TESORO GOLDEN SABRE

[simonbaker]

coil noise

I am interested in noise people talk about, where it is from.

In my laboratory (spare bedroom, no workbench), with my ridiculous unshielded coil and breadboard circuit, the coil creates the major part of noise. Not unexpected, it is a huge antenna for any kind of emf.

If I disconnect coil from circuit, noise drops down factor of ten (but still a lot).

So only way to observe typical working noise must be outside I assume. (But then scope not available. Maybe can run it from car battery.)

I am interested if anyone can do this: get outside with a scope and detector. Measure noise (I guess at output of LM308 ) with coil connected, then disconnected. Then measure noise shorting inputs to op amps one at a time up the chain, how does the noise change? What is the critical source of noise?

You would guess that LF353 pre-amp and LM358 front stage would be where noise is critical. Why is LM358 not an ultra low-noise component, like a biFet op amp?

Another source of noise would be subtle jitter in the JFet gate driver circuits. Very difficult to see because such big strong signal. But if LM393 triggers at slightly different points, it shifts driver square wave a little, causes "phase noise" so to speak. A little noise in the TX oscillator can change the zero crossings of the the LM393 that makes the gate driver signal, making "phase noise". But you hope that the same noise goes into the coil and back out the RX signal and gets balanced out. Who knows.

The wires from the descrim switch of course can pick up noise, but is after the LMM393, hopefully swamped and no effect. But that noise can maybe feed through the JFet gate to the JFet Source and get into the LM358 input.

So main experiments are:

1- noise with coil.
2 - noise with coil disconnected.
3 - noise with front LM358 input grounded before the 100K resistor.
4 - noise with front LM358 input grounded directly.

-SB

[Max]

Yes i have almost the same experiences.
Usually i put TL082 when not having LF353, works just fine there. NE5532 is just not working at present setup. I think it will work just fine too, if we readjust components arround it. TL072 is actually TL082 so..same story - it can be used there pretty successfully.
Recently i got LS204 in metalic case. Not tested yet, but i will test those for sure.
It is not a big deal to replace and readjust front end at TGSL.
What bugs me more are LM308 and LM393. OK..TL081 also tested instead LM308 and to tell you the truth; those really do the job with less noise.
But LM393 is a real pain in the .......coil!!!
I am sure that TLC2262 can replace those, even work better, but i simply cant find those in local shops!
Or even better TLV2262.

Another thing...LM358 could be replaced with something better, but which one? I was thinking to put there 4 x opamp instead 2x LM358.
Is it good idea?
I am planing to redraw pcb for that matters soon.
What should i consider to put there? TL074,TL084? LM324? LF444?
So far i used mainly LM324 in many circuits and those suits all the demands.

I am quite unexperienced refering some specific questions, so i will freely ask here, please dont laugh;
are there any changes (benefits,drawbacks) if two double op-amps are replaced with one 4xop-amp? Refering hums,power drains, signal paths etc.etc...?
Reasons why am i asking this funny question is more than naive..but hey, i want to learn and be sure.
Theoretically it should be the same thing; 2x double or 1xquadro...same thing.
But in practice i noticed some thing; usually those cheap chinesse detectors DO have quadros more than singles? Why? Production costs?
Other hand, branded machines usually do have plenty of "doubles" and rarelly some "quadro"....
Ok...many branded's do have TL074, 27m9, LF444 and similars... and also more "doubles" but my (weird) statistics is pushing me to start thinking on this as some special reason.
I havent seen any 27mxx or LF... on chinesse toys, but mostly LM324's and TL064's. Again, on branded machines usually are mentioned and very rare "quadros" like TL064 and LM324..?
Is this only my imagination or there is something else there?

Hi,
the LS204 is good there, tested too... (just forgot about before you wrote in your post...) so can use there.

The 5532 is a transistor input amplifier... and probably the reason why it's not so smart there is related to that. Fet amplifiers are fairly better at TGS preamp.

You're right about the chinese Mds don't use the good components... reasons are related to costs... cause also they need to product hundred thousands of that machines... and they must cost really few , so single piece cost is a big issue in that scale of production.

