SMT Bandito Info/Build

[Silver Dollar]

Well today it seems to work like always. I think it changes the GEB setting somehow.
After I ground balanced the extra depth was gone!

It's running reasonably good but still has "run on" after a target goes by. It's on the verge
of oscillation. I tried 5K to ground on the outputs of the last filters as suggested in another
thread but it didn't do much. I narrowed the frequency on the first filters and that helped a
bit. I don't have any more ideas on how to tame this beast!

[Koala]

Well today it seems to work like always. I think it changes the GEB setting somehow.
After I ground balanced the extra depth was gone!

It's running reasonably good but still has "run on" after a target goes by. It's on the verge
of oscillation. I tried 5K to ground on the outputs of the last filters as suggested in another
thread but it didn't do much. I narrowed the frequency on the first filters and that helped a
bit. I don't have any more ideas on how to tame this beast!

Yep it's hard to get consistent results when testing.

Been working on my Baracuda and a small difference in threshold ruins the results as does the charge in the batteries.


Had inconsistent results when test my IDX until everything was in a metal box. Did find grounding all the pots and coil connector helped a lot but still not so good.

Get a bit more depth out of the IDX by ground balance slightly positive and cranking up the threshold. One video on YouTube shows the Bandido ground balance slightly negative which seems to be confirmed by the link

[Silver Dollar]

I tried powering the TX off the input 9v to get more power. The TX went up to 16V peak to peak but
it was unusable due to oscillation! It oscillates at 15 hz. Not sure where that is coming from as I retuned
the filters a bit. It shouldn't be affected by the TX. The RX residual voltage was only 400 mv. I have lots
of decoupling around but it seems some signal is radiating and causing this. Maybe shield the GEB pot
wires?

I have the gains lowered. I am using 500k in both the filter stages. It operates the same as with 1 Meg
and 681K which tells me all my improvements are in the area that oscillates. I'm worried that in real
ground conditions I will be limited further so I need to get a handle on what's causing this oscillation...

[Koala]

make sure you don't loose sensitivity to very small objects by increasing the TX voltage. I know golfnut uses this mod to good affect on his IDX. Some tried the same mod but had worse sensitivity to small target. They had no more depth but hit on coin size targets better.

[Silver Dollar]

I saw the depth lower with a bigger TX before. 9V seemed to be the sweat spot.
But I now have 10.2V at 12.5 khz and by tuning the RX have gotten a good
signal.

I compared the original Bandito to my SMT one today and the SMT one beats the
original by 1" on each test. Then I tried a few different speakers and gained 1"
by using an old CB radio one. It's louder too! Now I have to make a volume adj
pot!

The final figures;

Silver Dollar 13"
Gold Ring 12"
Coins 9"

But these are only with that "special" speaker. It allows higher Sens somehow.

[Koala]

wounder if the audio lacks some punch to drive the speakers. I did some experiments with headphones on the IDX and the lower the impedance the greater the depth in all metal mode made no noticeable difference in Disc mode. Always meant to change the mpsa13 for a mpsa14 but never got round to it as I am always using the detector.

[Silver Dollar]

I found some problem using the 9V for the TX. I think the speaker causes problems on the 9v.
The thing oscillates implying positive feedback. The opamp filters are on separate channels so
should act differently. The only place for a problem is at the TX or RX input. The speaker will
radiate a magnetic field though I tried a 25 ohm speaker from a TV that had metal shields on the
back and no improvement. This CB speaker seems to have a limited bandwidth that somehow
reduces the feedback. I might try removing the transistors feeding the speaker and use an
external amp. Ivonic had problems when adding headphones so there's something funny there.

What is the difference between MPSA13 and 14?

I did notice the original Bandito has loud audio. The SMT one didn't but is close with the new speaker...

[Koala]

What is the difference between MPSA13 and 14

Same just higher gain

link

[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?)

[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".

[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]

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]

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]

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.

[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!