50W LM3886 Power Amplifier

50W LM3886 Power Amplifier

This is the second revised version of a 50-watt LM3886 power amplifier, intended to drive two bookshelf speakers. The LM3886 chip produces such excellent sound that I decided to use it to build another amplifier. The schematic is based on the schematic in the chip's datasheet with minor modifications. I removed the delay capacitor connected to the MUTE pin because it's better to use a separate DC protection circuit with similar functionality. I created the output inductor L1 by winding 15 turns of enameled wire around resistor R7. The wire diameter must be at least 0.4 mm. The entire section is wrapped in heat-shrink tubing.

I used a 47µF/63V nonpolar capacitor as C2. It can be a regular electrolytic capacitor, but a nonpolar or bipolar capacitor would be better.

The transformer is 2x24V AC / 105W. Testing was conducted using an 8-ohm dummy load, and the large heatsink only warmed up after several hours of playing music from my computer at maximum volume. The transformer is a bit weak for this amplifier; perhaps 150W or 200W would be a better choice.

The power supply is very simple – a bridge rectifier and four 10,000 microfarad/50-volt capacitors.

If the input is disconnected and open-circuited, there will be a slight buzzing sound, which can only be heard by putting your ear very close to the speaker. But once the amplifier is connected to the signal source via cable and there is no signal, it becomes completely silent.

In addition, if the heatsink is isolated from the chip's metal plate by some mica pads, then the heatsink should preferably be connected to ground to prevent humming from being introduced into the open input.

You can install it without an insulating pad to achieve better thermal conductivity, but then the heatsink itself must be isolated from the metal casing that is normally connected to ground.