The SD2100 is a great machine used one for 10 years (standard, not modded) rarely used any coil other than the 18" mono.
Somewhere on one of the forums I put up the tuning method that I mastered. (And it works) That machine talked to me, used it on ground that others said was impossible with a mono.
Finally sold it and upgraded to the 4500.
Found an old link with my tried and proven method.
https://golddetecting.forumotion.net/t1323-sd2100-improvements?highlight=sd2100+tuning
Just in case the link doesn't work;
Hi Zac,
Here is a sure method for setting up your SD2100;
Tuning your Minelab SD 2100:
Firstly you probably HAVE missed many nuggets with your SD "warbling" in your earphones. When I now get the slightest variation in the "hum" I scrape off the top layer of rocks, grass etc and if the signal has improved it is usually a small target, hopefully a nugget.
Getting back to tuning:
With the machine turned on and holding it at waist height with base of coil vertical, rotate 180deg, noting which direction the warbling is greatest.
Lay the detector and coil on the ground with the coil tilted up at about 45/60 deg and facing direction of strongest interference.
Place one hand on the box to keep it steady so there are not any false signals (as you can well imagine the 1 & 2 balance positions are not ultimately tuned at this stage) with your other hand using the small screwdriver, rotate the tuning screw clockwise. (At this point it may be easier to remove your back pack and lay it next to the detector) If you haven't achieved any improvement after say 20 rotations clockwise, rotate anticlockwise for 20 rotations (back to starting point) then keep rotating anticlockwise for another 20 rotations. (This pot does not have a "stop" so it may take time.)You may feel like a bit of a dork out in the middle of nowhere down on all fours with your butt in the air but believe me it is worth the effort.
If you persevere eventually the threshold will become a steady Hummmm! You will only need to readjust if you move to complete new mineralised ground or your machine again becomes unsteady. After you have your machine humming steadily stand up and go through the 1-2 positions of balancing your machine.
At this point it is advisable to select the Tone that most suits your hearing.
Using a small target (shotgun pellet is ideal) scrape a small hole and place target in the hole. Now swing your coil across the target, vary the tone until you get the clearest/ sharpest signal that suits your hearing.
LOW and SLOW and ALWAYS investigate any change in tone no matter how slight, those little grammers soon add up.
Pinpointing your signal:
When a signal is targeted, draw a line through where you think the target is, now step around 90deg and again swing and again draw a line through where you think the target is. Where the two lines cross will be approximately where your target is laying. (After you become confident you will find only imaginary lines are required.)
Coils:
Mono coils have a different target centre to your DD coils, practice with both using previous pinpointing method until you are confident. If the ground is highly mineralised and your machine continually chatters you may need to use your DD coil only.
Tip:
If your signal varies considerably while using the pinpointing method it is quite possible your target is ground noise. (Scrape of the top layer of dirt, the signal should increase if it is a target.)
Good luck on your next visit to the goldfields.
Regulator:
12V regulated to 7.2V is the way to go, add to this a signal enhancer and you have a very efficient detector.
Nightjar
