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I'd like to use this RCA jack in a project that detects roughly the volume level on an RCA audio source. The circuit filters out the DC line voltage, amplifies it with a PNP transistor and then shifts the AC audio signal ~+2.5V so an Arduino can read it.

In my circuit I'm measuring the signal on the tip and just pulling the sleeve to ground.

I've read this great post over at CUI and understand that the shunt (pin 3) acts like a normally closed switch between the sleeve and the shunt.

What's the appropriate way to prevent the this from floating and picking up noise when there's no source plugged in? I gather that it's normal to either put a pull-up or pull-down resistor on this type of shunt. I'm just not sure what would be correct here.

For reference, I'm using this circuit as an amplifier with a voltage divider and .1pF cap to between the amplifier circuit and the arduino.

RCA Jack w/ 1-Tip, 2-Sleeve, 3-Shunt

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Just connect pin 3 to pin 1. That way, when the input signal is disconnected pin 2 will be grounded and there will be no noise pickup.

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  • \$\begingroup\$ Thanks! Sometimes the simple answer is just too obvious to see right away. \$\endgroup\$ – Aaron Ciuffo Mar 25 '19 at 8:15

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