma-Delta systems generally need to run at least 64 times the maximum signal frequency. There are significant efficiency penalties associated with clocking that much faster.

    Even after taking careful measures to minimize the error sources cited above, negative feedback is required to obtain good performance. Negative feedback is problematic in a Class D amplifier because the output filter necessarily inserts a delay, which tends to destabilize any feedback loop.

    The Class D amp is essentially a buck converter. Buck converters need compensation to remain stable for the same reasons. In order for feedback from the output to be applied without inducing a tendency toward oscillation, the feedback must be processed.

    The Bridge Tied Load Variation on Class D amplifiers

    The BTL form is more flexible, and it exhibits less bus pumping.

    Filterless Variations
    In some cases, the reactance of the speaker itself is relied on to filter out the chopping frequency. That can be satisfactory, but it requires the speaker to dissipate extra power due to the high-frequency ripple current. Not all dynamic speakers are sufficiently inductive at those frequencies to be efficient as a filter. Equivalent Series Resistance, ESR, causes analogous losses in piezo speakers.

    Care must be taken to avoid damage to dynamic speakers in the filterless case. Above the audible range, voice coil movement is proportional to 1 / frequency2. If the modulation frequency is high enough, the movement is small, so the voice coil won’t hit the limit of travel and cause damage. As long as the speaker is sized to dissipate the extra energy, the filterless variation can be satisfactory.

    The awkward overall conclusion is that the efficiency advantages of Class D amplifiers stem from the digital nature of their output, while the performance disadvantages of Class D amplifiers stem from that same digital nature. What is really called for is a digital amplifier with an analog output. There is now an option in that category, enabled by improved FET switches and a control strategy called Predictive Energy Balancing (PEB).

    Reply
  7. Tomi Engdahl says:

    New approaches to switched-mode audio power amplifiers (Part 2)
    http://www.edn.com/design/consumer/4410605/New-approaches-to-switched-mode-audio-power-amplifiers–Part-2-

    Because PEB allows an output to be regulated precisely on a cycle-by-cycle basis, instead of on the average, PEB enables an entirely new form of switched-mode amplifier.

    The PEB calculations are done in real time by the circuitry

    These calculations can be done in analog or digital fashion.

    In operation, the amplifier uses flyback energy transfers to push the output away from zero. It uses reverse flyback transfers to draw energy back from the speaker to pull the output towards zero. The inductor in a PEB amplifier is active at the switching frequency, so a much smaller inductor filters the digital power switching to produce an analog output, when compared to the inductors needed to filter Class D amplifiers. PEB amplifiers can be fully bipolar, or can be offset to drive the output above and below the power supply voltage

    The speaker could just as well be connected between the output and ground with a coupling capacitor to remove the DC bias voltage.

    Because of their differences from Class D amplifiers, there are a few cautions to observe when applying PEB amplifiers.

    Because the energy balance scaling is in proportion to the ratio of the switched inductance and the load capacitance, the PEB gain needs to be matched to the capacitance of the load.

    In the case of a dynamic speaker, which is inductive, not capacitive, a capacitor is added at the amplifier output to set the PEB scaling and the output ripple. Then, the resistance or inductance of the speaker has little effect on the dynamic performance. For piezo speakers, the PEB scaling must be set to match the chosen speaker’s capacitance.

    The theoretic maximum efficiency of Class D and PEB amplifiers is 100%. As a practical matter, both types of amplifiers can be expected to run in the region of 90% efficiency.

    Conclusions
    By rearranging the same circuit elements now employed in BTL Class D amplifiers and by adding predictive controls, real improvements in fidelity and efficiency of power amplifiers have been achieved. Since changing the control intelligence does not add to the cost of an integrated circuit, these benefits can be realized without an increase in cost. In fact, system costs can be reduced by eliminating filter inductors and by generating less waste heat. PEB amplifiers are particularly well suited for driving piezo loads.

