The 100W + 100W Stereo Amplifier Board using 2SC5200 and 2SA1943 power transistors is a discrete Class-AB stereo amplifier designed for builders who want a strong, serviceable, and thermally stable audio solution. Unlike IC-based amplifiers, this board relies on individual power transistors, making power supply design and heatsinking critical for reliable operation.
This documentation is written for users who will actually assemble, power, and run the amplifier in real-world systems, focusing on practical electrical and thermal considerations.
Amplifier Topology
The amplifier uses a complementary push-pull output stage built around the 2SC5200 (NPN) and 2SA1943 (PNP) transistor pair. These transistors are widely used in audio amplifiers due to their high current handling, stable gain characteristics, and predictable thermal behavior.
Each channel has its own driver stage, bias circuitry, and output transistors. The stereo channels share a common dual-rail power supply but remain electrically independent in the signal path.
Output Power Explanation
Under suitable operating conditions, the board can deliver up to 100 watts per channel. Actual output depends on:
- DC supply voltage after rectification
- Speaker impedance (4Ω or 8Ω)
- Heatsink size and airflow
When powered correctly, the amplifier delivers clean stereo output suitable for music playback without audible distortion during normal use.
Power Supply Requirements
This board requires a dual-rail DC power supply. Power is typically derived from a center-tapped transformer, followed by rectification and bulk filtering capacitors.
Typical supply characteristics
- Center-tapped AC transformer
- Approximately ±35V to ±45V DC after rectification
- Adequate current capacity for both channels
Using an undersized transformer or insufficient filtering will cause voltage sag, excess heating, and reduced audio performance.
Speaker Load Compatibility
The amplifier is suitable for use with 4Ω and 8Ω speakers. Driving lower impedance loads increases current draw and heat dissipation, so thermal management becomes especially important with 4Ω speakers.
Always verify speaker wiring before powering the amplifier to avoid accidental short circuits.
Heatsink and Thermal Design
The output transistors must be mounted on an appropriate heatsink. The heatsink should:
- Provide sufficient surface area for heat dissipation
- Be securely mounted using thermal compound
- Allow airflow around the fins
If the transistor metal tabs are electrically live, insulating pads or mica sheets must be used to prevent short circuits.
Input Signal and Grounding
The board accepts standard line-level audio input. Input wiring should be kept short and routed away from power lines to reduce noise pickup.
A star-ground layout is recommended to minimize hum and ground-loop issues.
Common Applications
- DIY stereo speaker systems
- Custom home audio amplifiers
- Workshop and small venue sound systems
- Educational amplifier projects
Initial Power-Up Checklist
- Confirm correct transistor orientation and mounting
- Inspect solder joints carefully
- Verify correct power supply polarity
- Power on without speakers connected
- Check DC offset before regular use
FAQ
Is this amplifier suitable for beginners?
It is suitable for users with basic electronics knowledge. Careful power supply design and proper heatsinking are essential.
Can the board operate on a single-supply DC source?
No. The amplifier requires a dual-rail positive and negative supply.
Does the board include speaker protection?
Speaker protection depends on the board version. External protection circuits are recommended if not present.
Can it continuously drive 4Ω speakers?
Yes, provided adequate cooling and a strong power supply are used.
Is this suitable for continuous high-power operation?
Continuous high-power use requires excellent thermal management to avoid long-term stress.
