Capacitor polarity?

[Ch0jin]

I posted this question here and on another forum, and it's funny how many different replies I got. Since there was no real concensus, I decided to just experiment. I tried the cap both ways on my Schecter, and turned it up loud enough that any hum/noise that would have been evident should have been so; my result? No difference. Just FYI, I used an Orange Drop cap in there.

Thanks, folks. I appreciate it!

Without speculating on why you got so many different replies, I can tell you that there absolutely is a consensus on how capacitors are used amongst those who know how they work, but you need to know the basics to tie all seemingly different replies together.

First and foremost what does a capacitor do? Basically a cap allows AC to pass though and blocks DC. In most circuits, regardless of the size, shape or construction, this is what a cap is doing. Passing AC and blocking DC. The reason caps have different values (measured in Farads) is that each value of cap will pass a different frequency of AC. A bigger value will let through lower frequencies and vice versa.

Secondly, and important to this discussion, there are two categories of capacitor. Polarized and Non-Polarized.

A polarized cap has a "+" and a "-" and can only be used in one "direction" in a circuit.

The most common example of these are called Electrolytic Capacitors and they typically have a "can" shape with two wires coming from the base (known as a Radial Lead package). They are also made in whats known as Axial Lead configuration, where a wire comes out of each end of the can, but these are less commonly used.

The most common use of a polarized "electro" is as a filter, and more specifically, to remove unwanted "noise" from a power source. In something like a 9VDC power brick for a stomp box, the circuit is designed so that the value of the cap will pass AC at the frequency that would otherwise make your rig hum like crazy. Hum is AC so the cap just shorts it to ground and kills it.

There are other types of polarized caps that aren't in the "can" format, most notably "Tantalum" type caps which due to their construction makes them more reliable than electro's, but only available in small values.

Why are some caps polarized then? Simply, because it's easier to make them that way. The larger the value, the harder it is to make a NP (non-polarized) cap.

Why do I need to use polarized caps "the right way round"?

That construction process I mentioned is, in part, simpler than the process for a NP cap because a polarized cap can only handle a large voltage difference on one direction. Almost like a diode if you like. A cap rated at 16VDC will happily take a voltage difference of, kind of obviously, +16VDC all day long. In reverse though it might only take one volt difference to cause a chemical reaction inside the cap that, if the voltage differential is high enough, will cause it to explode. Yes explode.

So, if it sounds like NP caps are more flexible and less likely to blow up if you use them wrong, you'd be spot on. In fact, in a lot of circuits you could in theory probably replace all the polarized caps with NP's to no ill effect, but as I said, it's much more difficult to manufacture NP caps over a certain value so we use polarized for some things and NP for others.

As I've alluded to, NP caps can take the same voltage differential in either direction which is why it's completely irrelevant which way they are used in a circuit. Whilst you certainly can get NP electro's in the "can" format, you'll usually see them as ceramic (the light brown disc shaped ones) or Metalized polyester film (known as "Film" and sometimes, "Green" caps) and more rarely as they are more expensive, silver mica, polyproplyene (which is what an "orange drop" actually is) and polystyrene types.

So to sum up.

Polarized caps must be used the right way and Non-Polarized caps can go either way round and this is due to how they are made.

You'll find NP caps typically up to maybe 10uF in various types and you'll see polarized caps from maybe 0.1uF all the way up to Farads with the very small values available in Tantalum construction and pretty much every value as an electrolytic.

To be specific about your original post.

Tone caps in a guitar are typically ceramic or polyester. Neither type is polarized so their orientation makes absolutely no difference. As I mentioned, Orange Drops are just polyproplyene caps which are also NP.

As Jim P said and as the Aikenamps link Tung posted suggests, some NP caps, due to their construction method can use the outside foil as shield for RF interference and in a high gain circuit like a guitar amp, taking note of this might help reduce RF interference. It makes NO difference to tone however and in a passive guitar circuit it's completely irrelevant.

This "outside foil" on a NP cap should NOT be confused with the "-" of a polarized cap. Two completely different subjects and usage.

Anyway, I'm starved. Hope that helps rather than hinder