This update of the MkI A/B-Y (first reviewed summer 2009) has an improved circuit, plus off/true bypass and phase reversal options.
Unchanged is the stainless steel case, meticulous hand wiring and quality components, on/off switch, unique ring-pull battery release and screw mounts
for pedalboard fixing.
The two knobs adjust each output's level; most of the travel is below the amps' own levels, after which you get a small clean boost of up to 4dB.
Try as we might, we couldn't induce a ground loop hum thanks to output B's isolated transformer that has a phase reversal option should you experience phasing issues between your amps.
With the pedal off, output A remains true bypass, letting you compare the Mosfet circuit and the bypassed tone; a minute difference is evident, with less presence and high-end when the switcher is on.
Adding pedals to the signal chain exacerbates that difference, depending on pedal type, the volume you're playing at and how fussy you want to be: only true, true bypass is ever totally tonally transparent.
You can buy a less expensive A/B-Y switch, but it won't be hewn from steel in England and designed to last a lifetime or three.