Useful electronic circuits for the hifi hobbyist

This is a small collection of simple electronic circuits I've found useful over the years. I made this partly because I keep having to track these down again, so I wanted to write them up in one place along with the sources anyway.

Amplifier circuit for analog VU meters

Along with an extremely in-depth and comprehensive description of the circuit, adjustments needed for meters with different parameters and possible variations. Remind me to clean up the compact PCB design I have for this and put it here.

LED level meter circuit

A simple but quite effective 10 LED level meter based on the half-wave peak detector design shown in the LM3916 datasheet.

Signal selector with electronic latch

Click here for black-on-white version

This one can be handy for anyone who wants a switch box with more than two inputs, but it's a particularly elegant solution for amplifiers (or any other situation where the input connectors and the buttons selecting between them are far apart). It can easily be split into two units connected by a small number of control wires for the relays, saving you from wiring all the inputs to switches on the front panel. It's also possible to get five inputs out of it by cascading the relays and adding a fifth button, I'll draw a schematic for that variation too sometime.

[based on a circuit on]

Passive line to phono converter

This one I wouldn't use for any permanent purpose unless there's absolutely no other way (it will pick up noise), but it can be a handy if you need a phono-like signal without a turntable (e.g. for quickly testing a phono input).