First off, if you select Vox-Wah, and turn the 'drive' to say 3-5 O'clock, In this position the 'wah' effect is either minimal or off & you actually have another treble booster which sounds quite different to the 'treble-booster' in the pedal section. Using it with some of the 'darker' Marshall models e.g. Plexi & JCM800 gives some great 'modded' type tones that lifts the higher frequencies and really gives you a great treble-boost - great for those 'Whole lot of love solo's' where you might want a brighter, slightly thinner, edgier sound from your Les Paul.
Second, if you select Vox-wah & set the 'drive' at circa 11:00am (& just play around with the 'drive' knob to find the right setting for you) you can get that great 'mid-choke' wah effect favoured by a lot of players that gives your tone a really interesting dimension.
Mix with some room reverb & tape-echo delay, crank up your amp - and raunch away! And if you find a setting you really like, just save it as a patch - no more struggling to get that half-choke open sound at a gig with the wah pedal on your VC4/VC12.
Rich