    Reply
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  11. Tomi Engdahl says:

    [Afrotech]‘s Guide To Class D Amplifiers
    http://hackaday.com/2014/06/09/afrotechs-guide-to-class-d-amplifiers/

    Hang around in any of the many guitar or audiophile forums or discussion boards for long enough, and eventually you’ll come across the arguments over amplifier topologies. One of the more interesting and useful of these classes of amplifier is class d – they’re extremely efficient and when well designed can sound pretty good. [Afrotech] is here to show you how they work, and how to build a 15 Watt amp using a $3 class d amplifier chip.

    To demo this, [Afrotech] used TI’s TPA3122 class d amplifier chip. It’s a pretty cheap chip for being a 15 Watt stereo amplifie

    Reply
  12. Tomi Engdahl says:

    I have taken this amplifier in use in Hifi system at seems to do it’s job well.

    Reply
  13. Tomi Engdahl says:

    Class D Amp with an H-Bridge
    http://hackaday.com/2014/12/28/class-d-amp-with-an-h-bridge/

    Class D amps are simple – just take an input, and use that to modulate a square wave with PWM. Send this PWM signal to a MOSFET or something, and you have the simplest class D amp in existence. They’re so simple, you can buy a class D amp chip for $3, but [George] thought that would be too easy. Instead, he built his own with an ATTiny and an H-bridge motor driver. No surprise, it works, but what’s interesting is what effect the code on the ATtiny can have on the quality of the audio coming out of the speaker.

    The microcontroller chosen for this project was the ATtiny 461
    The heavy lifting part of this build is an L298 chip found on eBay for a few dollars.

    Class D AVR
    http://www.georgegardner.info/electronics/class-d-avr.html

    Reply
  14. Tomi Engdahl says:

    Class D audio power amplifiers: Adding punch to your sound design
    http://www.edn.com/design/power-management/4443229/Class-D-audio-power-amplifiers–Adding-punch-to-your-sound-design?_mc=NL_EDN_EDT_EDN_analog_20170105&cid=NL_EDN_EDT_EDN_analog_20170105&elqTrackId=8a47a762bede4362a401be03200dacbd&elq=5f9b5fd786164463a212d94d88f5e3f2&elqaid=35405&elqat=1&elqCampaignId=30952

    Class D amplifiers were first conceived in 1958 and so much has been written about the different architectures that were cited just in 2016 which improve different aspects of their performance.

    I will share these recent techniques with you in this article.

    Such recent design improvement techniques are Power Supply Rejection Ratio (PSRR) improvement, lower distortion, Electro-magnetic Interference (EMI) reduction, Intermodulation (IM) distortion improvement, quiescent current reduction, Total Harmonic Distortion (THD) reduction, and driving capacitive transducers in electrostatic loudspeakers.

    Reply
  15. Tomi Engdahl says:

    The future of Class D amplifiers
    https://www.youtube.com/watch?v=98QQ43qgzbg

    Can Class D amplifiers ever sound as good or even exceed the performance and sound quality of more traditional Class A/B or Class A amplifiers. Find out when Paul launches into this controversial subject.

    Reply
  16. Tomi Engdahl says:

    http://www.dx.com/fi/p/y148-audio-amplifier-module-93121#.W1Xdm7h9iUk

    -Malli: Y148
    -PCB board
    -Hyväksyy YDA148 tehokas digitaalinen äänen valtaa vahvistimen IC
    -DC tulojännite: 9 ~ 15V
    -Virta: 2 ~ laskettua arvoon 4.5a
    -Teho on DC 15V input: 15W x 2 (8 ohmia) 30W x 2 (4 ohm)
    -Teho on DC 12V Käyttöjännite: 10 w x 2 (8 ohmia) 20W x 2 (4 ohm)
    -Tarvitsee jäähdytyselementti 4 Ohm, ei tarvitse kiihottaa kaatoallas 8 Ohm
    -Taajuusvaste: 10Hz ~ 20KHz (+/-0 .2dB @1 KHz)
    -Load puhuja: 4 / 6 / 8 ohm
    -SNR: on ainakin 90dB
    -Harmoninen: THD + NC enintään 0.1%P=0.1W

    Reply
  17. Tomi Engdahl says:

    YDA148
    http://download.yamaha.com/api/asset/file/?language=ja&site=jp.yamaha.com&asset_id=46252

    YDA148 (D
    -510) is a high-
    efficiency digital audio power amplifier IC with the maximum output of 15W
    × 2ch.
    YDA148 has a “Pure Pulse Direct Speaker Drive Circuit”
    that directly drives speakers while
    reducing distortion of pulse output signal and reducing noise on the signal

    YDA148 features Power Limit Function, Non-
    clip Function,
    and DRC (Dynamic Range Control) Function that were developed by Yamaha original digital amplifier
    technology.
    YDA148 has overcurrent protection function for speaker output terminals, high temperature
    protection function, and lowsupply voltage malfunction prevention function.

