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I built the following active rectifier schematic on a breadboard, and inputted a 15 KHz 1V peak to peak sine wave from my signal generator.

The output looked like a sine wave and I have no idea why. Attached is the oscilloscope picture. I ran a simulation that said it would work (also attached). I know the signal was amplified correctly (on the positive swing), I could read that on the o-scope....but why wasn't it rectified?

The negative swing on the output was from 0 to -700 mV, which is the forward voltage of my diodes. Is that just a coincidence? The positive swing is from 0 to 1V. Maybe it has something to do with the simulation not accounting for real world characteristics?? Any help would be greatly appreciated.

Attached is another o-scope capture showing the input (blue) and the output (yellow). I think the phase shift is due to the amplifiers.

schematic

simulate this circuit – Schematic created using CircuitLab

Oscilloscope CaptureSimulation using everycircuit.cominput vs. output breadboard

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    \$\begingroup\$ Show us a pic of your breadboard. What did you use for a power supply? \$\endgroup\$ – brhans Aug 28 at 1:23
  • \$\begingroup\$ I added the breadboard picture above. For a power supply I used a 12V input from a AC->DC converter with a 9V rectifier and an inverter for +-9V to feed the amplifier rails. \$\endgroup\$ – Sal M Aug 28 at 1:33
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    \$\begingroup\$ Could you elaborate a little on this inverter? Have you actually measured the +9V & -9V supply rails? And the R1 on your breadboard looks suspiciously like a 10k, not a 1k - maybe it's just the lighting ... \$\endgroup\$ – brhans Aug 28 at 1:44
  • \$\begingroup\$ Well I feel like an idiot, that worked! Guess I was staring at it too long and looked right over it. Interesting that a 10K in place of R1 would cause that behavior though.....I wonder if the math works out...... \$\endgroup\$ – Sal M Aug 28 at 2:29
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    \$\begingroup\$ Just finished up the math, and having a 10K resistor at R1 in my circuit yields the exact results I found on my oscilloscope. It just messes with the summing amplifier in the second amplification stage. \$\endgroup\$ – Sal M Aug 28 at 3:07
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If I am not seeing wrong, you used 10k resistors instead of 1k. Not a bad idea, but then R2 and R4 should be 20k. The breadboard is a mix of the 1st and 2nd schematic. I'm sure this is the problem, and also explans why the negative half has slightly less amplitude than the positive one.

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