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Getting the most out of your GP Extreme, by Jack Lange

© 2001 Jack Lange

Jack Lange
World Famous Australian Professional Prospector and Gold Tour Guide.

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The GP extreme is the best goldfields detector ever made but many operators aren’t getting the most out of it because they aren’t fully familiar with its controls or potential. It behaves and sounds differently to the SD2200D and preconceived ideas have to be put away. It is more hi tech, and sensitive and capable of getting more gold but takes a little understanding.

Firstly after turning it on, it can take a couple of minutes to warm up and allow its magnificent ground balancing ability to operate smoothly. Any tests done during this initial couple of minutes will be incorrect. On odd occasions my GP has “chattered” a little, particularly on hot windy days. This slight hiccup goes away of its own accord after a minute or two and shouldn’t be considered a fault. In these conditions it pays to use the “tune” button to stabilise the machine at the beginning of such extreme conditions. As I said, the ground balancing ability of this machine is the best yet, and I was able to use the big 24″ UFO mono coil everywhere I tried it in North QLD, though some areas were quite mineralised.

Simple to Use
The GP has a number of new switches which can be confusing at first, but a beginner cant go wrong by simply leaving them all in “normal” position, where coils and conditions being equal, it will still outperform the SD200D. But to get the most out of the GP there are certain settings to be aware of.


As most users realise, when using a DD coil, the “E” setting converts the coil to a mono by isolating one of the D windings in the coil. This makes the coil more sensitive on small gold, but it will not be as powerful as a true round mono coil of the same length, on nuggets of several grams upwards. A round coil will always detect deeper than an elliptical, or single D coil winding of the same length. You would not use this “E” setting in very hot ground, as the “normal” or double D setting will smooth out ground noises far better.

The users manual doesn’t suggest it, but while using any double D coil in the “E”
(mono) setting I was able to use the discriminator to detect surface iron. The discriminator didn’t work as well as it did on the DD (“normal”) setting but it still helped to a degree. By the way, the discriminating ability of the GP has been noticeably improved over the SD2200D, and it will discriminate more deeply or on smaller iron targets, almost to tack size. A powerful magnet can save a lot of scratching around in the dirt for those tiny ferrous bits.


This control doesn’t affect the volume of the threshold as might be expected. Rather it affects the strength of the signal on both quiet and loud targets. The manual explains this clearly so I wont elaborate here. But As the GP has more threshold and signal volume than the SD2200D, I have not needed to use an external volume control which is what a “signal enhancer” really is. Some operators use one for more volume control, although most operators probably wont use an enhancer on this model. I personally would have preferred a plain volume control on the GP Extreme which affects both threshold and signal volume, just like the old time detectors had. I have always left the GP volume on max which means I occasionally have to put up with a large target blast.


This control is really a bonus because most detector operators didn’t expect it and hadn’t come across one before. It does have some benefit but it’s not a huge advantage and Minelab could have easily left it off. I use it on maximum because it makes the signal stand out more clearly in that setting, however, in really noisy ground, the signal stands out more clearly with the dial wound down a bit. In 95% of soils you cant go far wrong by having it set anywhere between 80% to max.


It’s amusing to hear all the different theories on threshold settings. Even some experienced operators debate this point. You would think they invented the machine instead of Bruce Candy, who said that we should set the threshold to a faint setting for maximum sensitivity. A threshold that’s too loud will drown out those faint deep signals. If you turn the threshold down till you can’t hear it, you will loose at least 15% depth! With the SD series, I found that when used with an enhancer, I got best results at the faintest possible stable setting, however the GP needs a slightly higher setting to give the best deep nugget signal.


Many operators are aware that the GP manual recommends “fixed” position for certain circumstances. But they think this only applies when swinging the coil over a faint target, so that you wont cancel the signal out. However the “Fixed” position also gives you a little more depth than the “tracking” position. When I am detecting new ground and speed of ground coverage takes priority, I leave it in “tracking” because the slight depth loss is of no concern. Once I find that new patch, then I use “fixed” for maximum depth. I slow my swing, relax and concentrate on those faint signals. Occasionally, I may need to switch to “tracking” to reground balance for a few seconds before I switch back to “fixed.”


This switch is no gimmick. It does increase depth on small gold and should be used if conditions permit. It works on nuggets of up to very approximately three grams. It depends on nugget shapes and their surrounding soils. The next time you get a small faint signal, flick over to ‘sensitive’ and see if the signal doesn’t get louder. It usually does. The downside is that on nuggets over a few grams you will actually lose depth but strangely enough, once the nuggets get to about 2 ounces, the ‘sensitive’ setting increases depth again! So be selective in using this setting. In very noisy ground don’t use it at all.


According to the manual, you only use this setting for deep bigger nuggets, but I find that it increases depth on small nuggets as well. I know of some experienced operators who use this setting all the time. I don’t, because it tends to make an invasive groaning noise that tires me, however when maximum depth is required in a selective area, say a deep concentrated patch, I use it to gain a couple of centimetres extra.


When detecting the salt lake areas of W.A, the depth advantages of this setting are phenomenal. If you are touring around W.A with a GP, then you have a real weapon in your hands.


Setting. Some of my customers are targeting areas near or under powerlines with good results because this setting enables you to detect very close to electric cables. You only lose a little depth in this mode when using DD coils, but when I tried this setting with the big Mono UFO coil, the detector barely worked, so I gather it only works with DD Coils.


Correct coil selection with the GP can make a huge difference to your success. I have generally preferred the Coiltek Manufacturing 24″ UFO mono elliptical coil for the following reasons.
1. The GP Extreme mates beautifully with mono coils generally.
2. I can get to the gold more quickly because of speed of ground coverage.
3. It gives the best depth on nuggets from about 1 gram up to several ounces
4. It is light and pinpoints well. I don’t use the skid plate, as the coil is so tough I doubt I would ever wear it out.
5. It will detect nuggets down to a fraction of a gram

For terrain that is too grassy or dense for the 24′ UFO then the 17″ Mini UFO is preferred as you can poke it around grass and bushes. Also, it is more deadly on the smaller gold.

Naturally if the ground is very mineralised and you cant effectively use a mono coil, then a double D coil is essential, and I use the 14″ Coiltek Manufacturing for bushy areas. In more open country where speed of ground coverage becomes important I would use one of the larger DD coils.


To get the absolute maximum depth on small nuggets, (conditions permitting) try the following settings on your GP: Fixed ground balance, Threshold slightly higher than absolute minimum. Maximum volume and signal control. Experiment with “Deep” Mode but if it gets too noisy, turn it back to “Normal.”
Use a 14″ Coiltek Manufacturing Mono or 17″ mini UFO mono. If the gold is around match head size use a 10″ Coiltek Manufacturing mono elliptical (definitely not in noisy ground)
Try this experiment. Bury a piece of metal about the size of a 1 gram nugget about 6″ deep. Set your GP in tracking mode in “normal” settings and listen the to the faint signal over the buried nugget. Now switch to “fixed”, “sensitive” and “deep’ and test the same target. You will be surprised at how much stronger the signal becomes, because you’ll be detecting deeper. If gold producing ground has been detected before with a SD2200D or SD2100 detector and they used a good mono coil-say 14″ round or 24″ UFO, and you search that same ground with a GP using a standard 11” coil you may be disappointed with the results. But if you try the above suggestions with the best mono coils and listen for faint signals, it can make all the difference.

As I said, if all this confuses you, don’t worry, start by using the standard coil and all the settings in “Normal” and you will still be using an excellent machine, but with experience, you will find extra advantages by experimenting. Good Luck out there!