PAM8403 Amplifier suddenly clicking and dying

[8bit_coder]

I bought 5 Class D PAM8403 amps off of Amazon. I was testing one of them with two 8 ohm speakers and everything was going smoothly. I was listening to music at a low volume, and I kept checking the temperature on the amp chip but it never got warmer than room temperature. Suddenly, I hear this loud clicking noise from my speakers. I managed to disconnect the amp from power quickly, but now it only clicks.

I managed to get a direct recording of the clicking sound: (warning, loud):
 RIP PAM8403.wav (1022.24 kB - downloaded 106 times.)

After letting the amplifier sit for a while(it got hot to the point of burning the tip of my finger but no smoke, while it was clicking) I hooked power up to it again and now it's dead silent, unless I play a really loud square wave of one hertz on my computer, I can hear a loud clicking along with the one hertz my computer is playing. I can somehow increase the frequency of the square wave up to about ten hertz and then it starts getting really hot again, without releasing the magic smoke.

What happened? I'm genuinely curious as to what happened and what was the fault of it.

[don.r]

Getting hot = something has shorted. Likely a failed transistor. Class D is a switching amplifier using MOSFETs on the outputs. Here is a quick guide to test them, best tested out of circuit.

[8bit_coder]

I'm wondering what would have made it short so spontaneously? It was working fine a minute ago and then it suddenly dies? That's weird.

[Zero999]

What was the supply voltage? Did you check is wasn't above 5.5V?

How long are the speaker cables? I wonder if having them too long could cause high voltages to appear at the amplfier's outputs.

[8bit_coder]

The supply voltage was a constant 5 volts from one of my trusted USB power banks, and the speaker wire length was about two meters long.

[Zero999]

Did you add any filtering?

I suspect the cable was too long. It's not designed to drive speakers through long cables which result in large current and possibly voltage spikes, especially if it was run, without the speaker connected.

The PAM8403 is designed to power speakers connected through short cables. It's meant to be used inside a device such as a laptop, not in a HiFi system, with external speakers.

To drive long cables, you'll need to add filtering inductors and capacitors and a transient voltage suppressor to the output of the amplifier.

[8bit_coder]

You're right, I had no filtering on the cables!

A suspect is an AM radio station that's about a mile away from my house, so it has strong interference with even my audio recording equipment and studio monitors(with chokes), and since I didn't have any filters on the output, the radio station's interference could have been too much for the amplifier to handle, and it went into protection, hence the clicking.

I'm guessing the two meter long cables were acting as a sort of antenna and amplifying the radio station's interference even more. Well, thanks for the info! I'll make sure to keep the wires of my other amps short.

[Zero999]

You're right, I had no filtering on the cables!

A suspect is an AM radio station that's about a mile away from my house, so it has strong interference with even my audio recording equipment and studio monitors(with chokes), and since I didn't have any filters on the output, the radio station's interference could have been too much for the amplifier to handle, and it went into protection, hence the clicking.

I'm guessing the two meter long cables were acting as a sort of antenna and amplifying the radio station's interference even more. Well, thanks for the info! I'll make sure to keep the wires of my other amps short.

RF pick-up will not be strong enough to kill the amplifier. The problem is, being a class D amplifier, it has a PWM output with very fast changing voltages and long cables can cause high voltage and current spikes, when the output abruptly changes from one voltage to another. Cables have inductance and capacitance. When there's a lot of inductance, high voltages can be generated when the current is suddenly interrupted. A couple of 6.2V zener diodes connected back to back across the amplifier outputs will help to protect against over-voltage. The main reason for having a filter is to prevent the amplifier from transmitting interference to other devices.