The interaction that occurs between the early germanium fuzz face and the VOX wah is a well-documented effect. There is an oscillation that occurs and becomes prevalent when you stop playing. This oscillation was even used by Hendrix as another effect when performing. Players would roll down the volume when they stopped playing in order to work around this interaction/oscillation. If you choose the fuzz face, this will occur with the VOX wah. If you choose a silicon-based distortion, you will lose the warmth that the germanium transistors provide. If you don't want the oscillation, but you do want the warmth, you might want to check out our JH2S. This distortion unit has the germanium transistors for the warmth, but eliminates the oscillation with special circuitry, giving you the best of both worlds.