A Simple Amplifier for Testing Audio Circuits

I am working on a stroboscopic musical instrument tuner at the moment. Once done it will let me tune my guitar, amongst other things. It will also generate a crude sine wave and play it through a small speaker, so that I can learn to tune by ear.

Working on this project made me realise that I was missing a handy piece of test equipment: a small, self-contained, low-power amplifier. I had bigger, more powerful amplifiers at hand, but what would be really neat is a compact, no fuss unit that I could use for testing audio circuits. So I set about making one.

The circuit is based around a classic LM386 design. This 8-pin IC needs only a handful of support components and will deliver 0.5 watts into an 8 ohm load. It may not sound like much but it’s more than enough volume for testing purposes. To simplify things a little, I used a Silicon Chip kit called the CHAMP. It differs very little from the application circuit in the LM386 datasheet.

To this basic circuit, I added a battery holder, DC socket (for an external power supply), power switch, “on” LED, input RCA, and a volume control with a nice old-fashioned looking knob. The whole thing was enclosed in an UB3 “Jiffy” box.

Here’s a diagram of the internal wiring:

Here is the drilling template and the front panel label, in case you’d like to make your own:

The project has turned out to be very useful and I look forward to having it on hand for future audio projects.