The mighty Class-D amplifier—build one yourself and be amazed by its efficiency. The heat sink barely gets warm!

Have you always wanted to build your own audio power amplifier? An electronic project where you not only see the results but also hear them?

If your answer is yes, then you should continue reading this article on how to build your own Class D amplifier. I will explain to you how they work and then guide you step by step to make the magic happen all by yourself.


Theoretical Basics

What is a Class-D audio power amplifier? The answer could be just a sentence long: It is a switching amplifier. But in order to fully understand how one works, I need to teach you all its nooks and crannies.

Let's start with that first sentence. Traditional amplifiers, like the class AB, operate as linear devices. Compare this to switching amplifiers, so called because the power transistors (the MOSFETs) are acting like switches, changing their state from OFF to ON. This allows a very high efficiency, up to 80 - 95%. Because of this, the amplifier does not generate a lot of heat and does not require a big heat sink like linear class AB amplifiers do. For comparison, the class B amplifier can only achieve a maximum efficiency of 78.5% (in theory).  

Below you can see the block diagram of a basic PWM Class-D amplifier, just like the one that we are building.


Basic PWM Class-D amplifier


The input signal is converted into a pulse width modulated, rectangular signal using a comparator. This basically means that the input is encoded into the duty cycle of the rectangular pulses. The rectangular signal is amplified, and then a low-pass filter results in a higher-power version of the original analog signal.

There are other methods for converting the signal into pulses, such as ΔΣ (delta-sigma) modulation, but for this project we will be using PWM.


Pulse-Width Modulation Using a Comparator

In the plot below, you can see how we transform a sinusoidal signal (the input) into a rectangular signal by comparing it to a triangle signal. 


Transform a sinusoidal signal (the input) into a rectangular signal by comparing it to a triangle signal

Click to enlarge


At the positive peak of the sine wave, the duty cycle of the rectangular pulse is 100% whilst at the negative peak it is 0%. The actual frequency of the triangle signal is much higher, on the order of hundreds of kHz, so that we can later extract our original signal.

A real filter, not an ideal one, does not have a perfect "brick-wall" transition from passband to stopband, so we want the triangle signal to have a frequency at least 10 times higher than 20KHz, which is the upper human hearing limit.


Power Stage—It All Sounds Good in Theory

Theory is one aspect and practice is another. If we want to put the previous block diagram into practice, we will stumble upon some problems.

Two issues are the rise and fall time of the devices in the power stage and the fact that we are using an NMOS transistor for the high-side driver.


The use of NMOS transistor for the high-side driver


Because the switching of the MOSFETs is not done instantaneously, but is more like going up and down a hill, the transistors' ON time will overlap, creating a low-impedance connection between the positive and negative power supply rails. This causes a high current pulse to pass through our MOSFETs, which can lead to failure.

To prevent this, we need to insert some dead-time between the signals that drive the high and low side MOSFETs. One way to achieve this is to use a specialized MOSFET driver from International Rectifier (Infineon), such as the IR2110S or IR2011S. Furthermore, these ICs provide the boosted gate voltage needed for the high-side NMOS.  


ICs provide the boosted gate voltage for the high-side NMOS


Low-Pass Filter

For the filtering stage, one of the best ways to do this is to use a Butterworth filter.


The use of Butterworth filter


These types of filters have a very flat response in the passband. This means that the signal that we want to achieve will not be attenuated too much.

We want to filter frequencies that are higher than 20 kHz. The cut-off frequency is calculated at -3dB, so we want it to be a bit higher in order to not filter sounds that we want to hear. It is best to choose something between 40 and 60 kHz. The quality factor \[Q = \frac{1}{\sqrt{2}}\].

These are the formulas used to calculate the values of the inductor and the capacitor:


\[L = \frac{R_{L}\sqrt{2}}{2\cdot \pi \cdot f_{c}}\]


\[C = \frac{1}{2\sqrt{2}\cdot \pi \cdot f_{c}\cdot R_{L}}\]


Building Your DIY Amplifier (Luke-The-Warm)

Now that we know how a Class-D amplifier works, let's build one.

