Here is rev2. I made some changes for the pickup's hight output impedance. V2 and R7 are NOT part of the circuit, but intended to model the pickup for simulaion. The diodes between the two opamp's are intended to protect the 2nd amp from damaging voltage. They may not be needed if use use an LM358, but when I looked at the Fairchild datasheet, it said min input is 0V, so I suggest to just leave them in. ( others will disagree, I"m sure ) Any diodes that will switch at audio frequencies will do for D3 & D4. Switch 1 and 2 can be a 3-way switch, as long as the swtich has 3 seperate pairs of contacts, and is not a 3-to-1. Otherwise, switch 2 can be a spdt. Make sure you use good, medium performance op-amps. A 741 probably won't cut the mustard.