Computer Audio Amplifier

I purchased a new computer system a few years ago, and it came bundled with a brand-name "200 watt" speaker system that sounded like crap. Not surprising, since the speakers were housed in small plastic cases. The 200 watts must be the figment of some marketing department. My old computer had a sound card with a built-in amplifier, so all I did was hook up two small but decent speakers and it worked quite well. Now, however, the sound cards do not have amplifiers so they must be provided.

I have built many LM380 audio amplifiers, and they are really easy to build. Although they are rated at just 2.5 watts, it is a true 2.5 watts, and is (sometimes surprisingly) sufficient for most applications. I decided to build a stand-alone amplifier using two LM380s, and a pair of good quality bookshelf hi-fi speakers. The basic circuit is very simple and taken more or less from the LM380 spec sheet. There is no tone control.

Amplifierr Schematic

There are two LM380 circuits, of course. I use a 2 pole 4 position switch for selecting up to 4 different inputs. The volume control is a ganged unit. And there is a 12 volt 1 amp power supply.

amplifier frontAmplifier back

amplifier insidespeaker

The amplifier board is built on a piece of copper clad board, to provide a good ground plane. Amplifiers often malfunction when the layout is neglected. All the input jacks on the front and back panels are insulated from the panel, to avoid ground loops. (The panels are grounded and the speaker jack grounds are directly connected to the back panel.) I added an extra switch and jack on the front panel as a headphone jack.

My speakers are quite efficient, and the amplifier provides more volume than needed. You may not be able to see it from the photos, but I glued small finned heatsinks to the top of the LM380s (I used the 14 pin DIPs) just in case.

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