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Minelab GPX-4500 Field Test - Arizona Outback

Field Testing Minelab’s GPX-4500



I looked down at the tiny glittering piece of metal in my hand and just shook my head. “You shouldn’t be here either,” I thought as I rolled it over letting the sunlight reflect off its golden surface. I had dismissed the nugget I dug only a few minutes prior as a fluke, after all, everyone leaves gold behind. But two nuggets off a hammered patch? I switched off the detector and found a shady spot to sit and regroup. I was pleased with the discoveries, but they had left me feeling puzzled. Both nuggets had been out in the wide open and neither were what I would call “difficult targets”. Truly they should not have been there. It could have been a coincidence, but deep down I knew it wasn’t. This metal detector was doing something different.

In the summer of 2008, the Australian-based company Minelab Electronics unleashed their most advanced gold detector ever; the GPX-4500. This upgraded version of their already popular GPX line boasts a number of new features that are sure to have serious nugget hunters smiling. Some of the biggest changes are the incorporation of SETA Technology, a Threshold Stabilizer, new pre-programmed Search Modes, Enhance & Sharp Timings, and a powerful Audio Amplifier built directly into the battery pack. These innovative additions combined with their already proven Multi-Period Sensing (MPS) and Dual Voltage Technology (DVT) has created one of the most formidable metal detectors on the market.

Being an avid nugget hunter for the past thirteen years, I was delighted at the prospect of field testing the latest and greatest creation from our friends Down Under. The rumors leaking out of Australia told of considerable improvements in performance and I was eager to put these claims to the test. During the course of several months, the GPX-4500 and I covered hundreds of miles hitting goldfields all across Arizona and even venturing into the deserts of southern California. My findings were impressive to say the least, however before getting into the actual field test, let us first discuss the new features which I felt made the greatest impact.

SETA: Minelab’s latest creation makes use of a new technology called SETA. Smart Electronic Timing Alignment, or SETA, ensures that the detector is precisely aligned for each individual Timing option. This improvement in calibration offers a significant gain in performance by reducing susceptibility to certain types of external interference and by increasing the detector’s immunity to highly magnetic rocks and soil. In a nut shell, it makes the detector run quieter, which allows the user to hear targets that otherwise may have been masked. Another bonus of SETA technology which hasn’t been publicized much is the fact that the ground balance setting of each timing is saved, so if you are switching between timings when investigating a suspected target, you won’t have to continually re-ground balance the detector. Simple, but very handy. 

Stabilizer: Before we talk about the new Stabilizer, it seems important to first discuss what it controls; the Threshold. The threshold is the constant background hum you hear while detecting. It gives our ears a reference point making it easier to notice changes in pitch and volume; such as when the coil crosses a bit of metal. Ideally, a threshold should be stable with little or no variation. Unfortunately, this is not always possible because of something detectorists refer to as interference.   

If you own any of the Minelab pulse induction machines you are undoubtedly familiar with interference. Interference is a chattering of the threshold caused by electricity or radio waves. The most common sources are power lines, underground cables, radar, or climatic conditions. In most cases this interference can be tuned out; other times it completely swamps the receiver making detecting near impossible. Like the GPX-4000, the GPX-4500 is equipped with an Auto Tune (AT) and a Manual Tune (MT) which can alleviate a bulk of this interference. Although these two features work well, often times they are unable to achieve a completely stable threshold; which is where the new Stabilizer control comes in. It controls the point at which faint variations in the threshold begin to be heard. In a sense, it is a fine-tuner that allows the user to clean up any instability in the threshold that could not be dealt with using either the AT or MT controls. In my opinion, the Stabilizer represents a huge step forward, especially for prospectors in the US that face an ever increasing interference problem. A stable threshold will most certainly improve the odds for success by allowing faint targets to become more obvious and by reducing unnecessary mental fatigue. Thumbs up to Minelab for adding this new feature!

Pre-Programmed Search Modes: The GPX-4500 lessens the learning curve by offering a number of different pre-programmed search modes. In addition to General and Deep, there is the Custom mode, which gives the user access to four other search modes specially designed for different applications. These are: Hi Mineral, Hi Trash, Patch, and Test A. All six modes can be modified with a person’s favorite settings, and Custom even allows them to be renamed. These modes are very helpful for new detectorists; especially if the GPX-4500 is their first Minelab. My personal recommendation for new owners is this: initially practice with the detector in the General mode. Simply turn on the machine, select (G) under Search Mode, ground balance it, and then go detecting. Once you have a day or two of experience under your belt you will be ready to move beyond the pre-programmed search modes and begin experimenting with your own setting combinations.

New Timings: The GPX-4500 introduces two brand new timing options: Enhance & Sharp. The Enhance timing is, in my opinion, one of the most powerful features found on this new detector. Like the Smooth timings found on the previous GPX-4000, Enhance was also designed to allow the operator to use monoloop coils in extremely mineralized areas. It is very effective at canceling out most ground noises and hot rocks, but unlike Smooth, it offers better depth penetration and an improved signal response on both small and large targets.

The new Sharp timing provides the most powerful detection field of all the Soil/Timing options. It can offer improved depth and is good for pin-pointing faint signals, but it is more susceptible to interference and will also increase the severity of false signals in highly mineralized ground. Because of this, it is best suited for areas with quiet soil and low levels of interference. More testing is still needed, however from what I can tell thus far, Sharp seems to work especially well with DD coils. Those that prefer to detect with DD coils will definitely want to experiment with this new timing.   

