TESORO GOLDEN SABRE

[simonbaker]

There are two experiments you could try:
1. Reconnect the feedback resistor to the output of the comparators, rather than the cathode of the diode.
2. Add a second feedback resistor to the other comparator.

This might have some interesting results...

Also, logically, if decide to use hysteresis, you would want a pot to control how much maybe? Why no pot?

But wait: I think problem with full hysteresis is: how signal turn off! Have to go negative equal amount? Target pulses assymetric. So maybe that's why only on one channel... but then only helps noise on one channel... I'm going crazy...

And also, summing of pos feedback with ground channel signal is ill-defined, only based on output impedance of LM308, not normal summing amp -- also not normal hysteresis amp where signal goes into inverting, pos feedback to non-inverting. Very funky circuit. But "feed-forward" of ground signal to audio is a real effect, verified by LTSpice; just not sure intentions of designer, artifact or design?

I will be doing some experiments. Unfortunately, real truth needs careful PCB each time, so have to do some fakery and strategizing...

Regards,

-SB

[Qiaozhi]

Also, logically, if decide to use hysteresis, you would want a pot to control how much maybe? Why no pot?

But wait: I think problem with full hysteresis is: how signal turn off! Have to go negative equal amount? Target pulses assymetric. So maybe that's why only on one channel... but then only helps noise on one channel... I'm going crazy...

And also, summing of pos feedback with ground channel signal is ill-defined, only based on output impedance of LM308, not normal summing amp -- also not normal hysteresis amp where signal goes into inverting, pos feedback to non-inverting. Very funky circuit. But "feed-forward" of ground signal to audio is a real effect, verified by LTSpice; just not sure intentions of designer, artifact or design?

I will be doing some experiments. Unfortunately, real truth needs careful PCB each time, so have to do some fakery and strategizing...

Regards,

-SB

For hysteresis to work, the output must be fed back to the non-inverting terminal (not the inverting).

[simonbaker]

hysteresis

(Hope this isn't duplicate post, lost one...)

Yes, positive feedback -- but usually signal goes into inverting input, feedback to noninverting when using hysteresis. TGSL has feedback and signal combine into noninverting input -- what is end result? Feedback voltage based on voltage divider of R40 with output impedance of LM308 -- who knows what that is? How much hysteresis? Seems very unusual, but maybe normal for MDs.

Regards,

-SB

[Qiaozhi]

(Hope this isn't duplicate post, lost one...)

Yes, positive feedback -- but usually signal goes into inverting input, feedback to noninverting when using hysteresis. TGSL has feedback and signal combine into noninverting input -- what is end result? Feedback voltage based on voltage divider of R40 with output impedance of LM308 -- who knows what that is? How much hysteresis? Seems very unusual, but maybe normal for MDs.

Regards,

-SB

The hysteresis setup with the TGSL is correct. It should be connected to the non-inverting input. Please read the attached document.

[aft_72005]

One last question - Are you using a homemade coil or a Tesoro original?

Hi Qiaozhi
Coil homemade DD 255x137mm wire size 0.3mm with varnish
Transmitter 106 turns 5.59 mh, receiver 110 turns 6.22 mh .
Best regards.

[aft_72005]

Can you post the schematic here?

This circuit uploaded in this thread at the past
And again .

[Qiaozhi]

This circuit uploaded in this thread at the past
And again .

Thanks. I just wanted to check which variant you were using.

One question: In the photo of your DD coil, it looks like the faraday shields are touching at the crossover points. Do you have some tape there to insulate them electrically? If not, you will have a loop in the shield where eddy currents will flow.

[aft_72005]

No, not any insulated between two coil .thanks for you point of view .
I try it .
Best regards.

[Max]

No, not any insulated between two coil .thanks for you point of view .
I try it .
Best regards.

Hi,
it's not just his point of view...

If you'll not remove that short circuit at coil your MD will never work any good.

Kind regards,
Max

[simonbaker]

The hysteresis setup with the TGSL is correct. It should be connected to the non-inverting input. Please read the attached document.

Yes, I agree, it is correct for hysteresis. (And good reference, thanks.) Reason I care is because we can't be sure of schematic for TGS, I try to investigate areas that look unusual.

With hysteresis, some things look funny:

1) only on one channel.

2) unknown amount. Referencing your document, it is classified as "non-inverting hysteresis, dual supplies" design. Resisitor R1 in the document is the output impedance of the LM308 stage -- did Tesoro designers measure that? Is it a reliable way to set hysteresis level?

