Jon wanted an amplifier that he could use to test tri-amping and room correction algorithms. We could have used our TAS5504 evaluation module but we wanted to gain some experience with Class AB amplifiers so we decided to make a board based on the National Semiconductor LM4765 audio amplifier. This is a dual amplifier package that can deliver up to 30W per channel.

The schematic is here.

1. Amplifier.

Each amplifier can be configured for Inverting or Non-Inverting operation. Also, each pair of amplifiers (U1 and/or U2) can be configured for BTL operation. This lets Jon configure one LM4765 as the tweeter and the mid-range while the other LM4765 can be configured as BTL for the woofer. Roughly, this should provide 20W/20W/40W for the tweeter/mid-range/woofer.

2. DAC.

We selected the PCM1690 from TI as the Digital to Analog converter. This part has excellent SNR (113dB) in a compact multi-channel package.

3. Power Supply.

The board takes +5V and +-24V. The +-24V is then cut down to +-15V using one LM317 and one LM337. The digital logic is supplied (+3.3V) by the interface board.

The Bill of Materials is here.

The layout is below. Click on the image to get a larger/detailed PDF.