The Box That Rox

For my birthday this year, the fine folks over at 83 Durant Street sent me an issue of the super-cool magazine, Make. It's a magazine that's chocked full of tasty little tech-y projects that anyone who likes to tinker with nifty gadgets will be immediately attracted to. And I was no exception. As soon as I saw their plans for the $5 crackerbox amp, I knew how I would be spending my free time for the next couple of days. While fairly simple as amp designs go, this little bugger does pack a good bang for the buck.

So, having a healthy level of nerdiness, I decided to document my assembly of the $5 amp for you dear readers. Here goes:

Last Thursday, I made a trip down to the local Radio Shack to pick up all the parts and components I would need. Another reason why Make is awesome: they give you a complete parts list of everything you'll need for the project. Not completely surprising, after getting everything (except the 8-ohm speaker) from Radio Shack, my $5 amp would exceed it's title. So, now my amp sings to the tune (literally) of a $30 amp. Oh well, it's a small price to pay for such a neat little gizmo, not to mention the learning experience I got from it.

OK, the next day (last Friday), I came into work and promptly (and somewhat proftly) got started building my amp. I'll keep things as abridged as possible in order to keep things from getting too bogged down in details. Following the handy circuit schematic they included, I got started.

The circuit was assembled on a blank protoboard. The first piece to go in is the socket for the heart of the amplifier: the op-amp chip:


After the socket was put in, a bunch of wires, resistors, capacitors, and the connector for the 9V battery that powers the entire amp were soldered in:


Once the electronic components were soldered to the board, the next step was to connect the control knobs (volume and gain), input jack, on/off switch, and speaker to the circuit board. First to be connected was in the 1/4" mono input jack. This is the jack that the guitar cable plugs into:



Next to be connected was the volume knob (a 25-ohm rheostat - for those who want to know):


Next, the gain control knob (used to control how "clean" or "dirty" the sound is), which was a 5-kohm potentiometer (again for the nerds out there), was connected. The weird thing about the gain control is that for some reason, the knob stem is way longer than it needs to be. It's about 2.5" long. I'll have to cut that down so the knob doesn't protrude too far away from the amp box:




Next the on/off switch. Quick word about this switch - I really like the fact that it has a metal plate showing the "on"/"off" text. Not only does it make it clear which state the switch is in, but I think it has a cool retro look about it:


And lastly, the speaker was connected to the circuit:


Unfortunately, the speaker I used here is a 4-ohm speaker, but the circuit calls for an 8-ohm speaker. The bad news is that the amp won't be as loud, but the good news is that the battery won't be depleted as quickly. I'm still planning on replacing this speaker with an 8-ohm speaker, but for now this one will have to suffice. Or I think I should just be able to add another 4-0hm speaker in series...we'll see...

So, that's it. That's all that goes into the "guts" of this amp. I hooked up a test input signal (just an electric signal set at a single audio frequency), flipped the switch to "on", and it worked! Even with the 4-ohm speaker the volume is impressively loud. And once I put the 8-ohm speaker in, it'll be even louder!

But where this baby really shines is with the housing for the amp. The original plans called for mounting the electronics inside a cardboard crackerbox. While I appreciate the gimmick-ness of the idea, I knew that if I used a cardboard box, the wear and tear I would subject it to would all but guarantee a very short lifetime. I wanted to use something more durable. So, I began looking for a more practical "box" to use as the housing for the amp, and when I eventually stumbled upon this cool little candy tin, I knew I was in business.

When I was finished making the circuit, I drilled a hole on the side of the tin for the jack and holes in the lid for the knobs and the on/off switch. Then I carefully mounted everything in its respective place in the box:


I snapped the lid shut and - PRESTO - the amp was finished (although I still have to drill holes for the speaker "screen"). But you get the main idea:


For such a little thing, it's pretty impressive looking. Particularly, I like how the knurled aluminum knobs and on/off switch give it a total old school look:




I know what you're thinking: Hey, it may look cool, but how does it sound? Well, let me get some video/audio of it in operation and I'll post them here soon - so stay tuned!