Hammerhead Compass?

[Al1g]

Hi
Completed my hammerhead, but when I speed up the main delay to around 8us (I believe), it chirps when I swing the detector. One way it chirps the other it is silent. If it is held still it returns to the usual puttering. Also the directions reverse around North. It is not a bad connection I have checked that.
Any ideas??

[homefire]

Coil and Cable shielded?

[Al1g]

Yea
Coil is shielded with graphite glue.
Coax from coil to control unit

[Al1g]

Also it still does detect metal.

[homefire]

What do you have the Delay time set for?

[Al1g]

I dont have two probes for my osc. but I believe its around 8 us.

[homefire]

Back it off a litte and see if it goes away.

[Carl-NC]

Most likely you've backed the main sample down into the non-linear region of the opamp. That is, you're partly sampling into the overvoltage region. When that happens, the late sample subtraction for Earth field cancellation no longer cancels properly.

- Carl

[Al1g]

Thanks. That did the trick!
Am I understanding it correctly, that IC6 is "clipping" during the pulse and if I sample during that "clipping", it will mess up the noise cancellation?

But....
I had to increase the main delay to ~30us
Thats terrible isn't it? Here are some pics of the coil if anyone can see what I did wrong.

This is the coil before the shielding was applied. Its made from the core of 75 ohm coax cable. It consists of two layers of 16 turns each

After shielding and YES I did leave the necessary gap in it!! The shield is made of Graphite glue.

Completed Coil in fiberglass.

[Al1g]

I posted this in the wrong place
Does anybody know how to edit posts?