Headphone amplifier / mixer

speaker picture
I had bought a small multi-effects box for bass guitar thinking it would allow me to play with headphones without disturbing neighbours. Unfortunately it couldn't drive my phones properly (headphones are 32 ohms?). Some extra amplification was necessary. Also, I wanted to be able to play over songs.

I decided to build a simple amplifier with a mixer, two stereo inputs would be enough.
speaker box circuit
This was going to be a temporary solution, so I didn't want to spend too much time with it. So I used a powered PC speaker as basis for the project. The thing was a really cheap one, think I paid two euros for it sometime at  flea market.

I made some quick tests and it wasn't as bad as I thought. I got plenty of volume into headphones, enough to compensate level drop from the passive mixing circuit.
mixer schematic
inside view
I built the amplifier into a metal box I had laying around. For safety and noise reduction I used a three-wire mains cable.

This little amp works pretty well. There is some hum in the background, but it doesn't get any louder when you rotate the pots. You don't even notice it once you start playing. Backing tracks sound also quite reasonable.

finished amplifier

©Jukka Korppi 2018
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