Under-desk Sound System

Because I took my amplifier and speakers to my other room in the city where I study I needed another solution for playing music in my hobby room, which is still located in my parent’s home. Luckily, I had two active speakers and a matching transformer (both from a broken Sony radio) lying around. Because my room was already crowded with all kinds of electronics, the only viable option was to mount the speakers under my desk.

When I investigated the innards of the (broken) radio to which the speakers where originally attached, I didn’t find a bridge rectifier or smoothing capacitors inside. The speakers itself however did include a bridge rectifier, so I simply assumed I could feed the speakers directly from the transformer without problems. Although this worked, it resulted in an audible and quite annoying hum. To fix this, I made a small PCB with a rectifier and capacitors so I could feed the speakers with smoothed DC instead of AC. This almost completely removed the hum.