First of all, I named this amplifier Luke-The-Warm because the heat sink only barely gets warm, as opposed to a Class AB amplifier, whose heat sink can get quite hot if not actively cooled.

Below you can see the schematic of the amplifier that I designed. It is based on the IRAUDAMP1 reference design by International Rectifier (Infineon). The main difference is that instead of ΔΣ modulation, mine uses PWM.


The schematic of the amplifier

Click to enlarge


I will now tell you some design choices and how the components work with each other. Let's start from the left side.


Input Circuitry

For the input circuitry, I decided that it was best to use a high-pass filter followed by a low-pass filter. It is that simple.


The use of high-pass filter followed by a low-pass filter


Triangle Generator

For the triangle generator, I used an LMC555, which is the CMOS variant of the famous 555 chip. The charging and discharging of the capacitor produces a nice triangle, which is not perfect (it rises and falls exponentially) but if the rise and fall times are equal, it works perfectly.

The values of the resistor and the capacitor set a frequency of approximately 200kHz. Any higher than this and we will run into trouble because the comparator and the MOSFET driver are not the fastest devices.


Triangle Generator



For the comparator, you can use whichever component you want—it just needs to be fast. I used what I had available, the LM393AP. At 300ns response time, it is not the fastest and can definitely be improved but it does the job. If you want to use other ICs, just be careful to check that the pins match or you will have to modify the PCB design.

In theory, an op-amp can be used as a comparator, but in reality op-amps are designed for other types of work, so make sure you use an actual comparator.

Because we need two outputs from the comparator, one for the high-side driver and one for the low-side driver, I decided to use the LM393AP. This is two comparators in one package, and we just swap the inputs for the second comparator. Another approach is to use a comparator that has two outputs, such as the LT1016 from Linear Technology. These devices may offer somewhat improved performance, but they could also be more expensive.

These comparators are powered by a 5V bipolar supply, provided by two zener diodes that regulate voltage from the main power supply, which is ±30V.





For the MOSFET driver, I chose to use the IR2110. An alternative is the IR2011, which is used in the reference design. This integrated circuit makes sure to add that dead time that I talked about in the previous section.

Because the VSS pin of the IC is tied to the negative power supply, we need to level shift the signals from the comparator. This is done using PNP transistor and 1N4148 diodes.

To drive the MOSFETs, we power the IR2110 with 12V referenced to the negative power supply voltage; this voltage is generated using a BD241 in conjunction with a 12V zener. The high side MOSFET needs to be driven by a gate voltage that is about 12V above the switching node, VS. This requires a voltage that is higher than the positive supply; the IR2110 provides this drive voltage with the help of our bootstrap capacitor, C10.





Finally the filter. The cut-off frequency is 40kHz, and the load resistance is 4 ohms because we have a 4-ohm speaker (the values used here will also work with an 8-ohm speaker, but it is best to adjust the filter according to the speaker you choose). With this information we can calculate the values of the inductor and the capacitor:


\[L = \frac{4\sqrt{2}}{2\cdot \pi \cdot 40000} H = 22.508\mu H\]


We can safely round down to 22µH.


\[C = \frac{1}{2\sqrt{2}\cdot \pi \cdot 40000\cdot 4} F = 0.703\mu H\]


The closest standard value is 680nF. 


Notes on Build

Now that you know all about the inner workings, all you have to do is read very carefully the next few lines, download the files below, buy the components needed, etch the PCB, and start assembling.


Low-Pass Filter

For the low-pass filter, you can use a 680nF capacitor to get as close as possible to the calculated value, but you can also use a 1µF capacitor without any trouble (I designed the PCB so that you can use two capacitors in parallel to mix and match).

