Capacitor mini-tutorial.

[DrNomis_44]

Hi everyone,

Thought I would do another mini-tutorial thread, but this time it is all about Capacitors.


Okay, so what is a Capacitor?, a Capacitor is an electronic component made up of two conductors which are separated by an insulator, the insulator can be made using a variety of materials which do not allow the flow of an electrical-current through them, these materials are commonly called insulators, one type of insulating material used in early capacitors is waxed paper, the only trouble with using waxed paper as an insulator is that it tends to degrade and go leaky over time, that is, it tends to let a small amount of electrical-current flow through it from one conductor to the other, ideally there should be absolutely no current-flow whatsoever, later capacitors used materials, like paper in oil,mica, ceramic, polystyrene, polyethylene, and polypropylene, insulators such as ceramic, polystyrene, polyethylene, and polypropylene tend to exhibit much better insulating electrical characteristics than waxed paper, paper in oil tends to be used in Capacitors intended for High Voltage applications, some Capacitors are made using Tantalum as the insulating material too, Mylar is another material that is used in Capacitors as well.

One of the most important electrical characteristics of an insulating material in a Capacitor is what's called it's working voltage, this is simply how much voltage the insulating material can withstand before it becomes punctured and then lets a small amount of current flow through it.

I have seen Capacitors that use ceramic as an insulating material, rated at up to 3kV working-voltage, that means that the ceramic insulator can withstand up to 3,000 Volts before puncturing, the working-voltage rating of a Capacitor is important because you do not want the Capacitor to fail under normal circuit operating-conditions, what you want to do is have the working-voltage of a capacitor to be higher than the highest expected voltage in a circuit, so say for example that you are building an FX pedal for your guitar and you know that it is going to be powered by a 9V battery, you can safely get away with using a Capacitor with a working-voltage rating anywhere from 16V to something like 63V, a working voltage rating of 1V is cutting it a bit close, and a working voltage rating of 6.3V is too low and there's a risk of the Capacitor literally exploding, I have actually had that happen to me at least a couple of times.

The conductors in the Capacitor can be made from a variety of conducting materials, like for example Silver, Copper, and Aluminium, to name a few, some Audiophile-Grade Capacitors are made using Copper Foil, I'm not sure what the insulating material is though.

Capacitors come in two basic types, Polarized, and Non-Polarized, Polarized Capacitors must be connected up in a circuit the correct way for them to operate correctly, whereas Non-Polarized Capacitors can be connected up either way and will still function correctly, if you connect up a Polarized Cap in a circuit incorrectly the Capacitor could explode.

Small capacitors are marked in values from about 1pF (pico-Farad), to something like .820uF or 820nF (nano-Farads)

The basic unit of Capacitance is called the Farad, which was named after an English Scientist/Physicist Michael Faraday, now, the Farad is actually a very big value of Capacitance, much bigger than what is used in most electronic circuits, but Capacitors with a value of 1 Farad actually do exist.

Here's a scale to show exactly how big a value 1 Farad is, considering that you will mostly encounter values in the uF (micro-Farads), nF (nano-Farads), and pF (pico-Farads):



1 Farad = 1000 mili-Farads.

1 mili-Farad = 1000 micro-Farad.

1 micro-Farad = 1000 nano-Farad.

1 nano-Farad = 1000 pico-Farad.

1 pico-Farad = 1000 femto-Farad.


Capacitors do one of two jobs in an Electronic circuit, they store energy, or, they block the flow of D.C. (Direct Current), and allow A.C. (Alternating Current) to flow, the tone Cap in a guitar is an example of a Capacitor used to allow A.C. to flow to circuit-ground, it is normally connected to a pot (variable-resistor) which gives us a way to control how much A.C. is allowed to flow to circuit-ground.

[Andy40]

Nice one Doc, very informative. whats your preference for caps used for different pups?

[DrNomis_44]

Nice one Doc, very informative. whats your preference for caps used for different pups?


For Single-Coils, if it's a basic Strat setup, I tend to stick with either the stock Fender value, which I think is something like .022uF, or it could be .047uF, or, I use the Eric Johnson tone-cap value of .1uF, if I'm making a Gibson-Style guitar I tend to go with the stock value of .047uF, it really doesn't matter too much to me with regards to the type of cap I use, for the Gold Strat and the HotRod Strat, I elected to use a .1uF paper in oil cap just for fun mostly, what cap values do you mostly prefer Andy40?

