IDX-PRO+VDI

[h9361]

That's very strange. This circuit works perfectly. Many people on the forum have built it and everything has worked flawlessly. You probably have a faulty component. Double-check everything.

thanks.
problem solved, +8V line in pcb-jumper had error.

[h9361]

That's very strange. This circuit works perfectly. Many people on the forum have built it and everything has worked flawlessly. You probably have a faulty component. Double-check everything.

Hello
Dear eduardo
I balanced RX and TX as follow:

Please see schematic (red circle), i saw that people fixed R43 as 2.2K and removed VR3 ( done as shorted line).
I also have done this, but i can not remove a ferrite using GB pot.

In addition, my sensitivity ls very low. for exp, smoke foil is detected from 25-30cm with 30cm coil.
I tested this foil from 80cm with E-Trace!
My coil details:
TX = 0.65 wire - 580uH
RX= 0.15 wire - 36.mH

[h9361]

The polarity of the transistor pins is very important. Some manufacturers change the pin order. I recommend using the MPSA13 or MPSA14. You also need to correctly configure the threshold level with the Pin-Point button pressed, ensuring the sound is soft and not bothersome. A very high threshold level can cause the transistor to overheat.

I connected scope to U8-Pin7 (GB pulse).
I change GB pot, but no change to Pulse-width GB in scope.

[eduardo1979]

Hello. This is the final schematic that I've used for a long time, and it works best. The coil is also very important.

[h9361]

Hello. This is the final schematic that I've used for a long time, and it works best. The coil is also very important.

Thanks.
Have you its PCB ?

About my PCB, please see the red circle.
I have pulse in scope, but GB has not any affect on Pulse width.
I think that changing GB pot must can decrease/increase pulse width.

[h9361]

Hello. This is the final schematic that I've used for a long time, and it works best. The coil is also very important.

Is it possible to guide me how to cancel RX and TX using AC multimeter?
I can not remove ferrite with any cancelling rx and tx.
I am using 4066 and TL064.
I nulled coil and my depth is nice but i can not remove ferrite

[Carl-NC]

I have pulse in scope, but GB has not any affect on Pulse width.
I think that changing GB pot must can decrease/increase pulse width.

The pot will change the delay, not the pulse width.

If you can't remove the ferrite, you may not have a sufficient GB range. Try using a different value C22 (higher, lower) and see what happens.

[h9361]

The pot will change the delay, not the pulse width.

If you can't remove the ferrite, you may not have a sufficient GB range. Try using a different value C22 (higher, lower) and see what happens.

Thanks dear Carl.
I nulled coil with very nice depth but the GB can not remove ferrite.
I checked GB pulse-delay on scope. The pulse move but the moving is very low.
Do you have any suggestion values?

[h9361]

The pot will change the delay, not the pulse width.

If you can't remove the ferrite, you may not have a sufficient GB range. Try using a different value C22 (higher, lower) and see what happens.

I tested C22 with 10P, 560P and 1n.
All result is identical and can not remove ferrite.

Ch2 = TX
CH1 = RX
My Scope can not show lower than 200mV.
If i decrease RX amplitude, my sensitivity will be higher.
But since you can not see in scope, i have to increase its domain.

I have tested several nulling. Only one mode, GB can remove ferrite but the detector can not detect any metals!
Anyway, this nulling with lower domain for RX (near a Straight line) has very nice depth and audio.
Original GB is 25K, but i can not find. So, i replaced it with 20K.
Before testing C22 with the new values, i tested the 20K with 50K, but no result.

[Carl-NC]

For GB to work, you need to get a timing pulse like this:

where the top waveform is a ferrite signal at the preamp output and the bottom is the clock signal at R42. Notice that the clock edges occur at the signal peaks.

[h9361]

For GB to work, you need to get a timing pulse like this:

where the top waveform is a ferrite signal at the preamp output and the bottom is the clock signal at R42. Notice that the clock edges occur at the signal peaks.

Thanks dear Carl.
My problem is solved.
My GB-Pulse delay is working, problem was for frequency of IDX.
About removing ferrite with coil, do you have a distance suggestion from coil? Which distance is better?5cm, 10cm or etc?!