Minelab GPX And White's TDI Tones Compared

[Steve Herschbach]

Daniel Teague Published on Dec 5, 2018 Some of you guys were curious as to the tone differences between a Minelab GPX and Whites TDI.  This is the GPX 4800 and TDI Beachhunter and a little bit of why I like the GPX better when it comes to relic and beach hunting.

 

[Jim McCulloch]

Daniel, interesting test. Repeated viewings of this video reveal that, when testing the TDI, your bobby pin and nail were passed over the coil at a 90% angle to the coil (end-first), whereas when passed over the 4800 those targets were totally broadside, giving the 4800 a far better "look" at those targets. Question: wouldn't such a radical difference in target orientation give radically different results? Just asking. Thanks and HH Jim.

[Daniel Tn]

Jim,

The short answer is no.  

The main point of the video was to demo the sounds of the pulse machines with a short example of why I prefer one to the other.

The sound of the TDI on a bobby pin is the same on the TDI longways or however you want to pass it across the coil.  With a nail, if you hold it a certain way, you can get it to respond on the edges of the coil and not in the center, and if you whip it rapidly by the coil, you can get it to give a double beep.  That's what I would do in the field with the TDI before I got a GPX...circle all around the target and speed the coil up really fast.  If I ever got it to give a double beep, then I reasoned it was a nail and moved on.  If the nail was bent or rusted more on the head...you wouldn't get the double blip.  I've owned all generations of the TDI...from the Pro, to the regular big box (even the tan colored box through hole design), to the SL and the one in the video was the new Beach Hunter.  IMO, a mono coil seems to help this somewhat but the stock dual field coil makes it tough to ID a nail.  Not sure how the mono coils handle bobby pins...the Beach Hunter version is the only one I have tried on the beach, and you are stuck with the 12" DF coil for now.

On the GPX side of it, on the bobby pin I can get it to entirely null on it or to give that slight high warble sound with the way it is held.  On the nail, if its within a few inches of the coil it nulls on it no matter how its held or oriented.  The distance from the coil seems to matter most...and how aggressive the iron disc is set.  If its set too low then it is more easily fooled by deep iron.  At the same time, if it is set too high, then you can pass over deep non ferrous targets...it will blank those out.  I tend to balance it. I try to run it as low as I can and try to find the breaking point of it at each site. If I'm getting fooled by too much deeper iron, then I will bump it up a number or two.  

[Jim McCulloch]

Daniel, excellent answer, and thank you for the time required for such a thoughtful response. Most of my detecting is done using a VLF for finding natural gold, and target orientation makes a huge difference in target response. So does searchcoil internal configuration. And  as you mentioned, so does size, and depth. For instance, when using a DD coil, a nail may give a (seemingly) non-ferrous beep when buried vertically, yet a different response from one angle, and a double beep from another. YET, a thin nugget, on edge, from the right angle, can likewise give a double beep. One needs to have a trained ear when audio response is the primary form of target ID. Thanks again, and HH.

[Jeff McClendon]

Hi Daniel,

thank you so much for making this quick informative video. It reinforces my decision to part with my TDI SL and pick up a used GPX 4800. There was nothing wrong with the tone options on the TDI. They just didn't give me as much information as I had hoped after using a GP 3000 for several years. My GPX 4800 tells me so much more through its audio.  I am amazed at how much tonal improvement was made by going digital with the GPX series.   

[Daniel Tn]

For what it's worth, out of the different models of the TDI, I found several the older ones to be better for my intended purposes of relic and jewelry hunting.  

The big box TDIs had at least 4 different models to it.  There of course, was the Pro and Regular...but there were 3 versions of the regular big box.  The first one was the tan colored box...those were actually more the less prototypes and what most refer to as the "through hole" design.  The next one is what I refer to as the small knob big box....all of the knobs are small and all black colored.  This is my favorite of the whole series...will explain a bit in a minute.  The later ones had bigger/fatter knobs with silver on top of them.  Then later on came the SL, then the SL special edition with the new paint job...then the Beach Hunter.

