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Anyone know what the threshold does on the XSII?...

A

Anonymous

Guest
i was out in my test area with a slight threshold like usual, set at 8.
i swept over all of targets like normal, i have mostly dimes in the area, but also a 12" deep quarter, and an 8" deep minnie ball, and a 6" nickel.
anyway, i decide to click the threshold all the way down to "0", and then re-check my targets again.
to my surprise, there's no difference detecting these targets. in fact i think they sound better with threshold at "0".
this includes a 9" deep quarter too.
what the heck is the threshold for on the XSII? it doesn't seem to do anything on my machine except make some 'hum' noise. <img src="/metal/html/confused.gif" border=0 width=15 height=22 alt=":?">
ok....for those that are going to say the threshold is for small targets, how small? for what? a BB? because it sure doesn't make any difference on a dime size target or larger.
no wonder i've been digging the back loops to civil war buttons. <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
seriously now, what would happen if i just hunted in threshold "0"?
i might just switch it to "0", because i don't think it makes any difference.
funny, most of the time anyway while i sweep the coil, the threshold disappears, and it's never made any difference in whether i detected a target or not.
why do most folks think you need a threshold hum on the explorer? i don't see any difference.
i've read before, i think right here on this forum, how important the threshold setting is. well, i sure would like to know why. anyone care to explain it to me.
thanks.
 
In 4 years of using the XS I never used Threshold, dang thing was too loud and it never hurt my finds, and yes, I find BBs and buckshot deep.
Don
 
Minelab Explorer Classroom Forum
Re: If you prefer to hunt in silent mode go down 1 notch below barely audible....
Posted By: Cody <Send E-Mail> (109-107.tqok-a3.cablelynx.com)
Date: Thursday, 3 June 2004, at 8:33 p.m.
In Response To: If you prefer to hunt in silent mode go down 1 notch below barely audible.... (Snuff)
One notch below sound is not a good idea becasue that is not the same as silent search. When you use a detector with silent search the point is set just below the point where the audio circuits produce sound and maintained at that point.
If you lower the threshold below the point of sound then minerals can drive that point even lower, detuning the detector, and greatly decrease depth. It is cricitcal to have a detetor that is designed to run with a silent threshold. Several are desinged to run with a threshold or silent but many are not and you can miss some good deep coins by setting the threshold down below sound.
HH, Cody
and
Minelab Explorer Classroom Forum
Re: Just leave on 3 or 4 and you will be fine
Posted By: Cody <Send E-Mail> (109-107.tqok-a3.cablelynx.com)
Date: Wednesday, 16 June 2004, at 12:54 a.m.
In Response To: Just leave on 3 or 4 and you will be fine <http://www.findmall.com/metal/html/nm.gif> (Deep South)
Threshold volume is a critical adjustment in that you can detune a detector if set wrong. The best place is where the individual user can just hear a faint whisper. This is the point were you can hear a very faint target above the threshold. If set to low you can miss those really deep coins and if too high then the faint sound of a target is lost in the volume of the threshold as it is to loud.
Set to the lowest sound you can just hear which is why they call it "threshold" because you are right at the threshold of sound.
Silent search should be avoided unless the detector is designed with a silent search mode. There is a difference between turning the threshold down to the place where it is silent and a silent mode. If you turn the threshold down below sound you don't know how far down that is from the threshold so if mineral drive the sound even more into the silent zone and you can really miss faint deep targets. A detector with a silent mode sets the silent mode just a hair below the threshold and keep it there with dynamic adjustments so you still have good sensititity to deep faint targets.
Some users will set the threshold to silent to kill sounds from soil with a lot of iron minerals as they tend to cause little pops and clicks that are common to high gain very sensitivity detectors.
The most sensititity point is where the user can just hear the threshold.
HH, Cody
 
sure does work and sounds nice in silent. wish i would have tried it before.
thanks.
 
Forgive this long drawn out post but there are several engineers and other that can check the explanation and knwo this is correct.
<span style="background-color:#ffff00;">I know of no other way to explain threshold than this so please excuse the technical parts of the explanation.</span> If we are going to drive a transistor amplifier/solid state amplifier into conduction we extract electrons from or inject them into the base of a transistor depending on if the transistor is a PNP or NPN type of transistor. The transistor is biased, operating point set, at a specific point. The transistor amplifier is in idle so to speak waiting for an input signal.
Let
 
This can be used to advantage in some interesting applications. Assume that we are under power lines or next to an electric fence and we are sure there are some goodies there. Nothing we do will let us detect next to the fence or area we what to seach. One thing old timers do that are use to the older detectors is start to reduce the threshold one click at a time which is similar to reducing the overall sensitivity of the detector. When we have reduced it enough so that we can search the area that was off limits before we are good to go. This in conjunciton with a small coil will allow us to find at least some of the target that others have missed becasue they could not detect the area with so much stray EMI present.
I never suggest this when the question comes up about electric fences because I think this is more of a method for very experienced users since we can really drop the overall sensivity way down. I don't think I have posted this on any forum. Many of us have done this for years to search next to electric fences or under high power lines.
HH, Cody
 
to the Explorer schematics?
Reason I ask is, in this day and age where an audio driver (power op-amp) chip can be as cheap as a stand-alone transistor, I wonder if Minelab even uses discrete transistors for it's audio amp.
Even if it is a single sided driver (transistor clamp to ground or high side), why wouldn't they simply drive the transistor with enough bias to cover all temperature variation possibilities, and capacitively couple to the speaker (to keep the resultant DC off of the speaker coil)?
Just wondering.
DAS
 
