What is the FX loop in my amp? How can I use it? Should I?
Many guitarists have seen the FX loop behind their guitar amplifiers but the people who actually know how to use the effects loop are not as many. No need to be afraid of it, the FX Loop is your friend when you want to insert certain effects to your sound, like modulations, delay, and reverb pedals.
What does the effects loop do?
1- What the heck are the preamp and power amp?
2- Why would it matter to place an effect before or after them?
So let’s start with the basics:
What is a preamp?
A guitar amp has two main sections inside, the preamp and the power amp. When you plug your guitar to an amp head and pluck a string, the guitar signal first arrives at the preamp stage. This is where the tone gets colour, in other words, this is where the amp affects the sound and people hear the differences in different amplifier brands. It amplifies the weak guitar signal to a level that the power section can handle it. Giving too much gain to the signal in the preamp gives overdrive and distortion.
What is a power amp?
A power amp produces a high current signal after the preamp to drive the loudspeakers. Commonly, the master volume knob controls the power amplifier. Power amps do not affect the tone in a noticeable way, in most cases they are designed to be transparent.
How to use the effects loop?
Here’s an example. You have a reverb pedal and you connected your guitar to this pedal and then connected its output to the guitar amplifiers input. Now your guitar signal first arrives at the reverb pedal, your tone gets reverbized and then it arrives at the preamp of the amplifier where the amp gives you overdrive. Now you are overdriving a clean signal with reverb.
If you would like to have your sound overdriven first and then you wanna add reverb to that overdriven sound, you would need to place your reverb pedal after the preamp. This is where FX loop saves you. You should connect your reverb pedal to the FX loop section of your amp (FX send into the pedal input, and pedal output to the FX return) and now your reverb pedal is placed after the preamp. Now you can connect your guitar directly into your amplifier, get any tone you want from the amp and your reverb pedal will affect the tone after the signal passes the amplifiers tone stack.
Why would it matter?
Because giving overdrive to a reverbed guitar and giving reverb to an overdriven guitar are two different sounds. Using the same guitar effects does not give the same results when you place them in different orders and the FX loop lets you insert guitar effects after the amp. You can learn more about the orders of the effects in the signal chain in this post.