Carl Martin Octa-Switch Mk3 Pedal The Octa-Switch MK3 has two external switching jacks for changing channels on your amp(s), or other operational features. The Octa-Switch MK3 has nine switches, the eight are presets and the ninth is an effect Bypass, which will bypass the Octa-Switch MK3 to your un-affected amplifier sound. The Octa-Switch MK3 has stereo outputs as well as the stereo return on Loop 8 (this is a stereo jack with tip-left and ring-right).