baracuda rev A silverdog bad performance

[nonkapo]

No answer but anyway. Just get out in the courtyard and the performance is better now. However i don't have yet the appropriate coil for it so the tests are done with the surf PI one (220uH 1.8ohm).
https://www.youtube.com/watch?v=seU5...ature=youtu.be
Few more questions arise:

1. How do you match the FET's and how critical it is?????
2. If the damping resistor is set what might be the reason for the coil ringing?(happened only with the basket coil).
3. Which op amps have you tried on the place of 357 and 5534? Please post only if you have done it and do not mind sharing the experience. Thanks.

[nonkapo]

there seems to be a lot of ringing or interference on that?

Yes interference.

The delay should not be below 20μs for this circuit

Please clarify which delay you mean? I have no delay below 20uS.

[Andi68]

The delay should not be below 20μs for this circuit

[kosacid]

there seems to be a lot of ringing or interference on that?

[nonkapo]

I think both the first and second sample timings are ok. Here the pic of the second one at 2v/div and 100us/div. About the coil... the basket one is the best performing so far.... Cant think of it as a rubbish. Do you all agree about the rest that offset and damping is done properly? May start checking with different manufactured 5534 ans 40106?!?

[Qiaozhi]

32 turns of 24awg on 190mm OD basket coil, 1,8 Ohm, 340uH

There's not much point using a basket weave coil with the Baracuda. The reason for that type of coil is to reduce the interwinding capacitance and produce a faster coil for gold nugget hunting, whereas the Baracuda has a single-stage pre-amp and is designed for use at the beach where sub 10us sampling is undesirable.
Try making a jumble-wound coil and redo your tests.

[Andi68]

I have to fit.
It is probably only a small mistake, but it is to be found.
You say the depth is bad, please give an example

[nonkapo]

With the other coils it is even worse.

[Andi68]

I mean, too many windings for this coil diameter
Try another coil
I think basket coils for a terrible crap

[nonkapo]

32 turns of 24awg on 190mm OD basket coil, 1,8 Ohm, 340uH

[Andi68]

Coil?

[nonkapo]

The detector acts exactly as it should. Delay and treshold pots work. The only issue is the low dept. Let me just do the video and you may get the idea.

[Andi68]

Hm, the signal looks unusual to me, maybe I'm wrong

[nonkapo]

The last photo - at which point was there measured?

Secondary sample pulse at pin 12 U4 (thats 10uS /div)

[nonkapo]

Sorry, it take me more than an hour to find the proper way of holding the probes and remote control of the camera together(god knows where i hide the tripod;-). So i miss the time for editing. Thats why some people have digital scopes.
The pics are in three different modes so i hope they give the clue. Do you think it is worth to play more with the offset or it does not make sense? i would like to set it away from interference but the chinese DSO is crap for that and the TEK will need mains.
Thank you.