3) How did Tesoro decide how much hysteresis to have? Hysteresis will create another threshold on the ground channel side in addition to the sensitivity control. If too much, hurts sensitivity. Other side not have it at all, different sensitivity?

Just want to understand it fully in case I work on mod that would affect it.

I appreciate your explanations and patience!

Regards,

-SB

[simonbaker]

This circuit uploaded in this thread at the past
And again .

Yes, good to post again, I had not seen this variant with audio switch and no threshold pot together.

-SB

[simonbaker]

sensitivity

A question for Max, Ivconic, Eclipse, anyone with good working TGSL:

When you turn sensitivity pot to most sensitive and test outdoors, what do you hear? Is it quiet? Or is there chatter?

If quiet, would it be worth trying to put a jumper across R37 (i.e. remove it) to allow reference all way to ground?

Right now, min sensitivity reference is 8 v / 2441 = 3.3 mV.

If your target signal is 4 mV, you only hear .7 mV top part. If less than 3.3 mV, never hear. So lose some sensitivity.


But if noise is approx 3.3 mV, nothing to do.

So it depends on noise. Maybe your PCBs are very low noise. Have you tested?

Cheers,

-SB

[eclipse]

Hi,
if you get 30° you can reverse leads at RX and get 180+30 = 210° that's about what you need to work good.

Kind regards,
Max

Bad news for me I tryed it and didn't work.
I can't affect phase shift no matter what I do.
Moving Rx and Tx gives me fixed shifting on 30 and 60 degrees (or whatever - it's far from the 200 degrees).
Wrong phase - no disc, bad stability also on tested stones (mineralized rock).
Bad news for depth lover like myself - nulled coil to around 2-3mV gives me depth for a huge coin (1 eu) at ~23 cm, really poor result.

Perhaps I was wrong changing stuff first, I needed to make one standard TGS with standard components and board. Now even if I am close to heaven just have no clue on how to reach it. Maybe PCB error?
Any volunteers for checking the board (sprint 5) which I used?
I'm deeply stucked in the middle of nowhere

[Unregistered]

corection

Hi,
C7 on the picture is 10pf ,not 100pf.

[Max]

A question for Max, Ivconic, Eclipse, anyone with good working TGSL:

When you turn sensitivity pot to most sensitive and test outdoors, what do you hear? Is it quiet? Or is there chatter?

If quiet, would it be worth trying to put a jumper across R37 (i.e. remove it) to allow reference all way to ground?

Right now, min sensitivity reference is 8 v / 2441 = 3.3 mV.

If your target signal is 4 mV, you only hear .7 mV top part. If less than 3.3 mV, never hear. So lose some sensitivity.


But if noise is approx 3.3 mV, nothing to do.

So it depends on noise. Maybe your PCBs are very low noise. Have you tested?

Cheers,

-SB

Hi,
it's difficault to answer that question... it's not always the same.

I talk about my experience. When I carry outdoor my TGS far from interferences I get it absolute quite, no chatters at sens to 10. This happens most of the times.

Sometimes, always outdoor, I switch on an get occasional chatters: have to say that in these places there are RF interferences, so are not ideal places to search with it.

That I reported is for coil far from soil.

Things that happens when my TGS is set to max sens on soil are similar: in much places I can run it quiet, just very rare, occasional chatters (who knows reason ??? maybe just internal instability) BUT other times well... I simply cannot lower the coil to soil... cause I get plenty of noises , chatters, whatever!

At first seems I've done bad geb tuning... but chatters stay on also with coil NOT IN MOVEMENT over soil... seems like radiated rf from soil enters the TGS amplification chain and show very strange interferences there!

Infact, these situations happen in that places I said above, with RF noise around from big power transmitters at few Kms.

In that last scenario is impossible stay at 10 of sens... have to reduce sometimes to 7 or even less.

On some very worse soil it happens also that noise is triggered by ground (too many iron minerals and imperfect geb I think) so have to put sens at just 6.

I don't tested the remove of R37 so far... but will try and report about... sure it couldn't be used in the worse situations... but when quiet it could be tested.

Really... when I set sens to 10 and get silent at home (not frequent situation , cause too electrical noise around) I can "detect" a switch commutation from a room 15meters far: TGS is a real beast of sensitivity when noise around is very low. Seems an LRL!

Kind regards,
Max