[sdiy] Capacitors questions

[Ryan Williams]

hi all,

I've got a simple question here about electrolytic capacitors. I 
understand that the positive side has to have a greater voltage than the 
negative side or else it will explode, but I don't understand how they 
work with AC signals when blocking the DC part of the signal. like this:

module_input----||-----module
                   +
incase it doesn't show up right, the '+' side is on the 'module' side.

how does this work? I've seen this on many synth diy schematics, but all 
the capacitor tutorials I've seen do not talk about this. It just 
doesn't make sense to me since the signal is AC.

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one more question: Does anyone know where to find 1% polystyrene 
capacitors in the US? I need them in 100nF sizes.

Thanks,
Ryan