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Fig. 1 - 140W Class AB Amplifier using MJL4281A and MJL4302A transistors with PCB |
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The Power Transistors
The MJL4281A and MJL4302A transistors are power transistors designed for high power audio, they have a collector-emitter sustaining voltage of 350 V.
It's high gain – 80 to 240, with the hFE = 50 (min) 8A collector current, and a low harmonic distortion, which makes a transistor excellent for high power operation and audio quality.
The Circuit
This circuit has a moderate complexity, it is not recommended for those who have no experience in electronics and in the assembly of amplifier circuits.
You should have minimum knowledge in an intermediate to advanced level to assemble this type of power amplifier.
The schematic diagram of the complete circuit, shown in Figure 2 below, is a very robust amplifier, with great sound quality and very stable, responding very well at all audible frequencies, with little attenuation in the 20Hz to 20Khz hearing frequency range.
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Fig. 2 - Schematic Diagram 140W Class AB Amplifier using MJL4281A and MJL4302A transistors |
Power supply
The power supply is symmetrical, with a voltage of +45V | 0V | -45V, and direct current, with at least 6 Amps of current. For continuous use, we recommend 4A, especially if used in a subwoofer.
In Figure 3 below, we have a suggestion for a power supply that we use in our projects. In this article, besides having the schematic diagram with the Printed Circuit Board, you will understand how to easily calculate your own Power Supply, with the desired voltage.
You can in the link below:
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Fig. 3 - Symmetrical Power Supply for Power Amplifiers |
Components List
- Semiconductor
- Q1, Q2, Q3 .... 2N5551 NPN Transistor
- Q4, Q6 ........... BD139 NPN Transistor
- Q5, Q7 ........... BD140 PNP Transistor
- Q8 .................. MJL4302A NPN Transistor
- Q9 .................. MJL4281A NPN Transistor
- LED1 ............. Light Emitter Diode (general use)
- Resistor
- R1, R3 ........... 2K2Ω resistor (red, red, red, gold)
- R2, R4, R8 ..... 22KΩ resistor (red, red, orange, gold)
- R5, R6 ........... 560Ω resistor (green, blue, brown, gold)
- R7 .................. 1K2Ω resistor (brown, red, red, gold)
- R9 .................. 1KΩ resistor (brown, black, red, gold)
- R10, R11 ....... 3K3Ω resistor (orange, orange, red, gold)
- R12, R13 ....... 220Ω resistor (red, red, brown, gold)
- R14, R15 ....... 0.22Ω / 5W resistor (red, red, silver, gold)
- R16 ................ 10Ω / 1W resistor (brown, black, black, gold)
- RP1 ................ 2K Potentiometer
- Capacitor
- C1 .................. 2.2uF / 25V electrolytic capacitor
- C2 .................. 330pF ceramic, polyester capacitor
- C3, C5 ........... 100uF / 65V electrolytic capacitor
- C4, C6, C7 .... 100nF ceramic, polyester capacitor
- Miscellaneous
- P1, P2 ............ Screw Terminal Type 5mm 2-Pin Connector
- P3 .................. Screw Terminal Type 5mm 3-Pin Connector
- Others ............ PCB, tin, wires, heat sink, soldering Iron, etc.
Printed Circuit Board - Download
We are offering the PCB – Printed Circuit Board, in GERBER, PDF and PNG files, for you who want to do the most optimized assembly, either at home.
If you prefer in a company that develops the board, you can is downloading and make the files in the Download option below.
Fig. 3 - PCB - 140W Class AB Amplifier using MJL4281A and MJL4302A transistors |
Files to Download, Direct Link:
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