TESORO GOLDEN SABRE

[Davor]

In case your front end preamp is LF353 you can gain some depth by replacing it with a better chip, my favourite is NJM2068, but NE5532 will do. You may want to replace the 4k7 resistors there with 1k resistors.
Try to get NJM2068 as it is much better regarding THD.

[sdesic]

Screencaps

[sdesic]

In case your front end preamp is LF353 you can gain some depth by replacing it with a better chip, my favourite is NJM2068, but NE5532 will do. You may want to replace the 4k7 resistors there with 1k resistors.
Try to get NJM2068 as it is much better regarding THD.

I have few NE5532 so I will try with one... Do I need to make changes ? Pinouts are same ?
Never heard of NJM2068

[Davor]

NJM2068 is a superb dual op amp that beats far more expensive ones in almost all aspects, and is very cheap - provided you find them.
Pinouts are the same.
Replacing 4k7 with 1k when you replace LF353 with a less noisy chip will both improve noise, and increase gain, while loading a coil a bit more, so your GB and Disc positions will slightly change, but you'll get more depth. If you keep LF353 the resistors may stay, as the LF353 is noisier than 4k7

[sdesic]

OK, ebay is good place to find them... but I don't have 15 days for delivery
I will try to find them closer and will try with ne5532

Can you comment my oscilloscope screens ?
I have tried basic nulling with voltmeter and then I half hot glued coils.
Did not use oscilloscope for phase ...

[Koala]

Finished second DD coil for my second TGSL kit.
Standard 30 cm for 1 EURO coin indoors with sens at 3/4.
What can I change to gain more depth ?

RX and TX caps ... to adjust freq.
15 nF (it is 10nF now) and 22nF and 220 nF ?

RX 6.5mH 25.8 Ohm - tried to be on that value - extra few turns
TX 6.0mH 24.5 Ohm

Leave TX alone does not have to be dead on frequency

Some depth can normally be gained by playing with the RX caps

Just make sure that disc and ground balance still work.

If you get the shape of the the two coils identical you can get a better null which also helps for depth.

Worth playing around as I normally get around an extra 5 cm ish optimizing my coil

Sometimes it can help if a small piece of iron or copper is attached to the coil near the cross over watch the scope trace on the RX and go for best null

Normally you only get about the coil diameter in depth for a medium coin in the soil so you are not so far off already.

On my IDX I have built several coils one goes to 40 cm air test and another 35 cm Prefer the 35 cm as more stable and there is not 5 cm difference in real ground

Shielding is another thing. Not having much successes with my latest builds. Still working on them.

[sdesic]

>Leave TX alone does not have to be dead on frequency
OK

>Some depth can normally be gained by playing with the RX caps
will try 15nF - now 10nF

>Just make sure that disc and ground balance still work.
Every time I do it from start... GB trimmer @ middle

>If you get the shape of the the two coils identical you can get a better null which also helps for depth.
>Worth playing around as I normally get around an extra 5 cm ish optimizing my coil
they are wound on Don's template, so they are same as can they be

>Sometimes it can help if a small piece of iron or copper is attached to the coil near the cross over watch the scope trace on the RX and go for best null
I would like to see that screens before and after
I don't understand it, my traces are few post before this - too technical for me
I am doing only 0,04mV AC part

>Normally you only get about the coil diameter in depth for a medium coin in the soil so you are not so far off already.
OK, my coils fits 27.5 enclosure

>On my IDX I have built several coils one goes to 40 cm air test and another 35 cm Prefer the 35 cm as more stable and there is not 5 cm difference in real ground
I don't see any field test - coin bed on internet so I can compare
Looked few commercial detector videos ... terrible results
Air test is OK but in ground ... or wet sand it looses half

>Shielding is another thing. Not having much successes with my latest builds. Still working on them.
my shielding is mylar - space blanket strips

[sdesic]

Changed few caps in place of 15nF (RX)
Nothing gained there. I have a lot of EM fields close by.
Returned to stock 15nF

Changed LF353 to NE5532 and at start it was better... minute after that EM kicked in
must try this in fallout shelter ... too much EM fields
I did not change 4k7 resistors yet to 1k

[sdesic]

BTW my GB trimmer is used every time to change - reject ferrite and to accept silver coin
at this moment it is over half to right

[paku]

you buy kit from silver dog or you just buy board from silverdog

[Koala]

>Shielding is another thing. Not having much successes with my latest builds. Still working on them.
my shielding is mylar - space blanket strips

Tried space blanket. Looks great conductive on one side coating so thin you can see through it. Shield works well if the coil does not touch anything. Long damp grass the the coil is unusable. Dry grass usable but not good. Found that everything causes chatter even touching the headphone lead. Factory coil is fine

Going to give it one more go. Pack the coil so the is a gap between the shield and the windings and as I wind the strip of the blanket make sure there is a small gap between each turn. Think any overlap between turns is acting as a capacitor.

Flat card with carbon/graphite on it worked the best. As I was not planing to use a shell packaging is a problem for me.

[sdesic]

you buy kit from silver dog or you just buy board from silverdog

full kit both times
about same results
three coils - first one was bad ... used some wierd glue and it shrunk after few days

[sdesic]

>Shielding is another thing. Not having much successes with my latest builds. Still working on them.
my shielding is mylar - space blanket strips

Tried space blanket. Looks great conductive on one side coating so thin you can see through it. Shield works well if the coil does not touch anything. Long damp grass the the coil is unusable. Dry grass usable but not good. Found that everything causes chatter even touching the headphone lead. Factory coil is fine

Going to give it one more go. Pack the coil so the is a gap between the shield and the windings and as I wind the strip of the blanket make sure there is a small gap between each turn. Think any overlap between turns is acting as a capacitor.

Flat card with carbon/graphite on it worked the best. As I was not planing to use a shell packaging is a problem for me.

So you are recommending graphite spray
Don't have that under my belt yet...
Ivconic has one idea... he uses shiled in epoxy ... printer toner mixed with epoxy

I have two layer of isolating tape... winding - tape - mylar - tape - hot glue (for now)

[paku]

can somebody explain what is that caps or resistor

[Silver Dollar]

Looks like 2.2 uf caps. By using 2 in parallel you get roughly 4.7 uf nonpolarised.