After zeroing, the search depth became worse!?

[Carl-NC]

You should not attempt to null your coils to zero. There needs to be a phase-offset appropriate to the design. In the case of the TGSL, it's needs to be around 20 degrees. Yes, you need an oscilloscope to do this properly.

I assume the phase offset is a result of the high inductances. If Raven did nothing to try to compensate for that, then he should still be able to null to whatever absolute minimum is allowed by the phase shift. The quality of the null should not affect detection depth, but would affect the overload point due a large target or bad ground.

[kt315]

Anatolij - you will need to translate that for those ignorant of the Russian lingo.

i'm just trying to give russian way of the balancing. what i see/read in ru forum. no more.

[Qiaozhi]

I assume the phase offset is a result of the high inductances. If Raven did nothing to try to compensate for that, then he should still be able to null to whatever absolute minimum is allowed by the phase shift. The quality of the null should not affect detection depth, but would affect the overload point due a large target or bad ground.

If you null the coils to their absolute minimum, then the TGSL will not be able to ground balance, and the discrimination will not work properly. The ground balance control needs to be set to its mid-position and the coils nulled so that ferrite is ignored. That position is where the RX signal is around 20 degrees offset to the TX.
As Ivconic says, you can do this without a scope if you're lucky. However, with a scope you can visually see and understand what's going on with GEB and DISC.

If the depth was initially ok, and (after adjusting the coil null) the depth was dramatically reduced, then suspicion points to the coil nulling as the culprit, assuming nothing else happened to the circuit that we don't know about. A scope is still the only way to track down the problem.

[Carl-NC]

If you null the coils to their absolute minimum, then the TGSL will not be able to ground balance, and the discrimination will not work properly. The ground balance control needs to be set to its mid-position and the coils nulled so that ferrite is ignored. That position is where the RX signal is around 20 degrees offset to the TX.

This doesn't make sense to me, but I haven't built the TGSL so I can't say what might be going on. But it sure sounds wonky.

[ivconic]

If you null the coils to their absolute minimum, then the TGSL will not be able to ground balance, and the discrimination will not work properly. The ground balance control needs to be set to its mid-position and the coils nulled so that ferrite is ignored. That position is where the RX signal is around 20 degrees offset to the TX.
As Ivconic says, you can do this without a scope if you're lucky. However, with a scope you can visually see and understand what's going on with GEB and DISC.

If the depth was initially ok, and (after adjusting the coil null) the depth was dramatically reduced, then suspicion points to the coil nulling as the culprit, assuming nothing else happened to the circuit that we don't know about. A scope is still the only way to track down the problem.

20-22 degrees, if i remember correct.
Yes. It is true; if not nulled well: it will reduce depths dramatically.
I used method without scope because i had very old oscilloscope at that time, i couldn't measure nor calculate any phase difference with it, so i didn't want to waste time and annoy myself with it.
It was much faster and easier with coin&ferrite method.
Closing or constraining coils bit by bit, testing with targets and all of the sudden it "clicks" to perfect position, giving maximum air distances on coin. Usually that's the spot of best balance for such coils.
GEB is set to middle position all the time, again you are correct. Usually i would leave DISC to minimum. Once it "clicks"; i just check the Disc behavior by rising it.
Another "side-indicator" is Al foil, thin and small piece. If it is rejected with Disc set on ~1/4; i know i have very good balance.
When you don't have proper measuring tools; you rely on various funny and weird indications and aspects that you learned in meantime.

[ivconic]

look on pic

[ATTACH]47624[/ATTACH]

There are pictures that worth a thousand words... and yet there are pictures that worth 1/thousand words.
I admit i don't understand it well.

[Ravensouth]

I have just measured the frequency and voltages with the oscilloscope. My Tx and Rx frequency is 13.4KHz. The audio signal is instead of the 453Hz come out with me 858Hz. Something is wrong with my circuit anymore. A few weeks ago I still measured at Tx 16-17Khz. The RX AC voltage, I only get down to 5V. Did I maybe make a short circuit somewhere?

[ivconic]

I have just measured the frequency and voltages with the oscilloscope. My Tx and Rx frequency is 13.4KHz. The audio signal is instead of the 453Hz come out with me 858Hz. Something is wrong with my circuit anymore. A few weeks ago I still measured at Tx 16-17Khz. The RX AC voltage, I only get down to 5V. Did I maybe make a short circuit somewhere?

Have you checked the minus rail?
13.4kHz seems alright to me.
Audio f is irrelevant, it depends on what pins at 4024 are used.
You can use any other division that suits your hearing.
RX AC down to 5v!??? Something is seriously wrong there.

[ivconic]

Don't bother yourself by trying to measure what's coming from 4024 to audio, since there are 3 divisions mixed together, making composite audio signal.
Focus on how to get proper minus rail, usually is -6.2V.
As for measuring the residual voltage at RX coil; you have two choices:
1) measure it just at front end output
2) measure it directly at RX coil leads
In both cases it would be in millivolts with no target close to coil.
Method 1) gives you more real picture of what would be processed in further stages, carrying also a front end offset (desirable to be less as possible).
Method 2) (my favorite) gives you "raw" situation at RX coil. Not affected by front end and offset.
Values that you are mentioning are strange, leads me to suspect your measuring equipment.

[Ravensouth]

I recently checked the negative rail. For safety's sake I will do this again. My whole case is shielded with aluminum and is grounded to counteract the interference.

[Ravensouth]

It will not be on the meters. With my multimeter the day before yesterday I also measured 5V at the Rx

[Ravensouth]

According to my multimeter, the Rx 240mV when I overlap the coils as far as possible. I'll see what's coming out of the cable.

[ivconic]

It will not be on the meters. With my multimeter the day before yesterday I also measured 5V at the Rx

That's huge!
I would expect up to 200mV bad balance at most.
15mV and close i would consider decent balance.
9mV and bellow i would say excellent balance.
Speaking on "raw" measurement, directly at coil leads.

[ivconic]

According to my multimeter, the Rx 240mV when I overlap the coils as far as possible. I'll see what's coming out of the cable.

Ok, now we are getting somewhere.
Let's remind on some facts:
wire gauge at both; TX&RX is 0.25mm (measured with no insulation, use lighter to burn resin insulation)
TX~ 5.7mH
RX~ 6.2mH
True?

[Ravensouth]

There are no 200mV. It was 20mV. I was wrong ... sry. Now I come to a value of 15 mV. My wire thickness is 0.25mm with insulation. My inductance was 5.4mH at Tx and 5.8-5.9mH at Rx.