TGSL Tuning & troubleshooting

[simonbaker]

An interesting read about noise coming from the coil and cable. It would also be interesting to compare a coil wound from regular Copper Wire to that of OFC (Oxygen Free Copper) Wire, which is also used in High-End Audio applications. And maybe this will also prove to be an easily, and readily available source to obtain OFC. Even cheap Sennheiser headphones and Ear Plugs use OFC nowadays, and also Polypropylene Microphone Cable has an OFC core, which is then specified by an OFC print on the cable mantel.

Also, using potentiometers of half the value specified will reduce the noise figures. This noise exists in nearly all pots that have been unused for a period of time, including those fresh from the manufacturer. When a potentiometer has passed its useful life, this noise can be a result of a worn and dried out resistance element. But, long before this point has been reached, the potentiometer may appear to be beyond recall because of noise caused by high contact resistance. Incidentally, no lubricant or other material should be applied to any part of a potentiometer. To do so, will cause deterioration of internal parts.

And how about Conductive Polymer (Conductive Plastic) Potentiometers ?

They have excellent noise figures, please check out the conductive polymer potentiometers from Bourns® and Omeg® (as examples).

Bourns® Precision Potentiometers and Turns-Counting Dials:
http://www.bourns.com/pdfs/bourns_pr...short_form.pdf

Omeg® Potentiometers and Switches:
http://www.omeg.com/

And a little off-topic, the Digital Chip solution from Dallas Semiconductor Maxim.

Dual, NV Audio Potentiometers Provide Low-Noise, Low Distortion Digital Volume Control:
http://pdfserv.maxim-ic.com/en/da/DS1881-AD.pdf

Just throwing a few stones in the pond, and waiting to hear about the ripple

Regards,

Robert

Thanks for those pot references. I'm feeling more and more that high quality pots are very important for these MDs. At least should get a few to test with.

Regards,

-SB

[Mullihaka]

dfbovers,

I have the one in the gift pack. I don't have the shields in the coils yet. The cable is from a thin USB cable, connectors cut off. The signals at pin 3 are approximately double to three times the amplitude at pin 5, so something new to start scoping.

Thanks for you proposal of sending coils for check! I'd like to have them but I don't want to take the risk of them being lost in their way or destroyed at the customs. I'm in Europe and I have some bad experience on sending strange looking objects between US and Europe.

I wish there was a pool of well working devices and coil sets in every continent/economy area to easily send them around as loaners.

Andy

[simonbaker]

dfbovers,

I have the one in the gift pack. I don't have the shields in the coils yet. The cable is from a thin USB cable, connectors cut off. The signals at pin 3 are approximately double to three times the amplitude at pin 5, so something new to start scoping.

Thanks for you proposal of sending coils for check! I'd like to have them but I don't want to take the risk of them being lost in their way or destroyed at the customs. I'm in Europe and I have some bad experience on sending strange looking objects between US and Europe.

I wish there was a pool of well working devices and coil sets in every continent/economy area to easily send them around as loaners.

Andy

Let's not forget GB channel detector is shifted maybe 90 deg from DISC channel, so wouldn't expect same signal. Depends also on settings of DISC and GB pots.

Also, All-Metal GB control signal to JFet is very weird, not a square wave, more like triangle, have never figured out exactly the concept behind that.

-SB

[simonbaker]

Too bad we can't all get into the same room somewhere for a day just to compare!!

Hollywood would be intimidated by all that sex appeal...

That would be a blast though!

[dfbowers]

Let's not forget GB channel detector is shifted maybe 90 deg from DISC channel, so wouldn't expect same signal. Depends also on settings of DISC and GB pots.

Also, All-Metal GB control signal to JFet is very weird, not a square wave, more like triangle, have never figured out exactly the concept behind that.

-SB

I would expect the signals to be different. I had a cold solder joint and the symptom that I was troubleshooting was a weak channel. The TGSL basically worked, but with reduced sensitivity. The inputs to the LM393s should basically be a varying DC signal though and you can get a good idea of how much noise is being picked up by just scoping pins 3 and 5 of u106. One observation I made during the whole building process. The amount of noise around you can have a very significant affect on the results you get! All my other detectors behave in a similar way. If I do some testing very late at night ,when the whole family turns everything off in the house everything works MUCH better!

