TGSL Tuning & troubleshooting

[lunamay]

hi
finaly i repeired my md..once i conected +to - and -to+..big mistake made by hot weather and to much sun on head:P:P:P..something has broken..i was looking for broken part and then i read that i should replace parts in audio circuit..now i can say to eweryone who will make this kind of mistake and uses a computer power suply for tests,that he should replace a 7808 part..i just did that and my md works great

best regards

[Vladimir]

hi
finaly i repeired my md..once i conected +to - and -to+..big mistake made by hot weather and to much sun on head:P:P:P..something has broken..i was looking for broken part and then i read that i should replace parts in audio circuit..now i can say to eweryone who will make this kind of mistake and uses a computer power suply for tests,that he should replace a 7808 part..i just did that and my md works great

best regards

Hi
I'm glad that your detector works again, it would be good if you present the measurement sensitivity in the air.
Regards

[simonbaker]

hi
finaly i repeired my md..once i conected +to - and -to+..big mistake made by hot weather and to much sun on head:P:P:P..something has broken..i was looking for broken part and then i read that i should replace parts in audio circuit..now i can say to eweryone who will make this kind of mistake and uses a computer power suply for tests,that he should replace a 7808 part..i just did that and my md works great

best regards

Glad to hear it. I hope you can save up for an oscilloscope soon, because that will allow you to really see how it works and allow you to make interesting mods and also give us data to help all of us with tuning.

Regards,

-SB

[nakky]

Yes, I could see that.. The shield should remove most of the undesirable effects though. Nakky, do you observe this at reduced sensitivity?

Don

Both coils are shielded
Reduced sens to zero, forearm still sounds
When disc at 7 pulltabs rejected,there is no sound of forearm

Grt Nakky

[dfbowers]

Yes, I could see that.. The shield should remove most of the undesirable effects though. Nakky, do you observe this at reduced sensitivity?

Don

Both coils are shielded
Reduced sens to zero, forearm still sounds
When disc at 7 pulltabs rejected,there is no sound of forearm

Grt Nakky

Wow.. I donno. The TGSL is not supposed to do that. Mine is dead quiet at near maximum sens and minimum disc. Although my X5 will sound slightly near a body and my Classic I will do the same thing.

Are you sure that you don't have a metal plate in your arms from a past life? (Just kidding).

I can only speculate without looking at it first hand. Grounding would be my first guess since I can reproduce that symptom by ungrounding my coils but I guess we have to rule that out.

Is your arrangement mechanically sound? How about the cable? Is your detector free from noise when you touch or move the cable?

Don

[dfbowers]

More on grounding and shielding.

In one of my previous posts I said that I was having trouble with wet grass. I have since discovered that one of my coils was improperly grounded.. I mistakenly tied ground to the non-inverting input (J2-1 instead of J2-2) inside the coil. Too bad it's already cast in epoxy! The coil works absolutely fine otherwise and is a "good" one. I just have to use it when it's dry outside.

Anyway..

I had set out to independently verify which coil grounding scheme is best.
I came to the conclusion that what is documented in the "TGSL coil making" pdf IS best. Most notable, I found that a much deeper null can be achieved when J2-2 is grounded inside the coil. Other ways seem to work OK as well, but just not as good. Even with no grounded RX at all, grounding J2-2 on the coil end and to both shields will give a much deeper null. My advise to everyone testing coils.. Do your testing with shields installed, grounded AND using your final cable, even if you do not intend on finishing the project! It does make a difference.

Don

[mikebg]

Don,
Please write as circuit diagram your mistakenly tied ground and post it in the forum. We will try to diminish the bad effect by adding external components.
Mike-BG

[pebe]

In one of my previous posts I said that I was having trouble with wet grass. I have since discovered that one of my coils was improperly grounded.. I mistakenly tied ground to the non-inverting input (J2-1 instead of J2-2) inside the coil. Too bad it's already cast in epoxy! The coil works absolutely fine otherwise and is a "good" one. I just have to use it when it's dry outside............

Don

You could probably correct the situation by reversing the leads of both coils.

[simonbaker]

In one of my previous posts I said that I was having trouble with wet grass. I have since discovered that one of my coils was improperly grounded.. I mistakenly tied ground to the non-inverting input (J2-1 instead of J2-2) inside the coil. Too bad it's already cast in epoxy! The coil works absolutely fine otherwise and is a "good" one. I just have to use it when it's dry outside.

Anyway..

