Silver Sabre Plus & PCB

[Leto]

Osc..

Hi Max, thanks..
I found those previous posts:

Originally Posted by Sean_Goddard
I have found from experiments with this type of oscillator used that the FET part is an "auto level control". It also seems to affect the purity of the Tx signal.

When you find a large target, the level of the Tx will dip slightly, not sure why Tesoro feel the need to compensate for this but at least I assume that is what they are doing, maybe also to compensate for different sizes of coil.

Originally Posted by Max
I don't know for sure but seems that the FET there is , as you stated, a feedback component. I think it serves to stabilize and keep osc working also with important variations on osc current. They maybe noticed that an overload on osc (due e.g. to a big target) causes sometimes the osc to shut-off so maybe the FET keep it running varing polarization network parameters also if big masses are near coil.
If it is so, without the FET if osc shuts off the detector will lose negative voltage rail and so all need resetting far away metal to recover it again.
This way there's maybe no danger of locks at osc sections even if big metals are near the coil.

I will put those 5 extra parts on my SS and see the differences. Or maybe I should learn PSpice or similar..
Does someone know anything about zenner voltage??
As a fact zenners are produced with large tolerances and I remember someone posted (ApBerg ?) that experimenting with zenners in Tx stage can vary performance.
Because I was thinking to run oscillator with bit higher voltage - would I need to vary zenner voltage also?

[Max]

Hi Max, thanks..
I found those previous posts:




I will put those 5 extra parts on my SS and see the differences. Or maybe I should learn PSpice or similar..
Does someone know anything about zenner voltage??
As a fact zenners are produced with large tolerances and I remember someone posted (ApBerg ?) that experimenting with zenners in Tx stage can vary performance.
Because I was thinking to run oscillator with bit higher voltage - would I need to vary zenner voltage also?

Hi,
ApBerg is right on voltage selection of zener. Cause it sets actually polarization by the fet it's really important having right voltage there.
I think that another important factor is the transistor gain, must be >250 to gain best efficiency from this osc. expecially in the simple schematic of it.

Anyway, I think that is about the same you already have, polarization network...could give you just more reliable operations in various conditions, not noticeable improvements in depth.

I cannot notice any relevant difference between GS osc and BandidoII in e.g. air tests. Also performances are about the same at least in air tests.

Best regards,
Max

[Qiaozhi]

question for more educated..

Probably all of you noticed two basic Tx oscillators types used in tesoro metal detectors. One one the left is the most basic form of Colpitts oscillator and it is used in SilverSabre and Bandido circuitry. The one on the right side is bit more complex and can be found in Eldorado, Golden & Royal Sabre, Inca,...

My question would be: what this resistor, capacitator, 4.3V zenner, diode and FET are for??

These components are for TX amplitude stabilization. Without checking, I think the Silver Sabre and Bandido detectors are using double differentiation, whereas the Eldorado and Golden Sabre use some autotracking on the first stage after the sample-and-hold. So the Eldorado and Golden Sabre might find some benefit from having a more stable TX amplitude. In practice it probably makes little difference.

[chemelec]

question for more educated..

Probably all of you noticed two basic Tx oscillators types used in tesoro metal detectors. One one the left is the most basic form of Colpitts oscillator and it is used in SilverSabre and Bandido circuitry. The one on the right side is bit more complex and can be found in Eldorado, Golden & Royal Sabre, Inca,...

My question would be: what this resistor, capacitator, 4.3V zenner, diode and FET are for??

For Fun, I built and tested Both circuits.

The Only differences I can find:

1) The one on the Right side has only about 1/5 the output signal as compared to the left one. So it will also produce a somewhat lower magnetic field on the coil.

2) But because of the Zener, .22 capacitor and the fet, it is better regulated and less succeptable to Power supply interference from other IC's on the board.

But I really don't this right one as being much of a useful advantage.

[Max]

For Fun, I built and tested Both circuits.

The Only differences I can find:

1) The one on the Right side has only about 1/5 the output signal as compared to the left one. So it will also produce a somewhat lower magnetic field on the coil.

2) But because of the Zener, .22 capacitor and the fet, it is better regulated and less succeptable to Power supply interference from other IC's on the board.

But I really don't this right one as being much of a useful advantage.

