TESORO GOLDEN SABRE

[aft_72005]

Hi Qiaozhi
Normal Sound loud with speaker Rdc =16ohm
Best regards.

[aft_72005]

Hi again Qiaozhi
I forgot ,Vladimir gave me tgs PCB file in proteus software format.
Best regards.

[Max]

The TGSL and the Classic III have very similar filter characteristics. So it's unlikely that this is the cause of the low audio.

In fact, I think there may be a mistake in the schematic. One of the original back-engineered schematics of the Golden Sabre shows the 100K feedback resistor connected between pins 5 and 7 of the comparator. In other words, it should be feeding back from the output of the comparator, NOT from the anode of the diode.

Try moving the resistor, and see if it makes a difference.

Hi,
yes, it's an interesting idea. I will try that.

At now I'm about happy using monostable-mod but must switch it off to center/pinpoint the target.

Kind regards,
Max

[Max]

How loud is the audio on your detector, and what impedance speaker are you using?
Also - which layout from Vladimir are you using? The component placement looks different to the file that I have on disk.

Hi,
the best I found are still old 16ohm speakers from old Apple desktop computers! These give a nice audio on all Tesoro's designs I've made.

The original speakers were also 16ohm stuff... I suppose the good quality of Apple's parts, so also speakers, explain why the sound is dang good with them!

Also... dimensions are small cause the speakers must fit inside a small desktop stuff in the 90's.

Kind regards,
Max

[Qiaozhi]

Hi again Qiaozhi
I forgot ,Vladimir gave me tgs PCB file in proteus software format.
Best regards.

Can you post the schematic here? Perhaps you can do a snapshot of the screen. We are trying to figure out if there is a problem with the audio in the TGSL.

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

[Qiaozhi]

Hi,
the best I found are still old 16ohm speakers from old Apple desktop computers! These give a nice audio on all Tesoro's designs I've made.

The original speakers were also 16ohm stuff... I suppose the good quality of Apple's parts, so also speakers, explain why the sound is dang good with them!

Also... dimensions are small cause the speakers must fit inside a small desktop stuff in the 90's.

Kind regards,
Max

Is it only Ivconic who has this audio problem?

[simonbaker]

"..Trying to understand your problem -- when you get crackle in audio, does output of U107a (LM358 ) look good, or does it look like it should crackle? In other words, is your mystery just after the LM358, or really the whole system?..."

At U107a outpup has -4.8v without detection and tends to zero when detection appears. At input (5.pin) is -5.4v and falls to -2.3v on detection.
Crackle appears due something unsolved in last stage from comparators to U107a. It is also strictly related to output impendance. Adding just a 10 ohms resistor in serie with speaker and crackles gone!? But in that case audio is pretty silent, hard to hear outdoor on real terrain..

Approximately how wide is the pulse at input pin5 during detection?

If signal only rises to -2.3 v, then either very quick pulse or operating in linear region of comparator I think.

Does detection input to pin5 look like a smooth pulse, or many separate pulses?

Regards,

-SB

[simonbaker]

Hi Ivconic,
I've tested the audio mod with transistors... used BD138 instead of BD140... not big deal... that have improved audio just sometimes, other times is not that good. The mod works... but on weak targets you could get similar problems than with just BC517... it's not a power problem but a "timing" problem.

When on for the enough time even the BC517 strategy pays: that happens on shallow targets.

I'm not totally sure of that but think...that the problem is that in TGS the timing of some blocks is made in a way you get weak targets as very fast transients on signal path. Too fast to get useful audio.

The device allow too fast recovery of amplifiers, so you'll get very weak audio cause of that when signal amplitude at coil is low and fast swinging like in the case of very small targets or far.

If you change the timing you can change this behaviour I think.

I will check at integrators... I suppose that in MDs like ClassicIII you have longer time constants so the integrators take their time before turning back to threshold, that's mainly due to cap values at there.

So, machines like ClassicIII you can sweep also more slowly, but TGS you're supposed to sweep at higher speed to detect stuff... you have lower weight also and machine is made for shallow nugget hunting... small stuff at few depth with large , fast swings!

The initial TGS intented use is what maybe turned design to that behaviour, but I have to say that situation at bandidoII is similar also, so it's probably a Tesoro's way of doing stay fast in the integrators chain and point to fast sweeps.

Kind regards,
Max

I don't know about ClassicIII, but I agree with Max about fast recovery. I did AC Analysis with LTSpice and op amp filters (LM358, LM308 ) are bandpass with center at 10 Hz. Transient analysis shows interesting transformation of detection pulse into three pulses -- down, up, down. TGSL detects middle pulse, but not big and fat and juicy as it could be.

I tried variation with bandpass set at about 2 Hz and much nicer looking, wider single pulse all the way. But inverted, so need to change something at comparators. Maybe not Ivconic's problem, but I'm working on it as a mod, looks better all around if it works, and should help audio anyway.

Regards,

-SB

[Max]

Is it only Ivconic who has this audio problem?

Hi,
no... the audio is weak on weak targets... but pleasant when stuff is bigger or at less depth.

Some speakers works bad on TGS even with targets at 10cm cause ideal situation is having a good sized but small 16ohm speaker with good response at low frequency.

So I found just these 16ohm from Apple are good... but when targets are far it gives just cracks not good audio, so the problem is still there at original schematic.

When using monostable I get 0.5-0.6s delay and so sound become a well wide pulse... no problems with it.

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

[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]

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.

[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

[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

[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...