I wasn't sure about using the threshold adjustment on my AT Max. I've seen posts saying it only works in All Metal Mode and not in the discrim. modes. I called Garrett. The lady knew her stuff. she said threshold can be used in any mode on the Max. She said neg. threshold can be used to quiet the machine if needed. My AT Max runs good at full sensitivity and -3 threshold with no loss in depth when I air tested. I tested the garrett 8.5x11 and 5x8 coils as well as a nel Big 15x17. all showed almost no loss in depth. If you drop sensitivity 2bars you start to lose depth. But with sensitivity set to minus one bar and threshold set to as low as minus 4 threshold, you don't lose any depth. Here's some average depths with penny, dime, nickel, quarter at those settings in All Metal Mode.

8.5x11 Garrett coil 13.5" to 16" air test

5x8 Garrett coil 12" to 13.5" air test


15x17 BIG Nel coil 14.5" to 17.5" air test

Drop sensitivity 2 bars even with 00 threshold you lose 2" to 3.5" of depth with each coil

Thanks for the info. I wonder how much moisture in the ground will affect your depth retention or loss. Summer here around southern Wisconsin the ground can get almost cement hard. Gotta get down about 8" before you even find any moisture in mid to late August. And thats hard digging. During that time period at a local soccer park complex I didnt find anything more than 3-4" deep and that place has been there about 10 years. So, either nothing deep or the lack of moisture killed my AT-Max on depth. I look forward to the spring thaw when the ground is pretty much mud as I've found a dime at over 15" with the AT-PRO. I'm sure the Max will go deeper in those conditions. We'll see come spring time.