Mar 16, 2014

Altoids Headphone Amp

          Here we have another simple LM-386 amp I made, this one made in the style of all the Altoids tin amps out there, though I used an aluminum gift card case instead of an actual Altoids tin.  I really like this one because it is so simple, sturdy and portable.

          I didn't draw out a schematic but it is pretty much another Smokey amp.  The differences are that it has no switches, power is turned on and off by the input jack, it has a 220 uF cap on the output, has a cluster of resistors on the output to reduce volume, and uses headphones instead of a speaker.

          So what is special about it?  Well, while it's not unique, it does have some nice features.  The casing was perfect because it was exactly the right height to accomodate the two 1/8" jacks and the 9v battery.  Pressure from the lid actually holds the battery from sliding into other stuff it shouldn't.  Also, the casing is all aluminum so acts as shielding and conducts the ground between the two jacks.  And fits into a pocket ;)

          The cluster of resistors is the simple volume control I made by experimenting around with resistance.  The resistors are a mix of three 39,000 ohm resistors and four 22,000 ohms which puts total resistance at 3,864 ohms.  If you had four 10,000 ohm resistors in parallel that would work well.  I just added resistors until it was loud enough without being obnoxious.  Another plus side of using lower volume levels and running through headphones not speakers is that there is nearly no audible noise or hum, no doubt helped by the shielding.

          One last thing that I like that makes a headphone pocket amp more fun than a speaker amp is that you can use whatever headphones or earbuds you like and it gives a different tone with each one.  It makes a good judge of headphone quality as well, since higher quality speakers use energy more efficiently and play louder than others.

         That's about it for this amp, there really isn't much to talk about, but it is really great and was a fun half-hour project.  I'd suggest something like this for a great first build, or an easy side project for more experienced engineers.  Pictures coming soon, peace out.

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