    Reply
  18. Tomi Engdahl says:

    DIY 300 Watt 5.1 Audio Amplifier
    https://www.youtube.com/watch?v=XuU4iNNn6xk

    Hi YouTube in This video I’m Going to Show You How to Make 300 watt 5.1 Audio Amplifier

    Reply
  19. Tomi Engdahl says:

    Why Class D amps have small power transformers
    https://www.youtube.com/watch?v=idCQtjro540

    Big power amplifies have big power transformers inside, but not so for powerful class D amplifiers. How can they produce so much power with such small transformers?

    Reply
  20. Tomi Engdahl says:

    DIY Class D Audio Amplifier
    https://www.youtube.com/watch?v=3dQjIeYoIdM

    In this project I will show you why a class AB amplifier is pretty inefficient and how a class D amplifier on the other hand improves this efficiency. At the end I will show you how we can apply the theory of operation of a class D amp to a couple of common components in order to create our own DIY class D audio amp.

    Reply
  21. Tomi Engdahl says:

    Optimizing Class-D Audio Amplifier Output Filters
    https://passive-components.eu/optimizing-class-d-audio-amplifier-output-filters/

    Careful component selection is the key to high-quality high-efficiency Class-D audio output
    When audio applications require the highest power efficiency, lowest heat generation, smallest size, and lightest weight, Class-D switched-mode amplifiers surpass the linear class amplifiers. This makes Class-D amplifiers the best choice for extending battery life in DC-powered audio applications, such as found in automotive sound systems. This article discusses how careful design of the output LC filter stage of a Class-D amplifier leads to high efficiency and high sound quality, and how choosing the right inductor affects these critical parameters.

    Reply
  22. Tomi Engdahl says:

    Class D Audio Amplifiers – Theory and Design
    https://sound-au.com/articles/pwm.htm

    Reply
  23. Tomi Engdahl says:

    A stupid looking class D amplifier modification idea:

    DIY-Mini Super Powerful Stereo Amplifier using PAM8403 | pam8403 audio Amplifier
    https://www.youtube.com/watch?v=fJ5gTDLMAng

    Super Powerful Stereo Amplifier using PAM8403 | how to make amplifier at home
    Super Powerful Stereo Bass Amplifier with PAM8403 module
    Can the output power of the sound amplifier be increased?
    In this video I show how to use the pam8403 module and how to amplify its output and build a 5 volt audio system for our car.

    The PAM8403 is a 3W, class-D audio amplifier. It offers low THD+N, allowing it to achieve high-quality sound reproduction. The new filterless architecture allows the device to drive the speaker directly, requiring no low-pass output filters, thus saving system cost and PCB area.

    Viewer comments:

    8 stacked together and still barely enough to push a 20 watt speaker. Super Powerful!

    these amps are already 4 ohm stable and youre running 8 of them into approximately a 1 ohm load, so each is probably seeing the equivalent load of an 8 ohm load. also youd get more power running them at their rated 5v instead of 3.7 or under load likely closer to 3v. also assuming they were all making their peak rated power you would be getting less than a typical car audio head unit.

    We almost can see the impedance say hello to those speakers… if you going to try this at home, please read about it…it save you a lot of trouble and a bit of money. Btw…you just need one AMP… not 8. Good video tho.

    Each module has only 3W, and 8 PAM8403 modules are superimposed and connected in parallel. How much W is this driven?

    hi mr yan jun around 24+24watt

    All boards become dead if we use in parallel or series

    5w is correct, since each amp puts out 643mW@3V (214mA), even though theyre labeled 3W. Its expected from a cheap amp though. Also the amps may be highpassed, which explains why the bass is weak.