No, but the priciples are the same even if we use a chip. I would be amazed to see any transistors in the Explorer. I think you know we are dealing with surface mount technology. However, it is easy to explain the threshold in terms of a single transistor amplifer than solid state solid state and digital electronics. I also taught digital electronics and solid state physics and it is common to use a single transistor amplifer to explain what a CHIP or solid state amplifer does since the priciples are the same.
I use the patents and am thinking of asking the folks at Minelab for the schematics so I can look them over for some of the questions about areas that are not explained in the three patents. I am a dealer for them but only signed on about 6 months ago although I taked to them back when I was still at the unviersity off and on for about 2 years. It was when I retired that I got into this more. I only sell to the univeristy and local community and don't do any Internet business. For the most part I only deal with the folks at the univeristy. I am also a dealer for Whites and do a lot with the DFX.
HH, Cody
 
i think that a gold dollar would be a good test.
somehow though, i think the manual is referring to things smaller than a coin, more like a BB when they say - Adjusting the level to 0 will ensure silent operation but could mask audio response to small targets.
however, if threshold "0" makes no difference in my test area, (which includes a 9" deep dime), i'm pretty sure one click below threshold to silent is not going to miss any coins.
i'll just have to try it out.
 
I hope it is not a gold dollar and you may well be right. That is the problem for me in that I have to use it enough in silent seach to know. I have found shots almost as amall as a BB and was amazed when I found the first one. I have never had any problems with the Explorer and depth. If anything I get tired of digging so deep when hunting in a field. I use a small spade and still get tired.
HH, Cody
 
about the "need" for a threshold for the transistor amplifier is concerned, we both know the principals are NOT the same. The op-amp based driver has all biasing, cross-over, temperature, and power supply rejection built into it, which is what makes it near ideal for any purpose, especially this one.
Imagine for a second how complex the discrete transistor solution would have to be in order to perform all of the functions the audio driver chip provides with as few as 3-5 external components. Imagine the level of sophistication it would take to reject the searchcoil drive pulses from the audio amplifier, and it becomes easy to see that no designer in their right mind would use a discrete implementation, unless they had some sort of canned circuit they patented and are drawing usage payments from. Of course then all it would take is a moderately informed designer looking over their shoulder to let management know "hey, you are paying for something that can be done better by a 17 cent chip, and would even save weight". Therein ends the discussion about discrete implemntation of the audio driver.
Seriously, I understand you like to share your knowledge, but wouldn't it be better if you prefaced your comments with an "if" or "one possible reason", instead of launching into a long diatribe of why the electronics MIGHT need a threshold in the old days?
To be clear, your stated reason for a threshold "that a transistor might not be biased fully" has zero application here if we decide (arbitrarily) that a full-blown audio chip is in fact being used.
Now, as for why the manual might indicate the lack of a threashold might mask a faint signal, this one is easy. With a steady threashold tone, it will be easier in some cases for the ear to discern the threshold dropping out and being replaced by a faint signal, than if that faint signal emerged from ZERO background (no threshold).
Again, an audio driver needs no bias or threshold signal to produce or maintain linearity. It's all designed in, over temperature, over power supply fluctuations, over significant ammounts of common-mode noise sources.
I hope this helps.
DAS
 
Sorry you did not care for the explanation or my writing style and will try to do better. However as that is not the topics we are intereted in on the forum we can move on from there. All that aside why not explain how the threshold works in the equations for ground compensation, detection and ID of targets. My assumption is that you understand this and can give a better explanation so we will all gain from the post. If it is how I write or explain things then we are all in trouble as I do an awful job of that.
The three patents are listed in the Owner
 
You are asking the real questions that interest all of us. The problems with solid answers are that the Explorer does not operate like a standard detector and that it is microprocessor controlled. We can only use illustrations that compare the operation to other detectors or circuits that have similar operating characteristics. As an example when we adjust the threshold we are actually supply input to the microprocessor. The MP operates based on an algorithm that attempt to give us maximum efficiency based on the input from the user. Then if we read what the Owner
 
Threshold can tell you if your unit is stable, tells you the amount of trash in your area by nulling, allows you to find good targets next to trash with experience.Depth differences are debateable as even Jimmy Sierra in a video stumbled over it and said it may give you a little more depth.
Some learn to love that little buzz in your ears while others prefer silent search. Minelab gives you a choice...
 
Dan,
I think you nailed this one. Threshold lets you know all is well with the detector. Silent search could also be done accidently with the power off and I know depth suffers in this mode.
I've heard some say they have found real deepies by hearing the threshold null, and not because of a tone. I suspect that they are using discrimination; if they had been using an open screen they would have heard an iron tone. All targets eventually fade to iron sound at the extreme range of detection.
Think this is another one of those personal preferences that doesn't really affect detector performannce.
Chris
 
But the main reason I started with no threshold is because with the settings I started with (given to me by the great BEACHCOMBER) the lowest threshold I got was too loud and very annoying, so I started the one click below and never looked back.
Every now and then I try the threshold, but I find nulling to be annoying and not telling me anything. I much rather hear the chatter of the iron hits, and that tells me much more than a null.
With over 4 years of almost year round experience with the XS, I stand on my finds.
Forgot to mention that three of the four years have been with the 8 inch coil also and I still get deep ones!.. <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)">
Don
 
but what you do get you deserve to miss some. <img src="/metal/html/lol.gif" border=0 width=15 height=15 alt=":lol">
 
I agree the 8 inch one gets real close to what the other one gets in the ground, maybe not in air test, but it does in the ground. That is like on a Fisher CZ, the difference in the 5 inch and the normal 8 inch, is very very little, maybe an inch at most. The bigger coil just lets you cover a lot more ground in less time.
 
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