Notice they're all out of stock. The DIP package for that op amp has been discontinued, and i'd prefer not to use discontinued parts even if there are some left.
I'm very certain that I built the circuit correctly, but I can check it again. Right 6Mhz should be enough, but due to the diode behavior the op amp will go into saturation which will limit the response.
"This basic configuration has a problem so it is not commonly used. When the input becomes (even slightly) negative, the operational amplifier runs open loop, as there is no feedback signal through the diode. With a typical high open loop gain operational amplifier, the output saturates. If the input then becomes positive again, the op-amp has to get out of the saturated state before positive amplification can take place again. This change generates some ringing and takes some time, greatly reducing the frequency response of the circuit
I'll try the second circuit again. I didn't try the improved circuit at the bottom, just hook that up to an RC lpf to output a constant peak voltage?
Edit: I did have the RL's (from first circuit here http://en.wikipedia.org/wiki/Precision_rectifier
) ground connected to a pot with a large cap (100uF) to remove the need for an inverting power supply. I think I also put a high pass filter on the input to move it's ground as well. I guess i need to play aroudn with it a bit more. Point is the first circuit did work below 5Khz or so.