They also use quads more for similar reasons... the quads have often costs similar to a dual ! So if use e.g. TL064 the cost (on hi-volume) is really near a TL062 and not 2xTL062 as one could expect: that's related to manifacturing of device... making a quad is not more expensive than making a dual in the silicon technology... and having one enclosure/package instead of 2 make , really, a cost difference instead. A machine for packaging will need double the time to make 2 epoxy enclosures instead of one, larger.

The difference... there IS. It's mostly related to noise propagation: even in quality parts, with extremely good channel separation, you'll get troubles from very near tracks of signal path! In cheap op amps the channel separation is rarely an issue... it's average and LM324 is an example of that.

We must think our MDs like hi-fi audio devices: most audio designers very often use dual op amps instead of quads just for the reasons of above.

Then there's also the supply rejection issue...to consider. A quad (not always) usually do not offer enough supply rejection compared to a dual design.

Are details... but important either when making audio hi-fi designs or good MDs, that's why big players like the dual op amps and usually avoid the quads.

An example: in Vladimir's TGSL design you use the TL082 instead of 2xLm308, right ? How do you feel about ?

I made the board, works good, but noticed that there are problems with the TL instead of 2xLM308... and problems are not related much to the quality of op amp (TL082 is better about noise respect to LM308 ) but to the too near signal tracks there: it's a layout problem!

So, the details are important when try to put to the extreme a good design.

We sacrifice space and components for the best results.

Kind regards,
Max

[Max]

I am interested in noise people talk about, where it is from.

In my laboratory (spare bedroom, no workbench), with my ridiculous unshielded coil and breadboard circuit, the coil creates the major part of noise. Not unexpected, it is a huge antenna for any kind of emf.

If I disconnect coil from circuit, noise drops down factor of ten (but still a lot).

So only way to observe typical working noise must be outside I assume. (But then scope not available. Maybe can run it from car battery.)

I am interested if anyone can do this: get outside with a scope and detector. Measure noise (I guess at output of LM308 ) with coil connected, then disconnected. Then measure noise shorting inputs to op amps one at a time up the chain, how does the noise change? What is the critical source of noise?

You would guess that LF353 pre-amp and LM358 front stage would be where noise is critical. Why is LM358 not an ultra low-noise component, like a biFet op amp?

Another source of noise would be subtle jitter in the JFet gate driver circuits. Very difficult to see because such big strong signal. But if LM393 triggers at slightly different points, it shifts driver square wave a little, causes "phase noise" so to speak. A little noise in the TX oscillator can change the zero crossings of the the LM393 that makes the gate driver signal, making "phase noise". But you hope that the same noise goes into the coil and back out the RX signal and gets balanced out. Who knows.

The wires from the descrim switch of course can pick up noise, but is after the LMM393, hopefully swamped and no effect. But that noise can maybe feed through the JFet gate to the JFet Source and get into the LM358 input.

So main experiments are:

1- noise with coil.
2 - noise with coil disconnected.
3 - noise with front LM358 input grounded before the 100K resistor.
4 - noise with front LM358 input grounded directly.

-SB

Hi,
a portable oscope will do that. I can't test for that but will be really interesting.

The big part of noise to consider is about 3 factors:
- electrical noise
- rf noise
- internal noise

For electrical noise (that always produce low frequency radiated EM noise too) I mean very low frequency kind of noise... like from e.g. a fluorescent lamp near... an electric motor running... oscillations produced in the bounce of a switch inside home... and similar stuff.

For RF noise I mean expecially radio noise from VLF/LW range to some MHz (short waves) + some very near transmitter running also in VHF/Frequency modulation too.

Which problems ?

Electrical noise is easy to see at home... any time someone will switch a lamp on I get sound in my TGS/TGSL from meters away... also from 15meters away! That's cause all the house is full of copper wires around... and any fluctuation will be a near fluctuation too... that propagates by wires and on other e.g. equipment like power supply, scope etc

At the end... if using battery, the stuff is about the same... I get sound from electrical noise at distance.

The RF noise is more subtle: you can't see it unless you know there is or you're looking for it.

When you're near a powerful transmitter , for example, you get all that noise for free!

That's disappointing sometimes. In a city/town you'll always get some amount of RF noise... and also e.g. mobile phones transmitters will give you troubles.

