Bryan Patterson 2-17-04;
"In this first picture I show you what to look for. This type of radio is the simplest to
modify into an amplifier if you are looking to use a radio boombox. However, if you have a radio with a single
PCB, (printed circuit board) you can still use this same process. It is just a bit harder to determine where to tap into.
More about that later.
For the simplest project unit, look for radios that have a
separate tuner board in them. You can identify this type of radio without taking it apart. How? Simple, just look for radios with the tuner dial on the opposite side of the
selector switch and volume control. Many radios with the dial type tuner will be set up this way.
For our first way to make this old boombox
into an amp, we will be using the
part previously used by the radio.
Make sure the unit is unplugged,
take the batteries out and remove
the case. It should look something
like this inside. Note that the
tuner and amplifier are separate
circuit boards. The tuner should
have a few wires coming off of it.
one probably being the antenna.
This one we don't need to worry
about. Look for any other wires
that go from the tuner board to the
amplifier board. They maybe
individual wires or a ribbon cable
like this one has. Cut these wires
and bare the leads going to the
amp. and make sure they don't touch
anything when you turn the radio
Using a non polarized .1uf (.1 micro farad) or larger capacitor, touch the ends of the wires you just cut. Listen to the speakers for noise when you touch them.
You are using yourself as an antenna to pick up the 60 hz
cycle from the lights in your
house, (among other signals) which
sends a white noise signal to the
amplifier. Note that the use of the
capacitor is just an option. Simply
using your finger or a needle would
work, but the capacitor makes it
easier to hear the sound. When you
find which wires make the noise you
have found the right ones. You
should be able to determine the
left and right channels on a stereo
unit. These are 2 of the 3 wires
you will be tapping into.
Now that we have found the left and
right channels we just need to find
the audio common wire. In some
cases it could be the same as the
common ground which seems to be so
in this case. More than likely you
will find the common on the same
ribbon cable. To figure out where
to connect the common, I recommend
making a test cable (shown in this photo). The test cable is just an audio cable cut and striped at one end. ( I attached alligator clips to the end of mine) Making sure the
stripped wires are not touching anything as you plug it into your audio source. take the bare ends and
temporarily attach the two insulated wires to the left and
right channels. The
non insulated wire is your
common and you will use it to probe around till you hear your audio source through the boom box speakers. Once you locate the 3 leads going to the amp. we will be using,
replace the batteries or plug the unit back in to
the wall. Use caution not to touch the
transformer or power supply. Switch your selector to RADIO.
With the two units now connected with your test patch cord, turn on your audio source and press play.
This test proved
successful in using the cable that went to the amplifier from the radio. In the
next picture we will show you how to use the other sources of your boombox if a
radio isn't present or just unavailable.