Tesoro Bandido III

[ivconic]

Hi, I actually tried the part of the schematic that generate the negative rail for the op amp and it does not work! It generates barely -2.7V and needs a voltage multiplier to be able to generate at least -5V. With some help I found out that the attached version works, I am still using it to power a couple op amps from +5V. Diodes can be replaced with 1N4148 and the 5kHz signal for the push pull stage generated by anything you want. Measured output voltage is about -7.5V

In real life it is working on many Tesoro detectors, TGSL etc.
At TGSL it is producing -6.2V from 8V supply, but "TTL" is 12-14kHz.
Why don't you try it with 12-14kHz?
Also you got it all wrong with bases resistors!

[ivconic]

Can you see where you made mistake?

[ivconic]

A third channel is sometimes provided in VLF detectors that can display a target ID, as this is based on the phase angle of the target, and this can be offset if there is an external ground balance control. It depends on how pedantic you are about the target ID accuracy.
In Tesoro detectors without a display (such as the Bandido) the third channel is a non-motion mode for pin-pointing. I don't know about the Bandido III variant without seeing the schematic.

Exactly!

[Pep_T]

In real life it is working on many Tesoro detectors, TGSL etc.
At TGSL it is producing -6.2V from 8V supply, but "TTL" is 12-14kHz.
Why don't you try it with 12-14kHz?
Also you got it all wrong with bases resistors!

I did not try changing the frequency, will surely do and see what happends. Of course pull up and pull down resistors are the wrong value, they should have been some x10 the base resistors to turn off the transistors when the input signal is floating, my mistake in the schematic, in real life they are 22k and works fine. Thaks for the tips and the info.

Can you see where you made mistake?

aaaah yes. The pullup and pulldown are directly into the base. Cant belive i missed it

[ivconic]

While it is true that most of modern op amp works with single supply, if the input signal goes negative the op amp must be able to work with that. Dual supply poses no problems, but with singe supply an input biasing stage would be needed that this schematic does not contain

Resulting in loosing half of a signal.
I don't know what to predict (never tried) when it comes to metal detector; but in small battery operated guitar&mic preamps, pedals, effects: it is usuall practice to split the power supply and use its half as "ground reference".
But in those cases too; the dual supply opamps are used too (TL071 series and similars).
I can only assume that if the same method is applied to metal detector, using single supply opamps; the signal span will be dramatically narrowed. Lose of informations in other words.
Probably harder to achieve accurate GEB&DISC functions etc.
But in direct sampling method it can be done. Wideband and fast RX frontend and signal directly fed into Mcu or some dedicated ADC before the Mcu.
But then... why complicating the things?

[ivconic]

I did not try changing the frequency, will surely do and see what happends. Of course pull up and pull down resistors are the wrong value, they should have been some x10 the base resistors to turn off the transistors when the input signal is floating, my mistake in the schematic, in real life they are 22k and works fine. Thaks for the tips and the info.



aaaah yes. The pullup and pulldown are directly into the base. Cant belive i missed it

[Aleks85]

Hello Carl, I have found another inaccuracy on your scheme from the message # 2.
I compared it with the old scheme and figured it out, but so that others don't get confused, I'm writing.
With respect.

[Carl-NC]

Thanks, I'll get it fixed.

[ivconic]

[Carl-NC]

Here is my updated schematic:

Bandido2uMax.pdf

[ivconic]

[ivconic]

...

[ivconic]

My 3D files are "rough" geometric shapes, because they were made in TinkerCad.
I'm not professional enough either.
It would be good if someone more expert processed them in a more powerful software.
I have all the relevant Autodesk software... but I don't have time to master it properly.
The edges of the box and parts need to be slightly rounded and the whole design refined.
Who has the will to do it; it would be useful for the forum and future detector builders.
I haven't finished the detector yet, it stands aside, because in the meantime I started working on Goldscan 4, which takes a lot of my time.
But I plan to finish this one soon. And I got the original coil, so I have no intention of making a coil.
The Tesoro concept is an old love of mine.
I have made so many of them so far. But the last one I did was ten or more years ago.
This is the first one after so long.
I like the Tesoro concept because it is unassailable in certain search conditions and on certain targets.
The old charm never fades.

[ivconic]

And something else interesting!
Now that Tesoro no longer exists, I assume that whatever is left of the factory has ended up somewhere.
Complete or in parts. I guess someone took all the unfinished products, already made boxes, sticks and other parts.
As well as molds.
I would be interested in getting some of that. But it is very difficult, almost impossible (for me) to get information.
For example empty original boxes... pcbs... stems, shafts, parts, coils...
My budget is modest. But I'd be willing to take some of that.
In my opinion, Tesoro should not have disappeared from the market.
It is too good a brand and has its own constant market... despite the flood of new offers.
Although Tesoro machines are quite modest in flat bench tests, in real working conditions they have their place under the sun.
And there is a so-called "niche" market still for them.
They are inviolable in given conditions and on given targets. I say this as someone who has been a seeker since 1987.
I guess I know what I'm talking about.
Let this be a kind of my appeal to bring Tesoro back to life.

[gurdal]

Hello great master Ivica,
I've needed these files for a long time,
Thank you very much for adding these files.
Kind regards
Gurdal