Resistors are quite possibly the most common electrical component that you’ll ever deal with. They are a critical piece of every electrical circuit you’ll ever use and that’s why it’s key for you to understand what they do and how.

WHAT IS A RESISTOR?

Resistors are passive electrical components that alter the flow of electrical current by adding resistance to the circuit. They have fixed values and have many purposes but are most commonly used to delimit electrical currents.

WHAT ARE RESISTORS MADE OF?

Modern through hole axial resistors are generally made of one of three compositions. Carbon, Metal or Metaloxide Film.

Inside the resistor, there’s a wrapped length of resistive yet conductive wire which (depending on the level of resistance) can resemble a coiled spring. The higher the level of resistance, the longer and tighter the coiled wire.

WHAT DO RESISTORS LOOK LIKE?

There are four standard types of resistors:

• Carbon film through-hole resistors
• Metal film through-hole resistors
• Metaloxide film through-hole resistors
• Surface-mounted resistors

CARBON FILM THROUGH-HOLE RESISTORS

Carbon film through hole resistors are low noise and low cost components making them a great solution for building DIY guitar pedals.

These resistors are available in 1 Ohmn to 10 Mega Ohmn ratings and have very low tolerences. 2%, 5%, 10% & 20% are the standard tolorances you’ll find with these resistors and the lower the tolerance, the more expensive the component.

METAL FILM THROUGH-HOLE RESISTORS

Metal film through hole resistors are very similar to carbon film resistors. However, instead of using a carbon conductive compound, they use a metal compound (either tin and antimony or nickel chromium).

These resistors are even lower noise than that of the carbon film alternative making them the ideal solution for building pedals.

METAL OXIDE THROUGH-HOLE RESISTORS

These resistors are similar to metal film resistors and the only real difference is the type of metal used for the film. Instead of being nickel chromium, these resistors use tin oxide.

The main benefit of these resistors is their high temperature resistance and their ability to handle higher wattages.

SURFACE-MOUNTED RESISTORS

Surface Mounted Resistors are generally only found in professionally designed and manufactured circuits as they require special tools to effectively work with. As they’re so small, they allow you to make much smaller circuit designs which can be useful when trying to reduce the overall footprint for an otherwise large design.

If you’re not sure whether to use surface mount or through-hole components in your pedal builds, take a look at my guide here on the differences between the two:
Surface mount vs through-hole components – what’s the difference

WHAT ARE RESISTORS MEASURED IN?

The electrical resistance of resistors is measured in Ohms (Ω). As this is the International System of Units (SI) for electrical resistance, you can also see this is KilOhms(KΩ) and MegOhms(MΩ).

1KΩ = 1,000Ω

1MΩ = 1,000KΩ or 1,000,000Ω

HOW TO READ RESISTOR MARKINGS?

The coloured markings, or bands, on a resistor will help you decipher their values at a glance. There are three standard types of markings for axial resistors. Four-band, five-band and six-band with the most common being the four band resistors.

On a four-band resistor, the first two bands determine the significant digits of the resistance value with the third band being the multiplier in a factor of 10. The fourth and final band signifies the tolerance of the resistor with the lowest tolerance being 0.1% and the highest being 10%.

On a five-band resistor, the first three bands determine the significant digits with the fourth and fifth being the multiplier and tolerance.

On a six-band resistor, the first four bands are the significant digits of resistance with the fifth and sixth being the multiplier and tolerance.

A chart to help you understand these values can be found here:

RESISTOR VALUE TOOL

To makes things easier, I’ve created a handy calculator here that you can use to calculate the values of your resistors. Simple change the value of the dropdowns to find the values of your resistors.

HOW TO TEST A RESISTOR?

Past looking at the bands, the easiest way to test the value of a resistor is by using a multi-meter. If you’re unable to decipher the bands on a resistor, you can use a multimeter on the Ohm setting and then by using the test leads on either side of the resistor, we can see what the resistance is.

Using a multimeter will also provide you with a more accurate reading as most resistors come with anything from a 0.1% to a 10% tolerance. This means that a 33k resistor could actually be a 30k or 36k resistor. Depending on the circuit, you may wish to test all resistors before adding them into the project and pick the resistors that are closest to the desired specification.

Why not check out my other posts about the other common components when building DIY guitar effects pedals here:

A Guide To Transistors For DIY Guitar Pedal Builders

A Guide To Capacitors For DIY Guitar Pedal Builders

If you’re new to this and would like to know where to buy resistors for your DIY effects pedal projects, check out my guide here:

Where to buy DIY guitar effects pedal components