    This is more than 5w, the lower your impedance the more power it doesn’t matter if he’s using a 3.7v battery, all that means is it will drain faster because it’s pulling more amps than the battery can handle, counting in voltage drop it would probably be around 4w to 5w, but if he can sustain the voltage it will be more than 5w.

    The video is good, I have nothing against it, and also everyone knows that this is wrong, impedance of different speakers, a lot of pan connected to each other, giving each other short.

    cute idea, but without an audio crossover using so many different speakers is a trash idea.

    It’s not fake it may possible but you need 5 volt 10amps adapter
    even if using lipo battery, the max current will be 2.5A. 5V cannot give more than 1.25A per channel. Simple ohms law I = V/R

    still with only 5V max current cannot be more than 1.25A ( 4ohm speaker )…also the limit of PAM8403 is around 1.2 Amp (input current) anything above that will cause amplifier to shutdown…BUT if you are so keen, why not give it a try ( you can use two 4ohm speakers in parallel ( net resistance = 2ohm)

    Shorting amplifier output with other amplifier.
    Nice.

    Reply
  24. Tomi Engdahl says:

    Mixing class A with Class D amps
    https://www.youtube.com/watch?v=eYNUfXh4iVA

    Is it a good idea to mix and match different classes of amplifiers together?

    Viewer comments:

    SMPS CLASS D ARE/IS AMAZING! Im totally fascinated by them – no transformer (sometimes), the full whammy of current, if needed. Also, they can come in small packages. When listening to another class of amp it is easy to fall in love, but when being bitten on the back of the ankle by class D with a good good dynamic recording – My GOD!!! I went to an event space in Birmingham (uk) and they had a very well set-up PA system…ummm….ahhhhh…..that;s a whole load of other stuff happening, which I dont know about actually. But, class D, in the right time/place/component – arghh!

    Well put, as with most things synergy is king. To my knowledge the majority of devices that deal with line level or lower operate in class A anyway, because it’s the simplest and the efficiency doesn’t really matter. Even at power amp level I doubt many people could pick out the sound of one class or another, assuming a good design. Personally I’ve always stuck with class A, but that’s really only because I love huge sexy exposed heatsinks on my amps. Plus the “free” heat output is quite nice in the winter.

    One of the simplest ways to improve the sound of your system is to stretch out the loudspeakers cables out and not leave them bunched up or coiled. You get more clarity and punch in the lower frequencies. Save a few bucks on new equipment.
    coiling your speaker wires would have more effect on highs than lows but that effect would be totally trivial at any frequency.

    Here is a list of amplifier classes: A, B, C, D, E, F, G, H, I, O, P and Q, but not all of them are usable for audio applications, as they are better suited some cases for RF amplification.

    What are the differences between Class A, AB, and Class D amplifiers?
    https://www.youtube.com/watch?v=rj6h4qYxkCc

    Good Job Paul! To recap what this video covers I would like to add in short, CLASS A is still the best audio amp technology however it is “heavy and hungry” (elephant). Class AB is very close to Class A with a little more efficiency, yet a good way to do clean full range signal amplification for audio (horse). Class D is the new technology to save the “planet,” not sure which planet, however is light, requires a lot of extra circuitry runs very cool and seems to work well with low power items yielding audio (smart phones, ipods, laptops, etc..) it would be the (hummingbird). Some Class D Amplifiers that are very well designed with the correct support circuitry can be surprisingly clean and great sounding… How LOW quality D set-ups should be avoided… Importantly, Just because a spec mentions Class D and PWN is not a reason to consider it a quality unit… Regards, Mark

    Hi Paul, and thanks for this excellent description. One of the things that scares me, as a radio engineer, about class D amps is the potential for the radiation of the switching frequency and its harmonics to cause interference to radio, TV and wireless devices. I have no particular axe to grind, and to me any amplifier is “good” if it faithfully reproduces the input waveform at its output. I’m just concerned that manufacturers will seek to drive down costs by minimising the output filtering and leave us with a big problem

    Reply
  25. Tomi Engdahl says:

    Class D amp fatigue
    https://www.youtube.com/watch?v=hRxYNbgHpxQ

    How real is the idea that one can become fatigued listening to music through a class D amplifier?