These capacitors need to be polypropylene or polyester—in general it's not a great idea to use ceramic capacitors with audio signals. And you need to make sure that the capacitors that you are using for filtering are rated for high voltage, at least 100VAC (more doesn't hurt). The rest of the capacitors in the design also need to have an appropiate voltage rating. 

I designed this amplifier for an output power of about 100-150W. You should use a bipolar power supply with ±30V rails. You can go higher than this, but for voltages of about ±40V you need to make sure that you change the values of the resistors R4 and R5 to 2K2. 

It is not necessary but highly recommended that you use a heatsink for BD241C as it gets quite hot. 



As far as power MOSFETs go, I suggest using the IRF540N or the IRFB41N15D.  These MOSFETs have low gate charge for faster switching and low RDS(on) for lower power consumption. You also need to ensure that the MOSFET has an adequate maximum VDS (drain-to-source voltage) rating. You could use the IRF640N, but the RDS(on) is significantly higher, leading to an amplifier with lower efficiency. Here is a table comparing these three MOSFETs: 


MOSFET Max VDS (V) ID (A) Qg (nC) RDS(on) (Ω)
IRFB41N15D 150 41 72 0.045
IRF540N 100 33 71 0.044
IRF640N 200 18 67 0.15



Now the inductor. You can buy one already made but I would suggest that you wind your own—this is a DIY project after all.

Buy a T106-2 toroid. It needs to be iron powder; ferrite can work but it will need a gap or it will saturate. Using the said toroid, wind 40 turns of 0.8-1mm diameter (AWG20-18) copper enameled wire. That's it. Don't worry if it isn't perfect—just make it tight.



Finally, all the resistors, unless noted (R4, R5), are 1/4W.



When I designed the PCB, I made it so that it is very easy to test. The input signal has its own connector and there are two spade terminals for ground: one for the power supply and one for the speaker.

To remove the hum noise (50/60 Hz, from the mains frequency), I used a star-ground configuration; this means connecting all grounds (amplifier ground, signal ground, and speaker ground) at the same point, preferably on the power supply PCB, after the rectifier circuit.

The complete Bill of Materials can be found in the files below, where you can also find the PCB files both in PDF format and as KiCAD files. 


  Class-D Amplifier BOM and PCB Files  

Final Thoughts

I hope that the information in this article is sufficient for you to build your own audio power amplifier. I hope it also gets you excited about building your own amplifier.


DIY Audio Power Amplifier


There are many things that can be improved in this project. You have all the necessary information and files, but you do not need to follow them to the letter.

You can use SMD components, improve the comparator circuit by using a complementary output one, or try the IR2011S instead of the IR2110. Just fire up that soldering iron, etch your PCB, and start working. It does not matter if it does not work on the first try.

It's all about trial and error. When you will finally hear that crisp sound coming from your speaker, it will all be worth it.

If you have any trouble with your build, comment here or post on the forum using as much information as possible. We will work it out.


Give this project a try for yourself! Get the BOM.




  • dendad 2016-08-30

    An interesting article, and well done to help understand these amps.
    A couple of points though..
    I feel the “+12V” and “+5V2” would be better labeled as “-18V” and “-25V”.
    As you have them it is rather confusing, even though you mention they are referenced to the -30V line.

    • Cezar Chirila 2016-08-31

      You do have a valid point. However, I do not think that having -25V going out of a 5V regulator is right. I checked and the guys at Infineon (IRAUDAMP1 reference design) use the same type of notation for their power supply.

      • dendad 2016-10-24

        It is perfectly ok to have “non 5Vs” coming out of a 5V regulator. All your voltages should be referenced to a common point. Having it as you show it, even if you are copping others, IS confusing. The regulator is just a component, not the final design. By the argument you put forward, any variable power supply that uses, for example, a LM317 regulator would have a 1.25V output all the time as it is a 1.25V voltage regulator. The LM317 is just a part of a circuit that happens to be a 1.25V regulator, but produces a variable output.
        The same way the regulators in this circuit are being used to produce “non 5V” power rails. They are just used to get a power rail that is offset by 5V from another rail. But all rails are measured W.R.T. 0 volts.

