SirAMP
A handcrafted portable bass amp made from scratch: from circuit design to a 3D printed enclosure that clips onto your trousers, so you can practise in silence.
Summary
SirAMP is a portable headphone amp for electric bass that I designed and built from scratch for my friend Siran, who had no amplifier and a small room with thin walls. Instead of buying one of the few portable amps on the market, I designed my own circuit: a USB-C charger and a 9 V boost converter for the battery, a pi filter and an op-amp-buffered reference voltage to keep the supply clean, a preamp with gain and volume controls, and a headphone amplifier. I drew it in KiCad, simulated it, debugged it on a breadboard with an oscilloscope I made from an Arduino Mega, then hand-soldered it onto a through-hole board. The enclosure went through many sketches before landing on a rounded star, modelled in Fusion 360 and 3D-printed, with a carabiner hook so it can hang from your trousers while you play. The project isn’t finished yet, since the enclosure still needs primer, paint and a clear coat, so this page is just a gallery of the steps so far.
Selected Pictures
The full circuit in KiCad, in four blocks. A TP4056 module charges the battery over USB-C and a boost converter raises it to 9 V, cleaned up by a 1 Ω and 22 µH pi filter. One half of a JRC4558 op-amp buffers a voltage divider to give a stable reference voltage, and the other half is the bass preamp, with its gain and volume pots. A TDA2822 drives the headphones, with a Zobel network on each output.