Also, I did notice that grounding the coil the wrong way had a negative impact on detection depth as well.. at least on mine.

Hope this helps..

Don

[dfbowers]

dfbovers,

I have the one in the gift pack. I don't have the shields in the coils yet. The cable is from a thin USB cable, connectors cut off. The signals at pin 3 are approximately double to three times the amplitude at pin 5, so something new to start scoping.

Thanks for you proposal of sending coils for check! I'd like to have them but I don't want to take the risk of them being lost in their way or destroyed at the customs. I'm in Europe and I have some bad experience on sending strange looking objects between US and Europe.

I wish there was a pool of well working devices and coil sets in every continent/economy area to easily send them around as loaners.

Andy

Andy,

I found a slick thing to do with a USB-2 cable. Get yourself a USB-2 EXTENSION cable.. Male on one end, female on the other. Cut the cable somewhere near the female (or male) end. Connect the plugs together and use it that way.. You can swap coils EASY!! Just make sure the the short end is near the control box.

Don

[Cyclonite]

Hi @dfbowers,

Nice idea, but I very much dislike USB Connectors, for they easily break, are susceptible to contact failure and distortion, and they also have no "locked" pull fixation mount. But this is just my humble opinion about USB connectors.

By the way, beautiful Metal Detector you have there!

If you have ever had a chance to walk around the equipment used for Pop Festivals, then you will see that they use Top-Notch Connectors. The kind of stuff you can mount on a Cannon, fire it off, and the Connectors will still be there where they have been plugged in. And not only that, they have excellent fixation mounts, and are designed to be plugged in and out many times without suffering loss of contact pin signal threw feed.

One connector that comes to mind is the XLR Connector, sturdy, robust design, well shielded, have extremely low threw feed resistance, ... and they are also very cheap too! Even the Gold Plated ones, which are less susceptible to environmental deterioration by for instance Oxidation, are also very cheap. Spending a little more money on Top-Notch Connectors will real save you a lot of hassle in respect to poor connectivity, ... now and in the future!

XLR connector:
http://en.wikipedia.org/wiki/XLR_connector





Limitations are thought to be, only three pins, but that's not true at all, ... for see here:

XLR4 (with four pins):
http://www.audiogoedkoop.nl/nl/kabel.../velleman.html









And another important fact worth mentioning, these outstanding connectors are not only limited to four pins ...

Just adding my 2 cents

Regards,

Robert

[dfbowers]

Hi @dfbowers,

Nice idea, but i very much dislike USB Connectors, for they easily break, are susceptible to contact failure and distortion, and they also have no "locked" pull fixation mount. But this is just my humble opinion about USB connectors.

If you have ever had a chance to walk around the equipment used for Pop Festivals, then you will see that they use Top-Notch Connectors. The kind of stuff you can mount on a Cannon, fire it off, and the Connectors will still be there where they have been plugged in. And not only that, they have excellent fixation mounts, and are designed to be plugged in and out many times without suffering loss of contact pin signal threw feed.



One connector that comes to mind is the XLR Connector, sturdy, robust, well shielded, and they have extremely low threw feed resistance, ... and they are also very cheap too! Even the Gold Plated ones, which are less susceptible to environmental deterioration by for instance Oxidation, are also very cheap. Spending a little more money on Top-Notch Connectors will real save you a lot of hassle in respect to poor connectivity, ... now and in the future!

XLR connector:
http://en.wikipedia.org/wiki/XLR_connector





Limitations are thought to be, only three pins, but that's not true at all, ... for see here:

XLR4 (with four pins):
http://www.audiogoedkoop.nl/nl/kabel.../velleman.html









And another important fact worth mentioning, these outstanding connectors are not only limited to four pins ...

Just adding my 2 cents

Regards,

Robert

Robert,

I would agree with that.. My choice of connector probably is not the best choice, and certainly not a positive connection! I have not had an issue with it.. yet, but I will consider it for my next project.

Thanks.
Don

[simonbaker]

I would expect the signals to be different. I had a cold solder joint and the symptom that I was troubleshooting was a weak channel. The TGSL basically worked, but with reduced sensitivity. The inputs to the LM393s should basically be a varying DC signal though and you can get a good idea of how much noise is being picked up by just scoping pins 3 and 5 of u106. One observation I made during the whole building process. The amount of noise around you can have a very significant affect on the results you get! All my other detectors behave in a similar way. If I do some testing very late at night ,when the whole family turns everything off in the house everything works MUCH better!