    • Cezar Chirila 2016-10-24

      Thank you for your input. Sorry this took so long. I have modified the diagrams and I now hope it is less confusing to others. Again, thank you for taking your time to give your feedback, I truly appreciate it.

  • qbx888 2016-08-31

    Great article! Please add more info about proper supply rates. You mentioned increasing input voltage to 40V but what is the lowest value? Which transformers do you recommend and what component next to it are necessary?
    Also I don’t see a potentiometer for change master value. Where it can be added?

    • Cezar Chirila 2016-08-31

      I wouldn’t go lower than 20-24V for the power supply ,but at least 30V is recommended. For low power amplifier, I think a different design would be better.
      If you are using a transformer (I recommend toroidal because of their size), and not a SMPS, you will need a bridge rectifier and some beefy filtering caps (I personally used 2x10 000uF per branch - positive/negative).
      About the potentiometer, although you could add one before the ” Input -P1” of value 100K, I suggest building a pre-amp circuit that also has tone control.

  • PickyBiker 2016-09-09

    This looks great. One question what is the power out one can expect from this circuit?

    • Cezar Chirila 2016-09-10

      Somewhere between 120-140W. It varies greatly (100-150W) depending on your power supply.

  • Colin55 2016-09-10

    How do you get +12v from a -30v supply ????

    • Cezar Chirila 2016-09-10

      It is +12V referenced to -30V. Imagine that we use a multimeter and we put the black probe (ground) to the -30V rail. If we measure the real ground (which is 0V), on the multimeter digit we would read +30V. If me measure “+12V”, on the multimeter it reads +12V. BUT, if we put the black probe on the 0V ground, on the multimeter we would have -18V. We measure the electric potential difference, V2-V1. When we measure “+12V” rail, we consider “-30V” supply to be V1. I used this notation because we connect the COM and VSS port of the IR2110 to the “-30V” rail.

  • Colin55 2016-09-10

    All voltages must be referenced from the 0v rail (called CHASSIS or earth) as this is where you will place the black probe of the voltmeter.
    The voltages on the 7805 will be minus 18.6v and minus 25v.
    Neither of the voltages will be stable as the minus 30v rail (line) is not stable.
    The 7805 voltage regulator will have no effect on stabilising the voltage.

    • Cezar Chirila 2016-09-10

      You are right that they will not be stable in regards to 0V, they will, however, be stable in regards to the negative rail, which is how the IR2110 is referenced.

    • Cezar Chirila 2016-09-10

      Thank you very much for you input. After the weekend I will test again the amplifier with a reactive load (speaker) and measure the distorsions when the 30V rail is not stable (50-80Hz input signal). On my previous test, the same as this, I didn’t had any problems.

  • ks1233 2016-09-13

    how about a nice power supply project along with a simple enclosure to complete the package?! also, is there a reputable parts supplier that you could recommend - the one that you used, maybe? thanks in advance!

    • Cezar Chirila 2016-09-30

      That is a very good ideea. If I find the time, maybe I will make a project article. About the parts, I bought them from tme,eu, which is an electronic components distributor for Europe. For US I heard about digikey, mouser and farnell/newark but I am sure that there are more.

  • Edwin G. Delgado 2016-09-27

    If I want to to build an amplifier in the 20 -  30 watts range, what changes should be made to the circuit?  It is just a matter of changing the supplying DC voltages?  Good circuit and a good DIY project from you…....

    • Cezar Chirila 2016-09-30

      If you want to build an amplifier with such a low output this schematic will not do it and it is a bit overkill I think. I would suggest to do a search for “Class D IC” and you will find some integrated circuits from ST and TI that are great. I think the datasheet for some also provide schematic and PCB. Here are some links : and . If you need any help, please do not hesitate to contact me.

