LM380  2.5 WATT AMPLIFIER

INSTRUCTION SHEET

Price - Stock No 410

Price - Stock No 411 (100mm Speaker)

Check your kit 

Schematic Diagram

PCB Layout

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.

TROUBLESHOOTING

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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