TESORO GOLDEN SABRE

[dfbowers]

Is that an onboard pot, or can we just switch wires to make it familiar?

Sounds like a nice model. It will be interesting to see how it compares with previous versions in real ground.

Did you find the resistors lay flat, or must they be mounted vertical in come cases?

-SB

P.S. If anyone has a complete schematic for the Silverdog/eduardo, can they post it?

I used the onboard pot. The problem is that in the AM mode there is a "range" where ferrite is rejected. It will be accepted on either side of that, and it must be set up on the correct "edge" of the null range, so you have to know what side you are on. When switching to the disc mode, quarters will be rejected on one side (CCW) and accepted on the other (CW) of the GB pot. The only other clue is that you will get a double or single beep with ferrite depending.. in the AM mode. If you GB in the DISC mode you will not notice this "feature"

With Ivconics version, the surface mount pot that I used tunes opposite.

Resistors mount fine. You must make sharp bends to fit in the holes, but no problems at all. The lead spacing for the polarized caps is a little wide but I can still fit them ok. They COULD be about 1mm further apart or use caps with narrower lead spacing. I can measure them and post. Again, not a problem.

Some of the holes have been enlarged as well so all external wires of about 20 gauge fit great now as well as the holes for the 7808.

I will post a revised schematic in the next few days and send a copy to Andy as well.

BTW. do you have an original schematic that I can modify or is the PDF locked? I have been doing screen captures in the past but resolution suffers a little that way.

Don

[simonbaker]

Still need a part 3! Troubleshooting.

Then 200 level, with all the equations and circuit analysis..

Sounds great! If I can help let me know. (Probably can't resist putting in 2 cents on occasion anyway...)

Cheers,

-SB

[simonbaker]

I finished TGSL#4 tonight.. This one with the complete kit from Silverdog. The parts selection is good! I was testing Euros in the 40cm range with excellent stability, so this one is a little hotter than my previous builds with Ivconics version.

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Also, Silverdog.. double check your ICs that you are shipping as I was missing one of the LM393s and had an extra LM358. Don't send me a replacement though as I have extras.

Good job!
Don

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Is that an onboard pot, or can we just switch wires to make it familiar?

Sounds like a nice model. It will be interesting to see how it compares with previous versions in real ground.

Did you find the resistors lay flat, or must they be mounted vertical in come cases?

-SB

P.S. If anyone has a complete schematic for the Silverdog/eduardo, can they post it?

[simonbaker]

For anyone's interest :

Here some graphs of a spectrum analyzer in practice ( averages are shown )


U103 Vin vs Vout ( 190 Hz) :


[ATTACH]15591[/ATTACH]


U103 Vout vs U104 Vout ( 190 Hz ):


[ATTACH]15593[/ATTACH]


U103 Vout vs U104 Vout ( 6 kHz ):

[ATTACH]15592[/ATTACH]


kind regards ,

Dennis the Mennis

Hi DtM!

Those are interesting graphs, but they don't make sense to me.

Can you describe exactly how you made the measurements, the equipment, any connections to your TGS?

Could you also make a similar spectral analysis of a simple resistor network (such as a voltage divider) for a reference?

Let's see if we can get better agreement with LTSpice.

-SB

[dfbowers]

Now all the previous boards have gone, I have just taken delivery of some new ones, based on the TGSL-EDU design by Eduardo, and very sexy they are too, black with immersion gold (well it is Golden Sabre)

Hopefully these are 100% correct.
It would be nice to have a matching schematic and "idiots" guide, I will start a new thread TGSL-EDU, and post details of these boards, if anyone can help populate the thread with useful info , scope pics, coil help etc.. it would be a great help to members

regards

Silverdog

I finished TGSL#4 tonight.. This one with the complete kit from Silverdog. The parts selection is good! I was testing Euros in the 40cm range with excellent stability, so this one is a little hotter than my previous builds with Ivconics version.

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Also, Silverdog.. double check your ICs that you are shipping as I was missing one of the LM393s and had an extra LM358. Don't send me a replacement though as I have extras.

Good job!
Don

[Dennis the Mennis]

Filter in practice : Spectrum Analyzer

I think I used to understand this stuff around 30 years ago - maybe not -- but this is my current "understanding":

U103 is basically just a slightly peculiar bandpass filter - peculiar because it has unity gain at zero and infinite frequencies (rather than zero gain) with a nice fat gain (36 db) at the center frequency of about 11 Hz. (Yes, capacitor C14 is a crucial player in the filter band -- it is not just a shock absorber -- the value is critical in shaping the filter.)