Lithium-Ion Battery: When I first tested the GPX-4000 one of the things I raved about was the addition of a lightweight lithium-ion battery pack. With the 4500 Minelab took it a step further by incorporating a powerful audio amplifier into the battery itself, eliminating the need to purchase an aftermarket booster. The amplifier can be easily adjusted via the LCD and is great for persons with hearing impairment or for those who like a little more volume when chasing very deep or tiny nuggets. I found the quality of sound produced by the amplifier to be excellent. Even when run higher than the factory preset of 8, target signals remained crisp and clear with minimal distortion. This new battery design is an absolute winner in my book. It packs enough power to run the detector for 12 hours, has a rapid charge time, and weighs less than two pounds!


The days I spent waiting for the detector to arrive seemed to be some of the longest of my life. I felt like a kid waiting for Christmas morning to come, and every car that passed by had me racing to the window. Finally when the brown truck arrived late one afternoon I knew I had struck gold! I grabbed the box so quickly the UPS driver barely had time to yell, “Hey, you’ve gotta sign for that!” Even before the detector was assembled I had already thought of at least a dozen places I wanted to try. I got myself so excited I swear I might have left that very moment had my wife not reminded me that it was nearly 7 o’clock at night! As anxious as I was, I knew that before I raced off to the goldfields there was one place in particular I had to go first. A special place…my test patch. 

I call it that because it is an area that I have hunted and re-hunted countless times over the years with at least a dozen different models of detectors. When I first discovered it back in 1996 it had been fairly rich. As the years passed the number of pieces I found during each trip slowly dwindled, and by the end of 2007 I was hard pressed to find a target there, let alone a gold nugget. In fact, my last visit there with the GPX-4000 had sent me home empty handed. Despite this, it possessed a number of qualities that made it an ideal location for evaluating new equipment.

For starters, the ground mineralization was severe. With a highly conductive layer of iron-rich red clay beneath and a surface blanketed in hot rocks, it offered some of the nastiest conditions I had ever encountered in Arizona. To make matters worse, there were power lines nearby which pumped out a steady stream of interference. All in all, it was a nightmare to hunt, but that is what made it so perfect. Whether the GPX-4500 was up to the challenge my test patch posed was something I was going to find out.

Despite the noisy soil, I decided not to use the stock 11” DD coil because many of the new features I wanted to try had been engineered for the monoloop coils. So, I put the DD away and opted for my trustee Nugget Finder 14” elliptical mono. After a brisk hike I reached the patch and began the normal startup procedure. I was pleased to find that the Auto Tune knocked out nearly all the interference coming from the power lines, and any chatter left over was easily disposed of by lowering the Stabilizer. The GPX-4000 had run quiet, but the stability of the threshold achieved with the GPX-4500 was a noticeable improvement. For the first hour I ran the GPX-4500 exactly the same as I did my GPX-4000. The ground was manageable, but the hot rocks still proved bothersome and I didn’t find a single metallic target. Next, I flipped into Smooth mode, but then thought better of it and went into Enhance instead. I had already hit the patch using Smooth on the GPX-4000; I wanted to see what Enhance had to offer. I also raised the Rx Gain well above the factory preset, increased the Target Volume, set the Motion to Very Slow, and adjusted the Audio Type to Deep. It was during this portion of my testing that the depth advantage of Enhance over Smooth became apparent.

The Enhance timings did their job. The ground noise was virtually nonexistent and all but the largest of the hot rocks were eliminated. With the detector running so smoothly, my testing was proving rather uneventful. I was actually considering moving to a new location when I hit my first signal. I had detected the flat many times because it was one of the few places not covered in brush. The signal I heard through the headphones was not exactly loud, but it was enough to stop me in my tracks. “Strange, that signal shouldn’t be here,” I thought, “maybe a buried hot rock.” When I had dug down several inches into the hardpack my heart beat a little quicker. This was not a hot rock. 

When I finally spotted the source of the noise I shook my head in disbelief. In my palm was a solid nugget weighing close to 2-grams! At nearly a foot, it was a decent dig for any detector, but surely my GPX-4000 should have hit it in Smooth. Everyone leaves targets behind, so it was possible I had just missed it. It was possible; but in this location, not likely. Any notions I had about it being a coincidences evaporated when I uncovered yet another nugget a few feet away. Like the first, it was out on the flat hiding at roughly the same depth. Although slightly smaller, it was still a nice solid piece. These finds were enough proof for me to know that I would have to re-hunt all my old, noisy patches in Enhance.

In the months that have passed since then, I have traveled extensively throughout the southwestern US. Not all of the places I’ve been have rewarded me with nuggets, but all of them have yielded targets that were missed with the previous models. From the testing I have performed thus far, I feel confident in saying the GPX-4500 represents the pinnacle in metal detecting technology. Its improved functionality coupled with the latest in high-tech analogue components and advanced digital processing has resulted in one of the finest gold machines on the planet. New owners can expect a smoother more stable threshold, better performance in mineralized ground, a crisper audio, and improved interference immunity. 

The GPX-4500 is capable of finding nuggets in even the harshest of environments, however with a price tag hovering around the $5,000 mark, it represents a significant investment. For those that only detect a few times a year spending this amount of money on a detector might not make sense financially. For others, like myself, that spend a great deal of time in the field it is definitely worth the upgrade. With today’s outrageous gas prices I need to make every mile count. When I have to spend a few hundred dollars in fuel traveling back and forth to the goldfields I want to have every advantage possible. If I have to part with a few grand to get a leg-up on the competition I’ll gladly do it. Because I know that even the slightest margin of improvement can result in making the discovery of a lifetime…or leaving it behind for someone else.

For more information on the new GPX-4500 you can visit Minelab’s website at, or the author’s website at:

Minelab GPX-4500 metal detector field test.
Minelab GPX-4500 Field Test - Arizona Outback


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