Delta Pulse - Take 2

[Emersonpaz]

I wanted to keep the original design with all its pots.

[ivconic]

I wanted to keep the original design with all its pots.

Originally there are 5 and i kinda count 7... although that part of video goes fast so i am not sure.
...
Is there a steel reinforcement in the floor, below the coil?
That would explain wobbly behavior.

[Emersonpaz]

In total there are 7 pots. In this link I raised the floor coil. https://youtu.be/Iuayv5dVxAQ

[ivconic]

In total there are 7 pots. In this link I raised the floor coil. https://youtu.be/Iuayv5dVxAQ

Am i wrong or this is somewhat better behavior?
I think is better behavior.
Meaning that indeed there is some steel reinforcement in the floor.
Although there is a room to improve damping more too.
Use Qiaozhi's method to distinguish best damping resistance for that particular coil.

"...Adjustment of the damping resistor is usually done by monitoring the pre-amp output. With a 10k pot in series with a 270R resistor, and both in parallel with a 1k2 resistor;
connect this across the coil, and adjust the pot until you achieve critical damping (no ringing in the pre-amp signal). Disconnect the resistor network and measure the resistance,
and then fit a damping resistor of the nearest preferred value..."

[Emersonpaz]

Thanks for the tip buddy. actually the damping resistor must not be correct as there is no adjustment for this coil.

[ivconic]

No sweat. Glad to contribute when see enthusiasm and good work.
...
As for so many "knobs" on front panel... well...
It is nice to have them all on front panel when testing and on workbench, in educational purposes.
But on real site in real searching you'll see how distracting those can be.
Itching you all the time to try slightly different setup on each of those.

[surfdetector]

Thanks for the tip buddy. actually the damping resistor must not be correct as there is no adjustment for this coil.

I did a video on making the damping resistor jig here:

https://youtu.be/CrJ5tFFmWyo

[kt315]

not so actuel for Delta Pulse. why? looking the pic.

[sunita.pradhan]

Question !!! Why a higher value damping resistor has good response to small objects initially... but performance degrades after sometimes. In my case of spiral COIL(335uH), 4 OHMs has very good response to small gold with quiet a distance for sometime but gradually performance reduces with time..and need to retune it again.

[Qiaozhi]

Question !!! Why a higher value damping resistor has good response to small objects initially... but performance degrades after sometimes. In my case of spiral COIL(335uH), 4 OHMs has very good response to small gold with quiet a distance for sometime but gradually performance reduces with time..and need to retune it again.

As I've said before concerning correct damping resistor values, slight underdamping can (in some cases) provide some extra sensitivity compared to critical damping, but the result is an increase in instability. In your case, the instability probably occurs because of component tolerance changes due to temperature.

[kt315]

DP is a deeper and works with long FIRST SAMPLE DELAY 40us minimum value.
in reality i set 110-120, that is clipping small ferrous targets out, just as a garbage.
if you re-tune the sch on short FIRST SAMPLE DELAY you have to remember (REMEMBER)
that you must retune the damping resistor more preciasely - just go in hammerhead, bara, surfmaster etc topics
where this matter is crushingteeth chewed everyday time.

[sunita.pradhan]

Thanks Qiaozhi & KT315 for your inputs !!

[Vadim18]

Hi to all.
From my experience.
If anybody want to use DP for big targets, say twice more big than rusty nails, and work with Delay in the middle (>=45uS) of position - no LF357 are needed, just use jellybean lf356, tl071, or even lf355.
Such broadband amplifier like lf357 is retribution for power simlicity, not for sensitivity and will add only unusable noise and treshold instability.
But, if main target for DP - coins, small targets, than you must hunt for lf357 treashure first.
Otherwise, just leave LF357 for Elon, if you don't need them. let them fly to space...
Good luck.

[kt315]

and work with Delay in the middle (>=45uS)
---
minimal FIRST SAMPLE DELAY in DP is 40us. it is not middle.
pleasure

[Vadim18]

Hi Anatoliy!
Maybe you mentioned some other DP circuit with modifications? Yes DP will be more usable with first sample greater than 40uS.
In my circuit i have 22-100 uS range.