    Viewer comments:

    Some of the earliest high-power Class-D amps were the Peavey DECA sound reinforcement amps made in the mid 1980′s. They sounded great, and were even used in some recording studios for driving monitors. But part of their good sound might have been the fact that their pulse rate was 500kHz, much higher than most Class D amps. This allowed the reconstruction filters to be tuned to a much higher frequency, which reduced their phase shift in the top (audible) octave.

    Reply
  26. Tomi Engdahl says:

    Why is Quiescent Current So Important in Class D Amps?
    Dec. 1, 2022
    https://www.electronicdesign.com/power-management/whitepaper/21255652/electronic-design-why-is-quiescent-current-so-important-in-class-d-amps?utm_source=EG+ED+Analog+%26+Power+Source&utm_medium=email&utm_campaign=CPS221121122&o_eid=7211D2691390C9R&rdx.identpull=omeda|7211D2691390C9R&oly_enc_id=7211D2691390C9R

    Previously hindered by cost, EMI/EMC issues, and poor THD+N, low-power-loss Class D amplifiers are now finding their way into today’s compact audio designs thanks to advanced modulation and feedback techniques.

    What you’ll learn:

    The benefits of using Class D amplifiers.
    What to look for when choosing a Class D amp.
    Making the tradeoff between THD+N and quiescent current.

    Back in the day (1970s), audio amplifiers like the Phase Linear 700 were designed with discrete power-transistor components. Huge audio power transistors like the 2N3055 and others back then were configured to drive massive audio power outputs that drove large audio loudspeakers. Rock bands used to place dry ice on stacks of these legendary 350-W/channel amps to cool them down.

    Fast forward to 2022 and we find audio design engineers loving the power efficiency of Class D amplifiers. The Class D amp outperforms any Class A, B, or AB linear amplifier architectures. With the latter amplifiers, significant power losses will occur due to biasing elements and the linear operation of the output transistors.

    The Class D amplifier is used in audio circuitry as a switch that steers current to the audio load. Consequently, only a small amount of power is lost in the output stage.

    Power losses, which are dissipated as heat, in a Class D amplifier are due to the output transistor’s quiescent-current overhead, switching losses, and on-resistance. Smaller heatsinks—even no heatsink—may be used in these amplifiers. Thus, Class D amplifiers are perfect for high-power, compact designs.

    In the early years of design, the power-efficiency advantage of classical pulse-width-modulation-based Class D amps had been hampered by external filter component costs, EMI/EMC compliance difficulties, and poor total harmonic distortion plus noise (THD+N) performance when compared to linear amplifiers. Now, the latest generation of Class D amplifiers employ advanced modulation and feedback methods to mitigate these potential drawbacks.

    Class D Amplifier Iq

    The typical definition of quiescent current (Iq) is the current drawn by an integrated circuit (IC) in a no-load and non-switching, enabled condition. A further definition of Iq is the input current that’s consumed by an IC in many of its ultra-low-power states.

    Used in battery-powered applications, which may spend a large amount of time in a standby or sleep mode, quiescent current can prolong a battery’s run time by years. A good example would be an ultra-low-Iq buck converter like the 60-nA TPS62840 to power an always-on application, such as in a smart meter application. In this case, it could enable 10 years of battery runtime.

    Typically, Class D amplifiers will be designed into battery-powered applications. Examples in today’s electronics world are smartwatches or a smart lock for the home. Such designs will need:

    Low, always-on power for long battery runtimes that can be enabled via ultra-low-leakage process technologies and creative new control topologies.
    Fast response times for such things as fast wake-up comparators and zero-Iq feedback control. This will enable fast dynamic responses with no compromise on low power consumption.
    Reduced form factors, such as area reduction techniques for resistors and capacitors. This will be crucial for proper integration into space-constrained applications while not affecting the quiescent power.

    Tradeoff: THD+N vs. Iq

    In many designs, Class D audio amps typically employ a closed-loop topology using a loop filter, pulse-width modulator (PWM), and a switching power stage. This will help to suppress the linearity of the power stage to improve the THD+N.

