Where do you place a compressor in the signal chain? This often asked question is actually an easy one to answer… the compressor goes first!
Put the compressor as the first pedal that the guitar plugs into on your pedalboard. The reason is that a compressor has a circuit in it that reads signal fluctuations and turns that into a dc voltage which controls the gain of the pedal. If the compressor is connected directly to the guitar, it can see the full range of peaks that is being generated by the pickups and is able to properly control its gain element.If you place the compressor after a fuzz or distortion pedal, then the dynamic fluctuations of the guitar signal are clipped off by the distortion circuit (or diodes) and the compressor does not have an input that is ideally suited for signal control. You can read more about how the dynamic range of a signal is modified in my article Compression and Limiting in Distortion Boxes.Another reason that the compressor goes first is that their design typically includes high gain. With the compressor pedal at the front, you will insure that the cleanest, least noisy signal is being amplified by it because any noise that is present will be amplified along with the signal. Also, the VCA chip uses in many classic compressors is not the highest quality and will contribute noise and distortion of its own, which is another reason to place it immediately after the guitar. High end compression devices often have a noise gate circuit that will make the low level hiss less obvious but this feature is seldom seen in stompboxes.
Some players like to put the compressor at the end of their signal chain to give a boost to the output driving the amp. In this case, the compressor is really only acting as a booster, and you would be much better off using a boost pedal rather than a compressor. Boosters, like the AMZ Mini-Booster or Mosfet Boost, are almost always quieter than compressors and a better choice for that application. Furthermore, with the compressor at the end, all of the noise from previous pedals will be further amplified by the high gain circuit.
Some people claim that you can place a compressor after a distortion box that has good ‘dynamics’ and use it for signal control. The problem with this is that there aren’t really any commercially available dynamic overdrive pedals… not even those with that buzz word in their name. Read my article linked in the earlier paragraph above to understand why. Even chorus or phaser pedals will have an adverse effect on the signal dynamics and a compressor will just amplify any noise added by those pedals.
Put the compressor as the first pedal in your signal chain and you will get better utility and function from it. If you want to add some drive to your signal, get a booster pedal instead and put it at or near the end of the pedalboard.