Saturday, July 4, 2009



Check Your Kit

  • Components
  1. Make a visual check of the P.C.Board to ensure no damage has happened in transit. Continuity of the tracks can be checked with a multimeter or an electronic Circuit Tester. Any breaks can be bridged with solder.
  2. Turn the Board over, track down, and push the 14 pin I.C. socket into place.
  3. Identify the resistors either by their colour bands, or with a multimeter. Bend the legs to match their holes and assemble them. It is a good idea to solder progressively as 4 or 5 components are mounted to the board.
  4. The 50K trimpot will fit the three holes in the board D 1.2mm. Push the legs right down.
  5. There are five electrolytic capacitors,three 2u2 and two 470uF. On each body you will find an arrow pointing down one leg. This leg is the -ve pole. From the drawing find the + and/or - signs and mount the capacitors in their correct positions. Bend the legs on the back to hold them in place and solder.
  6. Six pins are in the Kit. These are soldered into the four 1mm holes where the Input wires and the Speaker wires terminate, and two to connect wires to the ON/OFF switch. Strip the ends of the Fig.8 wire, tin them, and solder to the pins. Usually the wire with the "trace" in the insulation is used for the Positive poles. Find the + and - signs on the speaker and solder in the polarity shown in the diagram. The jack can be connected to the input lead, but join the terminals of the two channels together with a short wire. This is done because the AMP is MONO only and it will amplify both channels into one speaker. Stereo jacks have two small black rings in the shiny shank.
  7. Turn the board over ready to mount the battery holder. Build a small amount of solder on the track at the two donuts, but keep the holes clear. Next heat the legs close up to the plastic and build some solder to each leg. Push the battery holder home and touch the tip to the piles of solder. They will fuse easily an hold the battery holder in place.
  8. The LM380 I.C. is packed in an antistat case. You will find that the legs are slightly wide to fit the socket. Turn it on its side on a flat surface and gently push down to bend the legs together a little. Repeat for the other side, and offer it into the socket. When it is ready to slide into the socket:
  • find the locating DOT on the top of the chip near one end. Make sure the DOT is where the diagram shows.
  • use gentle pressure to push it home. I.C. Inserting tools are available. They make the process of pushing the I.C. into the socket much easier.

You are now ready to test your Amplifier. Connect a 9V battery and plug the jack into the output socket of your machine. Adjust the volume of your radio to a comfortable level and use a small screwdriver to adjust the trimpot to get clean undistorted sound from the speaker. Speakers work best in an airtight box made of particle board or similar, and glued together. The hole for the speaker in the front panel of the box should be a neat size to suit the speaker, and can be covered with speaker cloth to give a neat finish. Your Library will likely have information about Speaker Boxes that you can research before you design your box.


View the Datasheet for the LM380.


If the Amp doesn't work check the following:

  • polarity of all five electrolytic capacitors.
  • the locating DOT on the LM 380 Chip is as the diagram shows.
  • the two resistor values are as the diagram shows.
  • carefully prise out the I.C. to check that no legs have been bent up under the body instead of into the socket. Replace it with care.
  • remove the battery holder and check all soldering. Re-solder any joints that look suspicious, making sure that the solder takes to the track as well as to the legs.
  • remove the end of the jack and check the soldering. Also connect your Amp to another radio to try to isolate the problem.

This is an extremely reliable circuit which presents no real difficulty in putting together, so in most cases the Amp will work first up.



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