The unity gain means that the output exactly tracks (output equals non-inverting input) any DC bias voltage (by nature of the negative feedback loop). It also exactly tracks high frequencies. Frequencies around 11 Hz are amplified greatly and so become relatively more important, thus the low-bandpass nature.

So, whatever DC bias appears at the non-inverting input will also be present in the output. This is not a "feature" I think, just an artifact that is tolerated because the next filter stage (LM308 ) removes the DC bias and rolls off the high frequencies. The Synchronous Detector (SD) "summing" capacitors C12 and C15 also roll off the high frequencies.

I believe it is the "bandpass" nature of the overall filter (removal of DC bias) that makes the TGSL a "motion detector" (i.e. if you leave the coil over the target, the signal will die out).

Those DC biases that appear at the non-inverting inputs of U103 are due to our "null" signal passing through the SD and accumulating on capacitors C12 and C15. They will be different for the DISC and GB channels because of the different sync pulse phases. But ultimately those DC biases are simply ignored -- their main significance, I feel, is that it means we have to choose a "null" signal phase that does not forward bias the JFets in the SD and screw up the works.

So bottom line is I just see U103 as a bandpass filter stage with an unfortunate DC gain of 1 that is a tolerated tradeoff for the advantage of using the non-inverting input as a high impedance input (to be easy on the SD).

-SB

For anyone's interest :

Here some graphs of a spectrum analyzer in practice ( averages are shown )


U103 Vin vs Vout ( 190 Hz) :





U103 Vout vs U104 Vout ( 190 Hz ):





U103 Vout vs U104 Vout ( 6 kHz ):




kind regards ,

Dennis the Mennis

[dfbowers]

It is a great overview. Maybe it should be added to Qiaozhi's sticky thread on the TGSL with Ivconic's info?

-SB

Still need a part 3! Troubleshooting.

Then 200 level, with all the equations and circuit analysis..

[simonbaker]

Here I am presenting the final version. I cleaned things up a bit and tried to clarify a few points that members had asked about. In particular, I added a few of Simon's plots that show the frequency response of some of the filter sections.

Don

It is a great overview. Maybe it should be added to Qiaozhi's sticky thread on the TGSL with Ivconic's info?

-SB

[satdaveuk]

dont worry, I use C version too and it works great.
I also tried B version but didnt see any changes.

Cheers mate, nice to here good tideings from time to time

[habitbraker]

Hi
I ordered BF245C before ic this message, checked the spec thought they may do, In your opinion Is it worth me fitting them or am i wasting my time, I dont worry to much either way because they were quite cheap.
Regards

dont worry, I use C version too and it works great.
I also tried B version but didnt see any changes.

[habitbraker]

Here I am presenting the final version. I cleaned things up a bit and tried to clarify a few points that members had asked about. In particular, I added a few of Simon's plots that show the frequency response of some of the filter sections.

Don

Great job Don! Thank you for your efforts!

[satdaveuk]

Try 2N4393, 2N5484, J113, BF245A.

If you can't find one of those, alternate choices are 2N4392, 2N5485, J112, BF245B. Use one of the first four if you can.

Some of those have reversed pin connection. Either use a multimeter to find the gate pin or else get that from a manufacturer's data sheet.

Hi
I ordered BF245C before ic this message, checked the spec thought they may do, In your opinion Is it worth me fitting them or am i wasting my time, I dont worry to much either way because they were quite cheap.
Regards

[satdaveuk]

http://cgi.ebay.es/20x-BF245C-SFET-N...item4aaa932dad

I just ordered a load of those for this project hope they do the job

[satdaveuk]

Here I am presenting the final version. I cleaned things up a bit and tried to clarify a few points that members had asked about. In particular, I added a few of Simon's plots that show the frequency response of some of the filter sections.

Don

Thanks so much for your efforts you done a good job
All the best
Dave

[dfbowers]

TGSL 101

Here I am presenting the final version. I cleaned things up a bit and tried to clarify a few points that members had asked about. In particular, I added a few of Simon's plots that show the frequency response of some of the filter sections.

Don