GPX 6000 Speaker Audio Feedback Fix - My Experience

[Dutchman4]

Just thought that I would share my experience with what Minelab has called "GPX 6000 Speaker Audio feedback".

As Steve pointed out in an earlier post, Minelab has recently documented this problem on their website:  

https://www.minelab.com/usa/metal-detectors/gpx-6000  then select "Updates" on the bottom of the first page.

As most of you know the symptoms of this problem is very erratic threshold audio when using the internal speaker.  Like any other speaker, the internal one creates an electro magnetic field, when in use, and it appears that the high gain/sensitivity of the the GPX6000 detects and responds to this very localized EMI and feeds it back.   What you end up with is this out of control  feedback loop that tends to oscillate and create a very erratic threshold.  When the wireless headphones are used instead then a typical more stable threshold is achieved.

Like many of you, I pretty much always use blue tooth headphones and have never used the internal speaker when prospecting but I decided that I wanted to have this repaired just so it was completed within the warrantee period.  I also didn't use the internal speaker because it was not practical and after it is repaired/updated at least that becomes an option.

On the Minelab website there are instructions for sending in your detector to the USA repair center for this "hardware update" if you choose to do.  I sent an email to the repair center including the serial number on the bottom of the control box and they replied that my detector was still under warrantee and qualified for this repair/update.  I chose to use USPS for shipping and I elected to insure it for $2000 at a total cost of $53 from Southern NV to repair center in PA.  To insure or not to insure is a personal choice but one benefit is the the unit has to be signed for by a person at the repair center receiving department.  I only sent the detector control box since my 11 inch stock mono coil works normally and the ears are fine with no visible cracks.  Inside the shipping box I placed the following printed information:

"To Repair Center regarding Repair Ticket #xxxxx:

The problem I have with this GPX 6000 detector is the unstable threshold due to audio feedback when the internal speaker is used instead of the wired or wireless head phones.
This is a known problem and is detailed on the Minelab website under GPX-6000/Updates and titled "GPX 6000  Speaker Audio.
Please perform the "hardware update" that is mentioned in that article, "Minelab have produced a hardware update that removes this effect."

I did this because I wanted it to be clear that this is the only thing that I wanted them to repair and not spend any time trying to trouble shoot or replicate other problems that don't exist with my detector.  After I sent the unit I received update emails from the repair center regarding progress through their system.  The total turn around time from the day I mailed the unit to the day I received it back was 10 days.  The repair center pays for the return shipping and it did need to be signed for by me upon receiving it.

I recently tested the detector, about 5 miles from my house, in a place with no known nearby EMI sources and also having mineralized ground.  My smallest test target is a piece of #8 lead bird shot that weighs around 0.06 grams.  In the past, when I have prospecting in various gold fields, I have found many small pieces of lead bird shot at around 1 to 1.5 inches deep.   I buried the #8 bird shot test target 1 inch deep in mineralized soil and the audio response was the same using the internal speaker or the wireless head phones.  I tried manual sensitivity setting of 1 through 10 and also Auto1 and Auto2 as well as normal and difficult, all settings produced a detectable audio tone response to the #8 bird shot target although the higher gains settings were slightly louder.

I personally don't believe that the detector is any less sensitive after the hardware update.  I would say it is the same and possibly slightly better but that is hard to quantify for my.  The fact that the threshold appears to be more stable might account for a relative improvement in sensitivity vs an actual improvement just because you can hear the target response more clearly over the threshold.  I do recommend having this update performed on your machine but in the end it is your decision.

Regards,  Ceril

 

 

[VicR]

I have been told that it is worth while getting this update even if you dont have the problem with the internal speaker (or dont use the internal speaker) - as explained to me by a person in the know at the same time as doing the speaker fix they give the unit a thorough service so i dropped off my 6000 at Minelab , Adelaide with coil and battery attached.

After two days it was ready to picked up.

So the service report read -

Control box - Full service check on control box with no fault found. Cleaned all internal connection and pins. Audio modification completed.

