TDI discrimination

[Geo]

Geo,

Just because all the LED's are illuminated doesn't mean the battery isn't part of the problem, so please try a different battery just to be sure. Like I said, almost all of the circuitry is used when you are operating with the GB off. There is just one opamp and associated circuitry that is turned on when the GB is on. Actually, there is a couple more stages that are operating but not heard with the GB off, but none of them should create a lot of noise.

I still think that some new noise making device is causing the problem and the problem is not with the detector.

Reg

Reg,
i have another one battery. Tommorrow i will charge it and i"ll give another one try!!!!

Regards

[Reg]

Geo,

If you added another vernier potentiometer (pot) in series with the original factory GB potentiometer, then your GB numbers will have changed as to where certain things happen such as where you will obtain the right ground balance. The GB pot increases the gain of the GB channel and if you added more resistance, you added more gain. This will increase the noise dramatically. So, to start with, turn the added potentiometer to minimum resistance and test again.

Did you adjust any pots inside the detector? Absolutely, do not do that. Some are extremely critical and others are just critical. All use special equipment to adjust properly.

Reg

[Geo]

Geo,

If you added another vernier potentiometer (pot) in series with the original factory GB potentiometer, then your GB numbers will have changed as to where certain things happen such as where you will obtain the right ground balance. The GB pot increases the gain of the GB channel and if you added more resistance, you added more gain. This will increase the noise dramatically. So, to start with, turn the added potentiometer to minimum resistance and test again.

Did you adjust any pots inside the detector? Absolutely, do not do that. Some are extremely critical and others are just critical. All use special equipment to adjust properly.

Reg

Reg,
I did not adjust any pots inside the detector. I only connected a 10K pot in series with GB for fine adjusting so the total resistance is about the same......
I don't know if a bad quality potentiometer can add so much noise. I put a new cheap Chinese potentiometer. Today when i made the test i had the 2nd potentiometer at zero resistance.
At morning i will see. Now i go for sleep, time is 01:45......

Regards and thank you

btw...I think that the schematic of GS-5 who there is at forum is very close to TDI except oscillator... VCO and schematic for delays....

[Reg]

Hi Geo,

Again, don't panic, I am sure the new GB vernier pot is adding more noise. That is also normal because of what the pot is doing.

Even a 10K can add a lot of noise because it adds a lot more gain to the GB amplifier.

When you adjust the GB pot and you listen carefully, you will notice that the noise level gets much greater as the GB pot is increased, especially when it is near maximum. It will do this with or without your new vernier pot. Now, when you add even more resistance, the noise will increase dramatically. So, I am fairly certain the additional noise is because of the added resistance and not because of a bad pot, bad wiring or some type of defect. Excessive noise will cause a dramatic drop in depth of detection because you can't hear the weak signals any more.

Just to be sure, adjust the new added vernier GB pot to one end and test, and then turn it to the other end and test again. I suspect that when you noticed your GB settings seem to have changed as to where the gold coin changes tones (when compared to your original tests that you posted quite some time ago) then the vernier pot wasn't at minimum resistance. The gold coin should change tones at about 7 on your GB pot with the vernier at one end or the other. There is no reason for it not to.

What is happening makes sense to me because I know exactly how the circuit works. That is why I say you shouldn't panic.

Reg

[Orbit]

whole problem isthe potentiometerthe !

Perhaps the Chinese defective !

[Geo]

Hi.
Finally i fixed the problem. I restored the GB as the prototype (one potentiometer) and now works fine. I don't know if the noise was from the potentiometer of from the cables or from both. Maybe one other time to make again the experiment and to try to solve this problem. Now it detects the gold sovereign with Gb=10 and delay=10 from 20 cm with low tone (as high conductive). Next month i"ll go again for test at the friend with the 45 buried gold coins. Also i will try a sovereign and a Caesar to see if they can detect the mystery coins. Of course i will inform you.
Thanks a lot for your help especially the Reg

Regards

[Reg]

Hi Geo,

I wish you would have done the testing I requested. I think you would have found the additional GB pot was set at max and the increased gain was causing the noise and not the pot or the wiring. The location of the additional pot in the circuitry was too far from the preamp to cause that much noise just because of parts, especially if all you did was to move one of the leads off the original GB pot over to the additional pot and add a short jumper from one pot to the other.

