Figure 1: Complete 10 Transistor 100W Audio Amplifier Circuit Diagram & Output Stage - Electronic Help Care
10 Transistor 100W Audio Amplifier Circuit Diagram (2SC5200 & 2SA1943)
A high-fidelity Class-AB complementary power amplifier schematic, bill of materials, and workbench assembly guide by Electronic Help Care.
This amplifier uses high-current complementary Toshiba output transistors (2SC5200 NPN and 2SA1943 PNP) configured in a push-pull Class-AB topology. Designed for high clarity, rich bass response, and reliable low-distortion audio output across 4Ω and 8Ω speaker systems.
1. Technical Specifications
| Parameter | Value / Specification |
|---|---|
| Topology | Class-AB Complementary Push-Pull |
| Power Output | 100W to 150W RMS (depending on rail voltage) |
| Supply Voltage | ±35V DC to ±45V DC (Dual Rail / Split Supply) |
| Speaker Load | 4 Ω to 8 Ω |
| Output Transistors | 2SC5200 (NPN) + 2SA1943 (PNP) |
| Frequency Response | 20Hz - 25kHz (±0.5dB) |
2. Complete Parts List (Bill of Materials)
- 2SC5200 (NPN Power Transistor): 5 pcs
- 2SA1943 (PNP Power Transistor): 5 pcs
- Emitter Resistors: 0.22Ω 5W ceramic power resistors (10 pcs)
- Pre-driver & Driver Transistors: High-voltage audio drivers (per schematic)
- Power Supply Rectifier: 35A / 50A Bridge Rectifier (1 pc)
- Filter Capacitors: 10,000μF 63V or 80V Low-ESR electrolytic (2 or more pcs)
- Decoupling Capacitors: 100nF (0.1μF) 100V ceramic / polyester film caps
- Output Zobel Network: Output coil (10-15 turns 1.0mm enamelled copper wire) + 10Ω 2W resistor
- Power Transformer / SMPS: 30-0-30V AC or 35-0-35V AC secondary (5A - 8A)
- Heatsink: Heavy-duty aluminum heatsink with cooling fan
3. Video Walkthrough & Sound Test
Watch the complete assembly, wiring, and oscilloscope sound test video below:
4. Circuit Working Principle
The amplifier is built around a classic 4-stage discrete architecture:
- Differential Input Stage: A matched pair of low-noise transistors handles the input signal and negative feedback loop. This stage sets the gain and ensures DC offset voltage at the speaker output stays close to 0V.
- Voltage Amplification Stage (VAS): Converts the differential current into a wide voltage swing running between the positive and negative power rails.
- Vbe Multiplier (Bias Servo): Mounted on the main heatsink to thermally track output transistors and regulate quiescent current, preventing crossover distortion while safeguarding against thermal runaway.
- Push-Pull Output Stage: Multiple paralleled pairs of 2SC5200 and 2SA1943 transistors deliver the high current required to drive heavy speaker voice coils without voltage sag.
- Insulation: Always mount 2SC5200 and 2SA1943 transistors on the heatsink using mica insulators or silicone pads with thermal paste. Ensure the transistor collector tabs do NOT touch the grounded heatsink!
- Star Grounding: Connect input signal ground, speaker return ground, and power supply center tap (0V) at a single star-ground point to avoid 50Hz/60Hz mains hum.
- First Power-Up: Never connect your speakers directly on the first test. Power up through a 100W incandescent series bulb. Measure DC voltage across speaker terminals; it must be under ±50mV DC.
5. PCB Layout Download
You can download the full Gerber PCB layout and project files from our official repository:
→ Download 10-Transistor Amplifier PCB Files on GitHub
Electronic Help Care Support
Have questions about PCB layout, biasing, or component substitutions?
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Email: srjewel2020@gmail.com
Website: www.electronichelpcare.com
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