The workshop needed some tunes and I had two LM380 2 watt amplifier chips in the parts bin. It was meant to be. This build consists of two LM380 IC's, a bunch of electronics and an MDF enclosure that's been coated in popsticks and aged with various methods to give it a classic look.
The body is just an MDF craft box from my local hardware store. I cut the popstick ends square and used white glue to secure them on the faces of the enclosure.
It looks a bit rough initially as the popsticks have various little deformities but it all adds to the look in the end.
A couple of the sticks lifted a little. Nothing some more glue and a gentle clamping can't fix.
It was given a decent sanding and holes were drilled to accept the various input and output components for the amplifier. It's a pretty basic unit so the front panel simply consists of an on-off switch, led indicator and volume dial.
To dull off the wood and give it some initial aged colourings, I used a vinegar staining solution. It's just white vinegar soaked in torn up steel wool for 24 hours. Wipe it on with a rag and give it 30 minutes to dry. For a stronger stain, leave the steel wool soaking in the vinegar longer and/or apply more coats.
To finish off the look I gave it a few passes with a blowtorch and rubbed the whole lot down with steel wool. It works best if you build up the look steadily. Give it a once over with the torch, rub it down and assess which areas need more. Once I was happy with it, I applied a couple of coats of linseed oil as well.
The enclosure needs some electronics to go inside, time to build the amp. The LM380 amps I've got are 2 watts a piece and don't require too many supporting components to get nice audio quality and volume.
After searching around and doing some experimenting, I ended up deciding on a slightly modified version of a circuit I found on elecfree.com. Their circuit is for a mono amp however to make it stereo, you just need to built two amps and put the left input channel through one and the right through the other. I've included my modified version below:
The circuit was then built on perfboard for a more permanent product. I added an indicator led and interrupt on the power supply line for an on-off switch. The LM380's tend to heat up a bit during operation so a couple of small heatsinks were also added to assist.
Most of the connections to external components use header pins so they can be easily installed and removed. I used a potentiometer with two sets of connections so the volume of both amps is controlled with the single dial. Some salvaged spring clip terminals are used to connect the speakers and it receives the input through a standard 3.5mm audio jack.
With the assistance of my old friend hot glue, all the components are connected and secured firmly in place. Had to do some minor carving work with my dremel for some of the components to fit nicely. The box has a hole in the bottom as it was being used for something else previously.
The amp consumes between 80ma and 110ma of current so it doesn't need a strong power source. It will accept 10v-20v input. I use an old 12v regulated wall wart to power the unit (formerly powering a modem) which works fine. Unregulated power supplies such as one I had from a drill charger introduce noise.
I'm happy with both the audio and visual quality of the end product. It deserves matching speakers though so I'll have to get that sorted.
- LM380 Datasheet - http://www.ti.com/lit/ds/symlink/lm380.pdf