Level Adjust Question

On the GP 3500 the level adjust is used for discrimination for steel and allows the signal to break up and blank out on shallow steel targets with DD coils.
I have also found when this is used at about the 12 oclock setting with a Mono coil it seems to alter the sound of steel targets which is use full and also shortens or compacts the signal response to allow multiple targets to be heard and picked out on a narrow coil swing.
Has anyone else seen or used this for this function with a Mono Coil ?
Mark

This dial is marked iron discriminate on the 3500
Mark

Hi MS, are you in All Metal mode or Discrim with the mono coil?

JP

Hi Jonathan
Yes that's with the iron discrimination on and in about 12 to 1 o'clock position.
I have only noticed this as I was using a DD coil and accidentally left the discrimination on when I changed over to a mono coil in trashy ground.
I normally would have never used this function as I didn't think there was any use with mono coils but as I said before it seems to alter the tone on trash targets but not to the same point on discrimination with a DD and also with a large coil ie 24" elipt mono seems to compact the signal response from multiple targets which rather than get get one signal you get definite individual target responses
Cheers Mark

If you thump a Mono coil flat on the ground in discriminate mode it will blank, and I think from memory it will also blank on some targets even good ones, but because there is not a second winding present it is NOT reliable so I would not recommend it for discrim purposes (although it is interesting what you have discovered).

As for the Level Adjust it has an impact on two things (Post Note: this info is only relevant to the GP extreme and GP3000), one is the level or amount of discrimination and the other is the level/amount of Pausing Effect on the Ground Balance assuming you are in the Tracking mode, from memory I used to run the Level Adjust on or about 12 O clock using the Medium Tracking speed. If the detector did not pause the GB over a suspect target you could balance one out very easily so there has to be a happy medium between enough GB to deal with ground noise but also enough pausing effect to pause on good targets but help track out ground noise responses. A general rule of thumb to aim for with the Level Adjust is three passes over a suspect target, if the response reduces considerably in three passes then it is most likely ground noise, I usually perform the test from different angles to be absolutely sure.

Hope this helps,

JP

Thanks JP that does help in what's going on.
I must admit I have been very happy with the design and functions of the 3500 and whilst I don't know much about the 4500s the 3500 is a very capable machine and even after a year and a half I'm still learning new tricks with it.
Cheers Mark

The 3500 was and still is an excellent detector, I loved the audio and really miss it compared to its newer digital brothers.

JP

G'day JP,Mark, I'm having a bit of a head scratch with these post's.
I am almost always in fixed but it was my understanding that in the
3500 the level adjust was set at the factory, ie non adjustable.

I know the Extreme and 3000 worked as described but they had a level adjust knob.

Can someone confirm the level adjust in the 3500 is incorporated in the discrim knob???

Good question Inhere, I'll have to check back with you on that one. I know it is not an option on the GPX-4000 but there is a Level Adjust control on the 3500 so presume it is still the case. Been a long while since I used a 3500 and some of the details slip through the old grey matter I'm afraid.

JP

Inhere your right, just dug out my old 3500 control box and the Level Adjust has been replaced by an on/off dial control. They ran out of room on the front end cap due to the new manual tune control and the three tracking speeds switch so "factory set" the Level adjust at the optimal setting.

Sorry all for the confusion.

JP

The reason I called the Iron Discriminate dial{ level adjust} was I was talking to someone with my findings with the mono coil and they said this dial was dual function .
So it sounds like this is not the case and the level adjust is fixed, so the altering sounds of metal/steel targets to gold/lead that I found is slightly altered in tone with a mono coil is due to a simple partial discrimination only ?.
The extra ability also to shorten or narrow the target response seemed to happen with the targets I was picking up and that is the reason I was asking this question to see if others have noticed this or not.
Anyway thanks JP / inhere and sorry for the mix up and it's fully understandable that can happen with so many models with changing names and functions .
Cheers Mark

Mark,
I think you'll find the GP3000 had it called the "level adjust" as it not only controlled the amount of discrimination, but also the pausing effect on target responses if detecting in tracking mode. I'm not sure about the GP Extreme as I never had one of those. The 3500 as JP says had the level adjust preset in the detectors electronics. Cheers.

Hi Mark, so Its not a level adjust.
Who cares it was still an interesting thread.
I'll give your findings a go next time I get a mono over a target, just to see if I can work out what is happening.

Cheers

Hi Inhere
I would be most interested in your findings
Cheers Mark

by Qld Sandy on Sat Apr 03, 2010 8:33 am "Mark, I think you'll find the GP3000 had it called the "level adjust" as it not only controlled the amount of discrimination (in Disc. Mode), but also the pausing effect on target responses if detecting in tracking mode."


Thanks Sandy, yes I knew that Level Adjust has a dual purpose on the GP-3000. And if in both Discrimination Mode and Tracking Mode are used at the same time I was told to put it at 12 O' clock.

BUT a question for anybody, on my GP-3000(or on a GPX-4500) if I use my (stock 11" or NF 20" XP) DD coil in Discrimination Mode(even with the Level Adjust set at max. fully clock-wise) will I lost depth as compared to All-Metal Mode ??

(Because on VLF machines, Dicrimination Mode has less depth than All-Metal Mode. Also usually the more discrimination you use, the more depth you lose. Do Pulse Inductions(PI's) like the SD/GP(X) series work the same way as VLF's in this aspect, or not.)

Thanks for any help!

The Minelab PI's do not lose depth when discrimination is used, however the more mineralised the ground the more unreliable the discriminator can become. Coin and relic machines with notch discrimination are different, to maintain full depth they need to use an all metal mode with either an Iron grunt or some other ferrous only indicator.

Hope this helps,

JP

Jonathan Porter wrote:The Minelab PI's do not lose depth when discrimination is used, however the more mineralised the ground the more unreliable the discriminator can become.

Coin and relic(VLF) machines with notch discrimination are different(they lose depth in Discrimination Mode but), to maintain full depth they need to use an all metal mode with either an Iron grunt(on the GMT) or some other ferrous only indicator(like Iron Mask-IM on the X-Terra 70-705).

Hope this helps,

JP

JP, I added my thoughts in (brackets) to help me grasp it better. Hope you do not mind. Thank you very much for your help, it makes things more clear to understand.

I think Discrimination Mode can be used in Psuedo Mono Mode on a DD coil. But very briefly, can a person use Discrimination Mode in XP mode ?? (If I had to guess I would say 'yes'.) Thanks again.

Discrimination is only reliable in DD mode with a DD coil, not any other mode.

JP