Can you use a SPST to turn on and off two power sources?

Question

I have several batteries in series and the ground point is in the center, such that I can achieve a negative and positive voltage. The OP amp uses both negative and positive voltage. Let's assume I am using two 9v batteries.

If I were to place a SPST on ground, is this sufficient? My confusion/worry is if I have the switch open, then it essentially is creating a 18V source:

With the switch open, the chip will have no source to the battery center tap. This seems safe but the chip would still be connected to both ends of the in-series 18V source (since it required the positive and negative 9v.)

Could the circuit somehow be closed inside of my op amp and pump double the voltage through my chip? Should I be using a DPST like this instead:

Answer 1

Your first drawing would leave your circuit powered by the full battery supply (+/-18 V?).

The second drawing, with the double pole switch will work, but it is more common to put switches in the "hot" wires, rather than on the ground side (or center, in this case) of the circuit.

Answer 2

You do have to use two switching elements, but not necessarily a DPDT switch. A SPST with several MOSFETs can cut it too:

^{simulate this circuit – Schematic created using CircuitLab}

This circuit works by controlling two switching elements, two power MOSFETs here, with a single SPST switch. If you used to need switched rated at several amps, this circuit calls for power MOSFETs rated for several amps but a switch rated for a few milliamps.

When the switch is open the two MOSFETs' gates are pulled to their respective sources, preventing both MOSFET from turning on. When the switch is closed the two gate resistors R1 and R2 forms a voltage divider, putting a voltage around 0V at both MOSFETs' gates. M1 will see -9V gate-to-source and M2 see +9V gate-to-source, turning both MOSFETs firmly on.