This this is the final portable mono amplifier. Designed around the LM386 IC (Datasheet here ) and running happily on a 9v battery, this amplifier can handle music from MP3 players, laptop, phones, guitar (my primary build purpose) and a dynamic microphone. I have actually used two versions of LM386; the LM386N-3, as the main amplifier which handles music (summing stereo channels into mono along the way) and the LM386N-1 as a pre-amp (used for guitar and microphone). The LM386N-3, delivers more power (700Mw; that’s about twice the power of LM386N-1) The speaker, which is attached to the project box is an old Nokia car phone box (look out from them on ebay for about £5) and is 8 Ohm, 3W. These speakers (there is a similar Motorola speaker which I believe is 5 Watt but sounds identical) come with a handy bracket which I have attached to the project box.
Despite what many say about the LM386 being ‘noisy’ or ‘distorted’ with music, I have to disagree to some extent. Certainly, with this build, the amp delivers a beautiful, smooth, clean tone for music, using just the main amp; It sure enhances sound output from the laptop dramatically too! If the preamp is used for guitar a suitable ‘dirty’ tone and very loud output can also be achieved.
Incidentally, the circuit on the bottom left of the above picture is a battery condition tester and illuminating a led to a different brightness depending on the battery strength; it has nothing to do with the amplifier really and has been omitted from the schematic. The central circuit is the main amplifier and, to the right, is the pre-amplifier which services microphone or grungy guitar sound.
Here is the schematic…happy building.
Since designing this little amp, I have found a better option for the same result. Still uses two ICs but provides a much more flexible sound output. In the schematic below, I have used LM358 as a preamp (with added tone) and the LM386. TL072 can however be used as a direct replacement for the LM358 and this is my preference.