Gold Bug 2, pulled plug wiring, need help

[Dave J.]

I wouldn't describe any induction balance system as "a walk in the park". But lower frequencies (say 5 kHz) are easier than higher ones (say 50 kHz). If what you actually want is VLF, no point in struggling with LF.

--Dave J.

[Davor]

Technologically it is not a struggle for me at all. Heck, I designed kW power blocks for MW. What I really want to know is - to what end?
It is true that you can not simply translate radio technology to metal detecting near field application, but I guess I got already what it takes.

Please correct me where I'm wrong:
- there is less atmospheric noise at LF hence less chatter and more gain for the same S/N (a motive)
- good conductors like copper, silver even brass are grouped together and indistinguishable by discrimination - which is kinda good for coin shooting as well (not bad)
- poor conductors are nicely spread over discrimination range, small gold becomes more pronounced (nice)
- stainless steel behaves oddly, and appears at random places over discrimination span (WT...)
- sea water becomes more noticeable, and detection depth becomes somewhat influenced by salt content in the soil (ouch)
- ground balance becomes a bit more tricky as the salt content influences it's phase (duh...)
- magnetic viscosity effects are less pronounced than at VLF ( )
- coil nulling becomes more demanding because of the stray capacitances (which can be fixed by balanced configuration)
- there are no stock coils around, except for the GB itself ( )

[Dave J.]

Sounds like you have a good grasp of the technicals. So back to the question-- "to what end?" That's a question only you can answer.

Engineers at several metal detector companies have designed "VLF" type machines to operate in the LF frequency band for the purpose of finding tiny gold nuggets. If you're looking for a stock coil, you'll probably find a White's GMT searchcoil easier to play with than the GB2 searchcoil.

Of course there are 2-box units that work in the LF frequency band primarily for locating buried electrically conductive utilities. These have more in common with conventional RF than with regular "metal detectors".

--Dave J.

[Davor]

Fair enough.

[bklein]

See same question in the Coil forum section. I posted photos of my GB2 plug.

[cnckecgo]

gain increase depth .gain resistance where

[Skippy]

That's not a Goldbug2, you should really start a new thread about your new type Goldbug.
However:
the front-end amplifier is based around the LTAFJ 5-pin opamp chip. It's a standard non-inverting amplifier configuration. If you halve the value of resistor R11, and double the value of capacitor C14, you will have double the gain (and about 14% more air depth). R11 will be low, maybe 20 - 100 Ohms. Just add another equal value resistor across it. Similarly, C14 will probably be 100nF or 220nF, just add another decent quality cap across its pads (use polyester or polypropylene type).

[dbanner]

Dave, Thanks for the reply. The wires are pulled out of the plug that connects to the detector box. I looked at another coil plug and it has 5 wires but mine only has 2. I trimmed back the insulation for 1 1/2 inches and there are only 2 (two) wires, orange & green. I can't imagine how it worked with only 2 wires. It should be a simple fix but I suppose I'll have to send it to Texas.

Just two wires is an impossibility, there must be more than two wires. Strip back the insulation some more or maybe within the two wires are two more wires. Strip back either the orange or green, there's bound to be more wires.

[dbanner]

another possibility is your detector is a pulse induction detector posing as an authentic gold bug 2. where did you get it from? Hopefully not from china?

[Laz]

Schematic for gold bug 2 . Thanks .

[cnckecgo]

5 '' coil

[Tim]

Coil specs for the GM and GB. This may help to design a gold coil. Basically RX is around 10xTX. Far removed from the specs of vlfs. This may be a good laymans indication for gold detector design or back-engineering.
As I have indicated in other posts, sometimes the technicalities of those well versed in trig,calculus and electronics are wholly unhelpful, especially when the calculations done prove to be only near the mark.
In my opinion laymans terms and generalisations are far more helpful in developing an understanding of the principals required for understanding metal detectors.
A list of basic rules would be the most helpful thing.
e.g higher cap values in an oscillator make lower frequencies.
Cap/R combination variations on op-amps affecting gain or offset/trigger levels on other IC's.
Even "basic"(to some) things that can be found in beginner electronics tutorials, such as diodes and clamping, as they relate to detectors.
To mention a few.

Once I get my head around enough of these "basics" myself I may endeavour to create such a list.

[cnckecgo]

Goldbug pro gain How depth increases