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Not A Fan Of The GPZ 7000 Yet.. But Hope To Be Soon

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I almost never took my GPZ coil off the ground and wore out several skid plates. Lifting off the ground is to deal with extreme ground. Generally not required in the U.S.

From https://www.minelab.com/__files/f/254716/KBA 24-1 Basics of the GPZ 7000 Technology Zero Voltage Transmission (ZVT).pdf

"In any of the above settings, it pays to swing the coil an inch or so above the soil surface if the soils are considered saturable (VRM). Saturable means that a detector ground balances well if the coil is raised and lowered down to about a few centimetres above the soil surface, and for the worst saturation, down to several centimetres, but not if the coil is swung up and down to a height lower than these saturation ‘height thresholds’ (e.g. down to the soil surface.) In addition, the degree of (VRM) soil saturation is considerably less for Difficult or Severe than Normal. As the metal detector coil is moved towards a soil, the transmitted magnetic field in the soil gets stronger. This causes a (very) small degree of VRM signal ‘saturation’ that happens to cause the resistive signal relative slope of the tilt to change. This is why the amount of VRM soil saturation is far less for Difficult and Severe than Normal. Soil saturation often requires the user to operate the coil several centimetres above the soil surface for best results.

However, whilst soils do have resistive signal that are very accurately log‑linear, unfortunately this is not perfectly accurate for some soils, and, because the GPZ 7000 has such very high sensitivity, even miniscule deviations in the straightness of the line of the log‑linear resistive signal will cause ground noise signals. Severe is less sensitive to these miniscule deviations than Difficult. Whilst the GPZ 7000 does not have a dedicated ‘salt’ detection setting (saline soils), the best Gold Mode setting for salt soils is Extra Deep."

That article was later refined into this newer article on the GPZ and bad ground....

https://www.minelab.com/__files/f/254714/KBA 27-2 Gold Detecting in Difficult Ground Conditions.pdf



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1 hour ago, Steve Herschbach said:

I almost never took my GPZ coil off the ground and wore out several skid plates. Lifting off the ground is to deal with extreme ground. Generally not required in the U.S.


I found the same thing. I always scrubbed my coil except in very hot ground (some areas near Stuart Mill/ St Arnaud and some areas around Maryborough)- I just lifted coil a little and it worked perfectly. I find exactly the same thing works with flat wound coils on the GPX.

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I have checked in on this thread whilst at work today and had time to ponder.  It's been a hard day 😉

There is a possibility that all the gold is gone.  It was only shallow and the GPX got it all.  But based on Steve H, JP, KiwiJW and heaps of others writing over time how the GPZ re-ignited patches that they felt were dead and buried - it seems unlikely that your little patch has flat-lined just yet. 

This quote intrigues me.  

14 hours ago, Jin said:

Only a few bits showed some wear most was prickly and sharp and hasn't traveled far. 

These bits are supposed to be the domain of the Z (or an SDC)!  These are the same bits that the GPX series supposedly struggle on.   So that just brings me back to the feeling that something is not right with the settings or some part of the set-up. 

If heading back to this same spot I would use:

Ground Mode - Normal (as long as it is usable). 

Gold Mode - High Yield. 

Threshold - 27 ish.

Sensitivity - only take it to a point where it is just starting to get unstable and then go back 1 setting.   I do understand that running hotter can also be advantageous and Steve H has outlined his insanely hot settings and Kiwi gets away with them too (and I've used these to clean out patches of tiny bits).  But just to start, this is where I would go and allow myself to listen for the tiniest change to that flat line threshold - rather than trying to listen for the 1 dollar coin in a tumble dryer full of 5 cent pieces 🤣

Volume - about 8.   

Volume Limit - about 10.

Audio Smoothing - Off. 

Ground Balance - Semi - auto.  


I know you also mentioned here and in your email that you tried Extra Deep.  From the GPZ manual - 

Extra Deep

This setting is specifically designed for searching for deeply buried nuggets. Large, deep nuggets (typically ≥ 50 grams) produce complex and subtle audio responses, so this setting should only be used by skilled operators. Shallow targets may be missed with this setting when compared to the ‘High Yield’ or ‘General’ settings. This setting is not recommended for general use.

The bold bits make me think 3 things. 

You mentioned that you reckon the run of gold is shallow.  So maybe not the best mode.   

A good mode for nuggets bigger than 50 grams (wouldn't that be sweet!).  Has this patch produced anything near that range or bigger?  

Complex and subtle audio responses - may be getting masked by the hot settings background noise?


Lastly, I would take the SP01 out of the equation for a bit.  This is in no way a slight at Pat or Nenad.  Regardless of brand I would suggest the same thing.  It is a matter of eliminating possibilities where something might be falling down.  Maybe the filter choice is not right, maybe the SP01 is faulty, maybe the WM12 is faulty, maybe there are battery issues, connections, etc.  I would just go back to the basic set-up and see what happens.   Boosters can be great but the basic Z and WM12 combo works pretty well too.   

Most importantly, don't give up on the GPZ yet.  It may be an ergonomic nightmare, have limited coil choice and be the price of a small car but it is an awesome gold finding machine and if I knew I had the time and the disposable cash I would have mine back in a heartbeat  😊


I hope something in all that dribble helps you to find the yellow stuff  😉




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Cheers guys, all good information and much appreciated.

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The biggest issue is the intrusion of Saturation/VRM into the threshold without the user realising it. Careful coil control is required to keep the coil right on the edge of the Saturation response so that it does not colour the threshold. Anything that colours the threshold impacts on depth because a disturbance in the threshold is the only way we can hear a target in the ground.

The GPZ has two receive windings, a bad operator can tilt (left to right tilt) one winding into saturation and remove the other causing an imbalance or if you like throw the windings out of Phase. Any variation in signal created by this will impact on depth, it has to because it lifts the noise floor. This is why I ALWAYS use Audio Smoothing on OFF, this lowers the electronics noise floor, then I focus on maintaining a smooth coil swing and height variation occasionally coupling the coil to the ground to see how much saturation there is and adjusting my swing height accordingly. 

There is no point getting the coil closer to the ground if the saturation level then masks a deep target response.


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Firstly, I scrub the ground (because I can where I am at)

Secondly, I run more conservative settings with my sensitivity down in the 5 or less, area.  Everything else is pretty much like Northeast runs.  What I found is that when I went back to my patches, I got nothing more until I lowered my sensitivity.  When I did this, the ground noise went away and I heard deeper targets.

Overall,  when I switched to the ZED, I find many more smaller targets that the GPX5000 was not sensitive to get.  If you have pounded areas with your larger GPX coils, don't plan on the ZED getting too much more.  It all depends on your patch, I guess, and what you've already pounded it with.   I *do* find the ZED more sensitive to improper handling and requires (in general) a slower sweep than the GPX. 

But I still love that I can get almost everything I need with this one coil.  My only gripe is that the 14" coil does not fit in all the areas I want to put it.

Good luck!


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