There's really no limit to what value you can use with Single-Coils or Humbuckers, a lot of it really depends on what sounds good to your ears, larger values of tone caps will tend to roll-off more of the highs in the tone you get, so, if for example, you're playing through a naturally bright-sounding amp, perhaps using a larger tone cap will compensate for the brightness, I think that's why Eric Johnson tends to like a .1uF tone cap in his Signature Strats, his stage rig setup tends to consist of a couple of Fender Dual Showmans for his clean sound, and a couple of Marshal Plexis for his Crunch and lead tones.


Mind you, for the majority of the time, I rarely ever use the two tone controls on my Gold Strat or the Hot Rod Strat, they are usually set on 10 so that they aren't reducing any of the highs in the tone I get, occasionally I might try experimenting with the tone controls though.


My Headless Guitar uses a .047 MKT yellow cap as the tone cap, and both the volume and tone controls are 500k log pots, in general, 500k pots tend to suit Humbuckers, whereas 250k pots tend to suit Single-Coils, but I have also found that you can easily get away with using a 500k log pot for the volume control with three Single-Coils, the guitar will just tend to sound a bit brighter at full volume settings.

[Simon Barden]

Gibson stock is 0.022uF, Fender stock is 0.047uF.

[Andy40]

I've only tried the stock values as Simon has pointed out and haven't experimented with different values. My only real preference is to use audio taper pots for tone and volume that way i get to roll off some treble gradually.

[DrNomis_44]

I've only tried the stock values as Simon has pointed out and haven't experimented with different values. My only real preference is to use audio taper pots for tone and volume that way i get to roll off some treble gradually.


I go with all audio-taper (log) pots too, it's a known fact that the human ear actually exhibits a logarithmic response to loudness, to make something appear to sound twice as loud as it did before, you need to increase the audio-power by four times, for example, say you have a 50 Watt amplifier that you play your guitar through, if you want your sound to be twice as loud, most people would think that you'd need to go to a 100 Watt amp when in reality you would actually need a 200 Watt amp (four times 50).

The reason why log pots are used instead of linear pots is so that the response sounds more even to the human ear.

[Muzza]

Couple of points for a diehard pedant as myself.

The insulated middle section of a capacitor is called the 'dielectric'.

The correct term for a polarised capacitor is an 'electrolytic' capacitor.

Other than that, your practical knowledge of the correct use of capacitors trumps my theory knowledge, so carry on Doc...

[Simon Barden]

The tone control capacitor isn't in the direct audio path, so it's really not that important as to its type, but higher tolerance varieties will give more predictable results. Some capacitor types also vary their value more with temperature.

The tone circuit in guitars is a form of an RC (resistor + capacitor) low-pass filter, where the cut-off frequency = 1/2*pi*C*R.

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So both the capacitance and the resistance value have an effect on the cut-off frequency. The bigger the capacitance or the resistance, the lower the cut-off frequency.

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But that resistance value isn't the value of the tone pot, oh no. It's the resistance of the pickup itself (or more correctly, the 'impedance' of the pickup, as its resistance will vary with frequency). Which is why humbuckers and high DC resistance single coils tend to use use lower value capacitance values than single coils with lower DC resistance values in order to achieve roughly the same cut-off frequencies.

You may be surprised to learn that a single-coil pickup and a 0.047uF capacitor arrangement has a cut-off frequency of just 564Hz. An 8k ohm humbucker with a 0.022uF capacitor has a cut-off frequency of 904Hz. Both of these are quite low values. So why doesn't the sound always sound muffled? Because of the tone potentiometer. This acts as a signal attenuator, so the amount of signal sent to ground via the tone circuit is at maximum with the tone pot set to zero - i.e. no resistance. With the tone control at maximum, i.e. maximum resistance, you've got almost none of the signal above the cut-off frequency being sent to ground, and so the signal sent to the output is nice and bright.

The above is slightly simplified, as in most instances, it’s not just the pickup’s resistance that makes up the ‘R’ value, but the resistance of the pickup and the volume pot in parallel. Because the volume pot has so high a resistance value compared to the pickup, it only has a relatively small effect on the overall resistance, but it isn’t negligible. For instance, a 6k ohm single coil with a 250k ohm volume pot has an equivalent resistance of 5.86k. An 8k humbucker with a 500k ohm volume pot has an equivalent resistance of 7.87k. So not that great a change, but the slightly lower value does push the cut-off frequency up slightly.

There are other complications to add in to make a 100% realistic simulation of a guitar's complete tone response, as the pickup itself has a capacitance an inductance, and the guitar amp's input impedance also reacts slightly and the guitar lead's own resistance and capacitance also form an RC circuit and filter off a bit more high-end frequency (which can sometimes be quite a lot).

