I started electronics recently and I'm trying to make the most basic mp3 amplifier. First I tried to make the amp myself with reused electronic parts but I didn't succeed… Amplify speaker with 9v battery and one transistor. Do you have any recommendations about it ?
So I decided to use a LM386 because it's easier. I found a module which integrates de LM386 on dx.com for 3$. This one http://www.hamgadgets.com/LM386-AMP-MOD. But I guess I can make it myself for less and probably better/stronger.
It worked pretty well with the 9v battery if I set the gain to 50%. I read it provides up to 0.3w of audio power so it uses 0.3w/9v = 0.033a max ?
On the module it says 5 to 12v and I read that a battery provide the amps depending on the voltage and the resistance. But then I decided to try connecting it to an outlet. I retrieved an old transformer : 9V – 300mA – 2.7w. The LM386 chip on the module fastly became very hot so I disconnected it. When I tried again with the 9V battery, the led still lighted up but the sound didn't pass through.
I know home current is AC and a battery is DC but I don't fully understand it. The AC current works on cycles (is it up only during short periods ?) and DC is a horizontal straight line (in a graph). Doesn't AC provides the amperage like a battery and the 300mA value is the maximum amperage ? Why did my circuit burn ?
Best Answer
A 9V output from a transformer will be alterating possibly up to a peak of 13 Volts and down to a negative peak of -13 volts. It will be doing this 50 or 60 times per second and I'd bet on the first negative cycle from the transformer you burned the chip and possibly damaged any electrolytic capacitor on the module.
I'd throw it in the bin and get a new one. Welcome to the learning process. Next time, add a bridge rectifier and smoothing capacitor and measure with a voltmenter to make sure polarity is correct and the dc voltage level.