DIY 2.1 Class AB Hi-Fi Audio Amplifier - Under $5

Hey everyone! Today I'm going to show you how I built an Audio Amplifier for a 2.1 channel system (Left-Right and Subwoofer). After nearly 1 month of research, designing, and testing, I have come up with this design.

In this instructable, I’ll walk you through the amplifier design process. First, I’ll show you how to select the perfect IC for your project. Then, I’ll show you how to find the right values for all of the components in the circuit, and how to change the gain and other parameters. Finally, in the end, I will tell you some tips to remove any type of noise.

After going through the entire instructable, anyone can design their own amplifier for different applications. I will try to make this instructable as brief as possible and easy to understand for everybody.

Okay enough for the introduction. Let's get started

Step 1: Selecting IC for Amplifier

Okay, so anyone can confuse between various options available for audio amplifier ICs. It's a difficult task to go through several datasheets. So, here is a summary of my analysis for some famous ICs in India.

Top audio amplifier ICs:

1. TDA7294 Datasheet

100V - 100W DMOS audio amplifier with mute
Short circuit protection
Can provide 200W in parallel

2. LM3886 Datasheet

High-Performance 68W Audio Power Amplifier w/Mute
Wide Supply Range 20V - 94V
Signal-to-Noise Ratio ≥ 92dB
Best Sound quality

3. LA4440/CD4440 Datasheet

Built-in 2 Channels (Dual) Enabling Use in Stereo and Bridge Amplifier Applications.
Dual : 6 W × 2 (typ.) ; Bridge : 19 W (typ.)
Minimum Number of External Parts Required

4. TDA2050Datasheet

32 W hi-fi audio amplifier
Wide-range supply voltage, up to 50 V
Cheap and easy to replace

5. TDA2030Datasheet

14 W hi-fi audio amplifier
Wide-range supply voltage, up to 36 V
Cheap and easy to replace
Can be bridged for more power

While selecting an IC, consider your expectation from the Amplifier and purpose of your project. If you want a high wattage amplifier with the best in class sound quality then go for TDA7294 or LM3886. But, if you just want to drive a 5W, 10W or 20W speaker than, 4rd and 5th option are best for you. You can also consider LA4440 if you want a simpler circuit (both left and right channel in a single IC).

Generally, you should pick an amplifier that can deliver power equal to twice the speaker’s power rating. This means that a speaker with an impedance of 8 ohms and a rating of 5 watts will require an amplifier that can produce 10 watts into an 8-ohm load. For a stereo pair of speakers, the amplifier should be rated at 10 watts per channel into 8 ohms.

Want to learn more about Amplifiers, click here

Step 2: Parts and Tools

I want to drive two 5W speakers for Left and Right channels which I extracted from an old CRT TV. So, TDA2030 is best for me but, you can choose TDA2050 for building Left and Right channels too.

Tools -

Multimeter
Soldering station
Hot glue gun
Pliers
Cutter
Shrink tubing

For TDA2030 Stereo Amplifier (Left+Right) -

TDA2030 (2)
Speakers (2)
Preboard
3.5mm stereo jack
1N4007 Diode (2*2)
Potentiometer or Trimpot 10K/22K (2)
Potentiometer Knob (optional)
Resistor 10(1*2), 100k(4*2), 3.7k(1*2)
Ceramic Capacitor 100nF(2*2)
Electrolytic Capacitor 1uF(1*2), 100uF(1*2), 2uF(1*2), 22uF(1*2), 2200uF(1*2)
Power supply: Transformer or DC adapter 12V 2Amp(min)
Heat sink (2)

For TDA2050 Subwoofer -

TDA2050 (1)
Subwoofer (1)
Preboard
Potentiometer or Trimpot 10K/22K (1)
Potentiometer Knob (optional)
Resistor 10(1), 100k(4), 3.3k(1)
Ceramic Capacitor 100nF(2)
Electrolytic Capacitor 1uF(1), 1000uF(2), 2uF(1*2), 22uF(1)
Power supply: Transformer or DC adapter 24V 2Amp (suggested)
Heat sink

For Low Pass Filter -

RC4558 (1)
Resister: 100K(2), 560(2), 22K(1)
Capacitor: 1uF(1), 104j(2)
Split power supply 9V to 12V

Now let's start with the TDA2030 Amplifier.

Step 3: Stereo Amplifier Circuit

According to the datasheet, the TDA2030 can output 9 Watts into 8 Ω speakers with 0.5% distortion on a 14 V power supply.

