The corsair SP2200 are great speakers, but they have some sort of factory defect in which the left speakers start to exhibit a crackle after some time. I decided to open mine and check what was causing it.
Please vote for me in the Fix & Improvement contest.
This fix is not confirmed yet to work on all cases, however, it does work for me.
As far as I know, I may be the only person to have attempted this fix and it may or may not be specific to my case/speaker.
Corsair has a great RMA service, and I recommend to talk to them. I only did this myself because I live in Panama and paying any kind of international shipping is cost-prohibitive.
I am not responsible for anything you do to your speakers.
Edit: Corsair seems to have discontinued this product, which makes this instructable even more important for those with crackly speakers than it was before.
Step 1: Dissassembly
First of all, the problem causing the crackle in the speaker is not in the left speaker, but on the circuits hosted on the right circuit. This can be observed by the fact that the crackling is present on the headphone output.
First, remove the speaker dust cover on the right speaker. You will find underneath speaker cover four Phillip screws. Remove all four of them.
On the base of the right speaker, you will find two rubber strips. Underneath the one facing the front of the speaker, you will need to remove three more Phillip screws. After removing those three screws, pry open the speakers starting from the upper side. It will require a moderate force to pry it open, but as long as you did not miss any of the seven screws it will open without being damaged.
The knobs can also be removed at this point. They are held by a friction fit, just pull them straight out.
Step 2: Dissassembly, Part II
Behind the volume knob, there will be a small nut. You can remove it by using a small needle nose plier. After separating the two halves (as much as the cable allows you to), there will be two screws holding the printed circuit board to the plastic case. (the printed circuit board is the green board, I will just refer to it as PCB) Remove them.
There is no need to separate the plastic case from the speaker; just lay both of them aside as much as the cable will allow.
Step 3: Possible Cause
My analysis leads me into thinking that the issue is an excessively high impedance after the potentiometer. This is because:
-At zero volume, crackling is not present since the line is tied to ground
-At max volume, crackling is not present or almost nonexistent since the line is tied to the audio source
-At mid volume, where the impedance is the highest, crackling is also at its peak.
Please confirm that your speakers exhibit the same behavior, else they could have an entirely different issue.
The theoretical solution (remember this is just a theory, nothing is confirmed) would be to add a preamplifier. Or, the easier case, to reuse the headphone preamp as a buffer, thus eliminating the need for extra pieces.
Step 4: Easy Way
The way I originally did the mod was the following
Remove the zero ohm resistors located in the upper left corner of the PCB; they will be marked R37,R38.
(The zero ohm resistor has a small zero written in it.)
Solder one wire to the upper connection of the resistors you desoldered, the other end going to R41 and R34. The connections must cross; The right one to R41 and the left one to R34.
Make sure that the wires are only soldered to the upper contact where the SMD zero ohm resistor was. the uncovered part of the cable must not touch the lower contact.
The headphone amplifier has a gain of ~5.7. That means that voltage would be ~5.7 times stronger than normal, potentially damaging the speakers. You must decrease the volume on software almost all the way to the bottom in order to compensate this.
That is why this is the easiest way, as you compensate the amplifier gain on your software. Failing to do this can damage the speakers. Also, when turning it on the first time, advance the volume knob very slowly as the setting and range may not be the same. Be sure to adjust the volume via software before doing anything the first time. Afterwards, the volume knob will work normally.
The best place to lower the volume is not the master volume you normally use, (for those who use it), but an option in the mixer panel often called as front.
Step 5: Correcting Amplifier Gain
It is also possible to reduce the gain of the amplifier as to avoid having to do software hacks.
To do so, identify the two smd resistors marked R26 and R16. They will have inscribed the value 12D; which is equivalent to 130k. Double check with a multimeter that the resistance across it is 130k; else you could be removing the wrong one. After removing them, you must replace them with one whose value is much lower; under 20k. Both R26 and R16 must have the same value.
The reason an exact value is not mentioned is because after I replaced the resistors by a pair of 20k resistors, the volume was still a tad loud (although better than without it). This means the resistor should be smaller, but I do not know the exact value. A lower value, around 16k, would be a good start. However, doing this requires soldering skills and trial and error, and unless you plug your speakers on different computers frequently, the software hack is usually enough.
For reference, replacing the 130k resistors by 20k would change the gain from 5.7 to 0.88 . However, it appears that the input filters form a divider with the circuitry in the amplifier. Fed directly, the gain needs to be lower to reproduce pre-fix volumes by hardware.
Step 6: Reassemble
Don't forget to place the nut on the potentiometer knob before placing the plastic cap. Enjoy.