SMT Bandito Info/Build

[Silver Dollar]

Well the wiring suggests there was once a center tapped coil (maybe the first generation?) there is a 5th
wire in the cable but the RX negative is tied to the shield and the TX uses the shield as negative. I believe
Ivonic rewired a stock Tesoro to his grounding scheme and it worked better. So why did Tesoro leave it wired
as it is?

They probably had trouble making those center tapped coils so found out by a slight rewire you could get
almost the same performance and didn't have to mess with the centertapping. The problem is the RX is
not really balanced and the TX can radiate as one of it's feeds is the shield!

The stock cable on my coil is 8" long too to allow hip mount so I'm going to use 1/2 of it on another unit.
It has 2 pairs with shielding on each and is soft and flexible. You can even use a centertapped coil and
ground the shield at the chassis.

I'm not sure the answer on the coils but using the stock coil on both my units the real Bandito works
much better. I'm going to try the SMT Bandito on batteries and see what it does...

You can add the Minelab Oscillator to the Bandito and run a 1 mh / 15 mh coil with it. It should work better
by 3 to 6 times but I haven't heard how much better it is. Some make the offhand remark that it's about the
same in the ground...

I'm looking for 6" in the ground with good disc and I assume I'll get around 1/2 the air results so a solid 12" in the
air should do it...

I have a bunch of Coils I made some stock, some centertapped, some shielded, some Minelab specs and a super set
with 36 mh RX centertapped. I was hoping to get the TGSL running right and use it to test different configurations but
I haven't been able to get it to work right. It is quieter now but still seems to choke up and not get the ultimate
depth. I saw 12" when it was oscillating but not now. I tried just about everything and it's still bad....

[Silver Dollar]

Doing some testing with the TGSL today. It was fairly quiet with occasional peeps.
It only got the big silver to 10" so I decided to up the gain of the first filter stage.
This will also tell me where the beeps are coming from.

Well I changed the resistor to 1 Meg and cap to 100n and got my 12" in the air!
But there are now a lot more beeps and chatter. It is still much different from the
original Bandito and I'm not sure why?

The input opamp seems quiet but the LM393 output seems to jump when a beep
occurs so maybe it needs some noise suppression? It could also be coming back
through the power supply...

If you notice the Bandito uses resistors to ground on the 393, maybe I'll try that and
see what happens;

[Silver Dollar]

Well adding the 10k's to the 393 seems to have helped. The audio is strong now and I heard
a good beep to almost 15"! But it started chattering again so not sure if it's usable. I added
the caps but it didn't seem to make much difference. I surmise they put the threshold for the
comparator above the noise so avoid "phase jitter", not sure but they seem to make my board
work better so they stay!

Note: I also upped the audio cap to 1000uf from 220uf as shown in Ivonics loud audio mod
(I thought the speaker might be causing the supply to glitch);

[Koala]

Wow. That's a 50% increase. With my IDX and a 27cm DD just under 40cm seems to be the up limit to work reliable. That's air test on a UK copper 2p same on an iron clad 2p. Did find that when testing it had to be in it's metal box otherwise the depth varied by a cm or more depending on the orientation of the board and cables or coil but in a shielded box and the coil on the stem the results were consistent

[Silver Dollar]

I was surprised and relieved to find it working good and getting the depth. Now to try a few different coils
and then find a box to put it in (doesn't fit in the Tracker case)...

Have you gotten all the parts to build up your board yet?

[Koala]

Multi turn pot solder and solder wick have turned up from China. Happy days got enough bits to start now.

Re looked at the Ivonic thread and on the first post there is a picture of the unit and it is a very old one in a large black case. Also picked up some .28 wire so can start on some coils. It's cold here at the moment less than 20C so the epoxy I am using takes a few days to set. Least with the windings I can put them in the oven. Just been repairing a car headlight and that's taken 3 day to semi harden


Thought the plan was for Bandido SMT to be going into the Tracker not the TGSL ? The board will be smaller

[Silver Dollar]

Yes the SMT Bandito board will work in the Tracker case. I'm not sure what to do with the TGSL.
I had bought a Tracker and a Bounty Hunter JR and planned on updating both but the SMT TGSL
never showed up so I only have the Bandito and a full size TGSL. I had just about given up on the
TGSL but now it is usable...

