TESORO GOLDEN SABRE

[Max]

Hi,
Max.
What did you use to fix the coils still?
I am using epoxy resin,but not setisfy!Hard to work with~~~!!!

Hi,
I always use epoxy. It's the only thing to use if you want make a real search coil. Almost all commercial vlf coils have it inside to seal and fix windings.

You can keep your nulling position easy and then obtaining a very rigid structure.

There are lot of instruction about it in some older projects documentation.
Already discussed many times here.

Best regards,
Max

[tiktak]

Hi,

Hi,
Max.
What did you use to fix the coils still?
I am using epoxy resin,but not setisfy!Hard to work with~~~!!!

[Max]

Hi,
Max.
Its not expencive around 1,2 euro.
I will try!
But still dont understand how to conect when nulling with shields!
I have to conect Tx to pcb and Rx to multimeter trough 1k resistor and 15n cap.But waht about the shield?Should they be conected and if so where?
Thanks

Hi,
to TX side GND on PCB. You have to connect both shields using two distinct wires at gnd point at tx lead in searchcoil. Then that unique wire goes to the TX PCB PAD.
After nulling you have to reconnect rx leads as before. If you swap rx-tx (during shielding phase) relative orientation you'll try to swap rx leads to gain correct phase as you've previously done before.

If you'll use foil use a roll say 2cm wide and don't overlap too much, but cover well and uniform.

Kind regards,
Max

[tiktak]

Hi,

Hi,
Max.
Its not expencive around 1,2 euro.
I will try!
But still dont understand how to conect when nulling with shields!
I have to conect Tx to pcb and Rx to multimeter trough 1k resistor and 15n cap.But waht about the shield?Should they be conected and if so where?
Thanks

[Max]

BTW I strongly think now that GSabre could be pushed, with some tricks, at more with DD22, like bandido... and even in the ground.

Don't know why but something say me that I haven't saw anything but just a part of its real potential.

It's very stable ! Or not ?

It's a rock... like bandidoII with right components... but here design supplied to old fashioned and noisy op. amps... and if you put some newer you'll gain more and more stability.

It's really good designed even if it uses old fets !

I'm thinking of pushing 10V on the positive rail to see what happens.

Kind regards,
Max

[Max]

Hi,
Max.
Unfortunatly when I try to seal the coil it moovs and now I cant get the same performance!!I were geting 27cm for I euro coin with TL072 insteed of 353!!
And now cant get the same.
How did you null again Rx when shields are aplyed?
You told me that I have to null without shields!But when I shield them how you find that null again?
I were playing with both and just found a very good spot!
Sorry I dont have 3240.I have 3130 and 3140 ,but they are both single!
I will buy tomorrow 3240,but have to finish that coil,so can compare and be shore that I get the same coils position.
Thanks

Hi,
check the price first for 3240... seems that in some places it costs like GOLD in weight! Don't know why... maybe cause is sometimes hard to find and required by some costly apparatus (it's an instrumentation op. amp.).

"You told me that I have to null without shields!But when I shield them how you find that null again?"

Yes I told you cause it's easy to try first without shields... cause you can e.g. modify (e.g. cutting away) the excess of turns to get right frequency etc.
But then you have to apply shields and re-null everything for a real "field-coil", where shield is mandatory.

Re-null as you already made after shielding and connecting shields to gnd as explained by Ivconic.

Don't worry you'll find a good null easier now that you have understand how.

Kind regards,
Max

[Max]

Hi all,
I've tested 2xLF351 instead of TL081 there... (first replacement for the old LM30 and things seem nice.
About the same, if not even better!

So good replacements with jfet inputs (tested) for LM308 here are now :
TL081
LF351

Problem is that 351, like 353 is obsolete now. So TL081 remain 1st choice,
cause it's really easy to find still today.

BUT ALSO (tested)
NE5534
OP07

seems fine there.

Think that for LF353 also LF412 or 442 could be fine. But don't tested yet.