Battery Pack - Service check on battery with no fault found.

11 inch coil - service check on coil with no fault found.

A few people i know have had this work done and swear that the machine is running a lot more stable - so i am keen to test it out as soon as the weather cools down a bit.

[phrunt]

I doubt anyone would be disappointed by the fix, it made a world of difference to mine as I’m a speaker user when I can but it also improved my experience using my Torus Bluetooth speaker, again the detector threshold remained more stable.  I recently tested it in a spot I had no end of stability issues even using the Bluetooth Torus and was doing regular factory resets to try keep it stable and I didn’t have to even noise cancel once the entire time I was there.

I think those that don’t want to do it because they think they may lose some sensitivity or depth have it the wrong way around, by not doing it they are the ones losing depth and sensitivity by having such an unstable detector.  We all know EMI causes sensitivity loss, this is no different.  Auto May just run higher when not being affected by self generated EMI too.

[jasong]

This is the idea I've been trying to preach about for years, in terms of where metal detectors can continue to improve, and why we aren't at a brick wall yet with detector advancement. Less EMI means more "effective" depth. Not just running higher gains, but allowing our own brains to more accurately process the most relevant information. Human brains, no matter how skilled a person is, have limitations when it comes to sensory overload where we have to listen to or see lots of data. The more there is, the more assumptions the brain makes. Even when sensory input is minimal, our brains still trick us by making assumptions and throwing away data (magic/visual illusions work like this). EMI is useless noise, and our brains will inevitably begin to discard the useless noise without our conscious mind realizing it - discarding some of the good signals along with the noise. Especially signals that very closely resemble the noise (edge of detection targets, other faint signals). This is what sensory adaptation is, and not even the most talented detectorist on the planet can avoid it - it's inevitable for us all even if we don't realize its happening.

The irony is - this general idea is what Minelab appears to be aiming to address with Geosense. But they did the opposite in a way by introducing their own noise into the hardware on the board, apparantly by using unshielded components near the speaker. That's fine, as long as it's corrected and explained so people understand and aren't left to guess what really happened. Calling it just an "audio fix" though is misleading by them. 

The problem is that Minelab's own hubris appears to have prevented them from really admitting they made a design error, which is why months later we still have people wondering if it's a fix for anything at all or just a dumbing down to decrease performance. ML publishing a partially hidden, misleading and vague article on "audio" has led to conspiratorial thinking now as people automatically equate more EMI with higher gains: thus the assumption among some is that the fix must be lowering gains or adding some kind of audio smoothing in, when there is no evidence that I'm aware of pointing to this. But of course Minelab has not bothered to clarify, as they almost never do.

Anyways, sorry for the ramble Dutchman. I'm glad to see other people posting their experiences, and I hope more follow your lead! More data is always a good thing. And these days it seems that it's up to us the customers alone to really figure out what is happening and to demand fixes when things are broken, this can only happen with communication between us all. 

[strick]

Mine's been to that repair shop twice. The first time was a couple months before they released that report in Australia. The repair shop said they could not find anything wrong with the machine but replaced my coil out of precaution anyways. The second time I just shipped in the control box in right after the report came out. I've probably sent in 7-8 detectors to the repair shop. They always do a great job. My best experience with the minelab repair shop was when I sent in my 2300 with only 6 months left on the warranty and they sent me a brand new machine. Still have not had a chance to test my updated 6000 out except in my yard so the jury is still out for me but I'm very happy to here that it has worked well for some of you. 

Quote from the Minelab report "Minelab has identified infrequent cases where users hear audio feedback when using the internal speaker." 

