Hi ronv,
I have attached the Circuit that nearly works, but not reliably. There have been constant modifications from the original circuit a year ago, some you can see.
The problems seem to be the large range of coil signal due to: Signal WIRE variations, and distance of coil to the WIRE. The main problem is low WIRE signal (I can control it somewhat, but once it's up to the highest level, this might still be too low if the coil is too far away...say 6 inches) The 2N3819 circuit was added that did the job, but caused the -IN pin on the LM324 to go below 0.3v making the internals collapsed.
With your circuit, it seems to me as an amateur, to be more robust. If it was possible to add a 2N3819 to the front of your circuit, as long as it doesn't cause damage, I think I could control the WIRE input to give the correct signal power.