Blending Piezo with Magnetic Pickup

[Corcia]

Hi Everybody!
i've installed in my maccaferri manouce (steel strings) guitar both a magnetic pickup and a passive Piezo (K&K Big Shot). first of all signals from the two pickups have (more or less) the same level; i would like to have the possibility to blend them but i can only use thombwheel pots, so a blending pot is not usable.
i've made a first try "copying" the Jazz bass wiring scheme (two independent volumes and one master tone) and implementing it with 2 500k thumbwheel pots but it is definetly not working as expected: when one of the two pots (any of the two) is turned to zero instead of having only one signal (only piezo or only magnetic) the Whole signal goes off, and in any position the sound is pretty much the same, acting on pots does not generate a great difference in sound.
i've checked the wiring more than once and everything seems to be ok...
any suggestion?

[Rick Turner]

You cannot blend piezos and magnetics passively. The pickups' impedances are so different that the lower impedance pickup...the magnetic...will essentially short out the signal from the higher...the piezo. You also cannot use 500 K pots passively with piezos. You can sometimes almost get away with a 5 meg Ohm pot, but piezos only deliver full frequency signal when actively buffered, and a 10 Meg input impedance (which is the "load" on the pickup) is a good starting point. Some will work OK down to a 1 meg load, some need as much as 100 meg.

Take separate outputs and mix them externally.