Actually, You can get a basic application circuit for nearly every IC in the datasheet. In the TDA2030's datasheet, there are two circuits, one with a single power supply and another with a split power supply. You can choose any circuit as per your needs. I am going to use a single power supply circuit because I will power it by 12 DC adapter. For the split power supply, you will need a 12-0-12 transformer.

First, let's simulate the circuit. So, we could see how it worked. The circuit diagram was made with Proteus.

Test everything out and make sure that your circuit is going to work before you start soldering.

Note: C2 and R7 wires are not connected. (Simulation Fig.)

Step 4: Modifying the Circuit

Let’s find out the best values for the components in the circuit. I’ll use the schematic above, which is the same as the one in the datasheet, but with a few modifications to set gain, bandwidth and help filter out noise.

1. Gain

The circuit in datasheet has a gain of 33 and will cause distortion. A good gain to use for home listening is around 27 to 30dB. This setting isn’t high enough to cause distortion and will give you a good range of volume.

Gain = 1+R1/R2

if R1 = 100k

then, R2 = 3.7k

2. The Zobel Network

A Zobel network helps to prevent oscillation that can occur from the parasitic induction of speaker wires. It also acts as a filter to prevent radio interference picked up by the speaker wires from getting to the inverting input via the feedback loop.
C6 and R8 form a Zobel network at the amplifier’s output.

C6 = 100nF and R8 = 10ohms, which gives an cutoff freq (fc) of:

fc = 1/(2*pi*R*C)

fc = 159KHz

159 kHz is above the 20 kHz limit of human hearing and well below radio frequencies, so these values will work fine. If the amplifier oscillates, R6 will be passing high currents to the ground so it should have a power rating of at least 1 Watt.

3. Bass

Capacitor C7 in the fig. is used to set the bass for the speakers, higher the capacitor value better the bass response of speakers. You can also use a variable capacitor to change the bass manually. (This bass is not related to subwoofer)

Tip: When I was building this amplifier, I doubt why we are using those extra capacitors and resistors, what they do, and what if we remove them. You can't ignore these questions if you're an electronics enthusiast. Go through page 10 section 4.3 in the datasheet to get a rough idea.

But I highly recommend this awesome tutorial by Circuit Basics. This article covers all the required details in depth.

Note: I will take above Fig. as a reference in upcoming steps.

Step 5: Connecting 3.5mm Jack

If you have an audio wire (with jack) or earphones, then multimeter is the best option to check the connectivity and to find out G-L-R connectivity. If you don't have an audio jack wire then you can use male or female connectors.

Connect 3.5mm jack to phone and other side open wires to the amplifier. Left to left side amplifier and right to right side amplifier with common grounds.

Check the attached photos for reference.

Step 6: Building the Amplifier

Start building with only one channel of our stereo amplifier. Carefully build the circuit on perfboard, you can take the help of PCB designs available in the datasheet. If you have doubts, you can first use a breadboard to check the circuit. But remember assembling it on the breadboard will have many open wires which may lead to a lot of noise in the speaker. So, don't think that circuit is wrong when you get buzz or hum.

Add a Potentiometer before capacitor C2 (Step 4 Fig.) for volume control, it's also very effective to reduce distortion. I used a trimpot for this purpose and permanently set the value of trimpot such that there will be no distortion at max phone volume.

After checking and testing the first channel, repeat the process and clone the exact same circuit on the same or another perfboard. Now you have two mono amplifiers, connect left channel wire to one amp, and right channel wire to the other amp with common ground to both. Use different trimpot for each channel and set the same trimpot value for both channels so that each channel will have the same volume.

You can use a potentiometer (instead of trimpot) if you want to change the amplifier's volume often. I suggest you to use a Dual Taper Potentiometer to manually control the Left and Right audio at the same time.

Power supply: The power supply you are going to use should be double the power required i.e. for two 5W speakers there should be a 20W power supply for best results.

Here I going to use a 12V 2Amp DC adapter (P=24W) for both channels.

NOTE: Check Step 9: Noise Reduction, before finalizing the circuit on perfboard.

Step 7: Sub-Woofer Circuit

For a woofer circuit, we needed to add a Low Pass filter before the amplifier circuit. For the subwoofer, the Low Pass Filter is very important, without it the subwoofer is just a high wattage speaker.

The Low Pass filter will only allow low freq audio to pass through. Audio Signal is first filtered to remove the high-frequency signals and allow only the low-frequency signals to pass through it. This low power signal is then amplified using a transistor driven class AB power amplifier.

