It is recommended that the MERCURY vacuum tube fuzz is placed first in your signal chain. There are several reasons for this. Firstly, the tube input stage of the MERCURY can interact with your pickups when connected directly to your guitar which allows for greater tonal variations. With the guitar volume up full the Helios can create some devastating, sustained, hairy fuzz tones, however when the guitar volume control is rolled back the MERCURY will clean-up to produce some beautiful and natural sounding (real!) tube bluesy overdrive tones. Additionally, the MERCURY has an incredible amount of gain and is super sensitive to any incoming signals and noise from other effects pedals – it will magnify anything you put into the input. This means any hiss, hum, small switching ‘pops’ or ‘thumps’ may become obtrusive. So for best tone and lowest noise results MERCURY first!