Also, I did notice that grounding the coil the wrong way had a negative impact on detection depth as well.. at least on mine.

Hope this helps..

Don

I agree, output of LM308s is best way to see the noise that would interfere with detection; also to see discrimination and ground balance in action. I think noise in my area very high and will try to get outside as soon as I can. Then maybe I can see the subtle factors like coil grounding. Your observations are definitely valuable -- especially since your TGSL is a good one!

Cold solder joint -- I don't even want to think how many of those I might have...

Regards,

-SB

[Mullihaka]

dfbowers,

I guess I will adjust the coils for 20 degree lag and cast them in some mass.That way I will have at least one stable part in the system. If I get 25cm with this machine with good beep, I'll be happy to pack it in a case and get some fresh air (finally).

Before mixing the potion, I'd like to make my mind to shield the coils or not. Have you compared the performance with/without shielding? Further, would single wire wrapped around the coils be sufficient, if I'm not afraid of radio disturbance? In other words, is it enough to help with the ground effect? I think Qiaozhi wrote some time ago that he uses single wire shielding. I don't remember having seen anything about it's performance compared to the kitchen foil or equivalent.

How do you route the coil ends from the cast mass to the connector ie are they fixed in the case some way?

Andy

[simonbaker]

dfbowers,

I guess I will adjust the coils for 20 degree lag and cast them in some mass.That way I will have at least one stable part in the system. If I get 25cm with this machine with good beep, I'll be happy to pack it in a case and get some fresh air (finally).

Before mixing the potion, I'd like to make my mind to shield the coils or not. Have you compared the performance with/without shielding? Further, would single wire wrapped around the coils be sufficient, if I'm not afraid of radio disturbance? In other words, is it enough to help with the ground effect? I think Qiaozhi wrote some time ago that he uses single wire shielding. I don't remember having seen anything about it's performance compared to the kitchen foil or equivalent.

How do you route the coil ends from the cast mass to the connector ie are they fixed in the case some way?

Andy

These are great questions and I hope you eventually try all ways. Past results should be retested periodically.

Also, it may depend partly on the ground you where you hunt. I think unshielded coil may be OK in some areas, like desert???

-SB

[dfbowers]

I have only tested 2 coils outside so far. One I shielded with aluminum foil tape and another with copper tape. The copper tape is REALLY expensive. I did not try an unshielded coil. The nice thing about copper tape is that you can easily solder a ground wire to it.

I have seen several older diagrams were a Faraday shield is made by just looping bare wire around the coil - almost the whole way around. It think that they were old BFO and crystal filter detectors. I could post a few diagrams out of an old book but I don't know if it's allowed here or not.

I don't know if the shields hurt performance or not, but from what I understand, the advantages outweigh the disadvantages.

I built Carl's HH and shielded one of the coils with metallized mylar and it seems to be more sensitive than Aluminum tape. You can get all the conductive mylar you want from a cheap survival blanket.

Don

[lunamay]

hi to all
can anybod calculate a coil for tgsl latest version but with 0.44mm wire?

best regards

[dfbowers]

Ivconic posted something a while back and it's starting to make a little more sense now. While experimenting with my latest TGSL circuit on my work bench, I noticed that the proximity of the speaker to the coil has much to do with the audio. If the speaker is within about two feet of the coil, the circuit could go into a slow oscillation after passing metal over the coil. Likewise, the orientation of the speaker in relation to the coil has some bearing on the quality of the audio - short vs long, broken vs solid sound! Audio can be improved by making sure that the speaker coil stays perpendicular to the search coil! (Not in the same geometric plane) In my case, it's a small 2", 8 ohm magnetic speaker. Just another variable to be aware of when testing an troubleshooting.. There HAS to be some magnetic coupling between the two and hence some feedback. It's best to keep the two separated as much as possible..

I can't find the exact post, but Ivconic mentioned that once he put his circuit in an metal enclosure, the audio improved. It seems to support my observation.

I will attempt to put together a short video demonstrating.

Don

[lunamay]

i noticed same thing..only on 5W 8 ohm speaker..like you said it's not good to keep the speaker near pcb and coil ..and metal encloser realy helps..me too
best regards