Minelab article GPX 4500 (with permission).

Minelab has given permission to post this GPX-4500 overview, which was written in May 08. Apologies in advance if you have already seen it. I was after some information to try to understand how the 4500 is different to the 4000. It was written by Nenad Lonic, one of their technical sales people.


An overview of Minelab’s GPX-4500 Gold Detector

On April the 7th 2008, Minelab’s new flagship prospecting detector, the GPX-4500 was released to the market. Although the name may suggest only a minor upgrade, Minelab have been able to squeeze an impressive range of improvements and new features into the hugely successful GPX-4000 platform.

Here is a quick summary of some of the new features found on the GPX-4500:

- SETA technology. (Smart Electronic Timing Alignment) to give greater stability and improved immunity to highly magnetised ground conditions.

- GB (ground balance) Off mode, for improved performance in non-mineralized soils.

- 6 pre-programmed Search Modes, to suit different detecting conditions: General, Deep, Patch, Hi Trash, Hi Mineral, Test A. All modes can be fully edited.

- New Enhance Timing – minimal ground noise, high sensitivity, good depth. For use in highly mineralised soils. Improved depth and sensitivity over Sensitive Smooth.

- New Sharp Timing – maximum depth and target response in milder soil types. Can be used to verify and locate faint signals.

- Target Volume – used to boost faint signals in quiet conditions for both headphones and speaker use, or can be reduced to smooth out random ground noises in highly mineralised soils.

- LCD is now backlit, and has an adjustable auto time-out to preserve battery power. It automatically switches back on when the Function Select or Setting knobs are moved.

- Audio Stabilizer – fine tune your selected Audio Type, for maximum stability and performance. Allows the user to set the point at which faint signals are audible.

- New heavy duty power cable, with over-moulded boots for maximum durability.

- Improved battery harness. Thicker straps and reinforced waist strap for improved support and a more comfortable fit.

- Modified end caps for greater control box adjustability, and improved balance when using larger coils.

- Li-Ion battery with built-in amplifier, to allow the use of an external speaker.


Here is a look at some of the new features in more detail:

PRE-PROGRAMMED SEARCH MODES

The GPX-4500 offers pre-programmed search models, for easy ‘switch-on & go’ detecting. In addition to the General and Deep search modes are four Custom modes which are accessed through the Menu: Hi Mineral; Hi Trash; Patch and Test A modes. All 6 search modes can be modified with your favourite settings, and the four Custom search modes can also be renamed. A list of different names are available.

- General is a good starting mode. It runs quiet and gives a good compromise of effective ground handling, good depth, and good sensitivity. Will work very well with the standard 11” DD coil for general use in the goldfields.

- Deep mode is optimised for an improved response on larger deeply buried targets.

- Hi-Mineral search mode is suited to areas of heavily mineralised soils, and should match up well with most DD coils in the Normal or Sensitive Extra timing. Some adjustment to the Gain may be required depending on the coil size and ground conditions.

- Hi-Trash is a specialty mode which works well in conjunction with the new Iron Reject function, and is specifically suited to areas with high levels of iron junk, where digging all targets is not practical. The combination of settings in the Hi-Trash search mode provide a cleaner more obvious rejection on iron targets, and desirable non-ferrous targets will still come through clearly.

- Patch mode is good for large open areas, where ground coverage and a sharp audio response is more important than depth and stability. It also makes a good pin-point mode for small targets.

- Test A is the fourth Custom Mode which has identical settings to General. This can be a good starting point to experiment with different settings, allowing the user to switch back to General mode at any time and compare the effect of any setting changes. When a combination of settings is found that works well for a specific scenario, an appropriate name of the users preference can be applied to the search mode.


Here is the full list of Custom Mode name options:

- Patch - Lo-Mineral
- Bedrock - Very Deep
- Pinpoint - Shallow
- Gridding - Hi-Trash
- Diggings - Beach
- Salt Lake - Test A
- Hi-Mineral - Test B


Note: The name of any of the Custom modes can be
changed. The General and Deep modes
(accessed on the front panel) have fixed names.



NEW TIMINGS

The new timing options make the GPX-4500 even more versatile. Users of the GPX-4000 have learnt just how valuable it is to have a range of timings, to optimise the performance of the detector in different scenarios. In addition to the four timings found on the previous model, the GPX-4500 introduces two new timings, Enhance & Sharp. The new Enhance timing is a powerful feature, similar to the Sensitive Smooth timing, but provides an improvement in depth and signal response on small and large targets. This will suit most goldfields with highly mineralised soil conditions, and will work well with most small to medium sized monoloop coils. In extreme grounds, particularly with larger monoloop coils, Sensitive Smooth may still be the better option.

The Sharp timing is more suited to mild soils such as white pipe-clay, schists, and some bedrocks, and will provide an improvement in depth and signal clarity compared to the Normal timing. In most goldfield soils with medium to high mineralisation, Normal will still be the preferred option, but because of the sharper audio response Sharp can still be used to pin-point or check a suspected deep target response.
SETA TECHNOLOGY

Previous GP series detectors used one universal electronic alignment suitable to all their timings. With a total of six different timings incorporated into the GPX-4500, it was no longer possible to rely on a single alignment, and so the Smart Electronic Timing Alignment concept was born. Through a process of dynamic noise compensation, SETA ensures that the threshold stability is improved and maintained, allowing you to operate the GPX-4500 with maximum efficiency under all conditions.

