Barracuda Legend Kit Problems

[6666]

Also the 330 ohm damping resistor was for a 450uH coil , if you are useing something else then the value should be adjusted for best damping.

Also if I remember rightly the part numbers are a bit of a mixture of the old schematics, so if any mods are done the COMPONENT needs to be properly identified.

[Koala]

Q Could you also do any testing with an English pound coin as well thanks, and what revision PCB do you have ?
Which schematic are you useing? on my REV2 pcb there are no caps on output of 78l05

Just put mine back together. New coil probably need dialling in. Getting faint signal to 11 inches and diggable at around 9 inches. This is with a speaker expect a bit more with headphones. From memory everything tested between 7" and 12" last time I tried it.

[Koala]

Mmmm if I sacrifice depth I get quite good discrimination. Rusty nail gives a double wobble and half a horseshoe close to the coil does not register. However as I move the horseshoe away from the coil there is a depth which gives a good tone.

Rev 2 board

[6666]

Thanks Koala, here is a very short video of a Bara that I repaired for a member here.

https://www.youtube.com/watch?v=sqMtzIPxv9I

[Qiaozhi]

@Qiaozhi, first off many thanks for all the work much appreciated...

My 40106 pulses are pretty much in accordance with yours as quoted in #432...
The correction of the power supply caps went a long way to cleaning up noise and signals are fairly clean now...
Only remaining noise is on the -5 volts supply but it's not major...

In the next revision of the board any chance we could increase the size of the battery wires, can't fit wire of any substance in them...

Mike

I've added your request to the REV-3 change notes.

[Qiaozhi]

Hi Q
The schematic with the orange writing should not be used, the orange writing is mine, I started to mod that old schematic which has mistakes but never finished it, dont use it.

You should be useing the hand written schematics by Alex and the pcb layout both attached they best reflect the REV2 pcb

How the REV2 pcb was arrived at went something like this, from what I can remember.

There were 2 old schematics that both had mistakes on, Alex redraw the schematic, APberg made a new PCB layout, there was a bit of discussion about layout with Silverdog and he had the REV2 pcb made and provided kits, the TIP127 was an option, the led on the audio output was an option,

An optional delay pot can be fitted , a link is provided between 2 spare holes on the REV2 pcb , which needs to be cut if a external delay pot is fitted.

and leaving out OR removing Q5 the mpf102 was an option for increasing stability with the threshold, I removed the mpf102 and the threshold stability improved a lot.

There was also some discussion about the 2 gate fets, weather they should be different fets or the same to help improve stability and sensitivity, so there is a mixture of gate fet combinations out there, apparently there were 2 different fets on an original PCB, I have 2 different fets but the Bara works fine, hope this helps.

Thanks. That's useful information.

[Michaelo]

Main Amp

Just noticed a few difference with two version of the schematic relating to the main amplifier circuitry...
Strangely enough they both differ from the recommenced "Frequency Compensation and Offset-Voltage Nulling Circuit" from the datasheet...

Would there be anything to gain from making these changes?

[Qiaozhi]

Just noticed a few difference with two version of the schematic relating to the main amplifier circuitry...
Strangely enough they both differ from the recommenced "Frequency Compensation and Offset-Voltage Nulling Circuit" from the datasheet...

Would there be anything to gain from making these changes?

Based on what we've seen so far, I would expect the answer to be "yes". However, someone should first check that the changes work.

[Koala]

https://m.youtube.com/watch?feature=...&v=Gs-AScbBGsg

Standard build rev 2

450uH coil measured

8.5"

[Michaelo]

Based on what we've seen so far, I would expect the answer to be "yes". However, someone should first check that the changes work.

I got some parts coming in from silverdog (any day now), when they arrive I will build it and slap the scope of it...
I've already included it in my schematic (other post) as datasheets are almost always correct
Mike

[Koala]

Just noticed that its a 3300uF and I am using a 4700uF doubt it will make any difference ?

[Michaelo]

3300uH is the minimum, anything more is perfectly fine... it might even be worth using two smaller caps in parallel so we don't have to lay the cap down on its side

[Koala]

Can't read the value but the red capacitor to the left of the delay trimmer looks a little large for a 6.8nF then again is could be 250V or something ?

[Michaelo]

In my last post is should be uF not Uh...
Koala, it's 6.8 alright.... I think it's only 16 volts though...

[Koala]

Just put mine back together. New coil probably need dialling in. Getting faint signal to 11 inches and diggable at around 9 inches. This is with a speaker expect a bit more with headphones. From memory everything tested between 7" and 12" last time I tried it.

Been doing a bit more tweaking. Changed for matched FETs and readjusted the POTs now getting nice beep to just over 12" on a pound coin but the iron disc is not so good. Still there. More of a rounded tone compared the coin which is nice and sharp.

Pretty good for a 8.5" coil and as far as I would like to dig in sand.

Offset I adjusted until distance started to reduce the turned the other way until it started to reduce again then split the difference between the two points.

Maximum depth on a small gold ring appears to at the point where the threshold stops chirping