Audio Amp 30W & Baxandall Tone Control DIY

1. Concept and Circuit Design

I have always believed that the best sound is the one you create yourself. In the late summer of 2025, I took on the challenge of assembling a compact yet high-quality 30-watt audio amplifier. The system is built on a modular principle:

• The Heart (PSU): To ensure stable operation, I used a transformer with specific secondary windings. A +12V / -12V rail powers the preamplifier (critical for op-amp performance), while a powerful +42V single rail drives the main power stage.
• The Brain (Tone Control): For sound shaping, I chose the classic Baxandall topology implemented with uA741 operational amplifiers. This allows independent Bass and Treble adjustment without introducing significant distortion.
• The Muscle (Power Stage): I relied on the proven TDA 2050 chip. It delivers up to 32W of power with very low harmonic distortion, making it an excellent choice for home Hi-Fi applications.

2. PCB Fabrication

For the power supply and tone control, I avoided generic boards. Instead, I manufactured them myself using the photoresist method:

1. Printing a negative photomask of the circuit.
2. Exposing the copper surface to UV light.
3. Developing and etching the board to achieve precise traces.

3. Assembly and Enclosure

I decided to give new life to an old device (Upcycling), giving the unit a unique retro-industrial look.

• Modifications: Drilled new holes for potentiometers (Volume, Treble, Bass) and installed a dedicated ON/OFF switch with an LED indicator.
• Connectivity: High-quality banana binding posts were mounted on the back panel for secure speaker connections.
• Internals: PCBs are mounted using standoffs to ensure proper isolation and airflow.

4. Final Touches & Conclusion

I used a label printer to create custom labels for all controls. The result is an amplifier that delivers punchy bass and crystal-clear highs—proof that with passion and a soldering iron, we can build gear that brings more joy than anything bought off the shelf.