Ok some wisdom from JP for detecting the deep with a DD[ a cut/paste]
Here are his suggested settings for a GPX 5000 (or 4500) for use in deep highly mineralised soils using Normal or even Sharp timings, using a B&Z Booster and dual speaker system wired in series.
Front end cap:
Search Mode: General
Soil Timings: Normal/Special
Coil/Rx: DD
Ground Balance: Tracking/Fixed
Menu Settings:
Main Menu:
Backlight: 0
Battery Test:
Volume Limit: 8
GB Type:Gen
Special: Sharp
Manual Tune: 128 (wherever threshold is stable)
General Menu:
Motion: Slow or Very Slow
RX Gain: 11
Audio: Normal
Tone: 60
Stabilizer: 20
Signal: 19
Target Volume: 8
Response: Normal
Tracking: Medium
Iron Reject: Off
OK now for coils, this is where you need a Hipstick or a PRO-Swing 45 because DD coils are heavy and for this application you need the biggest one you can swing, my preferred coil for this type of detecting is a Coiltek 24" monster DD, I've found slugs up to 21 ounces at depth using this method so be rest assured it works! In a pinch the Minelab 18" Commander DD is a good option or if you can find one a Nugget Finder 20" DD but their rare as hens teeth these days (I have one stashed away here somewhere

).
You will notice in the settings I've chosen Normal over Deep in the Audio filtering, there is good reasoning for this, the gains made on large deep targets using Deep audio is negated by the Stabilizer, the Stabilizer will provide far and away more info than Deep could ever do, if you try to combine the two you will drive yourself nuts with the signal response, so keep it clean and simple and use Normal audio. In a pinch you can opt for Quiet mode but it does take a lot of information out of the signal train so be prepared to learn that methodology too.
Now your probably wondering about EMI? EMI is less problematic when using a Normal type timing compared to Enhance or Fine gold, the Smooth class of timings use a lot more inbuilt Gain compared to Normal timings and as such tend to be more problematic in noisy areas, to convince yourself of this detect for an hour using Normal then swap to Fine Gold and listen carefully to the threshold, you will notice a gritty wavery instability to the threshold, after an hour your brain will filter that noise out so you don't even notice it anymore, it is this trickery I want you to tap into in getting your brain trained for the extra information provided by the elevated Stabilizer settings.
The Stabilizer is a control that lowers and raises the threshold floor filtering, lower numbers raise the floor allowing less information through thereby presenting a smoother sounding threshold to the human ear, however you are also removing good information, higher numbers lower the floor allowing more info in but also making the detector sound jittery. If you run it flat out for a long period of time your brain will start to become conditioned to the noise so that when you back off to a lower number the threshold will start to sound stable again but you will now be able to run a much higher number than you would have been able to previously, your aim is to run the Stabilizer around the 17 to 18 mark.
Once you've conditioned your brain you can then start to experiment with Gain, I would rather see a lower than FP (11) Gain setting than back off on the Stabilizer numbers, however none of this is set in stone and your particular detecting environment and personal experience will dictate your final choice.
For those using old technology like the SD2200d set it to CH2 and Deep run at least an 18dd,Get a booster for it and set threshold paper thin.Less racket and far more effective on triangle dirt
JP