Hi Gary,
I've both, one on BandidoII (used your first PCB design) and the other on GSabre... I've built some days ago ...both work really good.
No great differences e.g. in air tests.
I've not tuned GSabre for maximum at now but think the real advantage of having a feedback controlled polarization network is in the amplitude stability.
This could make difference on bad soil (with much mineralization) or when e.g. iron oxides are just near the coil (hot rocks) cause it can feed other block always with about same amplitude of sinus wave.

That's true just for a limited interval when not too much metal or oxides are near the coil, but could make the differece in bad soil conditions.

At first I was thinking it's a kind of protection from overload due to big targets... but now I think that amplitude control is related to expected soil conditions.

I think that they used the feedback in GoldenSabre or Eldorado too cause they were intended as for "advanced" users (gold nugget hunting mainly), where bad soil conditions are easy to find.
In (marketing intended) "recreational" (coin hunting in parks etc) ones (bandidoII etc) they used the simple version.

Kind regards,
Max

[Max]

These components are for TX amplitude stabilization. Without checking, I think the Silver Sabre and Bandido detectors are using double differentiation, whereas the Eldorado and Golden Sabre use some autotracking on the first stage after the sample-and-hold. So the Eldorado and Golden Sabre might find some benefit from having a more stable TX amplitude. In practice it probably makes little difference.

Hi,
one thing make me dubt :

in bandidoII there is a non-motion all-metal mode...

I think that amplitude control would advantage more BandidoII on that thing (non-motion mode) avoiding e.g. drifting or falsing due to bad soil... than e.g. GoldenSabre that's a full motion detector, and so have no need of amplitude control for that, have a silent-SAT design.

Of course, there is also the +V/-V argumentation... in Bandido +5/-3.2, in GSabre +8/-6.2 ... of course some mod. would be required to fit the feedack version on BandidoII. TX osc must use 5volts only in bandidoII.

Then also about power... less voltage , less power... maybe they just wanted the maximum amplitude on BandidoII cause of the already small power !?

Just my thoughts.

Kind regards,
Max

[Qiaozhi]

For Fun, I built and tested Both circuits.

The Only differences I can find:

1) The one on the Right side has only about 1/5 the output signal as compared to the left one. So it will also produce a somewhat lower magnetic field on the coil.

2) But because of the Zener, .22 capacitor and the fet, it is better regulated and less succeptable to Power supply interference from other IC's on the board.

But I really don't this right one as being much of a useful advantage.

Thanks Gary. This is as I expected, except for the amplitude of the output signal from the stabilized circuit. This seems very low. But certainly the purpose is to stabilize the TX output against power supply variation, and has little to do with coil loading.

[Max]

Thanks Gary. This is as I expected, except for the amplitude of the output signal from the stabilized circuit. This seems very low. But certainly the purpose is to stabilize the TX output against power supply variation, and has little to do with coil loading.

Hi Qiaozhi,
maybe you're right. I've noticed that on simple version (no feedback) amplitude is already stable. 5V supply are stabilized by a voltage regulator in BandidoII.

In GSabre it's the same , but regulator for +8V, stable output... it use lm2930-8.

If one use e.g. 7808 can have problems related to output variations when battery voltage goes down , due to 3volt dropout of 7808.

But original schematic have LM2930-8 so... no big dropout problems (same as in e.g. BandidoII).

The feedback provide amplitude stabilization... that's sure.

I think it's related to gnd signal.
Geb filter gnd signal away using geb trimpot and phase information to rotate coordinate system but then amplitude vary at oscillator output moving the coil during sweeping in bad soil. I think that they want avoid , with feedback, that variations.

Maybe I'm wrong. Don't know for sure.

Best regards,
Max

[chemelec]

Hi Qiaozhi,
maybe you're right. I've noticed that on simple version (no feedback) amplitude is already stable. 5V supply are stabilized by a voltage regulator in BandidoII.

In GSabre it's the same , but regulator for +8V, stable output... it use lm2930-8.

If one use e.g. 7808 can have problems related to output variations when battery voltage goes down , due to 3volt dropout of 7808.

But original schematic have LM2930-8 so... no big dropout problems (same as in e.g. BandidoII).

The feedback provide amplitude stabilization... that's sure.

I think it's related to gnd signal.
Geb filter gnd signal away using geb trimpot and phase information to rotate coordinate system but then amplitude vary at oscillator output moving the coil during sweeping in bad soil. I think that they want avoid , with feedback, that variations.