But the basic principles are that the higher the value of the pickup resistance x the tone capacitor value, the lower the cut-off frequency. So for higher resistance/impedance pickups, you need lower value capacitors to achieve a reasonable filter cut-off point, and for lower resistance/impedance pickups, you need higher value capacitors to get a reasonable cut-off point. The higher the resistance value of your tone pot, then the less the higher-frequencies will get filtered off and the brighter the guitar tone will be with the tone pot set to maximum. So for brighter single coils, this is another reason why 250k tone pots are used in comparison to duller sounding humbuckers which typically use 500k tone pots.

[DrNomis_44]

Couple of points for a diehard pedant as myself.

The insulated middle section of a capacitor is called the 'dielectric'.

The correct term for a polarized capacitor is an 'electrolytic' capacitor.

Other than that, your practical knowledge of the correct use of capacitors trumps my theory knowledge, so carry on Doc...


You're absolutely correct Muzza, I should have mentioned that the insulator is called the dielectric, and that the correct term for a polarized cap was an electrolytic, good call mate.


@ Simon Barden Cheers for adding that bit of electronics theory, that explains in greater depth what is going on with the tone controls of an Electric guitar, my take on the low-pass filter formed by the resistor and the capacitor is that it is acting as a voltage-divider, you have the pure resistance of the resistor combined in series with the impedance of the capacitor, except that the impedance of the capacitor is really resistance to A.C. signals.


The windings of the pickups, the tone and volume control, and the tone cap in an electric guitar are all part of an A.C. circuit, both the pickups (since they are comprised of a number of turns of wire around a metal core, effectively an Inductor), and the tone caps, exhibit something called an impedance, impedance is something which is similar to resistance except for one thing, it is dependent on frequency.

Since a pickup is effectively an Inductor, it's impedance will increase as the frequency of the A.C. flowing through it increases, on the other hand, the impedance of a Capacitor will decrease as the frequency of A.C. flowing through it increases.

Another thing that happens in A.C. circuits is a phenomenon known as Phase-Shift.


Here's something interesting that happens in an A.C. circuit, say for example we build a very simple series A.C. circuit, consisting of an Inductor and a Capacitor, if both the Inductor and the Capacitor have a value which exhibits the same impedance value at a particular Frequency, but exactly 180 degrees out-of-phase, the result is that the two impedances, being equal and opposite in phase, will tend to cancel each other out, and what's left will be the pure D.C. resistance of the circuit, not only that, the A.C. signal at that particular frequency will find it very easy to flow in the circuit, our simple series A.C. circuit is said to be resonating at that particular frequency.

Current-flow in an electrical circuit is rather like the flow of water through pipes, it will tend to flow through the path of least resistance.

[corsair]

Great stuff, chaps!!

While I happily change tone caps in and out as capriciousness takes me, I was always a little fuzzy as to why the tiny value changes of the capacitors could cause relatively large tonal changes - so, kudos!!

[GregLane]

Could someone please tell me what the values of the caps are in standard pit bull kits. Particularly LP, ST, TL and SG models?
Has anyone tried to wire the caps so they could be unplugged and replaced with different sizes.

[GregLane]

Having another shot. The above question slipped to the bottom with the recent activity.
Can anybody help?

[WeirdBits]

The kits typically have 0.022uF for humbuckers (LP, SG etc) and 0.047uF for single coils (TL, ST etc). There are some aberrations, I think the GR-1SF has two 0.047uF's supplied to go with the Filtertron style pups, and some others with quirks like that.

You can wire in a socket for the caps (I do it tweaking pedal circuits sometimes) or use screw terminals, but there's always a chance they could come loose at some point. It's more a question of, is it worth it? You can test caps with clip leads easily enough before committing, and it saves you having install sockets.

[GregLane]

Thanks Scott
I am starting to plan me rewiring. It's incredible what I' getting involved in with this building. All I wanted to do was l learn to play the bloody things eight years ago as my third childhood project.

[Simon Barden]

Third childhood? I think I'm still on my first! ;)

[DrNomis_44]

Note:

Because this thread is a mini-tutorial, please feel free to add more info on capacitors, just so we can build up a good resource for those new to building guitars and guitar electronics.....cheers mates!!!

[Muzza]

Just a point of interest, in America, they often call them 'condensors'.

[DrNomis_44]

Just a point of interest, in America, they often call them 'condensors'.


Yep, I think they used to be called condensers in the UK as well.