LM4780 Audio Power Amplifier Project

The power amplifier project obtained its A4 name due to the four separate power amplifiers contained in this unit which offers great flexibility using different modes of operation.

Four LM4789 are being used by this amplifier which works in inverted parallel mode. They are capable of delivering significant peak currents into lower impedances since each of these offers around 50W into 8 Ohms. The heart of the amplifier is formed by a large custom-made torroidal transformer designed with a low flux density for reduced mechanical noise while incorporating an electrostatic screen to attenuate interference.

It can operate in the modes of operation including 4-channel 50W per channel operation for surround-sound or multi-room operation, 2-channel bi-amped mode for suitably bi-wireable loudspeakers, and 2-channel bridged mode that offer around 15W per channel. These modes can be combined in home theater application where rear speakers are driven separately and a center speaker could be bi-amped or bridged.

A pair of heatsinks forms the sides of the amplifier and each heatsink assembly has two power amplifiers and a mode select switch. The power supply is managed by the control circuits ensuring that large inrush currents are prevented.

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