"Explain Like I'm 5": Resistors March 17, 2016 16:45

What are resistors?

Resistors are one of the core building blocks of electronic circuits. Even the shortest signal path in the studio can contain dozens or hundreds of resistors.

Resistors are incredibly simple components: they’re basically wires that don’t conduct as well as regular copper. The degree to which they're bad at conducting (or good at resisting) is their resistance.

But despite being simple, they’re also incredibly powerful and versatile. The circuit inside our SB2 Passive Summing kit, for example, contains only resistors.

A through-hole, metal-film resistor.

What do resistors do?

They resist the flow of electrons. In other words, they limit the amount of current that will flow in a circuit. In the trusty electricity/plumbing analogy, resistors are different widths of pipe.

What can resistors do in a circuit?

Countless things. Resistors are required for creating filters, setting the brightness of LEDs, setting power supply voltages, controlling the response of a microphone capsule, etc. This is why you’ll find resistors in practically every electronic circuit.

Two resistors configured as a voltage divider
By Velociostrich (Own work) [CC BY-SA 3.0], via Wikimedia Commons

What do resistors’ specs mean?

Despite being the simplest of components, resistors have a lot of specs. For simplicity’s sake, I’ll just go through the most important here.

  • Resistance: The degree to which it resists the flow of electrons, expressed in Ohms. A 1 ohm resistor is one where 1 volt will create 1 amp of current, or 1 watt of power. Nice and tidy!
  • Tolerance: The precision of a resistor’s value, expressed as a percentage. For example, a 100R 2% tolerance resistor could have an actual value 98R and 102R. Most often in audio we use 1% tolerance resistors.
  • Wattage: How much power a resistor can handle. Resistors dissipate power by turning it into heat. If a resistor gets hotter than it can handle, it’s value will or change or (more fun!) it will combust. The most common wattage in small-signal audio is 1/4W.

Do resisitors have a sound?

No. For all intents and purposes, resistors do not have a “tone” of their own. They don’t saturate like transformers or have phase effects like capacitors. They may have different self-noise levels and tolerances which can affect the performance of the circuit as a whole, but in general resistors by themselves do not have a "sound."

How do I identify different resistors?

Through-hole resistors (as opposed to surface-mount, which we’re usually not using for DIY) are wrapped in a number of colored bands which tell us the resistor’s value and tolerance.

The metal-film resistors that are most common in DIY projects use a five-band code, where the first three bands represent the first three numbers of the resistance value, the fourth band is the multiplier (ie., how many zeros come after the first numbers), and the fifth band is the tolerance as a percentage.

Of course if you don’t want to bother learning or looking up color codes, you can always identify resistors with a multi-meter.

Why do resistors common resistors have such weird values (4.7, 6.8, etc.)?

Back in the day when resistors had very wide tolerances of 20%, it made sense to manufacture only values that were about 40% from each other with a bit of overlap. Thus 1.5, 2.2, 3.3, 4.7, 6.8, and 10 became the standard values for each decade (10x, 100x, etc).

Nowadays tolerances are much better and you can buy a resistor in practically any value. However, the old common values are still made in greater quantity, so they’re cheaper and more reliably stocked. This is why you still see many more 47k than 50k resistors, for example.

How’d I do?
Did that make sense?
Did I miss anything?

Please let me know in the comments below!