How To Connect A Guitar Preamp To An FX Return Loop


Let’s look at how to connect a guitar preamp to an FX Return loop on a tube amp.

Guitar preamp pedals such as those from Kingsley Amplifiers and Two Notes have become a popular method for adding variety to your guitar tones both live and in the studio. To achieve this you simply plug your guitar into your preamp, connect the output to the ‘Return’ jack on your tube amp. It’s that simple. There are however a few points of interest along the way, here’s a few of them.

A little Valve Amp primer

Valve amplifiers often comprise of two sections. The preamp section typically governs the tone controls (treble, bass, mid etc) in the amp. The power section typically manages the output to the transformer and the speaker.  Of course, other variations occur too.  It stands to reason then that replacing your amp’s preamp stage with another will affect it’s tone, headroom and perhaps it’s feel (dynamic response).

Here’s a great video from ‘That Pedal Show’ that demonstrates in depth how different preamps and drive pedals sound when connected to an amps FX loop.

FX Loops in general

Let’s start by pointing out that not all FX loops are created equally. FX loops were initially created for connecting FX pedals to your signal chain. Be aware that not all FX pedals are suited to connect to the FX loop on your amp. Typically, Choruses, Flanger and Delay have been  the appropriate candidates, overdrive and distortion have not. This artical will only cover connecting preamps to your FX loop as a method of replacing the front end of your amp with another.

Connecting the Preamp

At the risk of stating the obvious yes, only one of the slot’s is used on the amp, namely the one marked ‘Return’. Here’s a real basic diagram:

Connecting a preamp to an FX Return loop on a valve amp

Tone Controls on the amp

When a preamp is plugged into the FX Return loop your amplifiers tone controls will no longer be in the signal chain. In other words they will have no effect. This is normal. Also note that the sound of the power stage of your amp without the preamp engaged may sound a little muffled. When you engage the preamp pedal again it will sound better.

Features on the FX Loop

Other features are sometimes added in the form of switches that change the signal level from instrument level (such as a guitar) to ‘Line’ level such as +4dBV. Some offer a true bypass switch for the purist’s too.


For more information about guitar preamps please see my artical on “Getting Great Guitar Tones With Guitar Preamp Pedals:

Hope you found this useful. Till next time…..