Minelab GPX 4000 Faulty???

[ikaruz]

Hi. I had a minelab gpx 4500 at the past. A while ago i sold it because i needed the money. Now i bought a gpx 4000. It came with a old 11"DD coil gp series, and it comes with a commander DD its oval 13" i think. I did some air tests. The air tests are only that. Air tests. But i got a little disapointed... I Changed the settings and all. But i got +- the same depth on the air with the gpx 4000 and the xp deus 2 with a 11" coil. I did the test with coins. Small medieval coins. Roman coins. big coins... I only get a little more deep with the gpx with big items...

Question 1: is it possible the detector its a little faulty?

Question 2: is it possible the coils are a little faulty?

Question 3: is it possible that its a conterfeit detector? 

Question 4: its a old model and it doesnt punch a lot deep like the gpx 4500 and 5000? Or the deep between them are very similar?

I got almost the same depth with the gpx 4000 and the xp deus 2...

Thanks 

[Steve Herschbach]

Never air test a PI against a VLF. The whole point of a PI is to retain good depth in ground that causes a VLF/Multi to lose 25% or more of it's depth. I detect ground where your Deus 2 would fail and the GPX get five times or more depth. If you are going to detect in the air or in very low mineral soils, you do not need a PI. Either test a PI against a VLF by burying test targets in highly mineralized soil or may as well not waste time testing.

Slightly modified post below copied from long thread at https://www.detectorprospector.com/topic/11421-fisher-impulse-aq-discrimination-explanation/page/15/#findComment-113487

 

Some people think a PI detects a lot deeper than a VLF and in the case of a very high power PI that can be true. But for what I would call mid-power PI detectors like the TDI SL or Garrett ATX, running off 8 AA batteries, the depth in low mineral ground running the same size coil is not much different than a good VLF. Assume just for illustration that a White's MXT with 12" coil and White's TDI SL with 12" coil get the same depth in mild ground on one particular test target.

Now we have a magic dial and can turn up the ground mineralization. As we increase the mineralization, both detectors lose depth. The MXT loses depth at a faster rate however. I can't give you an exact ratio, but you can reach a point where the TDI now goes much deeper than the MXT. Yet the TDI is still getting less depth also.... it just does not lose as much depth as quickly as the MXT.

It is also the case that with a PI if you have no ground balance filter engaged you can get the best depth in low mineral ground. Simply engaging the ground balance filter immediately robs a little depth. However, by engaging the control you do better in high mineral ground by comparison to the MXT. Whether you engage or disengage the ground balance circuit depends on the ground you are in.

PI detectors do best by comparison to VLF detectors when ground conditions are the worst. The milder the ground, the less good a PI looks by comparison to a good VLF, to the point where you are better off with a good VLF due to the superior discrimination. Where I am in Nevada a White's GMT or Goldmaster 24K or even MXT is a better all around gold prospecting detector than a White's TDI SL in a lot of the desert soils due to the mild ground conditions, and the hot VLF detectors can detect tiny gold nuggets a TDI can't see even in direct contact with the coil.

To sum up, the pulse induction will shine best where ground conditions are the worst. In general sands derived from volcanic activity and granitic rock, with high magnetic mineral content. People in mild sand and gravels... not so much. In those situations the main benefit of a PI is the ability to effectively run coils much larger than those available for most VLF detectors.

 

 

[ikaruz]

Yes. I need to bury items to test more. But i thought even in air the gpx would punch deeper. Thats my confusion

I have ground very mineralized too..

But between gpx 4000,4500 and 5000 Will the 4500 and the 5000 go a lot more deeper than the 4000?

 

 

 

[Steve Herschbach]

On 7/23/2025 at 12:33 PM, ikaruz said:

But between gpx 4000,4500 and 5000 Will the 4500 and the 5000 go a lot more deeper than the 4000?

No, unless a specific timing on the newer models not available on the 4000 will help. The so called Fine Gold setting on the GPX 5000 helps in areas where there are hot rocks the GPX 4000 can't deal with. Fine Gold is not deeper, less actually, but handles bad hot rock situations better. But few people have ground like that. Just one example, but depending where you are a 4000 may be every bit as good as the later models.

 

[ikaruz]

Ok.. so if air tests can be very similar, the real test is at the ground and if gpx 4000,4500,5000 are very similar, for medieval coins, roman coins, artifacts, for you wich are the best coils i can get?

Here at europe Will be easy to get brands like minelab commander, detech, and sometimes a random coil at eBay...

[Steve Herschbach]

2 hours ago, ikaruz said:

Ok.. so if air tests can be very similar, the real test is at the ground and if gpx 4000,4500,5000 are very similar, for medieval coins, roman coins, artifacts, for you wich are the best coils i can get?

Here at europe Will be easy to get brands like minelab commander, detech, and sometimes a random coil at eBay...

Whatever worked best for you with the GPX 4500 as far as coils go. You know your ground and desired items better than I do. 15x12 Commanders are nice. 

[ikaruz]

Ok thanks