Maybe I'm wrong. Don't know for sure.

Best regards,
Max

As near as I can tell from My tests, There are No differences between the two circuit Outputs, relative to ground effects or metal coming near the coils.
The Both seem to respond the same to these.

And Just because the Power supplies are Already Regulated, It does not stop Unwanted Signals (Noise and some Oscillations Riding on the DC Voltage) from entering this oscillator via the supply.

That Zener/Fet circuit may help reduce this possibliity.

[Max]

As near as I can tell from My tests, There are No differences between the two circuit Outputs, relative to ground effects or metal coming near the coils.
The Both seem to respond the same to these.

And Just because the Power supplies are Already Regulated, It does not stop Unwanted Signals (Noise and some Oscillations Riding on the DC Voltage) from entering this oscillator via the supply.

That Zener/Fet circuit may help reduce this possibliity.

Hi Gary,
I think is matter of millivolts there, I dubt one can see e.g. on scope if not watching at the extrems of the sinus wave... difficault to simulate at workbench ground signal and read out its influence in the two different circuits.

I've tested for few minutes GSabre in my small test garden and find it's more stable on soil than BandidoII.
Where with BandidoII the geb calibration procedure is a bit difficault, using a multiturn pot and you can't miss even a few degree rotation of geb pot. without compromising the geb settings, with GSabre I've found a wider interval in which actually it's ground balanced.

Of course, your observation and Qiaozhi's thoughts are right about supply voltage variations rejection.

I agree with both of you on that... if there is a voltage supply variation the feedback came in place mantaining the amplitude at right level.
All right. Totally agree on that.

But also if there is an external perturbation that cause the osc signal amplitude vary, it's the same... at least in a limited interval.

I've made just a simple test of few minutes. But seems much more stable and easy to geb-tune than BandidoII. BandidoII need a multiturn pot for geb tuning... GSabre just a trimpot, not a case. Tesoro set that pot in factory... and then the machine it's ready for various soil conditions: that say everything for me.

I think they fix the geb trimpot for the right phase of a "medium soil" and then leave the fet do all the rest of ground signal ignoring for you, instead of rotating a pot like in bandidoII, to keep ground influence smaller as possible.

Best regards,
Max

[Max]

claims

Hi,
I remember that Eldorado was claimed of "Built-in Mineral Rejection" by Tesoro.

It had a 3 and 3/4 turn geb pot (similar to BandidoII) , cause it was a really complete machine, but there was that claim:

"Built-in Mineral Rejection" ... that now make sound one bell in my head.

If it is so... maybe the feedback can work as I think !?

Or that claim was just referred to the geb circuitry only ?

I don't know.

Kind regards,
Max

[Leto]

Silver Sabre X

Thanks for replies,
very helpfull insights...

About this SS project:
Its a Love&Hate relationship I developed with this detector...
I guess everyone who spended too much time with one single project knows What I'm talking about .

Here are the changes to the circuit and new parts:

• I decided to use Eldorado type oscillator..
• Input voltage regulator changed to L4902A (dual 5V)
• new are two paralleled MAX1682 voltage doublers for TX oscillator (with on/off switch)
• for each op-amp IC power supply two bypass capacitators were added
• potential divider for signal coming from Tx (stability issue..)
• phase reference network changed to Eldorado configuration
• optocoupler for/with 555 audio
• few other changes according to SS2 shematic & geotech..

Everything was tested with old PCB I made.
New one will be ready in folowing days..

[Leto]

what's that squeeking..??

Hi finally I'm back home,
the PCB was assembled and tested:

• power converter works ok, boosting detection up to 20%
• bypass caps (or maybe GND planes) made detector more quieter..
• discrimination tested with trimmers on board - working ok
• sound - bad - not well behaved, not good idea to use 555, at least with this circuit. Treshold pot almost uneffective

I'll play with this one for a while - changing values around 555, but will probably jump back to ICL7660 generated sound as in original.
Has someone tried 555 as sound stage in Tesoros? Any experiences?

[ivconic]

!?

I totally missed this thread so far!!???
Analog Tesoros became my favorites, means that i am very interested about this too. Very good work Leto!
Previous SS pcb you posted here is interested much!
I will make this ASAP.
Bravo! Good job! Excellent!
BTW thank you for posting pcb here...
Regards!

[aft_72005]

Hi Leto
Please say more about your latest changes on silver saber.
Regards.