LM4780 Audio Amplifier
A compact stereo amplifier built around the LM4780TA, with an LM1036N preamplifier, PIC-based VU meter and custom power-supply electronics.
Introduction
This project is an audio power amplifier with a Hi-Fi preamplifier. The LM4780TA is an integrated stereo power amplifier in a single package. It can deliver approximately 60 W per channel, with a specified THD of about 0.5% at 60 W, which is a solid result for this type of construction.
Because I needed to build the amplifier quickly, I purchased a ready-made amplifier PCB from EZK. It cost approximately CZK 200 including the passive components. I obtained the LM4780 itself as a sample directly from Texas Instruments. The metal enclosure was reused from an old router.
Power Supply and Mechanical Construction
The amplifier requires a symmetrical power supply. Several additional voltages are also needed for the auxiliary circuits, so the enclosure contains a separate power-supply PCB. To save space and reduce mains hum, I used a toroidal transformer together with a mains interference filter.
Hi-Fi Preamplifier
The preamplifier is based on a published design using the LM1036N. This is a capable analogue tone and volume-control IC. I used precision IC sockets and film capacitors to improve reliability and electrical performance.
VU Meter and Cooling
For the level indication, I used a compact PIC-based VU meter design. Its small size made it suitable for the enclosure. I programmed the PIC using a JDM programmer. The circuit worked correctly on the first attempt, and I can recommend this design. I also added a small DC-DC converter to power the cooling fan.
Construction Gallery