    If the designer chooses not to use a higher-order loop filter or a higher switching frequency (fSW), the PWM-residual-aliasing distortion introduced by the feedback loop will limit the minimum THD+N.

    Summary

    The 1970s brought us excellent audio electronics solutions. Unfortunately, the size and power consumption of these devices were typically large and cumbersome. Still, they could produce good quality audio.

    In today’s electronics world, quiescent current dominates audio applications. Audio device users want smaller, lightweight, but ultimately good audio devices. Enter Class D amplifiers, which are a key ingredient to making it happen, especially in portable and battery-powered designs.

    This article demonstrated how to choose a Class D amplifier, with some specification tradeoff decisions. In the end, we find that it’s possible to have excellent audio performance with compact, lightweight designs that last longer than ever on a battery-operated power supply.

    Reply
  27. Tomi Engdahl says:

    Why is Quiescent Current So Important in Class D Amps?
    Dec. 1, 2022
    Previously hindered by cost, EMI/EMC issues, and poor THD+N, low-power-loss Class D amplifiers are now finding their way into today’s compact audio designs thanks to advanced modulation and feedback techniques.
    https://www.electronicdesign.com/power-management/whitepaper/21255652/electronic-design-why-is-quiescent-current-so-important-in-class-d-amps

    What you’ll learn:

    The benefits of using Class D amplifiers.
    What to look for when choosing a Class D amp.
    Making the tradeoff between THD+N and quiescent current.

    Back in the day (1970s), audio amplifiers like the Phase Linear 700 were designed with discrete power-transistor components. Huge audio power transistors like the 2N3055 and others back then were configured to drive massive audio power outputs that drove large audio loudspeakers. Rock bands used to place dry ice on stacks of these legendary 350-W/channel amps to cool them down.

    Fast forward to 2022 and we find audio design engineers loving the power efficiency of Class D amplifiers. The Class D amp outperforms any Class A, B, or AB linear amplifier architectures. With the latter amplifiers, significant power losses will occur due to biasing elements and the linear operation of the output transistors.

    The Class D amplifier is used in audio circuitry as a switch that steers current to the audio load. Consequently, only a small amount of power is lost in the output stage.

    Power losses, which are dissipated as heat, in a Class D amplifier are due to the output transistor’s quiescent-current overhead, switching losses, and on-resistance. Smaller heatsinks—even no heatsink—may be used in these amplifiers. Thus, Class D amplifiers are perfect for high-power, compact designs.

    In the early years of design, the power-efficiency advantage of classical pulse-width-modulation-based Class D amps had been hampered by external filter component costs, EMI/EMC compliance difficulties, and poor total harmonic distortion plus noise (THD+N) performance when compared to linear amplifiers. Now, the latest generation of Class D amplifiers employ advanced modulation and feedback methods to mitigate these potential drawbacks.

    Some key features might be loudness or output power and speaker/voice coil efficiency. There’s an industry standard for specifying the power level of an amplifier: the output power at 1% or 10% THD+N.

    Next, designers need to select the number of channels at the selected power level. A standard power level in the audio industry is usually the output power level at either 1% or 10% THD+N. When specifying a power level, be sure to note if it’s peak or continuous power. Most likely, designs will be a stereo amplifier configuration, so two channels will need to be created.

    Class D Amplifier Iq

    The typical definition of quiescent current (Iq) is the current drawn by an integrated circuit (IC) in a no-load and non-switching, enabled condition. A further definition of Iq is the input current that’s consumed by an IC in many of its ultra-low-power states.

    Used in battery-powered applications, which may spend a large amount of time in a standby or sleep mode, quiescent current can prolong a battery’s run time by years. A good example would be an ultra-low-Iq buck converter like the 60-nA TPS62840 to power an always-on application, such as in a smart meter application. In this case, it could enable 10 years of battery runtime.

    Typically, Class D amplifiers will be designed into battery-powered applications. Examples in today’s electronics world are smartwatches or a smart lock for the home. Such designs will need:

    Low, always-on power for long battery runtimes that can be enabled via ultra-low-leakage process technologies and creative new control topologies.
    Fast response times for such things as fast wake-up comparators and zero-Iq feedback control. This will enable fast dynamic responses with no compromise on low power consumption.
    Reduced form factors, such as area reduction techniques for resistors and capacitors. This will be crucial for proper integration into space-constrained applications while not affecting the quiescent power.

