25-02-2013, 06:58 PM
When thumbing through some old magazines I came acress a neat little 2 Watt amplifier design in March 1984 Radio and Electronics World, sadly, long since defunct, along with so many other electronics mags - Radio Constructor, ETI, Hobby Electronics, Short Wave Mag to name but a few.
The LM386 IC is widely used as a 500mW amp and you can buy ready-made amps based on it for about a fiver from China - very neat they are too. However, for a bit more power, the LM380 IC can give a good account of itself and can be found cheaply on e-bay. I've attached a copy of the' R.E.W' article and have also attached a cleaned-up version of the PCB artwork which I've 'Photoshopped' because that shown in the article is very poor and is unusable. (It's not to scale either).
The circuit is very simple, and could be built without resorting to a PCB, but a word of warning - the IC needs to be adequately heat sinked. This is normally achieved - as in this design - by an area of the PCB foil to which pins 3, 4 & 5, and 10,11 & 12 are soldered. There pins are connected to an internal heat sink in the IC package. It's for this reason that an IC socket ought not to be used as the heat sinking won't be as efficient.
There are LM380-based kits available cheaply on internet - I've looked at several out of curiosity, and though they invariably use a PCB, most make no adequate provision for heat sinking.
The LM380 IC also comes in an 8-pin version, which for heat sinking purposes and power handling is best avoided in preference for the 14-pin version as specified in the attached article.
Hope that might interest someone.
(Amplified PC speakers can often be found in charity shops and at car boot sales, which are useful as bench amps for test purposes and save the hassle of building one.)
The LM386 IC is widely used as a 500mW amp and you can buy ready-made amps based on it for about a fiver from China - very neat they are too. However, for a bit more power, the LM380 IC can give a good account of itself and can be found cheaply on e-bay. I've attached a copy of the' R.E.W' article and have also attached a cleaned-up version of the PCB artwork which I've 'Photoshopped' because that shown in the article is very poor and is unusable. (It's not to scale either).
The circuit is very simple, and could be built without resorting to a PCB, but a word of warning - the IC needs to be adequately heat sinked. This is normally achieved - as in this design - by an area of the PCB foil to which pins 3, 4 & 5, and 10,11 & 12 are soldered. There pins are connected to an internal heat sink in the IC package. It's for this reason that an IC socket ought not to be used as the heat sinking won't be as efficient.
There are LM380-based kits available cheaply on internet - I've looked at several out of curiosity, and though they invariably use a PCB, most make no adequate provision for heat sinking.
The LM380 IC also comes in an 8-pin version, which for heat sinking purposes and power handling is best avoided in preference for the 14-pin version as specified in the attached article.
Hope that might interest someone.
(Amplified PC speakers can often be found in charity shops and at car boot sales, which are useful as bench amps for test purposes and save the hassle of building one.)
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'