I had set out to independently verify which coil grounding scheme is best.
I came to the conclusion that what is documented in the "TGSL coil making" pdf IS best. Most notable, I found that a much deeper null can be achieved when J2-2 is grounded inside the coil. Other ways seem to work OK as well, but just not as good. Even with no grounded RX at all, grounding J2-2 on the coil end and to both shields will give a much deeper null. My advise to everyone testing coils.. Do your testing with shields installed, grounded AND using your final cable, even if you do not intend on finishing the project! It does make a difference.

Don

Thanks for those experiments, they are very interesting to me. When you get time, it would be great if you could go into more detail of each connection and what you observed -- a diagram would be nice.

I really don't have a good understanding of what the shield is doing or shielding us from -- electrostatic gradients; high voltage "static"; EMF, etc., and why the different grounding configs have the effects they do.

I believe graphite type shields are also used as discussed on these forums (fora?). It would be interesting to mix sufficient graphite into the potting resin and see what kind of shield that makes instead of foil.

Regards,

-SB

[simonbaker]

In one of my previous posts I said that I was having trouble with wet grass. I have since discovered that one of my coils was improperly grounded.. I mistakenly tied ground to the non-inverting input (J2-1 instead of J2-2) inside the coil. Too bad it's already cast in epoxy! The coil works absolutely fine otherwise and is a "good" one. I just have to use it when it's dry outside.

Anyway..

I had set out to independently verify which coil grounding scheme is best.
I came to the conclusion that what is documented in the "TGSL coil making" pdf IS best. Most notable, I found that a much deeper null can be achieved when J2-2 is grounded inside the coil. Other ways seem to work OK as well, but just not as good. Even with no grounded RX at all, grounding J2-2 on the coil end and to both shields will give a much deeper null. My advise to everyone testing coils.. Do your testing with shields installed, grounded AND using your final cable, even if you do not intend on finishing the project! It does make a difference.

Don

Even with no grounded RX at all, grounding J2-2 on the coil end and to both shields will give a much deeper null.

Would you clarify that sentence? How can J2-2 be grounded but RX not grounded? What do you mean by "coil end"?

Did you experiment with grounding one coil shield but not the other?

By "both shields" I assume those are the coil shields, not the cable shields (since you typically use a cable with one shield -- but Vladimir for example uses cable with two shields).

Another thing I'm not clear on is the value of shielding the TX coil -- how much difference does that make? What is the principle? It would be interesting to see performance with only RX coil shielded.

One more question -- how did you experiment with the grounding? Did you make a special coil with all wires exposed?

We can stay busy a long time with these combinations!

Regards,

-SB

[simonbaker]

You could probably correct the situation by reversing the leads of both coils.

I think then coil shields not directly grounded.

-SB

(which brings up a point. If if cable shield is grounded at PCB side only, and coil shields connected to cable shield only (not TX ground wire in coil head), then easier to switch leads like pebe suggests. But would it work as well? Another config to try.)

[dfbowers]

I think then coil shields not directly grounded.

-SB

(which brings up a point. If if cable shield is grounded at PCB side only, and coil shields connected to cable shield only (not TX ground wire in coil head), then easier to switch leads like pebe suggests. But would it work as well? Another config to try.)

One difficulty I am having with trying different grounding configurations is that the coils seem to null at different places depending upon where the shields are grounded, so I don't think that I can cast a set of coils in epoxy with wires exposed. I'm just going to have to make several complete coils and evaluate from there. I may be able to make some sort of quick disconnect to try different cables though. Waiting for epoxy to harden..

[Vladimir]

If I understood well, there is a substantial lack of understanding of concepts, Shild the coil and GND on the board are exactly the same and thus should be connecting. Depending on the type of cable used, it can be different connecting from Shild cable. But the basic concept SHILD-CABLESHILD-GND must be respected.
Regards

[Krzysztof]

Hi Dfbowers.
Modest attention.
In radioamateur and measurement systems, the general principle has always been to connect the screen to the ground only on the PCB. Reason - the countervailing currents.
The combination of ground to the coil and the PCB exits the screen frequency, then the earth loses its meaning.
Do you have a good electrical connection to the Al foil in the head coil?
It is always problematic.
Best regards Chris.

[Qiaozhi]

The shield of the cable should only be connected to the GND on the PCB. One wire from the RX pre-amp (the one that goes to the inverting input of the opamp) should be connected to the shield in the search head, not GND on the PCB. Obviously other configurations do work, but the way Tesoro does it results in less noise pickup. Some of the Chinese detectors provide the GND connection in the socket on the control box, but the reason has more to do with flexibility, allowing the coil to be used on many different designs, rather than best practice. However, be aware that each configuration changes the balance of the coil. You can try wiring the RX coil without connecting one side to the shield, or even using a center-tapped RX coil with the tap connected to the shield. It may be purely subjective, but it appears to me that Tesoro's approach is more stable, less noisy, and easier to coil balance.