TESORO GOLDEN SABRE

[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

[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

[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

[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?

[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?

[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

[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

[aft_72005]

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

[aft_72005]

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

[Qiaozhi]

Hi to all
I built TGS, it is working well .as you see, my PCB design by Vladimir,
Although ivconic PCB design was very good. I built Vladimir PCB times ago.
And At this week montage it.
Thanks for PCB from Vladimir, also thanks from ivconic and Max and Qiaozhi for very
Good comments in the matter .
Best regards.

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.

[aft_72005]

Hi to all
I built TGS, it is working well .as you see, my PCB design by Vladimir,
Although ivconic PCB design was very good. I built Vladimir PCB times ago.
And At this week montage it.
Thanks for PCB from Vladimir, also thanks from ivconic and Max and Qiaozhi for very
Good comments in the matter .
Best regards.

[Qiaozhi]

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

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.

[Qiaozhi]

On a different note, I also want to ask Qiaozhi some more about output of comparators and design of that section. (I think a very big challenge in understanding MD design is that there are two different operating regions -- large signal and ultra-small signal. There can be significant differences in how the components work and are employed in those regions. Sometimes non-ideal characteristics may be crucial.)

R40 feedback after diode maybe provides hysteresis, but also does interesting "feedforward" function that affects audio.

Let's take example of coin detection. It causes small positive pulse in both ground and disc channel. Comparators U106 will create large square pulse when both inputs go above sensitivity level. Then something interesting happens.

Resistor R40 and Diode D12 perform a "clip and add" feed-forward function. Comparators output, instead of going to V+, is clipped to level of output of U105 (which is also the input to ground channel comparator), the ground channel signal. This clip level is approximately ground. So comparators output looks like a big square pulse with a little signal on top of it. The little signal is the ground channel signal.

Now it goes to input of U107a, the final LM358. If you adjust the "threshold" pot just right, the square pulse will be level adjusted so the darlington transistor, referenced to ground, will strip off the square pulse and the driver of the Darlington will just be an amplified version of the ground signal that went into the comparator.

So what is the function in this case? The comparators simply serve to form a logical "AND" gate that passes the amplified ground signal to the audio output. The audio will be proportional to the ground signal. Actually, the diode may provide some logarithmic amplifying, which is good -- boosts small signals more than large.

However, if you adjust the threshold differently, then you will change character of the audio. In one direction, you will cause just the top of the ground signal to pass through to the audio, causing a skinny pulse. In the other direction, you include more of the square wave from the comparators, maybe saturate the LM358 and Darlington.

In addition to this, there is some low pass filtering being done with capacitors C24 and C25. The effect seems to be to round off the square pulse from the comparators. If the coin signal pulse is wide, then very little effect. If the coin signal pulse is very narrow, then the filtering can cause the square wave to never reach the peak -- and it falls beneath the Darlington cutoff, you never hear it. I think this filtering is to block noise chatter from quick noise voltage spikes triggering the comparators.

The question I'm driving at is: what was the intent of the original designers? Was it to use the ground channel signal to control the audio proportionally? If so, the threshold should be adjusted just right and never touched.

Or is the audio supposed to mainly be driven by the square pulse from the comparators? If that is true, then the feedforward circuit is just an artifact. However, in that case the audio loudness would be mainly determined by the width of the detection pulse, not the amplitude (up to a point).

So how you adjust the threshold makes completely different kinds of audio response. The proper amount of gain in the final LM358 would also be intertwined in the question of how the designers intended the audio to be controlled.

I am wondering if so many changes were made to the original circuit we lost the original idea the designers were intending.

I'm hoping these ideas can lead to adjustments to improve the audio. The difficulty is getting good audio in both cases: tiny signal, and bigger signal. There should be many things to try. It would be very useful it Ivconic could take picture of signals of crackling audio as it goes through channels, maybe we see where it happens.

Maybe these are crazy thoughts, hard to tell in middle of night...

Cheers,

-SB

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.

[Qiaozhi]

Quiaozhi, can you help here a bit?
You mentioned monitoring of gates at TGS using scope. So i tried and there are some oscillograms at both gates, yet i dont understand how can i change something there? Turning geb, oscillograms at both gates are changing from one shape to other and that is all!?
So...i dont have reference oscillograms to compare and see if something could be better...what to change, how to influence arround zero crossing point etc.etc.

Hi Ivconic,

I don't understand what you're asking here, especially as I thought you were already using this method of "nulling" the coil. What you are looking for at the output of the ground balance gate is a DC level. With the ground balance pot in mid-position, you then need to adjust the coil positions to achieve a minimum voltage level at this point. Was that the question?

Other thing; today i made small 18cm DD coil for TGSL. I nulled it usuall way trying to achieve less possiblle residual voltage. And when nulled in that manner and tested - bad behavior, coin at 18cm with clear sound, but over 20cm up to 27cm pretty cracked and short audio. So nulling failed. Than i renulled it but this time using only a coin and ears....and achieved to null it to detect same coin at 22cm with nice audio. Again over 22cm up to 27cm cracked and short audio. Conclusion - everything is about coil!
After a while i decide to let it as it was at moment - 1e coin cleary detect up to 20cm in air and with short unreliable cracks up to 27cm.
Ok...coil is done, considering 18cm diammeter i think those air performances are optimal. But another problem appeared (deja vu) - silent audio.
Up to 15cm on coin, audio is almost good. From 15cm to 22cm it decays and become bairly audible and very, very short.
So i got mad and started to experiment wildly. Changed almost all suspectable semiconductors, changed some values...nothing, same behavior.
Arround last LM358...that 2K2 (also 10K suggested) ...when i put 2K2 even on previously well nulled coil (with almost good audio) audio starts to behave as with not well nulled coil. When 2K2 replaced with 10K than audio looks fine. Same thing with threshold components..if you change on one side - you loose on other side!?
No benefits.
All day i spent on experimenting...same story ; changing some components to achieve louder audio - loose on audio quality ; cracks appeared...
All day same story...
So i was thinking; maybe problem is somewhere else, keep in mind that i tested and experimented today with TGSL which has audio mod included (2xBC547 + BD140)....
Damn! I stucked here and cant make any move forward!
How come that Classic III has louder audio without cracks and TGS with almost same logic doesnt?
What is the catch?
I came to level where depths are not an issue any more, does not interesting me to improve it more and more. Only thing left unsolved at TGSL is damn audio. No matter what i modded and tried so far...no huge steps forward, no radical improvements...
I am considering to switch to some other design and to leave TGSL as it is.
What do you think about this problem?

I'll have a look at this. More later...

[ivconic]

"..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..