Discrete Class AB Transistor Audio Power Amplifier Circuit Diagram
This is a class AB transistor power amplifier. It is a simple amplifier to build, uses standard parts and is stable and reliable. The entire circuit utilizes commonly available components and may be simply built over a general-purpose board. But this amplifier has very good sound quality.
There are eleven transistors, including four in the output stage. Q1 and Q2 transistor must be between 3 and 5 amperes power transistors. Q4 and Q5 must be between 100mA and 500mA driver transistors. Other transistors are 10mA small driver transistors. Q1, Q4 and Q2, Q5 are complementary pairs, they make complementary darlington pairs.
| PART LIST | |
| R1 | 1.5KΩ ¼W |
| R2 | 150Ω ¼W |
| R3 | 1KΩ ¼W |
| R4 | 0.22Ω 2W |
| R5 | 0.22Ω 2W |
| R6 | 39KΩ ¼W |
| R7 | 1KΩ ¼W |
| R8 | 120Ω ¼W |
| R9 | 6.8KΩ ¼W |
| R10 | 6.8KΩ ¼W |
| R11 | 47KΩ ¼W |
| R12 | 47KΩ ¼W |
| R13 | 2.2KΩ ¼W |
| R14 | 180KΩ ¼W |
| R15 | 18KΩ ¼W |
| C1 | 22pF Ceramic |
| C2 | 4.7µF 16V |
| C3 | 1000µF 25V |
| C4 | 100µF 25V |
| D1 | 1N4148 |
| D2 | 1N4148 |
| Q1 | 2SD313 |
| Q2 | 2SB507 |
| Q3 | 2SA733 |
| Q4 | 2SB560 |
| Q5 | 2SD400 |
| Q6, Q7, Q8, Q9, Q10 | 2SA733 |
| Q11 | 2SD400 |
| LS1 | 4Ω 20W SPEAKER |
Power output of the amplifier
| Supply voltage (Vs) | = 20V |
| Speaker impedance (R) | = 4Ω |
| Peak to peak voltage (Vpp) | = 20-2 =18V |
| Peak voltage | = 9V |
| Maximum output (Pmax) | = 9V2/2R |
| = 81/8 | |
| = 10W |
10W is much enough for the day today home usage.
Amplification of this amplifier (A)
| A | = R6/R13+1 |
| = 39KΩ/2.2KΩ+1 | |
| = 18 |
Volume control can be added to the circuit by connecting a 10KΩ POT in series to the input of the amplifier.
Q1 and Q2 must be kept sufficiently cool, so it is mounted on a suitable heat sink. If you used single heat sink please use insulation between transistors and heat sink.
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