Minelab’s multifrequency BBS (Broad Band Spectrum) detectors such are the Sovereigns and Excaliburs are known to ignore iron. You can turn on the threshold tone to audible, which gives a whiny hum (it can be a pain if you put it too loud). Go over iron, and the hum will disappear, making the detector silent for a moment.
My first Edition Minelab The Sovereign (1991) works fine with the Minelab coils, which normally do not detect iron. When I finally got my Detech 12″ coil and went to used it on the beach for a whole weekend (almost 10hrs), I only dug these iron/rusty stones. What a disappointment, after an earlier 3-hr hunt which gave silver and coins with the small coil. I lost so much time digging these iron blobs, which were also often quite deep. I thought it wasn’t the same behavior as my small Minelab coil, so I tested the coils at home with some of the iron/stoney things.
–Lowering sensitivity would make the detector react on a smaller distance, so you wouldn’t be digging the deep blobs anymore, but you lose sensitivity. Plus, in comparison, the Minelab coils still would give NO reaction at all, even if you rub the stone against the coil.
– Changing Disc and Notch is not helping either. Again losing depth.
Luckily I can use the coils on my Excalibur the same as the original coils, so I can use them without digging any rustballs. I do have a word to say about Detech service: it is non-existing. I wrote English and Bulgarian (?) mails to ask for more information but they never even replied. The shop where I bought it from would replace it, but asked a lot of questions whether I had used the correct settings (groundbalance, disc..) so seemed the guy didn’t know how the BBS detectors work. I gave up until I cut the cables from my Excalibur and tested the Detech on this detector, which worked fine. So I figured the problem was not the coil but the old Sovereign. Wanting to go even bigger and refusing to buy any more Detechs, I bought a 14″ NEL Thunder coil, knowing it would probably not work on Sovereign but I’m ok using it on the Excal. I know the online sales page often lists the Sovereign models without the first type, but now you know why :p
I recently had an offer to buy a Sovereign Elite (about 2002) for a low price but I’m not sure that is going to happen, since the guy isn’t replying to my messages anymore. I can only contact him via the secondhand website. I assume this version works with all 3rd party coils so that would make it possible to go out and not use the Excalibur, which is still a bit of a fuss with all the headphones and straps.