gratefulfrog:
Are there any subtle things I may be overlooking here? I can just use the 2N700 as a SPST switch and combine them to make other switches by interconnection the gate pins?
The source and drain terminals of the 2N7000 will act as a switch, controlled by the gate terminal, under the following conditions:
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The source terminal is within 1V or so of ground potential.
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When the switch if off, the drain terminal is no more than 0.5V below the source terminal.
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You don't try to pass more than about 75mA through the switch when it is ON.
These conditions should be straightforward to achieve in the system you describe. If it helps, you can drive the gates of several 2N7000s from the same signal, if you always want them all to be in the same state at any given time.
I'm not sure what you expect to achieve by reversing the phase of a pickup signal, I doubt you will be able to hear any difference. I suggest you try it using a mechanical switch first.