DIY Audio Custom SoundBar with Peerless Full-Ranges and Gainclone Power

This project up a few weeks ago with some woodworking help from my friend and some sanding help from his wife. The goal was to build mains to mate with my sub. I chose the Peerless 3″ widebanders and an LM1875-based chip amp mounted inside the enclosure. The end result…

It’s made of MDF with a wood veneer over it. Here were the plans I drew up…

One speaker enclosure on each side housing two speakers a piece. The amplification is mounted in the middle area.

I bought the chip amp on ebay. It uses the National Instruments LM1875 amplifier and has a Toshiba NE5532 op amp as its front end. It accepts transformer input of +/-18vac. I’m underpowering it a bit because the transformer I had handy was only about +/-15vac. But that’s ok because I’m running with each speaker pair in parallel, giving a 4 ohm load when the chip amp wants an 8 ohm load. It’s current-limited, so if I ran it full bore into 4 ohms I wouldn’t get max power anyway.

The gain of the amplifier was way too high for my needs, so I had to reduce it considerably. The amplifier itself was already running at close to its minimal stable gain, so I had to reduce the gain of the op amp circuit to 1. And then I needed even more attenuation so I soldered resistors to the input, which you can see below attached to the big orange input capacitors. I also changed out the input resistors so as not to change the input impedance of the amp.

Below is a picture of the amplifier, transformer, fuse holder, and connectors mounted to the back board. It uses a computer type power connector and RCA jack. Mounted to the RCAs are capacitors that highpass the input signal at around 200Hz.

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