About Guitar Capacitors
Capacitors are useful in guitar wiring because they can be used to route high frequencies away from the guitars output jack and away from the signal that goes into the amp. The effect of this is a softer, warmer, more mellow tone which is controllable depending on the value of the capacitor used.
The range of frequency that is sent to ground is determined by the value of the capacitor. Generally, Capacitors in the range of .001 mfd (micro farad) to .1 mfd take out highs in the frequency of the guitar signal that often sound pleasant. The .1mfd capacitor will sound very muffled because much more of the high and mid frequencies have a path to ground. The .001mfd capacitor will be hard to even notice because only the harder-to-hear high frequencies will be effected. The most common values found in guitars are .022 mfd and .047 mfd capacitors. Quite often .022 mfd capacitors are paired with humbuckers and .047 mfd caps are paired with single coil pickups.
How Different Capacitors Sound
Both the video and the audio clip below are comparisons of the guitar signal when having different value capacitors in use. In both examples the tone control is fully engaged so you hear the full effect of the capacitor. Keep in mind it is not normal to use the guitar capacitor fully engaged but for the sake of comparing the sound of different values I thought it more appropriate to do it this way. In the audio example I am playing through a Stratocasters neck pickup. In the video example I am playing through the same Stratocaster but with the neck and middle pickup wired in series so they behave more like a humbucker. The capacitors used in both examples are Sprague "black beauty" capacitors.
Audio Example Of Different Capacitors
The Neck Pickup Link To Mp3
1st phrase - with no capacitor
2nd phrase - .003mfd
3rd phrase - .006mfd
4th phrase - .01mfd
5th phrase - .02mfd
6th phrase - .033mfd
7th phrase - .047mfd
Types Of Capacitors
Suitable for Guitar
Ceramic - These are the cheapest capacitors on the market and are often found in cheaper guitars. There is a lot of debate as to whether or not these capacitors sound worse than the other types. In my opinion it is not a noticeable difference. I believe the only difference in tone is a result of their varying tolerances which are not as precise as other time of capacitors. That can even be a benefit. Get a handful of the same value and you might find one stand out as better to your ears than the rest! It will still be a lot cheaper than one oil/paper cap. Ceramic capacitors almost always have a 3-digit code printed onto their body to identify their capacitance value. Just fill in the three digit code to find the value of your capacitor:
Film - Film caps are made out of polyester (Mylar), polystyrene, polypropylene, polycarbonate, teflon and metallized paper. Famous capacitors for guitar wiring like the Sprague "Orange Drop" and "Black Beauty" caps are film-type capacitors and are considered quality. The capacitor in the picture to the left is a Sprague Orange Drop which is quite a high quality capacitor. It is used in many higher model guitars these days and I would recommend it. Compared to vintage capacitors like the Black Beauties, they are far more reliable and cheaper. Although I have used Black Beauties in a few projects on this site I would recommend saving your money. I have not noticed any audible difference between them and any other capacitor. The vintage capacitor market right now is really quite absurd. A .05 cent metalized film cap will sound the same as a 10 dollar vintage capacitor. Even in their time, Black Beauty capacitors were not even considered high quality.
Oil/Paper - Oil/Paper capacitors are made out of, you guessed it, oil and paper. These are considered the best capacitors that money can buy although I do not hear much of a difference between these and other capacitors at all. I believe these were never actually used in vintage guitars but I might be wrong. Personally I think you are better off saving your money. A cheap cap will sound just the same and you can spend the money on trying different values of cheaper caps to find your own tone.
Electrolytic - Electrolytic capacitors are polarized (although there are special ones which are not) and are mostly used to filter direct current in active circuits. These are used in active guitars as a way of keeping the direct current from the battery out of the way of the a.c. audio signal as well as smoothing ripple in the application of regulating voltages in power supplies. Unless you want to build the Tillman Preamp you will not need to use these in any projects on this site.