Could you expand on that?The circuit is garbage. It was an Instructable posted (or copied) by a 10 years old kid who knows nothing about electronics:
1) The transistor's base-emitter burns out and/or the stereo output feeding it also burns out because a current-limiting resistor at the input is missing.
2) A protection diode is missing. The transistor is damaged when the input voltage swing is more than 5V peak (only 1.5W into 8 ohms) because its max allowed reverse voltage is only 5V.
3) The LEDs burn out because they are also missing a current-limiting resistor.
I'm here because this is the same project I'm about to start working on, and I know enough to know things are missing, but not enough to know exactly what to use or where to put them. I'm working from an 8.5v source to a TIP31C hooked to a sound line to turn the transistor on and off, and using 3V - 3.4V LEDs @ 24mA max continuous / 75mA max peak, two in sequence with a 1/4W 100ohm resistor to keep the current somewhere between 17 and 25mA (depending on voltage).
I used a couple of online LED calculators to figure out the number of LEDS and what resistor to use. I assume I need a resistor in the line between the stereo input and the transistor, but I don't know how much because data sheets overwhelm me.
I'm also not sure where to put the protection diode. Is it between the 8.5V and the first LED, between the last LED and the transistor, or between the transistor and ground, or does it even matter at all and it stops reverse voltage across the circuit? Does the size/type of diode matter, or will it allow (nearly) zero voltage/current one way and as much as I need the other? The LEDs have a reverse current of <=30uA and reverse voltage of 5~6V.
If I can draw up a better version of this circuit, perhaps I can start spreading the info around to more amateurs to do it right the first time.
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