Yes, there has been some delay between posts, I apologize, but life is busy as usual. This week I wanted to cover the topic of pickups for string instruments. So I play electric bass and wondered the other day how different pickups get different tones and sounds out of them. You can have warm, mellow, fuzzy, even screechy tones all based on the different models.
To answer this, we need to see how a pickup actually “picks up” the string vibrations, and it does so through Faraday’s Law. Faraday’s Law states that changing a magnetic field creates an electric current. Now the magnets mounted on the instrument are static, but the strings which vibrate are not. The vibration of a string disrupts the field and causes an electrical signal to be the output. The only time this is a problem is when a harmonic results in a node occurring over the pickup and register as silent due to the string not oscillating at that point. This is where multiple pickups can be handy as they can add a signal together if both register a frequency or one can register a frequency if the other has a node above it.
Here is a picture of the system used to pick up an electrical signal.
Many pickups are single coil as shown by a single row of magnets. While this may be a cheaper option, it is more prone to interference from surrounding equipment and signals. The most commonly used alternative is a Humbucker.
Humbuckers work by using two coils housing magnets of opposite polarity. This creates signals out of phase in each coil. If these coils connect correctly it results in external electromagnetic fields, such as from power lines, to be canceled out and the guitar signal is doubled.
This diagram shows a simple circuit for a pickup. The resistor for tone effectively acts as a filter for higher level frequencies. Adjust the resistor and the frequencies which get cut also changes. The resistor bellow controls volume or amplitude of the signal before it travels through the cable to the larger amplifier. Every single one differs slightly so that the signals to every pickup on an instrument can combine and create a unique sound.
Thanks for reading!