At the moment my best performances are still with LF353!

Kind regards,
Max

[tiktak]

Hi

Hi,
Max.
Unfortunatly when I try to seal the coil it moovs and now I cant get the same performance!!I were geting 27cm for I euro coin with TL072 insteed of 353!!
And now cant get the same.
How did you null again Rx when shields are aplyed?
You told me that I have to null without shields!But when I shield them how you find that null again?
I were playing with both and just found a very good spot!
Sorry I dont have 3240.I have 3130 and 3140 ,but they are both single!
I will buy tomorrow 3240,but have to finish that coil,so can compare and be shore that I get the same coils position.
Thanks

[Max]

Thanks.
I think that have one.Will see.
And will tell you.

Nice. Then post the results...

[tiktak]

Hi,

Thanks.
I think that have one.Will see.
And will tell you.

[Max]

Hi,
Max.
What you think about CA3240 insted of 353 or:LM358D ;LM2904 ;LM258N ?
Plese help!
I will have 353 after 2 weeks!

Hi tiktak,
I think positive of it (CA3240) cause seems good.

1.5TΩ mosfet inputs... seems fine. Problem is that you have to test in circuit to say that's better than TL072.
Other things for me aren't so good, btw 158/258/358 are about the same stuff.
LM2904 seems about a step above 358, no good here.

I get less bleeping with NE5532 but lose performances... (probably cause of input stages) so I think your CA3240 could be good alternative for 353.

Buy one and test.

Kind regards,
Max

PS:
Not too seem too techical but... from what I see seems good as inputs, very good (look at Q9, Q10 config).
I think would be nice instead of 353.

[tiktak]

Hi,

Hi,
Max.
What you think about CA3240 insted of 353 or:LM358D ;LM2904 ;LM258N?
Plese help!
I will have 353 after 2 weeks!

[Max]

About the 33K resistor and all the story

Hi all,
I've replaced the 2K2 resistor with the 33K that is indicated in schematics and lose some audio! (as expected)

Just small beeps when coin is near 26-27cm from center of coil... almost weak and unuseful... and one could miss much targets that way.

The gain reduction is not good if you want detect stuff at depth.

Then unsatisfied of result I've put a 1K resistor instead of that 33K... and wow it's singing BUT there is some small instability due the too high gain.

So I remounted the 2K2 as in the PCB drawing.

I think that the 1K is ideal if you can keep detector stable (somehow) and avoid bleeping.

The AD712 could save the day but I haven't ! And can't test.

I think that I gained 2cm with 1K instead of 2K2...
then mounted NE5532 instead of LF353 but lose some depth (1-2cms)!
With again LF353 too bleeping convinced me remount the 2K2, at least for now.

BTW changed also the 5pF cap with 10pF... and results are the same.
So no need to change it at preamp (LF353).

Best regards,
Max

[Max]

REVISED FULL SCHEMATIC

Hi,
I've changed the wrong values and revised full schematic, according also to the "GSabre light" values.

If someone will find any new error or mistake, please post here.

Kind regards,
Max

[Max]

Hi Max,play with the 33K for sound.Grt Nakky.

Hi Nakky,
yes is on my "list" ! This set the gain of last stage. Also the darlington gain is another good issue. Actually I have instead of 33K as in schematic, the 2K2 value as in PCB diagram. Think that 1Kohm could be better.

Other thoughts are:

I was thinking just avoid the C517 and wire a small audio amplifier like Leto have done before. A TBA820M (1.2W, low quiescent current , audio amp.) could solve some of the problems related to weak audio in a good way I think: it don't waste energy (just few mA) when no sound, then get really an audio boost when I need sound (1.2 W is a convenient power for e.g. a small 8ohm speaker), thus resolving also the impeadance problem.

Of course, no VCO that way, but if one need VCO, could wire between circuit and tba820m an LM566, like Ivconic have done, then getting the audio power from the TBA820M.

Best regards,
Max