If you want a 50W OCL main amplifier circuit, high quality and save money. You can use it to amplify the normal sound in the home. At the level of pleasant sound power. It was the first amplifier circuits that I created. Also, we will see this circuit in a generally affordable amplifier.
Because it has fewer components, transistors-2N3055-MJ2955, a low noise IC-LF351, a few parts. You can buy easily.
If compare it at the same volume level is cheaper than other circuits.
Table of Contents
Main power amplifier working
Designers set this circuit in “Direct Coupling All Complementary IC Drive”. The heart of the circuit is IC1(LF351). It is the differential amplifier pre-driver circuit.
Note: I chose LF351. Because of the lower noise reduction circuit. Also, high-frequency response than IC741. While you may use a TL071 or NE5534N is good quality as well.
The output signal of IC1 flows through two 1N4148 diodes D1 and D2 to the transistor drivers Q1(BD139), Q2(BD140).
Then, these current come to two main transistor output Q3 (MJ2955), Q4(2N3055).
The small Potentiometer VR2-1K is adjusted the idle current of this amplifier circuit. This circuit is so easy to adjust.
If you do not have an ammeter, you do not need to measure the IDLE current. You just adjust the VR2 at middle only (very simple!)
Instructions on how to building
- Check the completed of PCB that defective, short circuit or not.
- First, do not connect to the output transistors(MJ2955,2N3055).
- Use a voltmeter measure voltage at output speaker and ground point.
- Supply to this circuit And must meter reading is zero volts. Or error must not exceed 0.5V.
- Put the output transistor into this circuit.
- The voltage must be OV the same, If non-zero, indicating that the bad output transistors.
- Connect speakers and input signal to this amplifier circuit. Let’s to listen the melodic music.
The Electronic parts.
IC1: LF351, TL071, LM741 normal op-amp
ZD1,ZD2: 15V 0.5W Zener diode
VR1: 50K Potentiometer
VR2: 1K pot
C1,C9: 10uF 16V Electrolytic capacitors
C3,C4: 47uF 25V Electrolytic capacitors
C2: 100uF 16V Electrolytic capacitors
D1,D2: 1N4148 Diode
Holding the output transistors onto the heat sink you must sure that:
1. The screws tight, not fell, the loose easily.
2. Do not the short circuit between the collector Pin(transistor body) and heat sink, Due to the installation of mica insulation is not well.
And….. This circuit may be good for you!
Besides this, we introduce these easy projects. Sometimes, you may like them.
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