This circuit scheme is an audio amplifier that can produce 35 Watt output with small distortion. The core of this circuit is LM391 type IC. LM391 IC is a driver devoted to driving the transistor-based amplifier. The advantages of this IC is its easy use and only needed some additional components only.
TR1 transistor serves to regulate the bias current of 45mA. Inductor L1 consists of 20 rounds with 0.9mm wire diameter. This wire should be wrapped around a resistor R16. At the time the circuit works, transistor Q3 and Q4 will experience heat. Therefore these two transistors must be installed heatsink. There are two options for using the final transistor. If a TIPXX type transistor is used, the cooling used may be heatsink board. But if the transistor is used with the TO-3 packaging type, it can be used heatsink with short wires connected to each of these transistors.
This circuit will work optimally at voltages between 25 VDC to 35 VDC. While the required current is not less than 5 Amperes. The amplifier circuit as shown in the figure is a mono system. If you want to use the stereo system, you can build two circuits. The Power supply used must be well regulated to prevent the sound of droning on the speakers.
35W Audio Amplifier Circuit based LM391 IC Part list:
| R1,3,5,8,10 = 1Kohm | C1 = 2.2uF 63V | TR1 = 10K Trimmer |
| R2,7,11 = 100Kohm | C2 = 4.7uF 25V | D1,2 = IN4002 |
| R4,6 = 4.7Kohm | C3,17 = 47uF 63V | IC1 = LM391 |
| R9,12 = 100ohm | C4,8,9 = 1nF 100V MKT | Q1 = BD139 |
| R13 = 47Kohm | C5 = 47nF 100V MKT | Q2 = BD140 |
| R14,15 = 0.15ohm 5W | C6 = 22pF ceramic | Q3 = TIP2955 |
| R16 = 1ohm 2W carbon 5% | C7,11,12,13 = 100nF 100V MKT | Q4 = TIP3055 |
| R17 = 10ohm 1W carbon 5% | C10 = 22pF ceramic | L1 = See text |
