Hi Tom,There are actually two parts to "supertuning a Tesoro". The first part you know, and that is to turn the threshold to maximum. The second part is not so well known.
The second part consists of adjusting the ground balance on those models that have an external balance control. Normally, this second adjustment means you adjust the GB such that when you lower the coil to the ground, the audio goes quiet when in the AM mode. This is done to compensate for the offset installed.
When in the Disc mode, one can simply turn the GB back while sweeping the coil close to the ground. Once you begin to hear "false" signals from the ground response because of the sweep, you have gone too far. Turn the GB back some from that point until all false signals just quit.
Normally, manufactures, Tesoro included, will build detectors such that the disc mode GB (ground balance) has an offset in the GB control when compared to the AM mode. This is done to eliminate false signals from hotrocks such as magnetite when the detector is properly ground balanced in the AM mode.
So, on many if not most detectors, the ground balance is always somewhat positive in the disc mode, when the GB is properly set in the AM mode. By adjusting for no ground signal offset when in the disc mode, the depth will be enhanced even more. Unfortunately, when this is done, then the AM mode doesn't work that well.
On a few of the early motion detectors, the AM mode and the disc mode were directly effected and there were no offsets. So, when the ground balance was adjusted for proper adjustment in the AM mode, certain hotrocks would cause a strong negative response in the AM mode. These same rocks would then cause a funny squall in the disc mode also. Once the offset was installed, the hotrocks no longer were a problem.
Since most people didn't understand the reason for the hotrock problem, it was easier to build in an offset than try to explain there was really nothing wrong with the detector.
Reg