My crossed parallel loop antenna is once again active, with a preamp. It started out using an LZ1AQ preamp, then went passive when that amp died (due to moisture). Now it is active again, with one of Everett N4CY's version of the LZ1AQ amp, with 2SC5551 transistors. The preamp is inside of a short piece of 2" PVC pipe, with end caps, and lots of silicone sealant around all the holes for wires

On LW and MW I can get decent nulls with it, sometimes very deep, WHP 580 out of Harrisburg PA can be nulled by over 30 dB. Not directional on HF, as expected, but it works quite well, signal levels sometimes not much weaker than my full size wire antennas. It also works quite well up on 11 meters.
I can highly recommend both N4CY's preamp as well as the crossed parallel loop overall.
For reference here is my original post about the antenna build:
http://www.radiohobbyist.org/blog/?p=2340