We all know the sound – that pesky buzz that can ruin a perfect take in the studio, or distract your audience when playing live. We’re talking about 50-60 Cycle Hum – the annoying interference that can really have an affect on your playing and tone. Today, we’re going to talk about Hum: where it comes from, and how we eliminate it with our friendly friend – the Humbucker!
What is hum?
Hum is an electromagnetic interference generated from AC current. Anything that is plugged into your main power lines is being supplied with AC, so, in theory, a multitude of household devices can emit Hum. Hum can be external or internal. External Hum is usually Electromagnetic Interference, or EMI. This is an electromagnetic signal from outside your guitar and is picked up by the pickups. Causes of this could be:
- Transformers (Outside, Wall Warts, Power Supplies)
- Dimmer Switchs
- Fluorescent Lightbulbs
- Your Guitar Amp (!)
You can test to see if your Hum is external by plugging your guitar in to your amp, hearing the Hum, and either unplugging your guitar or rolling down your volume. If the Hum disappears, you have EMI, or External Hum. (We can help you here!) If you still experience hum when you disconnect your guitar, your hum is further down the signal chain, like your pedals or your amp.
How Does Hum Enter Your Signal?
Through your pickups!
Your pickups are like microphones, or antennas for magnetic energy. As the signal emitted from these devices (see list above), your guitar’s pickups act as an antennae and “picks up” or “receives” the signal. Once the pickup receives the signal, it induces a tiny amount of voltage in the coil which is sent to the amplifier to be amplified louder.
Single Coil Pickups are the main culprits here. If you want to eliminate 60 (or 50 in other parts of the world) cycle Hum, you need to eliminate Hum at the source – this is where Humbuckers come in!
How Do HumBUCKERS WORK?
Seth Lover patented the guitar humbucker in 1955, and the Humbucker has gone through many, many variations of its design since then. There are many ways to get hum-cancelling – all of which use two coils. You can stack the coils, create a dummy coil, use a Left / Right design (see our Split Blade or Split Jazz Bass), or a simple Side By Side (like a Gibson Humbucker). A Humbucker works by using two coils, and reversing the coil direction and the magnetic direction of the second coil.
Let’s first talk about Single Coil guitars, like a Strat or a Tele. When you use positions 2 (or 4) on your Strat or Tele, you notice that the Hum disappears from the signal. This is just one of the ways to make a hum-cancelling pair. In a Strat, you have your Bridge wound one way, and magnetized one way. Your Middle Pickup is completely opposite – in Coil Direction and Magnetic Direction. Take a look at the image below.
When you choose just the Neck, for example, you get Hum. When you combine the Neck with the Reverse Wound / Reverse Polarity Middle, the Hum gets cancelled out. Two coils put into the same pickup looks like this:
EMI, or Electromagnetic Interference, doesn’t need a Magnet to get picked up. The coil itself really acts as an antennae for EMI. It can ignore the magnetic pull (the Magnet is really for the Strings.) When this happens, it looks like this:
The Black line represents the Guitar’s signal, and the Red line represents the Hum. Another coil wound in the opposite direction would cancel out the hum. HOWEVER: your pickups are now out of phase. We can fix this by reversing the magnetic direction again, to put them back in phase. Remember that the EMI ignores the Magnet? Well check this out – Here’s what happens when we add another RW/RP coil:
The Guitar’s signal is in Phase, but the Hum’s phase it reversed! Let’s put it all together:
There you have it. As you can see, the Guitar Signal is still in phase by reversing the Coil Direction AND the Magnetic Direction, but the Hum is out of phase with itself, cancelling itself out. Goodbye, Hum!
We hope this helps demystify a classic guitar pickup. There’s plenty of ways we achieve Hum-Cancelling – take a look at our Humbuckers page to see what designs we’ve chosen! Until next time!