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.

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!)

The DC dual power supply +35V GND -35V, 3A for Mono and 5A for stereo system.

Instructions on how to building

1. Check the completed of PCB that defective, short circuit or not.
2. First, do not connect to the output transistors(MJ2955,2N3055).
3. Use a voltmeter measure voltage at output speaker and ground point.
4. Supply to this circuit And must meter reading is zero volts. Or error must not exceed 0.5V.
5. Put the output transistor into this circuit.
6. The voltage must be OV the same, If non-zero, indicating that the bad output transistors.
7. 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
Q1: BD139
Q2: BD140
Q3: 2N3055
Q4: MJ2955
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

The caution.
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.

There are two circuits like the above circuit. I collect old circuits. Sometimes you may see them on a power amplifier in your house.

70W OCL amplifier

Younger brothers and sisters a student takes an interest to build electronics project for their teacher. Then, choose this circuit. Because of building easy to be valuable certainly. It is Main Power Amplifier Circuit 70W RMS in model OCL Class AB.

Use pillar equipment is IC-741 and Transistor 2N3055, MJ2955 a little this equipment circuit. If friends want to get high power about 70W RMS. You should use a voltage Supply of +38V, and -38V. The usability should adjust VR1 be appropriate.

Class AB, 65W Power Amplifier using LF351, TIP3055 and TIP2955

I like the mini power amplifier less 100W because it is low cost and easy to make a project. The 65W Amplifier Class AB. I use main part electronics are IC LF351 and transistor two-part TIP3055 and TIP2955. The LF351 is a low-cost high-speed JFET input operational amplifier.

The TIP3055 and TIP2955 are small size but have high power. This is circuit want Voltage supply +38V and -38V at current 3A min. Have output power 65W to 75W at 8ohm speakers.

And….. This circuit may be good for you!

Note:

Besides this, we introduce these easy projects. Sometimes, you may like them.

• 55W RMS classic OTL amplifier
• 30W RMS amplifier with tone control
• MOSFET Amplifier OCL 50W

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