The advantage is that a thin shield will block most of RF noise!

But then electrical noise you'll not solve even with shield.

Internal noise depends of components: use less noise rated and will get real advantages. E.g. avoid old TL062...and use TL072/TL082 and also LM358 if you can (use e.g. TLC2262 there or other), you'll notice the difference.

Kind regards,
Max

[aft_72005]

Hi Max

Air test : The coin with 25mm diameter from 30cm of coil .it isn’t very
Good result when compare with your built and ivconic
Also the test area contains heavy electrical interference and noises.
Because My office placed in power cable factory

why don't you try something shielded cable instead ?

I using shielded wire with 2mm dia .

Also, the CHAIR ! Are you sure the chair has no metal inside like iron rivets or nails ?

The chair, check it, contain very small staples. Not under coil, far it
Thanks for your guide .
Best regards.

[simonbaker]

Hi,
a portable oscope will do that. I can't test for that but will be really interesting.

The big part of noise to consider is about 3 factors:
- electrical noise
- rf noise
- internal noise

For electrical noise (that always produce low frequency radiated EM noise too) I mean very low frequency kind of noise... like from e.g. a fluorescent lamp near... an electric motor running... oscillations produced in the bounce of a switch inside home... and similar stuff.

For RF noise I mean expecially radio noise from VLF/LW range to some MHz (short waves) + some very near transmitter running also in VHF/Frequency modulation too.

Which problems ?

Electrical noise is easy to see at home... any time someone will switch a lamp on I get sound in my TGS/TGSL from meters away... also from 15meters away! That's cause all the house is full of copper wires around... and any fluctuation will be a near fluctuation too... that propagates by wires and on other e.g. equipment like power supply, scope etc

At the end... if using battery, the stuff is about the same... I get sound from electrical noise at distance.

The RF noise is more subtle: you can't see it unless you know there is or you're looking for it.

When you're near a powerful transmitter , for example, you get all that noise for free!

That's disappointing sometimes. In a city/town you'll always get some amount of RF noise... and also e.g. mobile phones transmitters will give you troubles.

The advantage is that a thin shield will block most of RF noise!

But then electrical noise you'll not solve even with shield.

Internal noise depends of components: use less noise rated and will get real advantages. E.g. avoid old TL062...and use TL072/TL082 and also LM358 if you can (use e.g. TLC2262 there or other), you'll notice the difference.

Kind regards,
Max

Another point: minimum sensitivity threshold is about 3.3 mV -- so theoretically we can't detect anything that is less than that at output of LM308. If people say detector is quiet, then what good is making circuit noise lower, because it is already below sensitivity threshold? If you currently use sensitivity at maximum sens, then making noise lower is only useful if you can then increase gain too.

So, if we have zero circuit noise, and no RF, etc., then existing design of sensitivity control limits depth of target. A little noise actually helps because it adds to target signal and lifts above sensitivity threshold so you hear it. But noise will make crappy audio because choppy when just at sensitivity threshold.

So if we make very low noise circuit, maybe need to make sensitivity threshold lower and increase gain.

However, if make sensitivity threshold lower, we have to watch out for complete recovery -- even tiny amount of residue can interfere with threshold if low enough. I notice this with LTSpice when trying slower response filters - recovery residue is problem for sensitivity threshold.

Just trying to learn all these factors, better know how to build good TGSL.

Cheers,

-SB

[ivconic]

Hi,

a portable oscope will do that. I can't test for that but will be really interesting.

The big part of noise to consider is about 3 factors:
- electrical noise
- rf noise
- internal noise

For electrical noise (that always produce low frequency radiated EM noise too) I mean very low frequency kind of noise... like from e.g. a fluorescent lamp near... an electric motor running... oscillations produced in the bounce of a switch inside home... and similar stuff.

For RF noise I mean expecially radio noise from VLF/LW range to some MHz (short waves) + some very near transmitter running also in VHF/Frequency modulation too.

Which problems ?

Electrical noise is easy to see at home... any time someone will switch a lamp on I get sound in my TGS/TGSL from meters away... also from 15meters away! That's cause all the house is full of copper wires around... and any fluctuation will be a near fluctuation too... that propagates by wires and on other e.g. equipment like power supply, scope etc

At the end... if using battery, the stuff is about the same... I get sound from electrical noise at distance.