The SETA process precisely aligns each individual Timing option. This method of calibration reduces the susceptibility to magnetic interference, and significantly improves the detector’s immunity to highly magnetic rocks and soils.

A bonus of SETA technology is that the ground balance setting of each timing is also saved, so if you are switching between two timings when investigating a suspected target signal, you won’t have to continually re-ground balance the detector. This is also handy if you wish to compare the effect of all timing options over a target signal. You can ground balance each timing option first, and then just switch between them whilst sweeping the coil over the target area.


GB OFF

Some soils (away from the goldfields) may be so neutral or non-mineralised that the Ground Balance has no effect. In these rare instances the Ground Balance can be switched OFF. It is very unlikely that this will have any real application in goldfield soils, and will be of more interest to specialist beach and relic hunters in loam or sandy soils.


BUILT-IN AMPLIFIER

Some operators prefer to use external speakers rather than headphones. They can be useful when detecting with a partner, or in hot and humid conditions. Since an external speaker has a higher gain requirement compared to headphones, in the past, a mini audio amplifier (booster) was required to power the speaker.

The newly designed Lithium lon battery pack supplied with the GPX-4500 now has an audio amplifier built in, which allows you to plug in an external speaker, without the need for any external boosters. The amplifier uses smart circuitry, which will automatically sense a correctly wired speaker, and apply an increase in Audio Gain. The level of amplification can then be adjusted by using the Target Volume control, found in the menu.

The design of the amplifier and the use of high-quality low noise components, ensure the signal response is clear and crisp, without the added background hum of some boosters.


TARGET VOLUME

The Target Volume controls the strength of target signals, and at high settings it will slightly increase the volume level of the threshold as well. This is useful for very windy conditions, for people suffering from hearing loss, or when using external speakers. With the audio amplifier built into the Li-Ion battery pack, you can plug a speaker directly into the battery, and set an appropriate level of amplification using the Target Volume control.

The Target Volume control also works when using headphones, and allows you to increase the strength of faint target signals, but can also be used to reduce or smooth out ground noise signals in highly mineralised soils. This is a powerful feature, and will work in conjunction with the Stabilizer control (see below), giving you the ultimate in fine tuning ability. A bit of experimenting may be required to find the optimum combination in different conditions. If you are using headphones, and you need to make adjustments to the Rx Gain, (due to a change of coil or location) make sure that the Target Volume is returned to the Factory Preset setting first. You can then fine tune it to suit the new conditions.


STABILIZER

The Stabilizer function allows the selected Audio Type to be fine tuned. It has a similar effect to the Gain control in that increasing it will provide an improved target signal, but it may also make the detector more unstable. Turning the level down, will improve the stability of the threshold. The Stabilizer is best left in the FP position until the soil conditions in the location are determined.

One example of when to use the Stabilizer is if Normal audio is giving stable operation, but Deep audio is slightly unstable, you can leave it on Deep and simply reduce the Stabilizer to say 7 or 8. Alternatively, you may wish to remain in Normal audio, but because of the quiet operation, you can increase the Stabilizer to say 12, to improve your chances of picking up the faintest response.

The Stabilizer affects the audio processing and does not change the power sent to the Receive circuit, so it has a slightly different effect to Gain. After making any adjustments to the Stabilizer, if the ground conditions change or you wish to change coils, you may need to reset the Gain, but before doing so, return the Stabilizer to the FP setting first. This will ensure you select the most appropriate Gain level to suit the conditions, and then you can fine-tune your audio circuit via the Audio Type options and Stabilizer function as required.

The Stabilizer can be thought of as a Signal and Noise control. As it is increased, faint target signals will be more obvious, but any noise will also be increased. Turning it down will reduce your ability to pick up faint signals, but it will provide you with a smoother threshold. It may be beneficial to experiment on an undisturbed target, to find out what the optimal setting is for the area you are in.


IRON REJECT

Iron Reject can be a useful tool when detecting in a high-trash area like an old mining site or a campground. The Iron Reject function on the GPX-4500 now allows you to set the desired level of discrimination, from cautious to very aggressive. The Iron Reject range of adjustment on the GPX-4500 has been reduced from 1-30 to 1-10, but the actual level of rejection has been expanded. What this means is that at high settings (7-10) it will be possible to reject iron junk at a greater depth, but you run a greater risk of rejecting any desirable non-ferrous targets, such as a small gold nugget, brass button, or gold coin.

This expanded range may assist in detecting areas that have previously been ignored due to the quantity of ferrous junk in the area. The area can be quickly scanned at high Iron Reject settings, allowing a large proportion of the trash to be passed over. This will improve your chances of recovering any valuable non-ferrous targets, or may at least prove the presence of gold nuggets in an old mining area.



The GPX-4500 has a number of new features that will improve your detecting experience. Spend the time to learn how to use it properly, and you only have to walk over the gold and other treasures, and the detector will do the rest.