TGSL Tuning & troubleshooting

[Nandor]

BKY1337 you must have the correct phase shift that's the main goal otherwise your detector wont work properly. No problem if it's chattering at max Sens it's because of EMI noise. Try to change some IC's as Homefire said that should help.

[BKY1337]

Did you use 1% on all resistors ?

If you socket all IC try swapping out U102 and U103 with spares if you have any. All Op Amps are not created equal.

No i did not, it was the Kit from Silverdog and he forgot one or two resistors , i replaced them with 5%. But i used this metal detector in the past and his depht was good , 38cm without shielding with other coil , but this was before i short connected the circuit.

[Nandor]

Hi! Big metal object is no problem but if it's a small one than the disc is off phase I think. At 3 out of 10 it should not detect iron at all, mine does this way. The Geb pot when is at <- Ccw position it's 100K so ferrite is accepted, at 40Kohm-50ohmK or half way it should not be detected at all, Cw -> is to reject ground.

[ripsdevala]

Need help, im suck with vlf, made 2 semi smd board here the two have diferent geb behavior

[homefire]

No double tone here.

[ripsdevala]

Hello! Do u all can reject iron in disc mode when waving very close on the coil? I cant, is this normal?

What is right geb pot behavior?
Test from Middle pot with 5cm ferrite:
Ccw double tone, cw reject ferrite completely
Or
Ccw double tone, cw single tone

[homefire]

Did you use 1% on all resistors ?

If you socket all IC try swapping out U102 and U103 with spares if you have any. All Op Amps are not created equal.

[BKY1337]

It was a little bit better with geb in middle position and sens at min but still not satisfying and its clackering again.

[BKY1337]

My Geb is where it was before when it rejected ferrite , sens was almost at maximum , was this wrong?
I need to put my coils from this damn enclosure and lay them on the table to test them.

I have wound my coils in the same direction. And the cables came out from the same place.

I could go deeper with the null voltage but my depht becomes less when i do this or its clackering.

[Nandor]

Nice improvement! 150mv is good. How do you null your coils? Geb pot at middle position, sens min disc at all metal and lowest Rx voltage. This worked for me I have 32cm with standard Geotech coils.

[BKY1337]

Okay, Nandor was right, I forgot Tape at the place where the coils are in contact. I have a clear signal now without interferences.
But my Depht is still poor, only 20cm with a Euro. 25 cm with a small Gold Ring.

I tried null voltages between 150mV and 600 mV at pin 7. I had much better results with my old coils which i have made with a Multimeter, i tuned them to 14,5 kHz and 13,95kHz.

Now i made them with my new LC Meter and i had 6,06 and 6,56 mH. With bending i can reach 6,0 and 6,5mH.

Frequency jumps from 14,2 to 14,7 at the DSO for the TX coil.

[BKY1337]

Do you mean the Rx coil? I measure my voltage at pin 7 and i have about 150 or 200mv . I also can see the wave in my oscilloscope and i can see it shifting through the null phase.
I have fixed my wire with tape at the coils this should insulate them from each other. When i change the connection of the RX coil then i get the double tone.

What do you mean with flipping the coil? My Rx coil is now above the TX coil. When i flip one coil then my connection cables will be at the wrong side. When i flip it in the other directen then i have to flip the TX coil too and it will be the same as now.

[Nandor]

The coil shieldings should not touch each other! You have to isolate the grafite spray coat with some isolation tape. The bad signal can be pre amp or maybe some of your channels is not working properly. How many volts do you have at pin 7 of LF353, the output voltage. It should be the ~45x of your residual balance voltage. Ex 4mv at receiver coil than output is ~180mV.
Bernte says it right.

[bernte_one]

double tones can be the sign for a wrong orientated coil, flip one side of coil and see if it gets better

i can not say it often enough, if you cant watch the Signal at Output at first amplifier- why you dont measure it direct on tx coil?

[BKY1337]

Yes , but i think nulling with this DSO150 is just as good as with a Multimeter. But its good for Troubleshooting.

I made a short video , i think this is the so called double tone. I changed the transistor to the original one and the detector became quieter. I have a strong signal till 10cm and then it becomes different.

https://www.dropbox.com/s/xd7hgywhhfgbxhh/CLIP2205.AVI?dl=0