TESORO GOLDEN SABRE

[simonbaker]

Hi,
that's not a solution !

Never decrease that sensitivity.... work always at 110% like russian reactors!

Returning serious...

Decreasing sensitivity is good when e.g. on soil... one have too much troubles at max sens then reduce... it.

But if device is quiet then you move it and sounds.... there's something wrong I think.

I think he has a mistake on either mechanical stability of the assembly... or electrostatic related "ghost" (means that pcb reads some static and thus give a false signal... if box is not at a potential like in the circuit... it will not act as faraday cage... but like the plate of a capacitor!)

Kind regards,
Max

Not as solution, as diagnostic. I want to know how high the movement signal is. So turn sensitivity to make less sensitive, does movement signal stop at some point, where?

From his other posts it seems he/she has a super-sensitive detector, 40 cm???

I agree sounds like mechanical. I would like to see photos - is his cable free to swing? Any suspicious construction? Too late I'm sure to see coil, but what kind of shielding? Is shielding loose? Is coil housing flexible?

What happens if put detector on table (no movement), and wave hands near coil? Wave hands near control box?

What kind of motion makes signal? Side-to-side? Up and down? Slow, fast?

Where is he/she testing? Outside? Inside? Near power cords?

Regards,

-SB

[Qiaozhi]

Sir Max Ivco Quzi and all
please help my device works ok TX freq is 14.7.
RX6.5mh TX6mh after sheilding which is exactly what Ivconic
said so the only problem now i have
just very very little movement the device gives signal
i have tried many many ways like nulling from 0mv to 40mv
nothing happned the stand is plastic tube the coil very stiff
and what else
please help..........
Max by the way when i read your responce to Simon about his drwing
10minutes laughing
thanks all

OK - from your description it is probably one of two things:

1. As Ivconic says, make sure you're using the right type of screened cable to connect the coil to the control box. Certain types can become microphonic, and produce noise when moved.

2. It sounds from your description of nulling the coil, that you have not understood the importance of getting the correct initial phase-shift between TX and RX. My suspicion is that this is most likely the problem. If you set up the coil correctly, and the noise is still there, then try the other suggestions that have already been provided.

[ivconic]

Yes; presuming coil was balanced properly, than only cable left to be suspected. If coil was balanced well and cable is the right one....than only wirements left.
Wirements at TGS is a bit tricky. You can wire it up on few different ways, but only one guarantee good stabillity and no falses.
In search head both cages and both coils ends are wired togather and further connected to cable shield, but also another isolated wire is wired to cable shield in coil. "Hot" ends of both coils are wired separatelly.So... you will have 3 separatelly isolated wires and cable shield arround them. That is situation in search head. On other end - pcb (through connectors) you will connect cable shield to pcb gnd and TX "hot" wire to TX output. Also RX "hot" wire and that separated wire (connected to shield in search head but separated in cable) to RX inputs. Do not make any connection between RX inputs and gnd on pcb! So...RX "gnd" is connected ONLY in search head to common search head gnd (both AL cages and both ends on cable shield + one separated cable wire)....
Sheeeshh...to much confusing here!!!
That's why is better to search back pages for sketch i posted. One picture can replace 1000 words!

In the past, during all those experiments with coil and cable wirements i tested almost all possiblle combinations and few different types of cable.
Some of those do work, but only this method i just explained, provide excellent stabillity and absolute immunity.
Undesrtand...?

[simonbaker]

Are these pictures you mean Ivconic?

(Grounding of RX lead through coil shields is curious.)

Can you confirm which of the RX inputs is the "grounded" wire? The one to the op amp inverting (-) or non-inverting (+) input?

Regards,

-SB

[Qiaozhi]

Are these pictures you mean Ivconic?

(Grounding of RX lead through coil shields is curious.)

Can you confirm which of the RX inputs is the "grounded" wire? The one to the op amp inverting (-) or non-inverting (+) input?

Regards,

-SB

Hi Simon,

It's the inverting input of the preamp opamp that is connected to the screen. Some back-engineered Tesoro schematics show a ground connection in the receive circuit (as in your post) but this is incorrect. The connection to ground (0V, screen) is actually made in the search head.
Ivconic's diagram shows the correct wiring for the coil.

[Max]

Hi Simon,

It's the inverting input of the preamp opamp that is connected to the screen. Some back-engineered Tesoro schematics show a ground connection in the receive circuit (as in your post) but this is incorrect. The connection to ground (0V, screen) is actually made in the search head.
Ivconic's diagram shows the correct wiring for the coil.