[Koala]

Surprised the TGSL has not turned up. Maybe a PM to Silverdog is in order. I know he been busy with the MiniPulse lately getting all the bugs ironed out.

[Silver Dollar]

No, I got the SMT Bandito from Silverdog, he shipped it fast! I had mentioned I wanted a SMT TGSL and
asked someone where they got theirs and they said they made it themselves so I asked if I could buy one
from them and they said they'd send it free. But it never turned up....

[Silver Dollar]

So I inventoried all my coils and found 2 shielded ones that are close to stock specs.
I wired them up according to the stock Tesoro wiring and tried to null them.
It was very hard to get a null and when I did I only got about 5" depth! Hmm
I wonder if the Alu shielding is reducing the sensitivity? It's not supposed to affect
it that much...

[Silver Dollar]

I unshielded the coils and attached the centertap to ground but still only get 5" of depth.
The inductances are close to the stock ones so what's going on? I didn't try adjusting the
ground balance or TX and RX caps yet. I expected 12" or so as the stoker was getting 16"...

I tried some other unshielded non centertapped coils and got 6" on Gold and 9" on silver
better but not as good as the stock one...

I put on a 14.7 mh Bifilar Center tapped RX and didn't readjust the RX cap and got 9" on Gold
and 12" on Silver. I'll try the 34 mh center tapped next...

But I'm still not sure why the big difference from stock to my home grown DD coil?

[Silver Dollar]

Well using the 34.5 mh coil and retuning the RX a bit I get 13 1/2" on silver and 10" on Gold.
Coils are a bit lower though and there's occasional chatter but not too bad. The sound is a bit
ragged and not as punchy as the original coil. Not sure if I should try to null and pot this coil or not....

[Koala]

Well using the 34.5 mh coil and retuning the RX a bit I get 13 1/2" on silver and 10" on Gold.
Coils are a bit lower though and there's occasional chatter but not too bad. The sound is a bit
ragged and not as punchy as the original coil. Not sure if I should try to null and pot this coil or not....

Are you making 27 DD If so I would expect the home made to surpass the original for pure depth. Always amazes me how much depth I get with an original whites 8". Having said that the coil is well nulled. Only a few millivolts on the output of the amp. Have not looked inside but suspect that a piece of graphite has been used. The sine wave is very choppy which is what i get if a piece a graphite between the two coils of a DD.

I have always used a space blanket for shielding again not as good as the original. Fine 95% of the time but in some conditions get an occasional chirp. Must be shield as on dry powder sand it work 100%. Not happy with the space blanket method because over time it starts to fail. Must be some sort of oxide forming or breakdown of the blanket

[Silver Dollar]

Yes the new coil is a 9" DD. Using the exact same inductance's/resistances and even the
same cable (stock was 8' I cut it down to 4' and am using 1/2 for new coil) I get much less
depth, I'm not sure what's going on...

I like thinner shielding but found it too hard to work with thin mylar as it kept breaking. I used
some mesh screening on another coil that worked good but added a lot of thickness to the coil
(It has to fit in the housing and be slightly movable). I had kitchen ALU foil on this one but took
it off thinking it was killing my signal...

[Silver Dollar]

It's funny when I work on the TGSL I wish it to be more like Bandito and when I work on Bandito I
wish it to be more like TGSL!

I decided to use the TGSL TX coil and 14.7 mh RX but then thought of swapping to the Minelab
oscillator and then remembered the TGSL doesn't fit in the Tracker housing. So I tried the Bandito
on the TGSL TX/14.7 RX and it performed poorly! A few inches less than the TGSL on most things.
(I got 16" on silver on the TGSL on one test!). But that's the board I will use in the Tracker housing
so I have to make it work with a new coil.

So I'm going to put the Minelab oscillator on the Bandito and try a few combo's to see how good I
can get it. Note: I ran the original Bandito on most of these coils and it worked much better than the TGSL
or SMT Bandito. It had less random beeps and better than SMT Bandito depth but a bit less than TGSL.
All in all a factory unit and coil is hard to beat!