The RF noise is more subtle: you can't see it unless you know there is or you're looking for it.

When you're near a powerful transmitter , for example, you get all that noise for free!

That's disappointing sometimes. In a city/town you'll always get some amount of RF noise... and also e.g. mobile phones transmitters will give you troubles.

The advantage is that a thin shield will block most of RF noise!

But then electrical noise you'll not solve even with shield.

Internal noise depends of components: use less noise rated and will get real advantages. E.g. avoid old TL062...and use TL072/TL082 and also LM358 if you can (use e.g. TLC2262 there or other), you'll notice the difference.

Kind regards,
Max

Thanks Max,
you put some light on my doubts. I wasnt sure but had some simillar doubts. Now is more clear to me and makes more sence.
Regards!

[Alexismex]

Thank you very much Max for your good explanation on dual amp, many times i think about that without response , now thank to you it is clear in my mind why it is better to design with dual amp,you win a 10 and a good beer , thank again,
saludos from Mexico
Alexis

[Max]

Another point: minimum sensitivity threshold is about 3.3 mV -- so theoretically we can't detect anything that is less than that at output of LM308. If people say detector is quiet, then what good is making circuit noise lower, because it is already below sensitivity threshold? If you currently use sensitivity at maximum sens, then making noise lower is only useful if you can then increase gain too.

So, if we have zero circuit noise, and no RF, etc., then existing design of sensitivity control limits depth of target. A little noise actually helps because it adds to target signal and lifts above sensitivity threshold so you hear it. But noise will make crappy audio because choppy when just at sensitivity threshold.

So if we make very low noise circuit, maybe need to make sensitivity threshold lower and increase gain.

However, if make sensitivity threshold lower, we have to watch out for complete recovery -- even tiny amount of residue can interfere with threshold if low enough. I notice this with LTSpice when trying slower response filters - recovery residue is problem for sensitivity threshold.

Just trying to learn all these factors, better know how to build good TGSL.

Cheers,

-SB

Hi,
yes you're right. If the device can run absoutely quiet there's no reason to limit the gain too much, so the sensitivity.

Of course, that's depends not only on design but on e.g. S/N due to construction (board, wires, components, soldering, ground plane if any, cleaning process, kind of box employed, wiring to coil etc etc)

In good construction practice, with very hi S/N I think is good push lower that threshold, gaining about detection.

I will try it soon.

Kind regards,
Max

[Max]

Hi Max

Air test : The coin with 25mm diameter from 30cm of coil .it isn’t very
Good result when compare with your built and ivconic
Also the test area contains heavy electrical interference and noises.
Because My office placed in power cable factory



I using shielded wire with 2mm dia .



The chair, check it, contain very small staples. Not under coil, far it
Thanks for your guide .
Best regards.

Hi,
ok, but 2.5cm coin at 30cm is not that bad too. It's a good result for an homemade VLF, considering also the TGS/TGSL has not a very powerful transmitter stage, but weak.

The wires are ok, and chair also.

I think then that maybe you need more careful tuning at coil, and find a place with less noise to explore all sensitivity of device.

If too noise around you'll not spot the real maximum sens of device cause noise will prevent you running it (stable) at maximum sens.

Kind regards,
Max

[aft_72005]

Hi Max
I am sure my test area full of electrical noises and interference because
TGSL out put sound with noises, especially when sensitivity pot. At maximum.
I carry it to my home , and test again .
Best regards.

[pulltabmike]

Good morning all,
I hope you all do not mind me jumping in, I have been following this project with great interest for a while now, and finally got the bug to build Ivconics TGSL version 2 weeks ago. I have been out of the electronics hobby for about 20 years, so I am quite a bit quite a bit rusty at it I see I have quite a bit to learn! I do have over 25 years experience detecting here in the States. So far, all of my problems have been centered around the coil. I wound a 11" DD, 100 turns TX, 103 turns RX. I am measuring 12V P-P and 14.7 Khz at TX with O-Scope. Aluminum tape used for shielding. My initial air-test depth results are below without the audio boost mod, with the detector at a slight chatter:

