Experimenting with the GMT and an external speaker

Thought I would share this with members, I have a GPX4500 and decided to get my wife a lighter detector to swing and decided on an almost new GMT with the standard and small coil. Initial experience was it was hard to get an even threshold in the Victorian goldfields without lowering the gain to about 3 or 4 whereas the book says 8 is the starting point. Lowering the gain by this much drastically reduces the depth and sensitivity to targets. If you air test while playing with the gain you will see a huge difference. Second issue was that my wife doesnt like headphones. The built in speaker even on boost is not much good. I had purchased a Nokia MD-11 mini speaker from Ebay for $11 that has a built in amplifier, runs on 2xAA batteries and has HEAPS of grunt to use with my 4500 portable battery pack. Have to use an adaptor (not sure why but don't insert the adaptor all the way in, just to the first click). Took the detector out a couple of weekend ago and set it up like this......

Turn on and ground balance, ramp the gain up to 10, then wind back to about 8, lower the threshold to just on silent so that irregular threshold can't be heard. Start swinging! This is an absolute DEADLY machine once you add the speaker, although I found no gold that day including with my 4500, this detector hit every target. ..........with this speaker and the threshold down near silent there was NO false targets or irregular ground noises, the finds ranged from tiny peices of wire that were almost invisible, and tiny tacs that would be hard to find even with my 4500 and an 8" coil........ to buttons, shot gun pellets and the usual rubbish. With the speaker there is no second guesing, the sound is strong and accurate. Another note on pinpointing........the detecting field on these starts under the top bar of the T printed on the coil NOT the tip of the coil. Test it out and please let me know if you find the same thing. Once I realised this I located and dug every target out in the first scoop. I will be taking this back to a patch that I found a few nice small nugs in with the 4500 and am confident that the GMT will find more. Happy prospecting to all!

sounds like a great setup will have to look into the mod once I get the camper finished thanks for the great story and info mate




cheers starry

Thanks Starry, that speaker is a gem, had a spare so tried it on my mates GP Extreme.......absolutely blew him away. Lot cheaper and less bulky than an inline amplifier and crystal clear sound.
Good luck with the camper.
Cheers

Hi Folks, Hi Mannalay, sounds like a good thing,what was that speaker listed under on ebay or was it a one off?
Regards
Wayne.

Buy off this guy, mobileland888, he's in Melbourne, delivered by post in a couple of days for just under $10 plus post.

http://www.ebay.com.au/itm/Brand-New-Nokia-Mini-Speaker-MD-11-Black-Buy-More-Save-More-/221010841487?pt=AU_MobilePhoneAccessories&hash=item337545cf8f

Cheers

HI Mannalay, I got one also on your recommendation, well spotted.
Sparrowfart.

mannalay, thanks for shareing you may have just saved me a couple of hundred dollars, I had have been looking at a booster speaker for the same reason, to get away from head phones. I have a TDI pro might try this little speaker first.
Cheers
Peter

I got one of these speakers for the TDI pro, and it's great. Made up a little bracket to mount it on the detector shaft beside the handle and a longer lead to chest mount if need be.
I have a very small bit of lead berried in the lawn for testing, i can hear the sound a lot stronger than i ever could with the head phones. Can't wait to get out next weekend. Very pleased with the result.

Cheers.

to see your new speaker system will let you hear the sound of heavy metals.

ivanll

Hi Mannalay - thanks for the tip. Just got a 2nd hand GMT so will try it out.

Did you ever get back on your patch to try it?

This is what i like about this forum, So many people prepared to share there experiences and finds/ideas.

Tested the speaker out at Tambaroora today & thought I 'd post some feedback.

Although only my 3rd time using the GMT I found the addition of the speaker was an improvement. Ran the gain at 8 for a fair while but did drop down to between 6-7 (had heard to drop to 5 for noisy ground so this was good) & it was more stable set to this. Was able to adjust the threshold to near silent & found the target signals a lot better with the speaker.

Found no gold but did find various small pieces of lead bullet head (looked smaller than 22 but bigger than slug gun?), aluminium (ring pulls + various very small to large pieces of cans) &, of course, various sized scrap steel all at good depth. The deepest find was a 1" square piece of rusty mesh down about 10" under some well imbedded rock. Was going to walk away once as the rocks were getting the best of me, & it was reading 75 on the iron probability meter, but curiosity got the better of me.

The tip that Mannalay gives about where the coil picks up (near the T) appears correct also. I have testing this out & I am finding the targets fairly quickly. Today I swept over an unfilled hole & got a good signal (was
about 70 iron probability though). Using Mannalay's theory I pinpointed the target about 1-2 inches to the left of the open hole & found a small nail head where I estimated.

This is probably the only small fault I have with the GMT in general - the iron discriminator doesn't always "grunt" at very small or flat steel, although when I have dug a "grunter" it is always steel, never lead etc.

Overall the addition of the speaker has given me some more confidence in the GMT & when I do stumble upon some gold it will pick it up.