But, we are not going to use TDA2030 for this amplifier because generally subwoofers are of high wattage and will require a high powered amplifier. I am going to use TDA2050 for this purpose because my subwoofer is 20W.

You can use any IC you want, just take the circuit from the datasheet, modify it the same way as we did with the TDA2030 amplifier and that's it now you're ready to go for the LPF.

For LPF you can use RC4558 IC. More details

But, I don't have 4558 so I tried building the LPF using LM741 which is not recommended but you can try. Actually, RC4558 is a dual version of LM741 op-amp.

I started building a 2nd order LPF using LM741 with cutoff freq of 160Hz, The LPF cutoff freq should be in the range of 80Hz to 200Hz. Then you need to power LM741 with appropriate supply (5V to 12V), you can use a battery for this purpose. I tested the LPF circuit on Breadboard and will finalize it with RC4558 IC once I will get it after Lockdown.

Tip: The subwoofer should be kept in a perfect enclosure for better Bass. A woofer kept on the table will never provide a good Bass.

Want to learn more about woofer circuits, click here

Power supply: The power you are going to supply should be double the power required. Here in our situation two 5W speakers and one 20W subwoofer sum up to 30W which needs 60W of supply for best results.

You can use a 24V 3Amp DC adapter (P=72W) for both the stereo channels and subwoofer or you can also power them separately using a 12V 2A adapter for two TDA2030 channels and one 24V 1.5A adapter for TDA2050 subwoofer channel.

Same for the transformers if you are operating on a split power supply.

Step 8: Heat Sink

The TDA2030 and TDA2050 need to be attached to a heat sink or it will quickly overheat and get damaged. The size of the heat sink you need will depend on your maximum power dissipation and the thermal resistances in the path of heat flow away from the TDA2030/50.

Check the heat sink temperature on full power use, if it becomes too hot change the heat sink to a bigger one or install a fan. You will not need a fan for this project because we are not dealing with huge power here.

Step 9: Noise Reduction Tips

So, until now you may have completed all the processes but still not able to get perfect noise-free audio. There are many reasons which can cause noise in the speakers.

1. Grounding the Amplifier

Grounding is one of the most important aspects of amplifier design. A poor grounding layout can be a major source of hum and buzz. A good grounding layout keeps the low current audio input and signal grounds separate from the high current power supply and speaker grounds. If high currents are allowed to flow through the low current grounds, a DC voltage will develop in the low current wires that will show up at the input and get amplified as hum.

To solve this problem, connect all the grounds (Audio input ground, Signal ground, Speaker ground) directly to power ground without forming loops. Don't ever connect any ground in the midway of other ground, all grounds should meet at power ground only or a ground junction. The ground networks are connected in a particular order so that high currents only flow through the low current grounds for a very short distance.

Check ground wire connections in Fig. These different grounds wire in the schematic are not for design. Always add all the grounds directly to the power ground to avoid loops.

2. Wiring the amplifier

To avoid interference from magnetic fields, try to keep the sensitive input and signal wires far away from the power supply wires, speaker output wires, transformer, AC mains wires, and rectifier diodes on the power supply.
Three power supply wires (positive, negative, and power ground) should be thick and as short as possible to minimize the inductance. Anything larger than 18 AWG should be fine.
The audio input and signal ground wires don’t carry a lot of currents so they can be the thin gauge. Solid core 22 AWG works really well and is easy to twist together.
To minimize the loop area, the following wires should be tightly twisted together:
- Power supply wires
- Speaker output and ground wires
- Audio input and audio input ground wires.
There should not be any open wires, it can catch noise.

3. Enclosure

It is very important to use enclosures. Metal enclosures are the most commonly used because they offer the best shielding from fluorescent light, radiofrequency, and cell phone interference.

Reference: Circuit Basics, Youtube

Check out these links for a more detailed explanation. (Highly Recommend)

Step 10: Final Words

How Does It Sound?

Overall, the amp sounds great. The bass, mids, and treble are all very clear and well balanced. It also has plenty of power. There’s more than enough volume for listening in my living room. There is no hum or buzz noise while the amp is plugged into the source (there can be surrounding noise when the audio jack is not plugged in the phone/laptop, So don't worry it's normal).

While the sound quality of the TDA2030 may not be up to par like TDA7394 or other, But is good to start with.

But there is no obstacle to create something better. This circuit is easy to modify, If you want you can also