1 Watt Guitar Practice Amp Cheap!

Ok, usually I wait before starting another project... but this fell into my lap.

A friend brought in his busted computer speakers, said, "They're busted." and wandered away.

I had just read the article on Make Magazine for the 5 watt cracker box amp and gears started turning. Why not?

Sure, I could of fixed the computer speakers... but really, why? I didn't need another set of computer speakers.

WHAT I DID NEED was a practice amp for my guitar!

Ok, some back story. I built a guitar for my brother-in-law and in the process found a cheap guitar that needed repairs. That project went on the back burner for a while. Also years ago, I was given a broken Fender Princeton 65 Solid State amp. Fixed the grounding problem it had and now have a functioning amp. Nice.

BUT it's LOUD! and I don't mean, just a little loud, I mean ALL CAPS LOUD! I can't turn it past 1 without disturbing the entire floor. So, good for stage, bad for practice. And I ain't ready for the stage yet...

So I disassembled the computer speaker subwoofer. Found some great parts for other projects in the future.

I tested the speaker, that worked, so onward.

Parts ordered from Mouser:

568-NYS229 1/4" Phone Jack $1.04

858-P160KNPC15A10K 10k Potentiometer $0.90

649-DILB8P223TLF 8pin IC socket $0.19

845-SB300 300 Tie Point project breadboard $3.19

534-233 9v Battery Strap with connectors $0.72

667-EEU-FM1E101 100uf 25v Capacitor $0.33

594-5063JD10R00FT .4watt 10ohm resistor $0.12

667-EEU-FM1E221 220uf 25v capacitor $0.46

75-562R5GAS10 1kv .01uf capacitor $0.43

667-ECQ-E4473KF .047uf capacitor $0.35

926-LM386N-1/NOPB Low Voltage Audio Power IC chip $0.98

Parts picked up at Radio Shack:

271-0265 25ohm Rheostat OPTIONAL!!!

270-0326 9v battery holder

274-0415 3/4" Hexagonal Knob

Just a note about knobs, I would rather have salvaged them off of some scrap.. but most electronics in my realm don't seem to have knobs! But for now on, I'm going to start saving them when I find em!

First and foremost, my proto-board from Mouser was different than the board shown at Make Magazine. The traces on the sides continued all the way to the end. So I had to move items to avoid having them just shorted out. The combination of the schematic and the image I created should clear things up. (I hope.)

At this point, you can decide if you want to use the 25ohm Rheostat. I think it's kind of redundant. The guitar has a volume knob, the potentiometer is a gain for the amp. It's your choice. You can just jump past it and wire the output of the 200uf capacitor to the speaker. I'll leave it for now, but I bought enough to do another amp, I may skip it next time. If you keep it, it gives you more control.

Everything all wired up, I put some power to it, plugged in the guitar and made some noise.

It's a grungy sound! With this circuit you have a choice of a little overdrive, or full throttle metal. Not much in the way of clean tone as of yet. But that's ok for now, we're open to mods later. Evidently if I put more power to it, up to 18v, the sound cleans up. I can dial back the gain, lower the volume on the guitar and get a decently clean enough tone to practice with.

Oh as a side note, I used scrap wire from an old computer. The USB cable had colored wire, so I just used that to keep things looking neat. Yellow there, white there, etc.

I toyed with the idea of having the knobs, jack and all that on the side, or the back where the original subwoofer had it's connections. But that was lacking some sense of style.

So, into the scrap pile!

Mac's are wonderful machines, and so recycle-able! The side panel is a thick chunk of aluminum. OFF TO THE SAW!

I cut out a 5"x2" piece, drilled some holes then sanded it on the belt sander. I think it would look better on front here. (that's just me. You do what you want.)

I also picked up a drawer handle from the hardware store. Cost me $3.78!!! So far the most expensive part of the build!!!

I have a step drill bit. These things are great for panel work, I sized the holes perfectly for each switch, potentiometer, rheostat and jack.

I've been experimenting with these print decal labels. I create some text in Illustrator, print it on a color printer, seal it with some clear acrylic spray paint then apply them to a panel.

Then several coats of clear acrylic to really secure them in place. I let the paint dry, gave it a light sanding to take down some high points with some 600 grit sandpaper then a final coat of clear.

The clip from Radio Shack to hold the 9v battery is behind the plastic piece where the original controls were for the subwoofer and speaker system. I used JB weld epoxy to fill the holes, let it dry, then touched it up on the belt sander and gave it a coat of black paint. It's 4 screws to replace the battery, but that isn't THAT big a deal. I could have popped for a fancy case/holder system but I didn't want to spend a lot. (I already spend $$ on that darn handle!)

Ok, I'm not going to embarrass myself by playing it, go build one. Or better yet, here's the link from runoffgroove.com of this amp circuit being played by someone who knows how to play already...

This whole build took me 2 hours from start to finish. I spent more time messing with the front plate than soldering the circuit.

Grab a box, make an amp.