Dabbling in Circuit Art: The LM386 Spider

Last month I built the DC40 receiver (and wrote a giant series on it: Part 1, Part 2, Part 3 and Part 4. And somewhat unofficially Here!) and at the same time, Hackaday.com posted their Circuit Sculpture contest. Would it be possible for me to combine projects, and submit the DC40 as a circuit sculpture of some sort?

As it turns out, no. The DC40 turned out cool, but it isn’t really a sculpture of any sort. But then, something happened.

Audio Amp. Again.

My biggest issue with the DC40 build was volume. While it sounded great it just wasn’t very loud. I struggle with poor hearing already, and wanted some good volume. The TDA2822M chip I was using for an amplifier was okay until it didn’t work anymore. The problem is that I was feeding it 13.8v, and it really needs 6-9 volts. The early uBITX suffered from the same problem.

LM386 to the rescue?

In a post about an upcoming version of the uBITX (v5, which should be a version that will fix all of the spectral purity issues the uBITX has encountered) Ashhar Farhan called the LM386 “the old frenemy of hams” and he has a good point. It’s not a particularly good amplifier IC, but it is easy to find, cheap, and easy to use in a circuit. It is for these very reasons that I chose it to replace the TDA2822m.

If you’re reading this, Ashhar, I feel your pain.

Trouble Begins

I purchased three LM386’s from Arrow Electronics and when the package arrived, I was equal parts horrified and amused to find that I’d purchased the SOIC version of the LM386 instead of the DIP version of it.

Well that’s just great. I have the chip I need, but it’s so small that I can’t hardly solder to it. Or can I?

Ignore that failed experiment in the foreground…

To use the chip I just need to break it out into something a little bit bigger and get the legs a little farther apart, and a little longer. I got out my roll of pre-tinned wire (it’s about 24ga) and cut 8 even lengths, about 3 inches long. My normal method of holding components together and heating them, then applying solder, did not work at this small scale.

Instead, I heated the wire, applied a little bit of solder to it, and then held the wire to the tiny leads, and warmed them with the tip of my iron. This both melted the solder and made the joint. It took a little practice to not have cold solder joints, but in short order I had broken out the SOIC LM386 into something usable for my purpose.

That big solder blob didn’t last very long, I redid it to make it look nice.

I posted this to the BITX40/uBITX Facebook group and one of the members commented that I should keep the spider-like shape when I build it into a circuit. I liked the idea a lot, and I thought that maybe that would be good enough for a Hackaday sculpture contest entry.

The Right Tool for the Job

It’s no secret that I love new tools! One of the things I have always wanted is a rotary cutting tool. Even as a kid I’d read Model Airplane News and was in awe of how simple some tasks were if one simply had a Dremel tool. But, I’ve never been one to spend a lot of money on tools. I’m all about the bargain! You can imagine my glee when I discovered the Wen Rotary Tool set for less than half the cost of a Dremel kit.

What the rotary tool allowed me to do was make rounded manhattan pads as you see below. By cutting the pads into pointed tips and then grinding them, it was possible to make a nice rounded end. And, for the center piece between pins 1 and 8 (the foremost below) I was able to use the cutter disk to cut away copper without even grinding through the long pad, and it gave me a spot to mount the capacitor to control gain.

The red wire along the perimeter is a piece of enameled copper salvaged from an old computer power supply. I straightened it, smoothed it, and then bent it to shape. I thin kit adds a nice touch and is a lot cooler than just running a jumper (which is what was needed).

Does it work?

Yes, it does! It works just fine, for an LM386. It connects via a cable to the DC40 receiver and another cable goes to a 3.5mm jack to plug in a speaker.

One thing I’ve decided not to publish is a schematic. It’s an LM386 circuit and there is already a glut of LM386 amplifiers on the ‘net, just a google away. I hope you have enjoyed the post, and don’t forget to go check out Amazon to find a good deal on that Wen Rotary tool. It’s extremely useful!

What about the Contest?

Ah yes, the Hackaday Circuit Sculpture Contest. I did enter the LM386 project, and it was well received but did not place even in the top 10. I didn’t expect it to really considering that there wre much more amazing projects entered. You should check them out!

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