BoomBox Amplifier - 1 -

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 back on. 

  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.

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