LOOKING FOR GOLDSCAN 4 Schematic.

[mschmahl]

Hello Reg.
Thanks for your description of the mod´s you have done. I have one original Goldscan 4 (without coil) and the homebuilt GS4 built similar to alex´s schematic.
My goal was to built a rig, that can find big Silvercoin´s (diameter 4-5 cm).
They are 40-60 cm deep on field´s, that have a lot of iron-trash from WW2 and part´s from tractors.
We don´t have a lot of hot ground and the rig should only find Silver, no Gold (we haven´t a lot here. I have found in ten years only 2 objects).
But I have no idea if the GS4 or TDI is capable of it. On test´s with the GS 4 Original and a homebuilt coil it was possible to cancel iron,
but i lost a lot of deep. But when it comes to cancel iron, than it cancel big Silver too.
And so I thought, the high- and low-conducter-switch can be helpful. Is this right?

[Geo]

Hi Reg.
Thanks for your reply.
The big problem with TDI is that it detect a rust iron wire 2 or 3 cm lenght at 20++ cm and see it as high conductivity. I can't go for hunting with 12" coil. The only way is to use the 60cm coil .... but with it all the small are going out ....


Regards

[Reg]

Hi Geo,

This conductivity thing is more complicated than simply the metal involved. For example, what K is the ring? It does make a big difference in how it would respond. The reason is the alloy content alters gold conductivity significantly. There used to be a website I would refer to but, unfortunately, the information is no longer posted by the company.

If it was, you would see how altering the alloy content can change gold from reading a relatively high conductivity to one that is about the same as lead.

Along similar lines, I have a few nuggets left that further confuse the issue. For example, most gold I found that was over 1/4 oz at Rich Hill AZ would respond as a high conductor, but other gold found a few miles away that was a half oz or so, would respond as a strong low conductor. In this case, the gold surface characteristics play a part but so does the chemistry of the gold. I even took 3 of the particular 1/2 oz nuggets and put them together. Even then the three together responded as a low conductor.

Now, to get back to your question, I can't give you a definite answer on whether the wire is actually a higher conductor or whether the magnetic properties also are involved. I just haven't spent enough time studying that aspect. I just know it does have an influence. In other words, I don't believe the iron object responses are purely the result of the conductivity, but can't tell you how to determine this.

Reg

[Geo]

Hi Reg.
Again thanks for your threads.
I have an question about high and low conductivity. My TDI (similar with GS 4) detects the rusty wires and the silver and copper coins as high conductivity and one thin gold coin as low conductivity. Is it possible a 3cm rusty wire to have better conductivity than a gold coin????. What is happening???. Does the gold coin has so large decay time??

Regards

[Reg]

mschmahl,

You asked about a high/low conductor switch. That is possible and not that difficult to do but it does require several changes, none of which are that difficult. However, to do this, you have to understand why the high conductor objects can be separated by the low conductor ones.

Now, the GS 4 has a form of ground balance. The iron signal channel is used to cancel out the ground signal that is in the gold channel. To do this, the iron signal has to be the opposite polarity such that when the ground pot is adjusted, there will be a point where the ground signal seems to disappear. This adjustment can occur in 3 of the 4 positions of the main operating 4 position switch. Looking at the GS 4 schematic by ALEX this would be the off position where the detector becomes a straight PI with no ground balance. In the other three positions of the switch, ground balance can occur.

When you adjust the ground balance (GB) pot, you adjust between the gold signal and the iron signal. When the ground signal is minimized, it just so happens that many of the signals from various objects are now positive signals while others are negative signals. The larger iron objects and certain non ferrous metals such as silver and copper will become one polarity while other coins, small gold will be the opposite polarity. So, by selecting which one, the positive signal or the negative signal, we can select between high conductor and low conductor.

This selection is done or can be done by selecting the outputs of U13b. You will notice there are two diodes in the feedback with signals from those diodes going to the next stage. By selecting one or the other output you can select high conductor or low conductor. If you allow both, then you have the all mode. The way the detector is built following the present schematic, you can select all or low conductor. If you chose either SEL mode, the positive signal is disconnected by SW1-b.

There is another mod that greatly simplifies this GS 4 design that works very well with the high/low selection and that is if you are willing to buy more expensive low offset IC's and use them instead of the TL064's you can eliminate several of the adjustments. IC's like the OPA4277, LT014, LT1114, or one of several others that have an offset voltage of 100 uv or less will allow you to eliminate some of the adjustments that are a pain to adjust correctly. This pots that can be eliminated are RV 5, 6 and 7 associated with U13 and RV 1 and 3 associated with U12. Each of the pots mentioned have a resistor connecting the center leg of the pot to the rest of the circuitry and this resistor can be eliminated also.

The key is to use very low offset IC's in place of the TL064's. Right now, you can purchase some of the low offset IC's for as low as $5 or even less for used LT1014's if purchased from ebay. The used LT1054's are $20 for 10 IC's.

Be careful when making a selection and keep the current drawn by each amp in the quad at 1 ma or less. Picking an opamp with a current draw of 5 to 10 ma per amp can cause loading of the power supply.

If this mod is done by selecting low offset opamps, then the high/low switch is quite easy.

BTW, the 4 position operating sel switch can be eliminated, thus further simplifying the design. SEL 1 and SEL 2 were designed so a person could hunt certain coins in England. One can still do this but would require a little more skill in the adjustment to accomplish the same thing plus other things.

Eliminate the probe circuitry and things become even simpler.

In other words, this detector can be simplified quite a bit for those interested.

