Summary of 50W Power Amplifier with LM3886
This article details a 50W power amplifier project using the LM3886 chip, featuring a simplified schematic based on the datasheet. Key modifications include removing the MUTE pin delay capacitor in favor of separate DC protection and creating output inductance L1 by winding wire around resistor R7. The design utilizes a 2x24VAC transformer, a bridge rectifier with four 10,000uF capacitors, and non-polarized capacitors for improved performance. Testing with an 8-ohm load confirmed excellent sound quality and manageable heat levels, though a higher wattage transformer is recommended for optimal power delivery.
Parts used in the 50W Power Amplifier:
- LM3886 chip
- Resistor R7
- Enameled wire (minimum 0.4mm diameter)
- Heat shrink tubing
- 47uF/63V non-polarized capacitor C2
- Transformer (2x24VAC / 105W)
- Bridge rectifier
- Four 10,000uF/50V capacitors
- 8 Ohm dummy load
- Mica pads (optional for isolation)
Description
This is my second encounter with LM3886. I was pleased of the sound this chip produced the first time, so I decided to make another amplifier with it. The schematic is based on the schematic in the datasheet of the chip with minor changes.
I removed the time delay capacitor connected to MUTE pin, because it’s better to use separate DC protection schematic which has similar functionality. I made the output inductance L1 by winding 15 turns of enameled wire around the resistor R7. The diameter of the wire must be minimum 0.4mm. The whole was wrapped with heat shrink. I used 47uF/63V non polarized capacitor for C2. It can be regular electrolytic capacitor, but it’s better to use non-polarized or bipolar.
The transformer is 2x24VAC / 105W. The test was ran with 8Ohm dummy load and the big heat sink gets only warm after hours of playing music from my computer at max volume. The transformer is a little weak for this amplifier, maybe 150W or 200W would be a better choice.
The power supply is very simple – a bridge rectifier and 4 x 10 000uF/50V capacitors. If the input is disconnected and open there is a little hum which can be heard only with an ear pressed against the speaker. But once the amplifier is connected via cable to the source and there is no signal, it becomes absolutely silent. Also if the heat sink is isolated from the metal tabs of the chips with some mica pads then the heat sink is good to be connected to the ground as it induces more hum in the open inputs.
It can be mounted without isolation pads for better thermal conductance, but then the heat sink itself must be isolated from the metal enclosure which usually is connected to the ground. How does it sound? Excellent 🙂
For more detail: 50W Power Amplifier with LM3886
- Why was the time delay capacitor removed from the MUTE pin?
It was removed because a separate DC protection schematic provides similar functionality. - How is the output inductance L1 constructed?
L1 is made by winding 15 turns of enameled wire around resistor R7. - What is the minimum diameter required for the enameled wire?
The wire must have a minimum diameter of 0.4mm. - Can regular electrolytic capacitors be used for C2?
Yes, but non-polarized or bipolar capacitors are better choices. - Is the 105W transformer sufficient for this amplifier?
The transformer is considered a little weak, and a 150W or 200W unit would be a better choice. - Does the amplifier produce hum when disconnected?
A small hum is audible only if the input is open and the ear is pressed against the speaker. - How does connecting the source cable affect the noise level?
Once connected to a source with no signal, the amplifier becomes absolutely silent. - Should the heat sink be isolated from the metal tabs of the chips?
Using mica pads to isolate the heat sink reduces hum induced by open inputs. - What happens to thermal conductance if isolation pads are omitted?
Omitting the pads improves thermal conductance but requires isolating the heat sink from the grounded enclosure.
