What exactly are "caps?"

joeprs

Member
Messages
1,516
Is it short for capacitor like pott is short for potentiometer?
Please forgive my ignorance.
I'm comfortable with the set-up and operation of electronics. I even scored an old tube tester which is a pleasure to own and I have no problem using it.
When it comes to the circuit board, I stay away.
Thanks

If unquiet reads this, I'm sure he'll give me a great explaination.
Thank you
 

Greggy

Senior Member
Messages
13,439
Unless I'm mistaken (entirely possible since I'm not an electronics wiz), a capacitor is a resistor just like a pot, with the following distinction, it discriminates along the frequency spectrum when bleeding off electrical signals. For example, a pot will send the entire signal to ground, thus attenuating the outputted signal evenly along the entire frequency spectrum (from full volume to silence). Whereas, a capacitor bleeds off the higher frequencies at a greater rate compared to the low frequencies (due to a differential ohm resistance at varying frequency levels), thus obtaining a hi frequency cut (in other words, your typical passive tone pot/capacitor system cuts treble output, it doesn't boost bass or treble).

Unquiet can administer an internet spanking if I've dropped the ball on this one.:D

Greg
 

VaughnC

Silver Supporting Member
Messages
17,999
Basically speaking, except for very high frequencies, resistors have a fairly flat frequency response. But capacitors have a different reactance (impedence) for each frequency, which is demonstrated by the mathmatical formula: capacitive reactance=1/6.28*frequency*capacitance. So, as you can see from the formula, for a given capacitor value, capacitave reactance is inversly proportional to frequency.
 

sws1

Member
Messages
11,665
Technically speaking, a capacitor is a device which allows alternating current (AC) to pass through it, but does not allow direct current to pass through (DC).

A classic example of where a cap is used in an amp is between each stage of the preamp. The output of each preamp tube has a very high DC voltage on it. This is required in order to make the tube work. Layered on top of that high DC voltage is the oscillating signal that comes from the guitar. I.E. the wave form.

Typically, this high-DC wave form is sent directly into a cap (in series), which blocks the DC voltage, but lets the oscillating signal proceed to the next phase. If you have a voltmeter, you can see that on 1 side of the cap, you have high DC voltage, and on the other you have a very low, if not zero amount. (Actually, if you have a signal coming into the amp, the amount of voltage on this side of the cap will be going up and down.)

The size of the cap determines the amount of bass that is allowed to pass through. The higher the value of the cap, the more lower frequencies that are allowed to pass.

That is what a cap does when it is is series (i.e., in line) with the signal.

What a cap is used in parallel (ala filter caps), they still do the same thing (that is, let AC through, but block DC). However, when the are in parallel to the main circuit, they effectively filter out ripple (or AC) that may be present in the line, and smooth things out.

There are other uses of caps in the amp, but they all still do the same thing. Block DC voltage.

(And to think that I learned all this stuff in just the past month.)
 




Top