December 2007 \ Features \ The $5 Traveling Practice Amp

The $5 Traveling Practice Amp

Dirk Wacker

DIY computer speaker mod
Premier Guitar December 2007
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3. Connect the input jack

Now it’s soldering time. First, get both cables inside the opened box and simply snip off or desolder the unneeded cable for the second box. If you are using the stereo setup, get only the presoldered input cable inside the box and don’t snip off the second speaker's cable! Solder the two twisted hot leads of the input cable to the tip of the jack and the two twisted blank mass leads to the sleeve. After you've finished this step, it should look like this:






4. Fine-tuning the amp

Believe it or not, that’s it! Plug in your axe for a preliminary test. You will likely discover that the amp is working, but that it suffers from a poor output level. This is because of the mismatched impedance – PC speaker systems are designed to work with a pre-amplified signal from your soundcard, not a passive guitar signal.

The best solution is to trace the first resistor on the PCB after the input and desolder it or snip it off, if possible. With that complete, you can take full advantage of the system’s built-in amp, with more than enough volume for bedroom playing. You can also use the headphone output for silent playing if your speaker system offers such an option.

If you’re not interested in tracing resistors, you could also consider using a booster or buffer in front of the box to boost the signal and/or change the signal’s impedance. It isn’t the most elegant solution, because you’ll have to carry another box with you and the main goal is to have a small and handy practice amp for your next journey, but it is something to consider.

So with a few quick solders, you have a portable practice amp, just in time for the holidays. It won’t sound like a cranked Marshall stack, but at least it offers a great clean tone to practice your skills, wherever you are.

Have a great one and I will see you next month!



Dirk Wacker has been addicted to all kinds of guitars since the age of 5 and is fascinated by anything that has something to do with old Fender guitars and amps. He hates short scales and Telecaster neck pickups, but loves twang. In his spare time he plays country, rockabilly, surf and Nashville styles in several bands, works as a studio musician and writes for several guitar mags. He is also a hardcore DIY guy for guitars, amps and stompboxes and also runs an extensive webpage singlecoil.com about these things.


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Comments

 (11 comments) display by
UsernameComment
Tyrone
on 01/12/2013 		Word to your mother.
Jashoy
on 12/14/2012 		iI want to buy that.
George
on 08/19/2010 		You could just get some mp3 speakers and plug into the headphone jack of a Vox Amplug Headphone Amp. Not the cheapest method but no mods needed.
Viktor
on 12/20/2009 		Nice article. I made this thing, didn't do it exactly like this (I used lots of duct tape :P). If I use headphones the thing is amazing. Nice clear sound, and just the thing when on the go. I also hooked up a 9V battery to it using some other instructions. But could someone tell me witch resistor is the correct one to snip of? The one marked R1? Or is that the wrong one? Is it possible to use a preamp from a small cassette player or something? And if so, how? I know next to nothing about electronics so I really just do it watch and learn :P
Eric
on 05/18/2009 		Great article...I have another question though that might require some electronics know how. I don't know if any of you have built the other LM386 based amps like the Ruby. I have, and they have a great crunchy tone for a little bitty amp. Most of the portable amps like the Little Smokey are based on the same circuit. When I opened up a set of these computer speakers, I noticed that the circuit is very similar. I'm thinking that a few resister and pot value mods could change this into a similar type guitar amp. Anyone on here know which values would need to be changed? The circuit is just enough different that I'm unsure of where to cut and paste. The original Ruby circuit is at www.runoffgroove.com, for anyone who's interested.
Matt T
on 03/08/2009 		I've built several of these over the years, the best solution is to use your favorite distortion pedal and dont snip the resistor, because it may not work on some models.
I suggest using this amp with a zoom g1 pedal, for $50 you get a whole bunch of amp models, effects, a drum machine and a tuner! and the zoom could run on 4 AAs.
Aaron E.
on 11/27/2008 		Hi, I REALLY wish it would have worked!! I even removed both resistors from where the original stereo 3.5 mm plug wires were soldered to the board, and soldered the guitar wire directly to the board where the resistor's "far side" had been soldered. Any ideas? Thanks!!
Ryan D.
on 07/10/2008 		just make a couple stacks and you got you decent rig, haha. Great article
Sam
on 01/15/2008 		Great article. I love building / modding things like this. More amps the better. I would like some more detail about removing the CORRECT resistor from the PCB. Thanks SS
Dirk
on 11/21/2007 		Hi Jane, you can use an adapter plug without any problems, but most speaker systems I have seen use very thin and fragile cables, so I don´t know how long this will last before it breaks or starts to fail. This cables are not made to bend them, so the best way would be to install an input jack and using a normal guitar cable.



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