The Funk Machine is a filter effect that can be used on either bass or guitar (or synth, Rhodes, harmonica, etc). It's also like an auto wah, given that the wah effect is controlled by the string attack of the player. Original units used 2, LM741 chips, but I've laid it out for an LM1458 (which is 2, 741 in a dual op amp). Don't try to use a TL072 or JRC4558, as they will not work in the circuit. Check out the discussion of this circuit over on Tagboard Effects for more info.