This is 60W RMS OTL integrated audio amplifier circuit using 2N3055 and normal transistor so cheap and can build easily and It’s durable and very loud sound for mini PA
From the previous project, some people say that Not suitable for a small party. Because of soft and does not durable. So I highly recommend this project are The classic OTL integrated amplifier that power output 55 watts.
The its feature is loudly than other circuits and watts are equal. the speaker has durability and be difficulty damage. And build easier OCL amplifier Although some people say that it is not good bass. But if you try, you may like it.
Principle and operation of this projects
The tone control circuit consists of Q1-transistor and IC1( op-amp IC-LM741). The signal input will enter to C1 and R3 into base of Q1. Which acts as matching between the input circuit and tone control-IC1.
VR1 is used to adjust the bass sound.
VR2 is used to adjust the treble sound.
Which this circuit can adjust the bass/treble to upper or lower up to 18 dB.
The output from the tone control will be entered through C8-capacitor to the level sound controller circuit is VR3-potentiometer and the loudness controller.
The signal from volume will enter through to base of transistor-Q2, To amplifier the signal higher, that enter to pre driver Q3, to drive the driver circuit with Q4, Q5 and the both power transistors Q6, Q7 next.
How to builds
Since the circuit is designed as well. So easy to create. However, to the best results. Should perform the following.
1. Check the correct finished in putting all components.
2. Do not connect the power transistor.
3. Use the voltmeter measures at 2 points C17, C18 compare to ground.
4. connects the positive 56 volts to this circuit and then adjust VR4 until read meter about 28 volts.
5. connects properly the power transistors to the circuit
The power supply circuit
In the figure 4, The voltage 56V for this circuit. We are derived from the bridge rectifier to change from AC40V. to as DCV. then pass the filter capacitors , and then will obtained is the 56VDC.
The transformer that use for the mono type, should use size is 2A and size under 3A in the stereo system.
The detail of parts list
Q1, Q3______________BC548 45V 100mA NPN Transistor
Q2_________________ BC557 45V 100mA PNP Transistor
Q4_________________ BD139__80A 1.5A PNP transistor.
Q5_________________ BD140__80V 1.5 PNP Transistor
Q6, Q7______________2N3055 100V, 15A, 115W, >2,5MHz NPN transistor
ZD1________________18V 1/2W Zener Diode
D1, D2______________1N4148___75V 150mA Diodes
R4, R11, R15, R16_____2.2K
R5, R6, R7, R8, R23____10K
R22, R26_____________20 ohms
R25, R27_____________120 ohms
R28, R29_____________0.5 ohms /1W
R30_________________10 ohms /1W
C1, C2, C12_______10uF 16V
C7, C8___________22uF 16V
C9, C13, C15_____47uF 16V
C11. C16_________220uF 16V
The detail parts of the power supply
T1___________Transformer Secondary for 40 volts 3A. ( for stereo system)
D1-D4________Bridge diode >3A.200V
C1___________0.01uF 100V___Polyester Capacitor
C2___________10,000uF 63V___Electrolytic Capacitors
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