Intro: Stereo Amplifier (6W+6W) Using LA4440 IC
Amplifiers are much needed for audio amplification. There are many dedicated audio ICs available in the market. They have different wattage ratings, power consumption,mono or stereo,etc.They are available in various packages like DIP,Pentawatt package( Many TDA series IC have this pack), SIP14H pack,etc. Today I will be talking about the LA4440 IC, which has a SIP14H pack. This is a very good and clean stereo amplifier. It can deliver 6W+6W output power, which is enough for your home theater. When used in bridge configuration it can deliver upto 19W of power. Talking about external parts, you will need a bunch of capacitors, a few resistors. I personally like it very much and I will recommend everyone to try this audio IC. It feels pretty nice when you are making your own amplifier without too much hassle. So let's get started.
Step 1: Parts Needed
1. LA4440 IC with heatsink
2. 47uF cap polar
3. 100uF cap polar
4. 220uF cap polar
5. 1000uF cap polar
6. 4.7uF cap polar
7. 10k pot
8. 2.2K resistor
9. 1K resistor
10. a small switch (only if you want a muting function or a dedicated power on off switch)
11. 3.5mm socket female and male
12. Screw terminals
13. Breadboard ( for testing purpose)
14. Solder board and soldering kits
15. 0.1uF (104) cap non polar ( these are optional)
16. 4.7ohm resistor ( these are optional)
17. female Barrel jack for power supply
18. some hookup wires
19. Breadboard for testing
20. 2 10W speaker
Step 2: Theory and Working Principle
I've completely read the datasheet and I myself did some modifications to make up my 6W + 6W stereo amplifier circuit. Download and print the datasheet from here http://www.onsemi.com/pub/Collateral/EN750-D.PDF
The circuit diagram is attached here.
The amplifier is a stereo amplifier. Hence it has 2 channels for audio input. So one IC is sufficient for a 6W+6W stereo amplifier. But for bridge amplifier you need two of such ICs. Since two amps are required for a bridge configuration. Bridge configuration can provide upto 19W of output power. But I will be using in stereo mode here. You can go through the datasheet for bridge configuration.
The voltage gain is fixed here at about 52dB. That is gain is about 400. Now we need control to our gain. So we add a 22k pot at the input side to vary the gain. so 2 pot for 2 channels( L and R). So after placing pot we can vary the gain from 52dB to -0.847dB ( that is 0). Apply the formula: gain= 20*log(Rf/(Rnf+Rnf')) and you will get it.See the pic attached here taken from the datasheet.
Now the 4,7u and 2.2k form a high pass filter with a cutoff frequency of about 15hz. Apply the formula fc=1/(2*pi*C*R) and you will get it.
The amp chip has a muting function. The 4 and 5 pins can be used for this, as per datasheet. I used only 4th pin. As per datasheet it is given that a voltage from 6V-9V must be given to the 4th pin, and that 9V I've provided from the power supply 12V itself, by using a potential divider. For greater attenuation use 5th pin, see the pic in datasheet.
The heatsink must be provided since this dissipates a lot of power. heatsink can be connected to the ground of the pcb. Some tips regarding heatsink from datasheet are also attached here. See them.
A zobel network of a 0.1uf + 4.7ohm can be used as per datasheet. Using non polar polyester cap is good since it has good temperature and frequency characteristics.
The function of all other components are given in the datasheet and also I've attached the important ones, if you don't have time to read it.
Step 3: Testing on Breadboard
Now for testing breadboad is necessary. Connect the circuit as per circuit diagram. The caps take too much space. Try to attach the caps as close to the IC as possible to reduce RF disturbances. Attach 2-8ohms (stereo mode) speaker. Cut a 3mm jack and insert the male pin into your mobile or any audio source and attach the wires to the inputs and audio gnd to common gnd. Give at least 12V(less than 18V) supply and test it. If you want to incorporate the muting function then you can do that. You will hear a lot of distortion in breadboard but don't worry. If audio is successfully amplified then you are all ready to go for PCB. All noises and disturbances will be removed after you pcb-fy it. After successfully testing, gather all components for pcb or zeroboard, whatever you may have.
Step 4: Making the PCB
Using EasyEDA and then ordering PCB from JLCPCB or PCBWay can be good but here I'm using simple zeroboard soldering method. Place and solder carefully. The caps will consume a lot of space but you have to keep the legs as close as possible to the Chip. So place them wisely and be careful about polarity in case of polar caps. Attach the various connectors for input and output and power supply. It might take a lot of time but be patient. Take the schematic beside you during the job.
After finishing the job test it again. I'm pretty sure that now you won't get that distortions which you got before. I personally like the amp board a lot and I regularly play musics in it. Place the speakers in a closed wooden box and feel the bass. You can also add a preamplifier low pass stage for more bass.
Congratulations, you have successfully build your own 6W+6W speaker. Please comment down below or mail me at firstname.lastname@example.org for any confusion.