US Penny – 12”
US Nickel – 13”
US Dime – 11”
US Quarter – 13”


All of my interference is electrical in nature (my workshop is in the attic of my home) and due to the fact that the coil is not secure. Any little vibration at the coil makes the detector go nuts!!! Once I finish tuning and securing the coil, will test outside. I know the figures above will only improve. For those that have gotten the circuit to where it is now, my hat is off to you, great work

Mike

[ivconic]

Good morning all,

I hope you all do not mind me jumping in, I have been following this project with great interest for a while now, and finally got the bug to build Ivconics TGSL version 2 weeks ago. I have been out of the electronics hobby for about 20 years, so I am quite a bit quite a bit rusty at it I see I have quite a bit to learn! I do have over 25 years experience detecting here in the States. So far, all of my problems have been centered around the coil. I wound a 11" DD, 100 turns TX, 103 turns RX. I am measuring 12V P-P and 14.7 Khz at TX with O-Scope. Aluminum tape used for shielding. My initial air-test depth results are below without the audio boost mod, with the detector at a slight chatter:

US Penny – 12”
US Nickel – 13”
US Dime – 11”
US Quarter – 13”


All of my interference is electrical in nature (my workshop is in the attic of my home) and due to the fact that the coil is not secure. Any little vibration at the coil makes the detector go nuts!!! Once I finish tuning and securing the coil, will test outside. I know the figures above will only improve. For those that have gotten the circuit to where it is now, my hat is off to you, great work

Mike

Hi,
not bad for a start.

"...Any little vibration at the coil makes the detector go nuts!!!..."

This is usually happen when cable is not suitable or not wired up correctly in search head or at detector. Other case is when GEB trimmer is not adjusted properly. To check this you can use ferrite rod and see if detection on it occurs. If yes than adjust GEB trimm softly to stop detection on ferrite, just to hear some rare "cracks" when rod is 2-3" away from coil surface. Doesn't matter if this done in All Metal or Disc Mode, in both ways you can adjust it. In case of Disc mode, keep Disc pot at "1"...
OK, in case you can not "reject" ferrite rod by adjusting GEB trimmer, than coil is not nulled well.
But first recheck cable wirements. You have some draw on these pages how to wire up that correctly. I posted it some time ago...dont remember on which page.
Wish you success, regards!

[Friday]

hi pulltabmike....
I will make TGSL 1265 latest version.did you use 0.25mm wire?
Regards....

[eclipse]

12 Volts is 4V less than normal, so you will surely loose some depth cos of that. Are you using zener diod 4v3 or lower than that?
Also what are the supply voltage? I get +8V and - 7V
12-13" is not bad result at all, some of us could not start that good with pcb#1 so ...

[Max]

Good morning all,
I hope you all do not mind me jumping in, I have been following this project with great interest for a while now, and finally got the bug to build Ivconics TGSL version 2 weeks ago. I have been out of the electronics hobby for about 20 years, so I am quite a bit quite a bit rusty at it I see I have quite a bit to learn! I do have over 25 years experience detecting here in the States. So far, all of my problems have been centered around the coil. I wound a 11" DD, 100 turns TX, 103 turns RX. I am measuring 12V P-P and 14.7 Khz at TX with O-Scope. Aluminum tape used for shielding. My initial air-test depth results are below without the audio boost mod, with the detector at a slight chatter:

US Penny – 12”
US Nickel – 13”
US Dime – 11”
US Quarter – 13”


All of my interference is electrical in nature (my workshop is in the attic of my home) and due to the fact that the coil is not secure. Any little vibration at the coil makes the detector go nuts!!! Once I finish tuning and securing the coil, will test outside. I know the figures above will only improve. For those that have gotten the circuit to where it is now, my hat is off to you, great work

Mike

Hi,
yes, you have to fix the coils cause vibrations will be detected easy.

In a part of my house I have used in past to test TGS/TGSL even my steps on the floor were detected... not to talk of heavy vehicles etc... any vibration detected like it was a seismic sensor!

Now I test in better conditions so I have not often that problems but sure it's always a good idea having good fixing at coils.

Anyway, I think your results are good enough to invest more time in critical tuning... on soil the tgs is amazing if not too minerals.

Kind regards,
Max