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X-Terra 705 Threshold.. Air Tests Added

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I had been running my threshold setting at 7 to get the slight hum in my phones and it finally dawned on me this is not an optimum setting for picking up deeper fainter signals since a setting closer to 0 should be best.  Having always ran the detector volume control in the upper ranges and using the headphones to control the audio level, I decided to switch it around by setting the headphones to max and using the detectors volume control to set the overall audio level.  This made a huge difference, now I can get that same slight hum with a threshold setting of 2. Subjectively there seems to be much less modulation on the deeper targets where now coins in the 10"+ range are much louder hits.  I'm also running the detector volume control at 4 to 5 to get the same audio volume I was getting before with it set in the mid 20's.

Tom 

OK so I decided to do some air tests to see what difference there is in audio modulation and on coin size targets there is a difference in audio the last few inches.

First number is a full audio report distance (or as close as my ears perceive it), second number is the distance target lost.  The difference between is the amount of audio modulation where the target volume decreases to the point the signal is lost.

The first column is with the headphone volume at max and threshold audible at 1 setting (0 is silent),  second column is detector volume at max with threshold at 7 (6 silent)

  • Headphones max......................-... Detector max
  • dime............. .............9" /10" ...- ..7" / 10"                
  • Buff nickel......9-1/2" / 10-1/2" ...-.. 8" / 10-1/2"
  • IH penney..........10" / 10-1/2"....-....9" / 10-1/2"   

As we see there is no difference in detection distance between the 2 settings but a more modulated audio response with the detector volume at max.

I also tried the dime with the detector volume at max with a 0 threshold setting and the results were a full volume report to 6" with a max detectable distance of 9", for a 1" loss. Because of this it is apparent that ML has designed the threshold level to follow the volume setting (7 equals 1) which would allow max sensitivity when the detector is used without headphones in cases where a high volume setting is needed to overcome ambient noise.   The loss of response on the dime indicating a negative threshold setting because at this volume setting 6 is actually zero.

Since these were coin sized targets and not tiny nuggets the difference could be even bigger when nugget hunting.

 

 

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Somebody convinced me a long time ago to always if possible run detectors at full volume. Some detectors do not have a volume control, and that is just the way it is. The claim back in the day was that lowering the volume on the machine actually did have an effect on lowering the sensitivity also, so the theory was run detector at full volume then adjust to suit with headphones. To this day that is how I run machines that have an actual knob control, like the Gold Bug 2. In other words, analog detectors.

My setup is 1. Low volume on detector. 2. Wave coil over large object and increase headphone volume to "safe" level on large blast targets. 3. Set threshold to suit. Works for me.

However, with digital I have been lazier. Like on my DFX. I just run whatever the default volume setting is and adjust headphones to suit. The default volume is quite loud, so much so that if I run without headphones I want to lower it, so increasing it to run with headphones never occurred to me. And my GPZ I run with the WM12 wireless module that has no volume control, so I am forced to adjust volume with the machine itself. I am not sure that the old analog volume rules apply as much to digital machines if at all.

I guess at the end of the day it just goes back to experimenting with and learning what you have.

The X-Terra 705 is one sweet all around detector. I could own one and nothing else and get by pretty well. I really like the all metal Prospect Mode, very powerful. The disc modes however always seemed lackluster in my ground by comparison. It always seemed to me like the gain could have been run higher in the disc modes.

Tom, I saw you were considering the Impact. It is like a Racer 2 Deluxe and as I recall you were not impressed with the Racer 2.

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Hi Steve

In disc with a wide open screen I set the threshold at 0 anyway for silent search.  Using a stock or modified coin mode is were this helps being able to hear the blanking of the threshold. 

Re the Impact,  I am not sold on it however, as it turns out I am getting the chance to test one here in a week or two.  Word is the audio is at least somewhat better than the blendy/bleedy R2.  It doesn't matter to me how well it performs if I can't adjust to its language.

Tom

Oh and by the way,  the proper way to set the volume is to start low and increase it to a comfortable level.  Try it, you will find it not set as loud vs the way you were doing it.

