TESORO GOLDEN SABRE

[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

[aft_72005]

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

[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]

Can you post the schematic here?

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

[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.

[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.

[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]

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]

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]

The hysteresis is still a mystery to me. The amount of hysteresis voltage depends on the output impedance of the LM308 circuit, which seems like a strange design decision, but perfectly possible. Also, the disc channel comparator has no pos feedback for hysteresis, so instability there would make a mess anyway. Should we try adding it there too as experiment?

Regards,

-SB

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...

[simonbaker]

The sole purpose of the comparators is to boost the signal level for small signals. This has the disadvantage of making all targets sound the same, except for some weak signals. In this case the pulse is only present for a short time, and gives a slightly lower output. On the plus side, you can hear weaker signals more easily. The hysteresis is an important part of the design, otherwise you will have a lot of instability, and the comparator stages will go into oscillation. Try removing the feedback resistor, and you will see the result.
The open-collector comparator outputs are connected together, such that the audio output is enabled whenever a metal target is present, and the target is non-ferrous.

The hysteresis is still a mystery to me. The amount of hysteresis voltage depends on the output impedance of the LM308 circuit, which seems like a strange design decision, but perfectly possible. Also, the disc channel comparator has no pos feedback for hysteresis, so instability there would make a mess anyway. Should we try adding it there too as experiment?

Regards,

-SB

[simonbaker]

Hi,
good parts... I like them. Will be nice when all assembled.

The interesting part is that the cracks and hums you'll hear when it will run at max sens... then you'll see really deep detection with so weak sound... that's furstrating cause you know it detects stuff but audio is so low and ureliable...

That's why this issue is so important: you'll gain in targets detection if fix audio stuff... so far I've found just monostable make real, huge difference there but sure it's not the solution we are looking for... we wanna a real tracking audio thing that will give strong signals also on weak targets...

We probably pushed TGS so hard on performances that the poor LM393 is not enough there... and a more dangerous beast is required, with enormous gain, reduced noise and tremendous speed!

The "fast and furious" comparator.

Kind regards,
Max

Yes, maybe push TGS beyond designers dreams -- crackle is just icing on the cake, lucky to get anything there . Perfectly reasonable that deep targets are raising the average noise which is what comes through as crackle -- but I can't see Ivconic's signals, can't tell. But still could be some filtering done to smooth raised noise into smoother pulse -- again, slower response (reduce 10 Hz center freq of filters) would help, or smarter filter after comparators.

But if signal looks OK as is, then should be possible to make good audio, need to keep dogging it.

Max talks about comparators used to boost weak signals, using linear region. That would be a nice cost saving trick by Tesoro to get double duty out of comparators. A more conservative design would put more gain in preceding filters so that noise is much bigger than linear region of comparators and easier to use sensitivity control to separate signal from noise. The problem with using comparators in linear region is that output signal is down near -V, and makes problems for next stage. Maybe Tesoro didn't expect to use linear region, circuit works very strange there (but works, icing on cake!).

So if you can detect coins at such low level, and have such low noise, try boosting gain of previous filters a lot and use comparators in normal operation, not linear region. Then maybe audio behave like shallower targets.

Really need to see signal out of LM308 during crackles at very slow sweep on storage scope somehow. How much noise; how much signal; etc. But too small I guess if in linear region. Maybe add a regular highspeed op amp with huge gain just to observe it for troubleshooting?

TGSL such a nice design, don't want to drop it.

Cheers,

-SB

[eclipse]

Hi,
good parts... I like them. Will be nice when all assembled.

Yup I like unbreakable and reiable stuff:
lower fiber rod + aluminimum shaft by Whites
Light weight aluminium box by Hammond
fiberglass coil 27sm also light and hard to break, alot more better than ABS plastics


I can tell soon if the "FnF comparator" is the LT1018
It's quite expensive stuff 5$ a piece so it should outperform the LM393,
about real advantages we can judge the permance results which I'll publish
as soon as I get everything OK.

[Max]

good job simonbaker, sounds like something interesting is going on there!
If you rise the pulse width exctraction with just a bit but not too much so that the rise and end sides of the pulse are not distracted, it will be definately improve the audio response with wider and lasting longer signal - thing we need so we can avoid short and num signal at large depth (as i heard, haven's seen it yet )
Bad side is that detection signal from a coin will probably sound like a horse shoe at 5sm.. im pretty sure the guys from tesoro played with it quite alot.
Cheers
Below its not a GP, its GS and coil + some hw for the coil

Hi,
good parts... I like them. Will be nice when all assembled.

The interesting part is that the cracks and hums you'll hear when it will run at max sens... then you'll see really deep detection with so weak sound... that's furstrating cause you know it detects stuff but audio is so low and ureliable...

That's why this issue is so important: you'll gain in targets detection if fix audio stuff... so far I've found just monostable make real, huge difference there but sure it's not the solution we are looking for... we wanna a real tracking audio thing that will give strong signals also on weak targets...

We probably pushed TGS so hard on performances that the poor LM393 is not enough there... and a more dangerous beast is required, with enormous gain, reduced noise and tremendous speed!

The "fast and furious" comparator.

Kind regards,
Max

[eclipse]

good job simonbaker, sounds like something interesting is going on there!
If you rise the pulse width exctraction with just a bit but not too much so that the rise and end sides of the pulse are not distracted, it will be definately improve the audio response with wider and lasting longer signal - thing we need so we can avoid short and num signal at large depth (as i heard, haven's seen it yet )
Bad side is that detection signal from a coin will probably sound like a horse shoe at 5sm.. im pretty sure the guys from tesoro played with it quite alot.
Cheers
Below its not a GP, its GS and coil + some hw for the coil