Over the years I've had lots of people ask me about
the battery-powered guitar amp I carry. It's a homebrew
conglomeration of off-the-shelf parts -- you can't buy one
like it already assembled, but you won't need a soldering
iron to put one together. I'm talking about simply buying
the right parts and plugging them together here. Easy project.
When I get a chance to put some graphics up I'll include a
schematic and a drawing. In the meantime, there's a description
and instructions below.
There are complete amplifiers available, of course. There's
the Pignose, which I hadn't heard of when I put mine together;
and tiny little Marshall and Fender amps (designed to look like
cute minitatures of their real ones), which only came out
recently. The Pignose is a useful little amp. The Marshall
is useless for anything except practicing alone. I haven't
tried the Fender, but it looks like the same sort of thing
as the Marshall.
My amp is far from perfect, but it's loud enough for jamming
along with other instruments except for drums, accompanying
an unamplified singer, or playing as I walk down the street.
As I mentioned above, you won't need a soldering iron for this
project. The basic parts list is:
A set of "powered extension speakers" designed to be used
with a Walkman-style cassette player or portable CD player. These
are usually powered by four C-cells.
A Radio Shack "project amplifier", the small, grey $12
unit powered by a 9V battery.
A coiled "patch cord" -- 1/4-inch to 1/4-inch phone plugs.
1/4-inch to 1/8-inch adaptor. (1/4-inch female, 1/8-inch male.)
Some sort of carrying case -- mine came with the speakers,
has a compartment in the middle between the speakers, and hangs
from a shoulder strap.
Additional parts, if you want to build a slightly more powerful
A second Radio Shack "project amplifier".
two 1/8-inch phone cables (mono).
An adaptor that receives two 1/8-inch mono phone plugs
and combines them onto one 1/8-inch stereo phone plug.
1/8-inch "gender changer".
1/8-inch phone Y-adaptor, one female end and two male ends.
How to wire it up
The simple version
Take the 1/8-inch stereo phone plug attatched to the extension
speakers, and plug it into the stereo-to-mono adaptor.
Take the mono end of the adaptor and plug it into the "Ext. Spkr."
jack on the small, grey amplifier.
Take one end of the 1/4-inch patch cord and plug it into the
1/4-inch to 1/8-inch adaptor.
Plug the small end of the 1/4-1/8 adaptor into the "Input" jack
on the small, grey amplifier.
Install batteries. Stuff everything into its carrying case,
leaving the end of the patch cord hanging out (so you can plug it
into your guitar), and you're all set.
The fancier version
Plug the extension speakers into the "gender changer".
Plug the two-mono-to-one-stereo adaptor into the other
end of the gender changer.
Connect the "Ext. Spkr." jack on each project amplifier
to one of the jacks on the adaptor in the previous step,
using the 1/8-inch patch cords.
Plug the male ends of the 1/8-inch Y-adaptor into the
"Input" jacks of the project amplifiers.
Plug the 1/4-to-1/8 adaptor into the Y-adaptor.
Plug one end of the 1/4-inch patch cord into the 1/4-to-1/8
Install batteries and stuff everything into its carrying
Turn on the small, grey amp (which I'll henceforth call the "pre-amp")
all the way. If you built the dual-pre-amp version, turn on either
or both of the pre-amps. The volume control on the pre-amp will be
a little awkward to reach when everything's in place, so it's best
not to have to fiddle with it, and I seem to have more control over
distortion if it's all the way up. Use the volume knob on your guitar
for your main volume control.
You'll notice that as you get louder, you start to get distortion.
If you want to play louder with a clean tone, turn on the extension
speakers and turn down the volume on the guitar. If you want to
play at maximum volume (extension speakers on and guitar all the
way up) you'll only have the distorted tone available, but indoors,
in a quiet or moderately noisy room, you should be able to play
at a useful volume either clean or distorted. On a city street,
you'll probably have to turn everything up all the way.
As the 9V battery in the pre-amp starts to fade, distortion will
show up at lower and lower volumes, so if you're trying for a clean
sound and can't get it, change the battery in the pre-amp.
If you built the dual-pre-amp version, you can start by turning on
only one pre-amp, saving the other for when the battery dies in
the first; or you can turn on both pre-amps for a littel more
volume. Each pre-amp goes to a different speaker, by the way.
The pre-amps are needed because the extension speakers are
expecting headphone-level signal going into them, and an electric
guitar doesn't produce enough power. So the pre-amps amplify
it to speaker level, but by themselves they sound pretty crappy.
Using the extension speakers simply as better speakers does a lot
to improve the sound, and using powered extension
speakers means that when we want a little more volume we can turn
them on for a second stage of amplification.
The Radio Shack pre-amps use an LM386 op-amp chip. It's not
quite hi-fidelity, but for a basic instrument pre-amp it's not
bad. The distortion comes from overdriving the pre-amp itself,
by the way, not from the pre-amp overdriving the extension
With such tiny speakers, you won't get a heck of a lot of bass,
unfortunately. That's the price of portabiity. This design works
pretty well for a guitar, but plugging a bass into it results in
more mud than music.