Hardware Blog: Doublet Amplifier

Have you ever seen a couple sharing a single pair of ipod buds, each listening with only one ear? That was the problem I wanted to solve when I started building dual channel headphone amplifiers while I was back in grad school. After a long day of soldering krytrons and high voltage capacitors in the plasma physics lab I would come home and...solder some more.

There were two design requirements I started the project with:

1. Each listener needed an independent amplifier channel.

2. The whole thing had to fit in an Altoids tin.

It works like this: plug your ipod or DVD player into the jack on the left side of the case with a male-male 1/8" audio jack. Headphones go into either of the two output jacks in the front of the case. Each knob acts as a combined on-off switch and volume control.

The design is based on a non-inverting op-amp circuit inspired by Chu Moy's original Cmoy headphone amp. The op-amps are Burr-Brown OPA2134PA which sound GREAT. You might wonder, "Why not just use a headphone splitter?" Well, that halves the power delivered to each set of headphones and sounds lousy. Also, if the listeners prefer different volumes you're stuck. This amp can drive big fancy headphones REALLY loud with very little distortion.

Back when I started this project I thought I would get a bunch of PCBs printed and start a little business selling the built amplifiers online. I sold about 15 before I had enough of the solder fumes and got tired of eating altoids and called it quits. I still have the PCB schematics and few unused PCBs. I'm rebranding it as the Octopart Doublet Amplifier.

I'll go into more depth about the design and part list in my next blog post. If anyone is interested in the leftover PCBs, let me know. When you buy the parts to stuff them, just let the distributors know that Octopart sent you.

Part 2: Schematic, Parts List and PCB