How do you know what caps to use?

[Joecool85]

I'm working on creating my own schematic and I don't know what size caps to use...I know that basically the bigger the cap, the more bass that is allowed through the circuit, but its not just an abitrary cap size is it?  Do you just adjust them to taste or is there some sort of formula?

I don't want to give out the whole circuit schematic as of yet (I haven't tried building it yet), but I can say its going to be a dual 2n3904 fuzz/overdrive style box.

[R.G.]

I'm working on creating my own schematic and I don't know what size caps to use...I know that basically the bigger the cap, the more bass that is allowed through the circuit, but its not just an abitrary cap size is it?  Do you just adjust them to taste or is there some sort of formula?

The basics of caps (at least for this discussion):
A capacitor has an impedance (See Geofex: "What's Impedance?") that decreases inversely with frequency. That is, as frequency goes up, the cap's impedance goes down. A resistor has an impedance that is fixed, the same for all frequencies. So a cap and a resistor can sort frequencies out - the cap lets through the higher frequencies better.

The sorting point is where the cap's impedance is equal to the resistor. A cap's impedance is Xc = 1/(2*pi*F*c) where pi is 3.14159..., F is the frequency, and C is the capacitance in Farads. A microfarad is one millionth of a Farad, or 10E-6. The sorting point is then the frequency where R = 1/(2*pi*F*C) and by some simple algebra, F = 1/(2*pi*R*C).  You will see the product R*C referred to as a circuit's time constant, as it has units of seconds.

All possible series and parallel combinations of a resistance and a capcitance have the same turnover frequency. The combinations only vary in whether the signal is passed through the RC or is shunted to ground. A signal passed through a series resistor with the cap shunted to ground is a low pass filter, because the capacitor shunts every frequency above the RC turnover frequency to ground. A signal passed through the cap with a resistor to ground is a high pass filter because at quite low frequencies, the cap blocks the signal and the resistor shunts the signal to ground; at high frequencies the cap lets signal through as though it was a short circuit. A parallel R-C combination in series is also a high pass filter; a shunt RC is a low pass filter.

If you're into designing your own circuits, it would be good for you to get some basic electronics under your belt before you get too deep into it, or you're going to get results that you simply don't understand because you don't have the background knowledge for it. Try looking up some basic electronics education on the web. It will help a lot.

[Joecool85]

Cool.  And I don't plan on really implementing my design for a few months as I want to build a couple other pedals first and also get some more tech under my belt as you suggested.  Any good sites you know of for basic electronic tech?  Or a good book?  I like good books.