      • adgj533 2018-12-28

        Hey Cezar, I had a few questions about this project: I am trying to build it at home. You mentioned that we need +-30V, but I also see +-5V going to the op amps. does that mean we need 2 power supplies? Also Where did you connect your ground on the pcb, Im having trouble finding the common ground you talked about.
        One more thing, I am familiar with Eagle, is there anyway to convert KiCad files to eagle or do I have to manually rebuild the whole thing on eagle?
        How would i add a volume control knob to this circuit?

  • johnl2 2017-02-25

    Hello, I have been working on this circuit for quite some time. I purchased all of the parts and I just cannot seem to get the HO of the IR2110 to produce voltage. There’s V going into the HIN, -30V. I went over the whole circuit several times to make sure everything is connected properly and it seems to be. Is this a common problem? I looked up the IR2110 HO not working and some hits come up. Or could the IC be bad? Any help is appreciated. This thing is driving me nuts!


    • Cezar Chirila 2017-02-26

      First of all, did you use my pcb or did you build in on a perfboard?

      • johnl2 2017-02-26

        I used a breadboard just to test it out and plan to move further later. I am wondering if the power supply ground is isolated from the circuit ground. I just had a cap blow in my face for the first time ever after connecting the grounds together! My email is .(JavaScript must be enabled to view this email address) if you’d rather email me. Thanks for getting back so soon.

      • PES DIGITAL AUDIO 2017-11-11

        Hello john12, really you can’t get the voltage value at the HO of IR2110, unless you connect the output MOSFETS, remember its a floating ground at VS, HO voltage can be achieved when the Lower MOSFET turns on. But there is other way to check it even though with out MOSFETS connected. Just understand how the circuit works.

  • prasad357 2017-02-27

    How can I convert this design into a constant voltage (100V),high impedance amplifier ?

    • Cezar Chirila 2017-02-28

      To be honest I’m not really sure. It would be possible in theory if you use the rectangular signal before the filtering (the last inductor and capacitors), which can be used with a transformer, but I do not know after that what needs to be done.

      • Carel Colpa 2017-04-30

        You use an audio transformer in the amplifier to bring your voltage up to 100V, this technology is used to drive speakers over a long cable.

  • Pier Paolo Baldi 2017-03-15

    Hi, all looks really great!
    Can it be good, also to ampliy ultrasound?
    What have I to modify to have in output an 25 Ohm impedance?


    • Cezar Chirila 2017-03-17

      Depends on the frequency, but keep in mind that this is an amplifier designed to go well with frequencies under 20kHz. With greater frequencies you would need to increase the PWM freqency to be much greater and also to change the output filter. Generally you would like higher perfomance devices, faster op-amp, faster MOSFET driver, etc. To be honest I do not know much about Ultrasound amplifier, but I will start with a schematic of that and see the requirements. The output can be 25 ohm impendance, no problem, you would just (again) need to adjust the output filter accordingly.

  • rezgar.s 2017-04-05

    can i use +-90 v supply?
    If its possible how much power i can get?

    • Rysdana 2017-10-07

      The thing is that class d has efficiency advantage depend on your need.

  • n289se 2018-02-09

    Can this amplifier deliver 60-120 watts into 16 ohms?

  • supertallarin 2018-03-05

    Hi, thanks for the post! I am trying to build one myself and I have a few issues. Is it possible to determine some sort of transfer function in order to get an expresion of the gain of the amplifier? For example, I want it to be able to deliver 100W when the load resistance is 8ohms, how can I check that through an equation? Something similar happens when you try to add negative feedback to improve stability, bandwidth and THD, I need to determine the feedback gain (and with that the total gain) by design so that I can then choose the value of certain components.
    Is there anyone with some experience in this issue that can help me out?

