Korpa 
The FS-14 is the ultimate companion for your HT MKII amplifier. Giving you maximum control over your rig, you can effortlessly switch between all three amp channels and their modes on the fly. This ergonomic footcontroller lets you instantly change your sound for the next big section change or song in your setlist.
The Boost and Reverb switches give you even more options, letting you get the most out of your HT MKII amp. Just click the Boost switch for an extra kick of “more”, perfect for letting your solos punch through the mix and get heard! The Reverb switch gives you access to the improved digital reverb onboard the HT MKII amps, enabling you to add some vibe to thicken up cleans, riff and solos.
Here's what Blackstar say about the FS-14 Footswitch Controller:
The optional 5-way FS-14 Footcontroller enables easy access to all Channels and Voices on your HT MKII amplifier. Not only that, but a global Boost function and Reverb switching offers maximum control over your HT amp.
