DIY Mono Speaker

This is a powered speaker that is intended to look a bit utilitarian. It is powered by a 9 volt wall wart and accepts an audio signal through a stereo 3.5mm jack. The stereo signal is converted to a mono signal through a resistor network before being fed into an audio opamp and finally a small power amplifier. There is both gain adjustment and volume adjustment. The speaker is a HiWave BMR12 full range square speaker. The stereo to mono is just two 4.7k resistors (one for each channel) feeding a 47k resistor. If you Google "line in stereo to mono circuit" the image will probably show up near the top.