Reg

[Reg]

mschmahl,

Keep in mind that the GS 4 will not ignore all iron objects. Small or thin pieces of ferrous metal will still sound off. It is the larger pieces such as a 3" length nail or maybe a screwdriver blade or larger that will be ignored.


When larger iron objects are ignored, other objects will also be ignored such as US silver or copper coins or other silver or copper objects that are coin size or larger.

When ignoring ferrous objects, only the signals that are negative at the output of the U13b will be heard. Use Alex's pdf schematic when looking for U13b.

Reg

[lucafa]

no resistence in my original goldscan 4

[Jose]

Hello Eduardo, Davor
GS4 homemade, no resistance of 1 K.
Carries out tests this weekend to see if there is difference.
Jose

[Davor]

I'm not sure if 1k would make any serious difference. The only consequence would be pushing UA709 output deeper into A class regime. It would not hurt anything either.

[eduardo1979]

Hello ABDW9
This is the way I set my GS4 and works well:
Do you have to be a leg to adjust RV5 U13 at 0 V instead of the leg 7?
"Yes !!!"
Adjusted R8, to 0 volts on pin "6" of 5534, with the coil connected, away from all metal.
All adjustments in position 2, "all metal", follow the steps outlined above in post 102.
After adjust RV7 to 0 Volts in pata "8" of U13 C, Change SW1 in position 1, "OFF", and adjust RV6 to 0 volts again in pata "8" of U13 C.
Check iron rejection mode is "SELECT 1" No. 3 of SW1.
Prepare a video later.
regards
Jose

The scheme has an error. I added in the scheme a 1K resistor, because missing. Greetings.

[Jose]

Hello ABDW9
This is the way I set my GS4 and works well:
Do you have to be a leg to adjust RV5 U13 at 0 V instead of the leg 7?
"Yes !!!"
Adjusted R8, to 0 volts on pin "6" of 5534, with the coil connected, away from all metal.
All adjustments in position 2, "all metal", follow the steps outlined above in post 102.
After adjust RV7 to 0 Volts in pata "8" of U13 C, Change SW1 in position 1, "OFF", and adjust RV6 to 0 volts again in pata "8" of U13 C.
Check iron rejection mode is "SELECT 1" No. 3 of SW1.
Prepare a video later.
regards
Jose

[ABDW9]

Hello Jose and all,

Deep is now good, but i can´t eliminate iron.

Must it be leg 1 of u13 to adjust RV5 to 0 V instead of leg 7?

How had you adjust RV1, RV3 and RV 4?
I have adjust RV1 leg 7 u12 to 0 volt, RV3 leg 1 u12 to 0 volt and RV4 leg 10 u12 to -7mVolt.
Which position have SW1(always 2 "All Metall") to adjust RV1-RV8?

Here is a Scopeshot of first sample.
bottom-line is Output of NE5534
upper-line is U5 pin6/11

First picture 5V/15uS
Second picture 5V/5uS

hi thanks for all
I want to see this work The Video

[Jose]

Thank´s for all your help.
Now the deep is good. But i can´t fix the problem with the iron.

I bought an original goldscan. So i can compare both.

I have changed the original GS4 so that i can use the military-coil with seperat tx and rx.

Are there other mod´s?
I have read something about a "single-tone-mod" and "high conducter and low conducter switch" from reg on the GS5 and GS4.
Does anyone knows more about it?

Señlales check for the integrator, in the channel of iron.
Deputy scheme GS4, home made.
Jose

[mschmahl]

Thank´s for all your help.
Now the deep is good. But i can´t fix the problem with the iron.

I bought an original goldscan. So i can compare both.

I have changed the original GS4 so that i can use the military-coil with seperat tx and rx.

Are there other mod´s?
I have read something about a "single-tone-mod" and "high conducter and low conducter switch" from reg on the GS5 and GS4.
Does anyone knows more about it?

[Jose]

Hi mschmahl
SW1, position 1 "OFF" is a common detector, does not discriminate, (does not remove iron).
SW1, position 2 "ALL METAL" is a ground effect detector does not discriminate, (does not remove the iron).
SW1, position "SEL 1" and "SEL 2" if it discriminates, (removes iron).
Use "SEL 1" for discrimination tests.
If ...., adjust RV5 for 0 volts at pin 7, U13: B; (This recommended "Gurus" elsewhere in the forum).
The other settings:
SW1, position 2, potentiometer "GND" to a minimum (side of R52).
Pulsar "RESET".
Adjust RV1 to 0 volts, leg 7, U12: B.
Adjust RV3 to 0 volts, pin 14, U12: D.
This mode setting RV3, I conducted to ensure that the voltages are equal at the ends of potentiometer "GND". In this way, does not affect the set "Threshold" as you move the cursor to "GND".
I found it easier, make some adjustments when RV1 and RV3, conform to 5 millivolts negative, instead of 0 volts.
RV4 adjustment is different from those described in the forum, maybe because I did not get the J113, and I use one on a replacement.
Try adjusting this way:
Release control "RESET"
After adjusting RV1 and RV3, switch SW1, to the point 1 "OFF".
RV4 adjustment at a point where the sensitivity decreases sharply.
This control back until you feel that the sensitivity increases, this can usually notice a slight instability or increased noise in the speaker, use maximum sensitivity, or a small metal object for testing.
From the point of maximum sensitivity and the gain drops sharply where is the best point. I have my doubts on this method, but is the only one that worked for me GS4 homemade.
You may need to repeat the settings for RV5, RV6 and RV7
The image of the oscilloscope, looks good.
Excuse my English, which is the product of the translator.
Jose