My machine was acting crazy with and without the speaker..I like to use my headphones so I'm hopeful that it fixes the emi thing as well...

strick 

[Dutchman4]

5 hours ago, jasong said:

This is the idea I've been trying to preach about for years, in terms of where metal detectors can continue to improve, and why we aren't at a brick wall yet with detector advancement. Less EMI means more "effective" depth. Not just running higher gains, but allowing our own brains to more accurately process the most relevant information. Human brains, no matter how skilled a person is, have limitations when it comes to sensory overload where we have to listen to or see lots of data. The more there is, the more assumptions the brain makes. Even when sensory input is minimal, our brains still trick us by making assumptions and throwing away data (magic/visual illusions work like this). EMI is useless noise, and our brains will inevitably begin to discard the useless noise without our conscious mind realizing it - discarding some of the good signals along with the noise. Especially signals that very closely resemble the noise (edge of detection targets, other faint signals). This is what sensory adaptation is, and not even the most talented detectorist on the planet can avoid it - it's inevitable for us all even if we don't realize its happening.

Thanks for sharing this important element and a very interesting "read" especially the "auditory" section of the "sensory adaptation" link.  It all makes sense that if you have a warbly/noisy threshold then after hearing that for a while your brain tunes it out when in fact that transition/break in the threshold is exactly what you should be listening for.  It puts a whole different light on "effective" gain/sensitivity. 

[Lynk]

My machine is currently being shipped back to me, but I am happy with the ease of this process. I was notified they received it on Jan 19 at 10:52am and was then notified on Jan 20 at 8:46am it was fixed and shipped. So fixed and shipped in less than 24 hours.

The perfect scenario is this issue didn't exist in the first place, but I am glad they are fixing it and in what seems like a fast manor. 

As has been said, it seems like a good idea for performance and resale value to have this fix performed while there is warranty remaining. 

 

 

[Gold Catcher]

It would be great to have some real answers about what impact the fix has for BT-only users. I suppose it is hard to convincingly quantify, and the reports of better threshold even without using the speaker could be a placebo effect. I guess we all want to believe that everything always gets better after a fix. The 6000 is a highly sensitive machine per design, and the threshold can be difficult to handle at times, even without any fault in place.

GC

[Dutchman4]

12 minutes ago, Gold Catcher said:

It would be great to have some real answers about what impact the fix has for BT-only users. I suppose it is hard to convincingly quantify, and the reports of better threshold even without using the speaker could be a placebo effect. I guess we all want to believe that everything always gets better after a fix. The 6000 is a highly sensitive machine per design, and the threshold can be difficult to handle at times, even without any fault in place.

GC

That is a tough question to definitively answer due to so many variables in the field that could impact before and after repair comparisons.  Only time will tell when more and more reports come in from users in the field with repaired machines.  I do share your placebo effect concern but I need to spend more time in the field with my machine to evaluate this. 

If I had a schematic showing the two components that were replaced and their location in the circuit path, when the speaker is enabled and not enabled, then that would help to understand the potential for overall threshold stability improvement.  Other posts about this topic seem to indicate that two unshielded "Inductors" were replaced with shielded inductors.  If these two inductors are always part of the circuit regardless of speaker being used or not then it could explain an overall threshold stability improvement and reduced EMI sensitivity.  Most inductors contain a small coil of wire that can essentially act like a micro antenna.  Any electromagnetic field could induce an unwanted voltage in the coil part of the inductor and introduce EMI.  The source of that unwanted field could be the speaker, the transmit part of the detectors coil or over the air EMI.  If the inductor is shielded then that unwanted energy is shorted/shunted to the ground plane and wont reach the coil inside the inductor, thereby reducing EMI sensitivity.  This is just my possible explanation of how their could be an overall performance improvement to the detector but I need to spend much more time in the field under actual conditions to support this.   

[Aureous]

2 hours ago, Gold Catcher said:

It would be great to have some real answers about what impact the fix has for BT-only users

I will be able to do just that later this coming week. I am sending mine off on Monday. I am also hoping that my NF 12x7 mono coil will arrive later this same week as well. I am hoping that combined, the 2 'fixes' will improve things a lot. A friend has had the audio fix done and swears that it makes a noticeable difference without using the speaker, either BT or wired headphones only. We will see....