Bandido 2 Modified

[bernte_one]

hello merc

can be that the self inductance / capacity on the multiturn pot works like a choke too and not like a pure single turn pot? i have a lot fantasy

[cr15]

Is there any problem with using a wirewound pot for a Ground Balance adjustment? I'm using a Vishay 50K 5-turn wirewound pot on my Bandio II and I'm wondering if the inductance is causing any problems.

Merc

Merc, I replaced the ground balance pot in my original Bandido with the exact same pot you have used, because the original became scratchy. There have been no discernible problems during the last ten odd years.

[bernte_one]

hello merc

etched my pcb last weekend (the one from above post b/w picture)
looks good

did yours run good? have you made a video?

[Merc]

I have not made a video of my Bandido II clone. It does work quite well. It does not have extreme depth but it is good enough for me. The discrimination is very good. What I really like is how light it is and it works on a single 9V battery.

But, now that you mention it, I could shoot a simple video and show you how it works and sounds. I'll try to have something on youtube soon and I'll post a link here.

Merc

[bernte_one]

i´m waiting for a hot video
detector sound is music

[bernte_one]

start next nights

[Merc]

Video

Looks good bernte_one! Let me know how it goes.


Well, I finally got around to making a video.
http://www.youtube.com/watch?v=7PKHtX1c-9k

Merc

[Merc]

I've made a fewer minor changes to my Bandido clone so I thought I would post an update.

First, the detector was very quiet even with sensitivity turned all the way to max. I wanted to be able to run it right at the edge of chattering. Originally, the sensitivity pot could only go near 0V. I connected the bottom side(maximum sensitivity) to the negative supply through a resistor. The resistor was found through experimenting. Now I can take the sensitivity adjustment slightly negative which gets me just to the point of instability.

Second, the ground balance was working somewhat, just not exactly right. I noticed this when I took of my 8 inch coil and put on the 10 inch open center coil(both Tesoro original). I could not reach ground balance. It was slightly positive with the pot turned all the way counter-clockwise. I watched how the signal shifted on my scope and I could see I needed a little less phase shift. I paralleled a 100pF across C12 giving a total of 280pF. Now I had range and I could go through the null point. I'm not sure why this was necessary to get the range I needed. I thought maybe because my oscillator frequency was off and was affecting the amount of phase shift. I measured the oscillator at 10.13KHz.

[bernte_one]

thanks for update merc

im working at igsl tgsl at next
after that the bandido follows i was at the point if writing a order list
so the update will be fitted in there

regards bernd

[Merc]

A few recent finds.

I've been using the Bandido clone quite a bit lately. Here are a few of the recent finds with it.

[Merc]

Kit

Is there any interest in a Bandido 2 in kit form? I'm considering putting together a complete kit; PCB, electronics, switches, case with drilled front panel with decal. I would also consider offering PCBs only. I have not totalled the cost of all parts, but I know some items are just plain expensive in small quantities.

Merc

[satdaveuk]

Hi Merc
Done a nice job here.
How does it perform up against Ivonics TGSL ?

Regards

[Merc]

Well, I don't have a TGSL to compare to, but I think it would be similar with a good homemade double-D coil. I have only used Tesoro factory concentrics with mine. It's not an extremely deep detector by any means. The main advantages I see are very good discrimination, simple, light-weight and it operates from a single 9V battery.

Merc

[Davor]

There might be a minor refinement on the front end that might aid a little bit to stability, and it is a mere resistor value change. Point is that using a common sense R26=R27 and R28=R29 yields in a mismatch of impedance at inverting and non-inverting paths against the ground. Point is that non-inverting path has impedance ~R27+R28, while inverting path has impedance of less than R26. Both referenced against ground.
Now, while there is no ground to be seen in the schematic, there certainly are some capacitive paths to it, and unless shielded, it will present itself to a frontend.

In case impedances are balanced you get behaviour very much like that of instrumentation amplifiers, but at less cost, and a finite (and not too high) input impedance. Maybe a bit tricky R values.

Here are my observations in LTspice, observe the I(R0) as an indication of balance. There are some ready made values for various gains, and normalised for input impedance ~1kohm (twice Zhalf)

[sbhumi]

i want to make that ,plz upload pcb schematic