  • DAEKH 2018-03-10

    How can I transform the circuit in order to allow me to have a right and left chanel? Is it possible (because I would like to build my own studio speakers) ? Thanks in advance (if you take care of this old project)

    • Dinca Andrei 2019-01-14

      Hi,a simple way is to make 2 PCBs and use 2 bipolar power supplys…

  • danishadvance 2018-03-20

    Can i use CD4504 level shifter instead of this 2 trasistor 2N5401 ?

  • danishadvance 2018-03-20

    Can you plz share the pcb layout of this schematic..

  • artmaster547 2018-04-18

    I have a question with regards to the selection of capacitance values for C12 and C13 how did you go about selecting those values is there a calculation that I could use, as I am designing something similar please?

  • Deshan Rajapaksha 2018-06-04

    It is good post & good job thanks admin   i will made it

  • adgj533 2018-12-28

    Hey Cezar, I had a few questions about this project: I am trying to build it at home. You mentioned that we need +-30V, but I also see +-5V going to the op amps. does that mean we need 2 power supplies? Also Where did you connect your ground on the pcb, Im having trouble finding the common ground you talked about.
    One more thing, I am familiar with Eagle, is there anyway to convert KiCad files to eagle or do I have to manually rebuild the whole thing on eagle?

    • Cezar Chirila 2018-12-29

      Hi adgj533! Don’t worry about the +-5V, that is regulated from the +-30V power supply using the two Zenner diodes D1 and D2. You are better of using either KiCad (Which is open-source - free and easy to learn) or start a new project with Eagle. You may run into odd problems by converting from one program to another and the time you loose looking for a fix might be greater than by just going with my suggestion. On the PCB, The ground connectors are near the -30V connector. There are two of them: One as an input, one as an output for the speaker, although it is better to connect the speakers direct to the power supply ground, to remove some humming noise. Take care!

      • adgj533 2018-12-30

        Hey cezar thanks for the quick reply. I thought u wouldnt even see my post. I am trying to build this amplifier at home.I want to add a pre amplifier circuit+ a volume control circuit, where would I add these things? Is it before the input of the amplifier? please let me know and thanks a bunch for your help

        • Cezar Chirila 2019-01-07

          Sorry for replying to you so late. For some reason I keep getting the notification emails in my spam inbox. If you want to add those, just add them before the class-D amplifier. So you have <Sound Source> - <pre> - <Class D Amp>.

  • adgj533 2018-12-31

    Hey cezar thanks for the quick reply. I thought u wouldnt even see my post..I want to add a pre amplifier circuit+ a volume control circuit, where would I add these things? if possible could you show me how to add it?  please let me know and thanks a bunch for your help

  • jbongiorno81 2019-01-27

    What steps would need to be taken to have a design such as this push lets say 500W into 4 or 8 ohms? I am currently working on a design for school and have been looking for insight from various projects. The amplifier would be embedded within a 2-way speaker.

    • adgj533 2019-02-09

      look at the reference design he used from infereon, that is something you might wanna use. Cezar’s design is more of an entry level or for hobbyist

  • adgj533 2019-02-09

    Hey Cezar, I had few more questions, I substituted 2n5401 with MPS751 bc it is unavailable in the market now. Also could you link me the heatsink you used?, I opened the files in kicad and it said that a lot of the libraries you used are missing, is it possible to send me your kicad libraries in a zip? just add at gmail to my username, that is my email. I appreciate you uploading the design so that others can work on it and thank you for your replies.

  • sdsds 2019-04-19

    Why power the input side of the IR2110 with -30 and -25 V? Since the comparators at the input are powered by +/-5 V, why not also power the IR2110’s input with that and avoid the level shifter?

  • Andesat 2019-06-04

    Hi Cezar, i have a power supply of +100v 0 -100v would i be able to use this circuit if i use IRFP260 .  what modifications will be necessary.

  • andershilmersson 2019-07-01

    How much distorsion do you get at different input frequencies? Which over tune frequencies (2:nd, 3:th etc)? How much is the 200kHz signal rejected?

  • Amit Yadav 3 2019-09-14