Method
When amplified in some capacity, the tuba and euphonium are both capable of using analog effects pedals. As in an electric guitar or bass, there needs to be some way to get from the instrument to the pedals themselves. Since miking the tuba or euphonium involves sending a signal out at microphone level, there must be a device of some kind that amplifies the mic level signal to instrument level. In the author’s experience, this is accomplished easily with some sort of on-stage mixer, or with a pedal designed to accept mic level signals (one example being the Boss RC-30 loop pedal, which has a built-in XLR input).
As described in the previous entry, an effective way to isolate the tuba/euphonium acoustic signal is to place a contact mic on top of a wooden practice mute, and then feeding that direct signal into the pedals.
There is virtually no limit to the ways in which the tuba and euphonium sound can be used in combination with effects pedals, and experimentation is highly encouraged.
Necessary information
For tubas and (to a lesser extent) euphoniums, it is helpful to use effects pedals that are specifically made for electric basses. Although there is not a huge difference between guitar and bass pedals, the latter are built for the lower frequencies encountered with the tuba and euphonium.
Amplifying the mic level coming out of the tuba to instrument level brings the risk of feedback, as the extra gain makes the signal more prone to getting out of control.
When using effects pedals, it is often better from a technological standpoint to have the sound of the pedals routed through an on-stage amplifier or speaker. Suitable choices for this include bass and keyboard amplifiers, as they both extend into the low range of the tuba and euphonium.
Notation
If the composer wishes to have the performer switch between multiple effects pedals during the performance, it is vital that the score clearly mark the changes when they are to occur. Suggested methods include a graphic component that indicates certain pedals, or the use of a staff whose lines indicate whether a pedal is off or on. See the musical example for a depiction of these methods. The works listed below by Clinton McCallum and Ruby Fulton in particular also give very clear demonstrations of this technique.
Relative Difficulty
Intermediate to Professional
Works to consider (bolded titles are particularly representative examples of this technique)
Wouldn’t Need You – Nicholas Deyoe
Jejunum Pummeller – Clinton McCallum
The Composer's Guide to the Tuba 