    Tradeoff: THD+N vs. Iq

    In many designs, Class D audio amps typically employ a closed-loop topology using a loop filter, pulse-width modulator (PWM), and a switching power stage. This will help to suppress the linearity of the power stage to improve the THD+N.

    If the designer chooses not to use a higher-order loop filter or a higher switching frequency (fSW), the PWM-residual-aliasing distortion introduced by the feedback loop will limit the minimum THD+N.

    Summary

    The 1970s brought us excellent audio electronics solutions. Unfortunately, the size and power consumption of these devices were typically large and cumbersome. Still, they could produce good quality audio.

    In today’s electronics world, quiescent current dominates audio applications. Audio device users want smaller, lightweight, but ultimately good audio devices. Enter Class D amplifiers, which are a key ingredient to making it happen, especially in portable and battery-powered designs.

    This article demonstrated how to choose a Class D amplifier, with some specification tradeoff decisions. In the end, we find that it’s possible to have excellent audio performance with compact, lightweight designs that last longer than ever on a battery-operated power supply.

    Reply
  28. Tomi Engdahl says:

    https://www.facebook.com/groups/DIYAudio/permalink/6633418433390613/
    What is the difference between Class-D and Class-G amps?

    Class G switches power supply rail voltage levels to reduce power losses in the output devices. Class D is a pulse modulated then filtered output. Two completely different things.
    Both are designed to reduce losses in the output devices. Class D transistors are either off or on, so it’s not a “linear” amp. It’s also not “digital” in the true sense, as the levels are not discrete like that. A well designed class D amp can easily satisfy Nyquist critera and produce quality sound up to beyond human hearing… Either way, there’s very little Current x Voltage losses. Class G simply uses rail switching to give enough voltage to a normal Linear AB amp to produce the desired levels. Class H is similar, but doesn’t switch the rail, it continually adjusts, Bob Carver designs being the most notable examples I think.

    Reply
  29. Tomi Engdahl says:

    Inside a 360W digital amplifier
    https://www.youtube.com/watch?v=dAM882I6u7g

    bought this amplifier purely so we could open it and take a look inside. It’s a modern class-D amplifier that uses pulse width modulation and filtering to achieve high power audio amplification efficiently with low heat and size.

    One slight correction. The incoming supply comes in via an NTC inrush current limiter which I inadvertently called a MOV (Metal Oxide Varistor).

    Initially I thought it might have a dedicated chip or module for the amplification, but it seems to use discrete transistors on the output with a couple of mystery chips. The power supply is notable for using a discharge lamp ballast control chip, presumably because it is a dual rail power supply with the zero volt output referenced to mains ground, and the two-MOSFET push-pull drive circuit makes it better suited to that.
    The way the four output transistors are pinned down onto the aluminium backplate is quite interesting.

    The areas of most concern for reliability are the ribbon cables and the solder joints on the speaker pillar terminals I’d rather the power had been linked across with a beefier dedicated wiring loom and auxiliary low current control cable. The IDC (Insulation Displacement Connectors) used with ribbon cable are alway problematic with high current.

    The unit has three operational modes:-
    Stereo – independent left and right channels.
    Parallel – One input fed to both channels (mono)
    Bridged – One input fed to both channels in antiphase to drive one speaker at higher power.

    The stereo and parallel modes have one speaker connection connected to zero volt/chassis level and the other connection is pulled between the positive and negative rails by two transistors.
    In the bridged mode both ends of the speaker can be driven to either supply rail by a full H-bridge transistor arrangement.

    The “ground lift” option just isolates the incoming signal cable’s screen from the chassis. Do not ever disconnect the mains earth/ground. There’s a rather unpleasant culture within the audio industry to “avoid ground problems” by cutting the earth/ground wires in the mains plugs of equipment. That is absolutely the WRONG thing to do, but is perpetuated by the vague word-of-mouth training prevalent in showbiz. Removing the safety earth/ground means that in the event of a fault full mains voltage can be present on audio cables, resulting in a serious shock risk and equipment damage.

    Reply

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