A previous review of this pedal initially made me hesitate, but I’m glad I gave it a chance. I don’t know what active bass was used in that other review, but I can confirm it works great with a Dingwall NG3 (Darkglass preamp), a bass with EMG-J pickups and EMG EQ, and another bass with EMG MMTW and MMCS pickups paired with a Darkglass preamp. All of these are 18v circuits.
This Morley wah absolutely screams the way it should on the six Metallica songs where Cliff used it (Anesthesia (Pulling Teeth), Seek & Destroy, For Whom the Bell Tolls, Fade to Black, The Call of Ktulu, and Orion). It shows just how powerful this effect is for metal bass — a sound we sadly only got a glimpse of because of Cliff’s early passing.
The controls are simple: fuzz is on/off, and the wah engages when you press down the expression pedal. At first, it can take a moment to find the “sweet spot” where the wah clicks in, but once you get used to it, it’s reliable. Keep in mind that Cliff often left the pedal parked with his foot in a resonant spot instead of rocking it constantly like Kirk does. There's no wet/dry mix for the effect, so definitely some of your bass frequencies will get cut, but that's the authentic sound of a fuzz pedal. This unit should be used for solo, not to follow the song.
Overall, I’m really happy with the sound this pedal gives my active basses. One tip: put a compressor before it in the chain — it keeps the signal tight and avoids pops or cracks.