/sci/ - Science & Math

What the fuck is wrong with this circuit? It seems sound in theory, but when I breadboard it up, I get all sorts of crazy numbers.

Here's the idea: The op-amp is wired up as a precision rectifier a.k.a a "super diode" with an unequal value for the input and feedback resistors such that when the signal is rectified, it is also amplified. When the switch is closed (on), a small signal of ~150mV AC goes in, and a half-wave rectified and filtered DC output of about 2.8V should be the result (when the voltage divider pot on the output is set to 5k ohms). When the switch is open (off), the circuit gets no signal, so there is nothing for the op-amp to pass and rectify, and so there should be no output at all. Normally, with no signal, the voltage at TP1, TP2, TP3, and the output should all be 0V.

When I actually breadboard this thing up and power it, TP1 and TP3 read ~4.5VDC, TP2 reads as ~5.4VDC, and on the output I get ~1.5VDC /with no AC signal on the input/. When I add the signal in, I get no change.

The op-amp I'm using is one half of a TL082 dual op-amp. I've tried each side of two different TL082 chips, and used both a bench power supply and a 9V battery. I've checked and rechecked the connections, even to the point of 2 complete scrap-and-rewires.

What is wrong with this circuit?