Hi,
yes, clear, that's my experience too: the gnd is due to coil internal connection not as reported at schematic level in wrong diagrams.

Ivconic's one is right; if someone use e.g. double gnd connection (at pcb level and at coil too) it will generate a gnd loop... with increase of noise impact due to the current that will flow in that closed loop in the cable.

That will strongly affect circuit performances cause of noise signal flowing there and thus propagation of it to other parts of circuit, cause of the very high amplification factors in the chain.

Then , also, the cable will show more sensitive to microphonic also, like you described, so will expose user to false signals at every, even small, vibration.

Kind regards,
Max

[simonbaker]

Hi,
yes, clear, that's my experience too: the gnd is due to coil internal connection not as reported at schematic level in wrong diagrams.

Ivconic's one is right; if someone use e.g. double gnd connection (at pcb level and at coil too) it will generate a gnd loop... with increase of noise impact due to the current that will flow in that closed loop in the cable.

That will strongly affect circuit performances cause of noise signal flowing there and thus propagation of it to other parts of circuit, cause of the very high amplification factors in the chain.

Then , also, the cable will show more sensitive to microphonic also, like you described, so will expose user to false signals at every, even small, vibration.

Kind regards,
Max

Thanks all for clarifying.

That ground in coil head is hard to understand theoretically, but if it works, it works. You would think at first it would ruin the "differential" effect of the RX leads and create more differential noise. Also, you would think it would create a large ground loop if you follow ground from oscillator to RX input. But if it works....

Regards,

-SB

-SB

[metaldetector107]

Mayday mayday mayday

Dear Ivconic????
i am sorry but i am realy confused
i know you dont like repeating question
but this time please dont
could u tel me the thread page of your coil wiring
if u cant remeber please trouble yourself and make another one for me
you it is realy good favor;;
beacuse i know i made mistake like till your last reply to me i was connected both
shield to PCB but still any slight movement sounds
abou the cable I am using a PI metal detector cable called P-158
the cable has two pairs of wire and each pair has its own shield
many many thanks
by the way iam not lazy i have downloaded all 137 pages of TGSL
abd reading them daily but still i am hopless with you and MAX and other gentlments

[Mullihaka]

Unwanted oscillation

Hi Andy,
seems you have a little problem there : the 700Khz you read are probably from self oscillations at that op amp.

The fact you read 130mA consumption is not so good... I think you've it damaged already.

My suggestion is , apart cleaning very well pcb as you can, desolder it... then remount the socket; try to add 100nF caps just under the ic socket at power rails and other lead to gnd.

That way you'll probably solve that, but have to use a brand new ic.

Other things that could be involved are pcb tracks... too near can be a problem and sometimes op amps use special ring guards for that at inputs (yes, the amplification factor plays a major role in that but not only)... but if you used any of the pcb designs here you'll probably need just that filtering at power rails.

Kind regards,
Max

I use hte PWB design attached in the first message of this thread. The bipolar capacitors are constructed of two 10u electrolytics in series, minus poles connected together.

The current consumption is 60mA. Is that correct?

There are 20mV ripple at 700kHz on the +8V rail, riding on 20mV ripple at the transmitter's frequency. How clean did you get that?

I have tried bypassing the 8V regulators in/output with 100n and the same for the PNP transistor's emitter of the negative voltage generator. No help.

I disconnected the 470n cap from pin 1 of the amp, that didn't help. Disconneting the 100k resistor from pin 3 did nelp a bit. I have a feeling, that the power rails should be cleaned before trying anything else. I can find ripple everywhere in the device, just can't find the source. Could the ripple be born somewhere else and it jsut get's amplified by the amp in question?

Andy
I have tried bypassing the

[ivconic]

Dear Ivconic????
i am sorry but i am realy confused
i know you dont like repeating question
but this time please dont
could u tel me the thread page of your coil wiring
if u cant remeber please trouble yourself and make another one for me
you it is realy good favor;;
beacuse i know i made mistake like till your last reply to me i was connected both
shield to PCB but still any slight movement sounds
abou the cable I am using a PI metal detector cable called P-158
the cable has two pairs of wire and each pair has its own shield
many many thanks
by the way iam not lazy i have downloaded all 137 pages of TGSL
abd reading them daily but still i am hopless with you and MAX and other gentlments

?????????!!!
Please, just look up; Simonbaker just posted it!

[simonbaker]

?????????!!!
Please, just look up; Simonbaker just posted it!

