SMT Bandito Info/Build

[Silver Dollar]

Well I opened up that Tesoro coil today. It is actually called Deep Search and it looks like an
omega possibly. Not sure why centertapped or why TX resistance is so much. Here's some pics;













The graphic paint reads 10k per inch in spots (bottom cover) and 5k per inch in other spots (top cover)...

[Silver Dollar]

Oh i found that quote from Davor "It has 20k in series with the bilateral switch that is 50% time open (thus behaving as a 40k resistor) and a 220n capacitor, giving a -3dB point at 18Hz"

I had good results on the SMT Bandito changing that cap to 20n = 180hz but not so good on the real Bandito, it seemed to allow more noise through...

[Silver Dollar]

I'm trying to figure out the filters just after the input opamp and it seems to be designed wrong.
The classic bandpass has a highpass set lower than the lowpass (say 1 khz to 30 khz) but the
bandito has the highpass higher than the lowpass (723 hz to 79 hz) somewhere I had a blurb
about how the 4066 switch affects this but cannot find it right now.

Does anyone have any ideas about why they set the filters like this?

[Silver Dollar]

Here's one more tweak. The 100n cap at the last LM358 determines the size pulse
that gets through to the speaker. I have reduced it to 22n in the past but here find
that a 47n + 22n (69n) gives the best response. I can discern targets to approximately
10 inches with this mod. Not sure how it will work in the ground but I believe you can
reduce the sens if it proves to be a problem...



(it's the one circled in orange)

It is very difficult to remove parts from this substrate so be careful if you attempt this mod...

[Silver Dollar]

I did a couple of Mods to the Original Bandito today. I will take it to the beach
this weekend and wanted it to be "tuned up" for the job.

I use a cap substitution box to set the RX cap to the best value. The cap is
actually 2 caps stock. A 10 nf is on the regular PC board so I removed that
and substituted some in it's place. The original measured 9.45n and the new
one is 11.1n. That gained me maybe 1/2" in the air, it doesn't make a huge
difference but maybe some marginal targets will be heard!

I also replaced the threshold pot on the back of the unit with fixed resistors.
That sets the amount of volume change with depth and I don't imagine ever
adjusting it.

I found the cap that sets the length of the tune on battery check beep too.
It was a 10uf on the back side of the sub straight and I changed it to 1uf
so now a nice short beep to let you know it's on but not announce it too much!

[Koala]

[ATTACH]30554[/ATTACH]

I got the widescan coil today. It is 7" and has a centertapped RX. A funny thing though the
RX coil measures 6.1 mh and 17 ohms but the TX measures 6.1 mh and 27 ohms! It almost
seems they swapped the TX and RX but the centertap is on RX...

It also doesn't perform as well as the Brown 8" concentric. On coins the Deepsearch does 6"
where the Brown Concentric does 7". I thought the DD coils were supposed to go deeper?

The null acts just like my homemade centertapped coil. With just TX connected a scope
across the RX reads 4.7V p/p but connecting the shield to ground gives no signal at all!
By the way there is no connection at all from the shield to RX or TX in the coil. The center
of the RX is tied to TX ground. The wire seems a bit cheezy and is very short. I'd like to
get inside it and rewire it at least and maybe lift the centertap? I started running an exacto
around it but it might be a bit difficult to cut all the way through...

I thought a concentric were deeper. DD have the same depth ish down the center of the coil where as the concentric is only deep at the center and drops off quickly.


Resistance of you new coil do appear odd

[Silver Dollar]

I got the widescan coil today. It is 7" and has a centertapped RX. A funny thing though the
RX coil measures 6.1 mh and 17 ohms but the TX measures 6.1 mh and 27 ohms! It almost
seems they swapped the TX and RX but the centertap is on RX...

It also doesn't perform as well as the Brown 8" concentric. On coins the Deepsearch does 6"
where the Brown Concentric does 7". I thought the DD coils were supposed to go deeper?

The null acts just like my homemade centertapped coil. With just TX connected a scope
across the RX reads 4.7V p/p but connecting the shield to ground gives no signal at all!
By the way there is no connection at all from the shield to RX or TX in the coil. The center
of the RX is tied to TX ground. The wire seems a bit cheezy and is very short. I'd like to
get inside it and rewire it at least and maybe lift the centertap? I started running an exacto
around it but it might be a bit difficult to cut all the way through...

[Silver Dollar]

Well it appears the TGSL works worst than the Bandito SMT now. I was getting 5 - 6"
and then tried a few different speakers. I found one that allows 8" or so but I'm not sure
it will fit in the case!

I decided to make a Minelab Coil for it. I have 1 mh TX and 14 mh RX but it didn't allow any
adjustment inside the coil shell so I took off the shielding and redid it with thinner tape. Now
it just makes it! That's another thing to watch for when building a coil. It doesn't matter if
it works great if it doesn't fit in the case!

[Silver Dollar]

Well I tried a DD but it came out a bit noisy and heavy! I tried using a centertapped
RX instead of shielding and used Concrete epoxy instead of potting compound.

I have the original Bandito coil and a 7" Widescan DD Tesoro coming.
I found that one for $35! It will cost me that to get the good potting epoxy!

I prefer working on the electronics anyways...

I just picked up an IDX board from Silverdog. I'll try putting that in my daughters
Bounty Hunter Jr with the 7" Tracker ID coil I got last week.

[Koala]

Both the build and size even with the same build quality you are going to add 2" by building a 10" coil over the stock 8" if depth is your thing.

I have two Whites 8" concentric coils I was surprised how well they were nulled there is only a few mV at the output of the pre amp I can't get anywhere near with my DD without using some ferrite to fine tune.

I only build DD because they are easier and the wider scan per sweep. Looking on YouTube at monte's nail board test a smaller concentric is the way to go in infested sites.

[Silver Dollar]

Do you mean a better null on the coil? My home built coils don't work so good so I have
been buying factory ones to make good detectors. I don't know the secret to making a
good coil I guess...

[Koala]

I found a smaller TX usually gives more depth but also it should be adjusted to
hit the power rail to avoid amplitude jitter then adjust the RX cap for best operation.

I wonder if any tweaks can be done to the original Bandito to gain the extra depth?
I wish I had another old CB radio to get another speaker...

I put the filters back to stock so there are just a few mods left. The input gain is
double and a cap here or there is a bit different value. Not sure I want to mess with
my "test Standard".

Pretty sure all older design Tesoro detector can be improved on with a better coil. Tesoro seem to have wanted a very stable detector. But this is the main reason that they had such a huge dedicated following.

[Silver Dollar]

I found a smaller TX usually gives more depth but also it should be adjusted to
hit the power rail to avoid amplitude jitter then adjust the RX cap for best operation.

I wonder if any tweaks can be done to the original Bandito to gain the extra depth?
I wish I had another old CB radio to get another speaker...

I put the filters back to stock so there are just a few mods left. The input gain is
double and a cap here or there is a bit different value. Not sure I want to mess with
my "test Standard".

[Silver Dollar]

Well the SMT Bandito just has a 3904 and 3906 and it's too loud with the CB speaker.
With a tiny laptop speaker the volume was a bit low, so maybe look for a better speaker?
More gain means more juice. I think the old speaker used more power too as my current
meter only goes to 24 ma and it overloaded with that speaker but the new loud one
still shows when sounding... (can't really read the value maybe 18 ma?)

[Koala]

What is the difference between MPSA13 and 14

Same just higher gain

link