Michael Chen from Panama wrote in about his troubleshooting and repair of his Corsair SP2200 Crackling Speakers. He has also entered this into the Instructable’s fix and improve contest so if you like it please vote for him.
“Here is how I fixed a crackling SP2200 speaker
However, the most interesting thing is how I troubleshooted the problem, which does not appear there since it is aimed to a different audience.
I first thought it was a faulty potentiometer, as I’ve had them fail like this before. After disassembly, I noticed they were ok, so I then checked for cold solders. Again, this was not the problem.
The moment of inspiration came when I found out that the headphone output on the speaker also exhibited this crackling. I started to reverse engineer the board and found out that after the audio input, it went through several rcl filters, the volume pot, and finally, the headphone amplifier (which is just a pair of op-amps). The crackling was being introduced further down the line and traveled back through the relatively high impedance line, this noise probably caused by the class D amp housed in the subwoofer.
I also found out that the impedance was very high after the filters due to high in series resistance.
The fix would be to add a buffer after the potentiometer so that the whole system was more tolerant to noise. The two op amps from the headphone amplifier seemed like an ideal candidate. A few jumpers later, the speaker was working perfectly, although the op-amp’s gain could do some adjustment to return volume control back to normal levels. Meanwhile, I just lower the volume on software.”