Tips & Tricks: Multi – Amp Setup – advantages and pitfalls

I guess none of the guitarists who have ever used more than one amp simultaneously would dispense with this kind of sound.
Regardless of whether you use a stereo setup, running a delay through both amps or chose a wet dry setup with the wet signal coming through the first and the dry signal through the second amp, the sonic enrichment will be amazing.

Some of the digital modulation effects already have a stereo output that can be used with two amplifiers.
But a setup with more than one amp is also more prone to mistakes.

Ground loops and hum

To avoid ground loops it is important to make sure that all amplifiers and the pedalboard are connected to the same power supply.
Ground loop hum arises when the signal chain is connected to different grounds.
If you notice a ground loop (by recognizing a low frequency hum coming from the speakers), please, do never (!) disconnect the grounding of the power plug.
This was very popular in the 80s but it can be life threatening or even lethal.
Today there are some useful devices that are able to eliminate the ground loop hum without endangering your life.

Phase cancellation

It is also problematically when the combined amps do not work “in phase”.
Phase cancellation emerges when the speakers of the amps do not work parallel.
In other words: one speaker moves forward first the other one moves backward first while the signal is produced.
This phenomenon occurs for example when the amplifiers work in different ways or when the speakers are wired differently.
By re-wiring one of the speakers or – faster and easier – with a device with a phase shifting you can simply rectify the phase cancellation.

Lehle

The Lehle P-Split II provides a very good solution for this kind of problem.
The galvanic disconnection of the signal avoids the appearance of ground loop hum.
Additionally, the Lehle P-Split II offers the possibility to shift the phase of the signal which can be pretty meaningful when you combine two amplifiers.

The Lehle Dual SgoS works with the same galvanic transformer but offers beyond that the option to control the different outputs separated from each other and to save your adjustments.

Radial Engineering

The Radial BigShot ABY also isolates the signal via a transformer to eliminate the hum. And it similarly enables you to shift the phase of one of the outputs.