Yes, a few messages before this one. Here is the link: http://www.geotech1.com/forums/showp...postcount=3409

It is the top picture you want to look at, showing the cable wires attached to the coils and shield. What isn't shown is that the black wire of the RX cable goes to the inverting (-) input of of the op amp in the RX circuit.

Regards,

-SB

[simonbaker]

I use hte PWB design attached in the first message of this thread. The bipolar capacitors are constructed of two 10u electrolytics in series, minus poles connected together.

The current consumption is 60mA. Is that correct?

There are 20mV ripple at 700kHz on the +8V rail, riding on 20mV ripple at the transmitter's frequency. How clean did you get that?

I have tried bypassing the 8V regulators in/output with 100n and the same for the PNP transistor's emitter of the negative voltage generator. No help.

I disconnected the 470n cap from pin 1 of the amp, that didn't help. Disconneting the 100k resistor from pin 3 did nelp a bit. I have a feeling, that the power rails should be cleaned before trying anything else. I can find ripple everywhere in the device, just can't find the source. Could the ripple be born somewhere else and it jsut get's amplified by the amp in question?

Andy
I have tried bypassing the

You have made the full TGS version which I think has notch circuit, so 60 mA probably OK - TGSL (lite) version has no notch circuit and uses about 30 to 40 mA I think.

Question: is the 700 kHz ripple in phase with the TX signal? In other words, if you trigger your oscilloscope on the TX signal, is the ripple stationary or does it run freely over the TX signal like a blur?

I get big spikes on my supply rails, but they are at the switching frequency of the negative supply push-pull transistors. They are in sync with the TX signal, so hopefully create a constant offset, not noise.

If the ripple is from some other place, I would think you would see it also in the other half of the op amp.

Try putting a jumper wire from pin 1 (output) to pin 2 (inverting input) of the LM358 and see what happens. If that amp is oscillating, it should change it.

A bad feedback capacitor with lots of inductance could cause oscillation in any of those op amps. Go to each op amp and jumper the output to inverting input and see if the oscillation stops anywhere.

Just some ideas...

Regards,

-SB

[ivconic]

Now is my turn to ask funny question;
have you ever noticed that capacitor-look-like component, usually present in older VCR's? Small component, exactly capacitor look, usually labeled as 0.47F (!!!!) 5V or 6V? Meaning actually 47 000 uF !!! Small...smaller than capacitors we are using mostly here.
So.. i took one recently and wired it parallel with one led diode and ps. Switched on ps and second after switched off. Led diode shined (diming down) for 2 minutes after!!!!!
So...actually it is capacitor. Hell of capacitor! Excellent to stabilize some voltage. So...here is my funny question:
How about, if we use that component(s) in TGSL? On very few places, especially on TX and eventually at chopper output (reversed, respecting polarities there)....ha?!
I asume, it will take a bit of time to charge fully from accu. So, after switching on, detector will be ready to operate after few seconds...
I never had any experiences before with this kind of capacitors....but shure this look like having some potentials to be used here...
I am very interested in your opinion..

[Qiaozhi]

Now is my turn to ask funny question;
have you ever noticed that capacitor-look-like component, usually present in older VCR's? Small component, exactly capacitor look, usually labeled as 0.47F (!!!!) 5V or 6V? Meaning actually 47 000 uF !!! Small...smaller than capacitors we are using mostly here.

This sounds like an unusual component. Are you sure it has this huge value of capacitance?
Do you have a photo?

[aft_72005]

Now is my turn to ask funny question;
have you ever noticed that capacitor-look-like component, usually present in older VCR's? Small component, exactly capacitor look, usually labeled as 0.47F (!!!!) 5V or 6V? Meaning actually 47 000 uF !!! Small...smaller than capacitors we are using mostly here.
So.. i took one recently and wired it parallel with one led diode and ps. Switched on ps and second after switched off. Led diode shined (diming down) for 2 minutes after!!!!!
So...actually it is capacitor. Hell of capacitor! Excellent to stabilize some voltage. So...here is my funny question:
How about, if we use that component(s) in TGSL? On very few places, especially on TX and eventually at chopper output (reversed, respecting polarities there)....ha?!
I asume, it will take a bit of time to charge fully from accu. So, after switching on, detector will be ready to operate after few seconds...
I never had any experiences before with this kind of capacitors....but shure this look like having some potentials to be used here...
I am very interested in your opinion..

Hi ivconic
Yes , it is 0.47F or 470000 microfarad . I saw it at motherboard of pc.
It is usually use instead of backup battery .
May be in your old VCR did use for memory saving and real time clock .
Best regards.