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On the E-trac and the CTX there is a lot more modulation between your set threshold and max volume. If I remember correctly the E-trac even has a specific control to adjust it, called variability. The 705 lacks a bit in that department. It is calibrated from 0 threshold to max volume. So when you drop max volume everything sounds just as large.

Hunting in disc you can't really connect and paint a picture what is going on beneath the coil. As much as the 705 is my pet detector, I'm in dire need of something with superior modulation in disc mode. And which suits my shot elbow. Can't handle machines which need to be swept fast.

Anyway the prospecting mode on the 705 is a work of art. More than deep enough even when hunting low sensitivity and a buttery smooth threshold. And you shouldn't reserve prospecting mode just for the 18,75 kHz coils. Try those 7,5 kHz coils and just walk away in amazement at the depth and sensitivity this little Minelab can achieve.

But then again don't believe me, I'm an official 705 addict.

 

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Part of my beef with the 705 was the faint target response on 10"+ coins. They were there but oh so faint.  Whether or not that was due to running the threshold at 7 or not I do not know.  Now with he Mars 10x13" Tiger coil in place of the 10.5" DD ML coil and the new set up, targets in that range are clearly heard.   Could be mostly attributable to the larger than stock coil or a combination of both. The end result is I'm happy with it as a deep coin hunter..

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6 hours ago, Steve Herschbach said:

Somebody convinced me a long time ago to always if possible run detectors at full volume. Some detectors do not have a volume control, and that is just the way it is. The claim back in the day was that lowering the volume on the machine actually did have an effect on lowering the sensitivity also, so the theory was run detector at full volume then adjust to suit with headphones. To this day that is how I run machines that have an actual knob control, like the Gold Bug 2. In other words, analog detectors.

My setup is 1. Full volume on detector. 2. Wave coil over large object and reduce headphone volume to "safe" level on large blast targets. 3. Set threshold to suit. Works for me.

However, with digital I have been lazier. Like on my DFX. I just run whatever the default volume setting is and adjust headphones to suit. The default volume is quite loud, so much so that if I run without headphones I want to lower it, so increasing it to run with headphones never occurred to me. And my GPZ I run with the WM12 wireless module that has no volume control, so I am forced to adjust volume with the machine itself. I am not sure that the old analog volume rules apply as much to digital machines if at all.

I guess at the end of the day it just goes back to experimenting with and learning what you have.

The X-Terra 705 is one sweet all around detector. I could own one and nothing else and get by pretty well. I really like the all metal Prospect Mode, very powerful. The disc modes however always seemed lackluster in my ground by comparison. It always seemed to me like the gain could have been run higher in the disc modes.

Tom, I saw you were considering the Impact. It is like a Racer 2 Deluxe and as I recall you were not impressed with the Racer 2.

Steve

The Fisher 1270 was like that.  The volume control also controlled the gain.  With the volume set high you could still get coin sized targets at good depths with the sensitivity set as low as 1.  Also if the machine got a bit cranky at high sensitivity lowering the volume smoothed it right out.  It wasn't just me that observed this behavior Keith S. also commented on it.

Tom

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The 705 has superior tracking without a doubt. But you need to turn it off in disc mode when hunting for those deep targets and still maintain a very accurate ground balance.

Several occassions I've had the slightest whisper of a target in disc mode, thinking it was a false. But there is no such thing as a repeatable false in exactly the same spot.

Switch to prospecting mode and it tries to track the target out. Then you really start to doubt yourself. But they do exist.

 

My settings for max disc depth on the 705.

2-tone, disc pattern all accept, threshold 1 point below audible, max volume, tracking off, sens just below falsing, GB spot on "actually listen to the minerals to get a really clean spot", noise cancel. And a little party trick, put a crosshairs on your coil. Not a hot-spot, but a real crosshairs N-S E-W.

You will catch targets with a correct non-ferrous audio and no TID, you will catch targets prospecting mode will try to track out,... you will need a deeper digger!

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I run my 705 on threshold of 1 so I can hear the faintest signal and the volume on max. Like Steve said the connection between gain or sensitivity and threshold is very much connected with the 705. You raise the sensitivity in upper ranges your thershhold with be louder and noisy. You back it way off and your detector will be quiet and you WILL hear your target if it is within the depth range that the 705 can reach. Trust the 705 it will never cease to amaze you.

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