Summing Amp for multiple coils

[Chris Turner]

Does anyone know if something like the Summing Amplifier Example 1 from https://www.electronics-tutorials.ws/opamp/opamp_4.html could be used to sum the signals for two or more coils?

[Dave H]

You could use that example but you might want to buffer each coil with a unity gain buffer with a 1M input resistor. A single quad op-amp could be used for three coils.

[J M Fahey]

True, that summing amplifier has low input impedance.
Each pickup sees its own Rin which is usually lowish, say 47 k or so, which loads it down.

You CAN use Rin=1M and Rf 1M for unity gain, but mixer becomes noisy , because it sees each pickup through a 1 M *series* resistor.

Notice it does not actually sum "voltages" but "currents" , shown as I 1-2-3

Another side effect is that it inverts phase.

[Helmholtz]

FWIW, high impedance PUs need to be terminated by a capacitance (typically provided by the guitar cable) to produce their characteristic sound. As active electronics isolate the PUs from the cable, it may make sense to add suitable capacitors wired in parallel with the coils.