About different manufacturer's Ground Balance knob selection.
Well, I haven't been around here for a while as I have been busy elsewhere and with our AHRPS Forums. Then I get an e-mail, or two, asking me to view and comment here so,m for what it's worth, I'll share my thoughts.
I do not mean to offend anyone, and if you are concerned about my comments, shoot me an e-mail at:
monte@ahrps.org
For those who haven't heard of me or read any of my posting, i have been involved in this great sport since I built my first metal/mineral locator at home in march of '65. That mean in two months I'll start my 48th year of very avid detecting. I not only enjoy detecting, but I started dealing in metal detectors in '77 (Garrett) and handled a few brands since then.
From 1983 thru the end of 2004 I was a Tesoro Dealer. I have also worked for one detector manufacturer, and I have been involved in working with prototypes from 6 or 7 manufacturers through the years. In 1981 I started doing metal detecting seminars, and continue to, to this day. No, I am not an engineer. Yes, I know how to make these things work and, to the best of my ability, I can sort through the strengths and weaknesses of different designs to evaluate their character for varying applications.
Now my thoughts and opinions:
mts said:
That is normal. As others have said, you can actually turn it almost 4 complete turns while actually affecting the ground balance. Beyond that it actually doesn't turn the internal potentiometer. It just lets the knob turn so that it doesn't strip.
The Ground Balance pots used by Tesoro, either their 3¾-turn or the older 10-turn designs, have the 'drag' feature at the ends of their adjustment.
Yes, you can turn either type fully one direct, then turn back the other direction half the number of full turns provided and be roughly at the mid-point of the variable control. Seldom, however, will you be close to a 'proper' Ground Balance setting unless you're in very mellow ground.
Also, it isn't a matter of 'stripping' the potentiometer. It is simply a decision made that relates to cost, as far as I am concerned. Also, if you loom at these potentiometers fro inside the control housing, it is quite apparent that their inner workings can easily become 'infected' or 'dirty' with dirt and sand and other matter that might (and will) enter many control housings.
mts said:
They talk about it in the manual if I'm not being clear. 
This is one thing about the Tesoro machines that I'm not wild about.
Nor am I. From the start I wondered why Tesoro would use a rather inferior part in the detector design. I personally prefer a true 'wire-wound' pot for this type of control function, which is what the majority of manufacturers have used. I am referring to manufacturers who put more time and effort and R&D into their products, and they can afford a better quality component.
I have spoken with four detector engineers through the years and brought up several questions, or simply heard their own views, about detector quality. They point out that better component selection is usually ± 1% tolerance for many parts, whereras some manufactures used ± 5% components. the result is more 'slop' in their design, calibration, and overall performance.
They also pointed out the better benefits of using a true 'wire-wound' GB control Vs the 'budget' use of the 'unending' pots like those Tesoro uses.
mts said:
They do it this way so that they can give you finer control of the ground balance setting (a 3.75 turn pot has more resolution than the standard 3/4 turn pot). But it can be confusing because you never really know where in the 3.75 turns the knob is currently sitting at without doing the whole 4 turns left and 2 turns right ritual to return it to the middle setting. Luckily, once you get it set for your soil you rarely have to change it beyond a small tweak or two.
Actually, Tesoro's use of the 3¾-turn posts has bothered many former Tesoro users who preferred the 10-turn pots for more 'fine-tuning' capability.
Also, you can't make a blanket comment about 3¾-turn Vs a ¾-turn GB control because a lot will depend on the rest of the circuitry design. The overall design can be such that the GB adjustment range can be sort of 'coarse-tuned' in the circuitry providing a more 'fine-tune' manual adjustment that is spanning only the truly functional adjustment range.
We could look at the adjustment on the new Garrett AT Gold which provides a setting to adjust a Ground Balance Window™ which broadens the GB range to make it less 'touchy' to ground changes. It is just an overall circuitry design by Tesoro that results in a rather touchy GB adjustment, and it is complicated by an equally touchy GB control pot.
Another example I can give is the modifications done my Bill Crabtree to the White's Classic series. I use my modified IDX Pro and it features a 1-turn (a title for a ¾-turn adjustment) GB control. I set it for some of the worst ground in my area, and it is mineralized around here, and I seldom ever need to re-adjust it unless there is a
drastic change in the mineral make-up, or unless I change a search coil and need to GB for that set-up.
ToddB64 said:
mts !
I have a Tesoro Bandido ll uMax with the 3.75 turns pot for GB. As the manual explains, you will feel a slight drag at each end of the adjustment. Personally, this has never been a problem for me to feel the drag. However, why wouldn't a pot with positive stops at each end of the 3.75 turns GB adjustment be easier for the majority of folks ? Would positive stops compromise the resolution somehow ?
The Tesoro pots aren't a 'problem' for me, either, because I know not to over-adjust and have a too positive GB setting. Doing so with most Tesoro models can result in the loss of silver dollars, silver and clad halves, and some other higher-conductive target, or at least impair the depth of detection. So I am never hunting with them 'at-the-end.'
Yes, a positive-stop type wire-wound pot would be better, Possibly better quality, better at not being open to contamination, and it would certainly let anyone know when they reaches the end of the adjustment range. That would also keep consumers from asking the initial question here about the drag factor. No, a positive stop type pot wouldn't compromise the resolution at all.
mts said:
Todd, no, positive stops would not compromise the resolution. And I agree that positive stops would be a lot easier to understand and use. I'm not sure why Tesoro did not use a pot with positive stops. Perhaps they are not easy to find. Or, perhaps they felt the current controls would be better for some reason. Tesoro has already gone above and beyond the call of duty by using the 3.75 turns pot. Compared to a standard 3/4 turn pot, the Tesoro version gives 5 times the resolution. So I commend them for spending the extra money to make the product better.
Once I understood what it was doing it became easy to use the product as designed. So it is really a minor issue. Maybe Robert from Tesoro can chime in and give us the thinking behind the design.
Many potentiometers can be getting harder to find with the big shift to touch-pads and more digital operation. (Blah!) I believe the reason Tesoro went with those pots as a young upstart company was because they were a budget item and affordable. They were both affordable and they worked.
After a while, maybe they just figured everyone who used a Tesoro knew about the mushy drag at the end and would be fine with it so they continued to use the bargain pots. Just a guess, of course.
My personal wish, and it has been for a couple of decades now, is that Tesoro would have put more R&D into their models and eliminated the glitches. Have a tighter Discriminate and All Metal Ground Balance reference, which most of them don't. Also, to use a higher-quality control pot for the Ground Balance adjustment, and while working on the circuitry make them far less touchy or reactive to slight GB changes or ground variations.
Okay just my 'chime' in this post.
Monte
Cheers 
........I suspect he didn't want to offend anyone who might have posted ideas different from his on why Tesoro decided to use a drag-type GB dial.
