Auditioning Tone Capacitors

In a nutshell, a capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates"). The process of storing energy in the capacitor is known as charging, and involves electrical charges of equal magnitude but opposite polarity building up on each side.

Capacitors are often used in electrical and electronic circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters, and that´s exactly what we use them for inside our guitars. Basically, our passive tone control can be used to dampen the high frequencies. When you close the tone pot, it rolls off the treble response, giving a more mellow tone. Adjusting this control affects the sound very noticeably, but it still is quite recognizable as the same guitar.

A basic rule for tone caps is that the bigger the cap, the darker the tone. Depending on the cap's value (capacitance), the effect can reach from "slightly warmer" to a "woman tone" all the way to "completely dark and clinically dead." Remember, the tone cap is always part of the guitar circuit and it even influences the tone when the tone pot is fully opened.

I often receive e-mails and calls from guitarists who don't use the tone control at all, mostly complaining about tones that are darke and lifeless, hotspots when closing the tone pot, and a basically useless taper of the tone control. I'm sure you've experienced the last problem; when closing your tone control, all changes occur between 10 and 8, and from 8 all the way to 0 there is no audible change of your tone. Don't worry, this can be solved. I hope that I can encourage you to give your tone control a second chance. It is really unbelievable how many tone colors can be easily dialed in with a proper tone control.

There are two basic parameters that we will talk about: the value (capacitance) and voltage rating of the cap, plus the type of cap itself. Both parameters will influence the tone a lot; this month, we will start with the value and voltage rating of the cap. Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. The voltage rating describes the maximum working voltage of a cap (potential, measured in volts).

Voltage Rating

One of my all-time favorite urban legends has to do with voltage ratings. You can read about voltage ratings of 400 volts – and higher! – for tone caps, and how this influences the tone. Do you ever talk about 400 volts coming out of your guitar? Of course not. Then how exactly does it influence tone?

As a basic rule you can say that every cap with a voltage rating of 0.5 volts or higher will work inside a passive electric guitar, with higher voltage ratings resulting in larger caps. The reason for the high-voltage tone caps that you find in guitars is easy to explain. A lot of popular caps, like the Sprague "Orange Drops," are for tube amps with inside voltage of 600V or higher. Nevertheless, the caps sound great inside a guitar, but an Orange Drop cap with a 10V rating would also sound great. A cap with a higher voltage rating does not sound different from the same cap with a lower voltage rating.

I've spent a lot of time with A/B comparisons, blind tests and measurements and I never could ear any difference. I'm not Eric Johnson, and I use my eyes instead of my ears to verify if the grass in my garden is growing, but you can try these tests yourself. Orange Drop caps are great for this experiment because they are available in voltage ratings from 100 to 680 volts.

Value (Capacitance)

Now that those rumors are debunked, let's focus on the more important parameter – the value of the cap. Remember our basic rule to help understand this parameter: the higher the capacitance, the darker the tone.

In the "golden days" of electrical guitars, Fender and Gibson used tone caps with a very high capacitance (0.1uf/0.05uF and 0.047uF/0.022uF, depending upon the time period). The 0.022uF value is still the standard today. If you need very dark and bassy tones, this value may work for you. For most of us, however, this value is much too large and the effect is more or less useless, resulting in the aforementioned problem of the effect only taking place between 10 and 8. The solution to the problem is simply a tone cap with a much smaller value. This little change will enhance the usability of your tone control dramatically, giving you a good evenness among the complete taper of the tone control without any hotspots, and every movement of the pot will result in a change of tone.

The value of your tone cap is always a matter of individual choice and needs, because everyone has a different ideal tone and everyone uses the tone control differently. Personally I use very small tone caps of 3300pF up to 6800pF, depending on the guitar and how bright it sounds. With these mall values I´m able to dial in a lot of tonal shades and colors all over the tone pot, and with every small movement the tone gets a little bit warmer and sweeter - not dull and dark.

Finding the Perfect Value

To find the perfect value for you, I suggest getting a piece of cardboard, two 10" pieces of wire, two solderable alligator clips and some cheap standard ceramic caps. The cheapest caps from a local electronic store are good enough for this, and the voltage rating is completely unimportant. Get values from 1200pF to .1uF, plus every value in between you would like to try. One piece of each value is enough. Glue the caps side by side on a piece of cardboard, with the legs reaching over the edges. Don't forget to note the value of each cap on the cardboard! Then, solder the alligator clips to the wires (one clip per wire, soldered to one end of the wire).

Now open your guitar and desolder and remove the existing tone cap. Solder the end of the wires opposite to the alligator clips to the points where the original tone cap was connected and close your guitar leaving the wires hanging out. Now you can change the different caps within seconds by simply connecting with the alligator clips. Play your guitar and use the tone control to see which value works best.

Hopefully you will be able to determine through this method what your favorite cap value is. My tip is to try 2200pF, 3300pF, 4700pF and 6800pF and listen to how they interact with the tone and taper of the pot. Chances are good that you will like them!

This is a very important step in converting your tone control to a useable and helpful tool in the future. Next month we will talk about the different cap types, and how to figure out which one is for you.

See you next month!

[Updated 11/23/21]