Okay...so my opinion on them is, the newest versions of the TDI have had some tweaks with the threshold to make them smoother.  The older ones were indeed a bit unstable...erratic if you will.  They were hard to get smooth, unless you turned them up really high and then you had trouble hearing those small subtle sounds.  Not so important for relic hunters but nugget hunters...that's a big deal.  So they smoothed the threshold out and now it purrs like a kitten.  But whatever they did...they took away the nuances for being able to tell a nail from a high conductor target. My best guess is, they sped up the SAT.  With the older models, on a coin or say Civil War bullet, the machine would almost "bog down" over them. It was a long drawn out audio signal.  The nails would be much shorter...almost abrupt sounding.  It was very simple to tell them apart.  With the newer versions...starting with the big box, big knob version and progressing thru the TDI SL...this is gone.  The bogging down sound is gone that is.  Now everything sounds the same to my ears.  The sound is chopped off and then it goes back to the threshold.  

[Mark Gillespie]

Daniel, believe or not using the small coil I bought from you many moons ago I can actually tell if a target is a bobby pin before I dig.  I was hunting with my TDI SL at a ball field where a lot of girl softball leagues play (looking for gold jewelry) and I was shocked at the number of pins I was digging.  I was hunting with my conductivity switch set to all with GB at 7 1/2.  I was almost ready to pack it up and head home when I noticed I could hear a difference.  Started experimenting and to my amazement I could hear a difference, the audio was slightly elongated with a slight jitter to the audio.  Ended up finding my best ever gold ring with the TDI and the small coil. 

 

[RickUK]

Enjoyed the video,i have used a GPX but i do own a TDI Pro,for my detecting needs which is mainly inland sites that have a very high mineral content then the only detector that will work on this and surrounding permissions is a Pulse machine and the machine that ticks my needs and requirements is the TDI,almost all the time i run it in low conductivity as most of my desired targets are silver hammered coins and celtic gold coins as well,and using low conductivity works a treat and very rarely do i dig iron,small iron is almost totally eliminated like nails etc,of course large iron objects like horseshoes then almost all machine including VLF will show these large items as decent ones.

Great video,could not see after a very long period of research see any major advantage that the GPX would give me over the TDI especially for our finds here in the UK,for me it all boils down to the reward to cost ration on my sites and it just did not stack up in favour of the extra cost of buying a GPX.Of course just a personal opinion

 

[Daniel Tn]

A person always needs to weigh out the options and advantages/disadvantages.  I personally wouldn't buy a GPX new...the used ones by relic hunters here in the US are fairly new, in good shape, and I have seen them sell for as low as $1,000 for a GPX 4500 that had only been used at DIV relic hunts.  They generally average $1,500 used though.  On the flip side, on the forums I have saw big box TDIs sell for as low as $400 but they generally fetch more on the auction site. The TDI Pro is what most people want and I see them go for $1,000 easy.  For me and what I do, there is enough difference for me to swing a few hundred extra towards the GPX in that case.  

The big killer for the TDI Beach right now, is the only coil offered is the 12" dual field.  For it to be successful, they are gonna need to offer it with coil options.  It is not so great in the water with that coil. For hunting wet sand it is great.  Actually in the water...nope.  Too big and too much flop from where the coil bolt mounts.  A 9 or 10 inch center mounted mono would have been perfect for it. The other thing was, they eliminated the conductivity switch and made it be locked in All.  For a beach machine I would have rather had the option.  

[Mark Gillespie]

Being a hard wired coil, I wonder if all the TDI coils would work, but would require internal work, which might void warranty if the end user changed.  Can't imagine the internal workings are different, jut water proof.  Now at the beach I always have my switch to all or the ground balance off:  This is a wonderful machine at the beach and since I don't venture into the water it's more than sufficient for me.

From page 11 of the manual:

"Target Conductivity Target Conductivity refers to the reactance of the target either above or below the ground balance point of the TDI. Generally-speaking, gold is considered to be a low conductor (high tone) and silver a high conductor (low tone). Iron often produces a confused, warbly pitch that jumps back and forth between high and low tones. The two-tone response is disabled when ground balance knob is turned to the OFF position.  Be aware that target conductivities can vary considerably, even targets of the same metal. Small gold nuggets are usually low and large gold nuggets are usually high, but where the transition occurs depends on the composition of the gold alloy. Be mindful that searching in low-conductivity mode could eliminate very large nuggets, if any happen to be in the area1. The same is true for relics and jewelry. Many bullets, buttons, and most buckles register as high conductors, but cuff buttons often respond as low conductors. Most small jewelry responds as low conductors, but larger men’s rings can easily fall in the high-conductive range. Most coins fall in the high range, except for e.g. US nickels and small or thin coins like hammered silvers or very small bronze coins."