Remember, the extra GB pot you were adding causes more gain in the GB amplifier. It is the GB amplifier that causes most of the noise you hear, so increasing the gain further will only create a whole lot more noise. I know, I have done this myself.

I am glad you are no longer worried. The TDI is a good detector that is difficult to hurt by simply adding a pot to it. When you feel comfortable, you might want to add the pot again. If you do, make sure you have the pot at minimum resistance setting and it shouldn't cause any problem and all things will check just like it isn't there. Then if you increase the additional pot, you will see it can add noise especially if the main GB pot is at 9 or above. Also, you will see that the point any object changes tone will change on the main GB pot. If the additional GB pot is at max, the transition point will be about 1 number lower with the value of the additional pot you selected.

Reg

[Geo]

Hi Geo,

I wish you would have done the testing I requested. I think you would have found the additional GB pot was set at max and the increased gain was causing the noise and not the pot or the wiring. The location of the additional pot in the circuitry was too far from the preamp to cause that much noise just because of parts, especially if all you did was to move one of the leads off the original GB pot over to the additional pot and add a short jumper from one pot to the other.

Remember, the extra GB pot you were adding causes more gain in the GB amplifier. It is the GB amplifier that causes most of the noise you hear, so increasing the gain further will only create a whole lot more noise. I know, I have done this myself.

I am glad you are no longer worried. The TDI is a good detector that is difficult to hurt by simply adding a pot to it. When you feel comfortable, you might want to add the pot again. If you do, make sure you have the pot at minimum resistance setting and it shouldn't cause any problem and all things will check just like it isn't there. Then if you increase the additional pot, you will see it can add noise especially if the main GB pot is at 9 or above. Also, you will see that the point any object changes tone will change on the main GB pot. If the additional GB pot is at max, the transition point will be about 1 number lower with the value of the additional pot you selected.

Reg

Hi Reg.
Sorry but i promised you to make a lot of tests and now i don't remember who test you want!!!, please remember me.
The GB potentiometer was not at max, so the noise was not from the high gain. I tried the detector with GB=3 or GB=5 or Gb=10 and the noise was about the same. Maybe a bad contact in the pot to made the noise..... For sure next time i will put a high quality pot and i will try it step by step. Yesterday i readed the schematic of GS-5 and i understood very well how works the GB and the gain of potentiometer.

Regards

[Orbit]

Hi Geo I do not understand what's in the table ( 1 2 3 4 5 6 7 8 9 10 11 ),,, 10 ms, 17,5ms and 25ms sampling I understand test on with included geb ,off geb ok ,thank you clarification orbit !!

[maikl]

Hi Geo I do not understand what's in the table ( 1 2 3 4 5 6 7 8 9 10 11 ),,, 10 ms, 17,5ms and 25ms sampling I understand test on with included geb ,off geb ok ,thank you clarification orbit !!

1 - 11 is Ground Balance

[Qiaozhi]

Hi Geo I do not understand what's in the table ( 1 2 3 4 5 6 7 8 9 10 11 ),,, 10 ms, 17,5ms and 25ms sampling I understand test on with included geb ,off geb ok ,thank you clarification orbit !!

This should be us (micro-seconds) not ms (milli-seconds).

[Reg]

Maikl,

The numbers will make more sense if you look at the TDI and see how the delay and GB (ground balance) controls are marked. Here is a pic of the TDI so the numbers make more sense.

Basically, if you look at the top of the chart posted by Geo you will see the words GB set and delay. The associated settings are directly below those words. So, Geo simply adjusted the GB to the different numbers and measured the results. The same goes for the delay.

Reg

[Orbit]

micro-seconds of course ! Does this mean ,to 1 = 10us , 2 = eg 11,5us , 3 = 13 us iand 11= eg 17,5us ?

[Orbit]

I see from 1 to 11 marked ground balance ! It has nothing to do with delay !or position pulse delay !

[Carl-NC]

No, delay is in us (10-25us), GB is an arbitrary 1-11. I don't know why that range was chosen. Edit: the GB knob adjusts the gain of the ground channel, not a timing parameter.