Threshold Pot doesn't work

[h9361]

What was the BEFORE shielding waveform look like.
If I see a comparison then maybe I could answer.

Thank you dear Walter.

[Carl-NC]

Did you leave a gap in the shielding? Did you connect the shield to the correct coil end (the one that is connected to ground or supply)?

[h9361]

Did you leave a gap in the shielding? Did you connect the shield to the correct coil end (the one that is connected to ground or supply)?

Thank you for your comment.
I checked it more and more. Yes, all of its connection is correct.
For more info, i am using litz wire. During my tests,first tip that i am realized is that existing spacer is very very important!
The second tip is type cable that is used for connection to main unit! Microphone is not good, RG series is a good cable and now my tp4 form is good with shield connection.

[Carl-NC]

Yes, you need a spacer between the windings and the shield wrap. Glad you figured it out.

[h9361]

Yes, you need a spacer between the windings and the shield wrap. Glad you figured it out.

Hello
Dear Carl
I hope you feel good. Please forgive me for my more questions.
As you know, i added G.B and a new Audio part to my HHD and it works very nice but i have a problem with its AutoTracking part.
I tested it more and more and it doesn't work at all. In other words, it has no effect on the HHD and it is non-motion mode.
But its motion mode is interesting because i have a nice audio in motion mode but i have a constant hissing sound in non-motion mode.
Do you have any suggestion for solving this problem?

[Carl-NC]

The design of the "New Audio part" must have near-zero input current, otherwise you will quickly rail out the input and nothing works. Otherwise, I don't know.

[h9361]

The design of the "New Audio part" must have near-zero input current, otherwise you will quickly rail out the input and nothing works. Otherwise, I don't know.

Thanks dear Carl.
My audio is Mr. Mickstv's schematic. The schematic is post integrator/BPfilter stages of PI design.
Before connecting the schematic to HHD, we must adjust output of first opamp to zero volt via a pot.
Is your near-zero input current as the zero volt of the first opamp?

[Carl-NC]

Either post the schematic or provide a link to it please.

[h9361]

Either post the schematic or provide a link to it please.

[Carl-NC]

I still don't understand. Is C8-R20 above the same as C19-R34 in post #335?
Back when I did the Hammerhead design I should have called this function "autotune," not "autotrack." It has nothing to do with ground tracking, it is merely a threshold retune feature. Normally this is done in the integrators immediately following the demods, not after the GB subtraction.

[h9361]

I still don't understand. Is C8-R20 above the same as C19-R34 in post #335?
Back when I did the Hammerhead design I should have called this function "autotune," not "autotrack." It has nothing to do with ground tracking, it is merely a threshold retune feature. Normally this is done in the integrators immediately following the demods, not after the GB subtraction.

Hello
Sorry for my delay answer.
No, both of c8-R20 and c19-R34 independent.

[h9361]

I still don't understand. Is C8-R20 above the same as C19-R34 in post #335?
Back when I did the Hammerhead design I should have called this function "autotune," not "autotrack." It has nothing to do with ground tracking, it is merely a threshold retune feature. Normally this is done in the integrators immediately following the demods, not after the GB subtraction.

Hello
Dear Carl
I hope you are in a good health.
As you know, i added GB in your HDD and it works very nice.
I also changed its delay 7-8uS (R42.a from 1.5K to 1K), it is working without any problem.
My TX pulse width is 100us, frequency is 1Khz.
Some days ago, i compared it with GPX5000 over Smoke foil box (Thin aluminum) with a commander coil 45cm.
GPX could detect it from 60-65cm (in normal delay) but my HDD could 45cm.
I think my HHD need to be changed so that it can detect such thin metal from high distance.
I also have removed your Audio part and used post 336 schematic.
Since you are a professional man in such science, can you tell me which change can improve the detection (thin metals)? Increasing TX, increasing Frequency, decreasing delay or etc?!
Thank you for your helping .

[h9361]

I still don't understand. Is C8-R20 above the same as C19-R34 in post #335?
Back when I did the Hammerhead design I should have called this function "autotune," not "autotrack." It has nothing to do with ground tracking, it is merely a threshold retune feature. Normally this is done in the integrators immediately following the demods, not after the GB subtraction.

I hope you see my post and suggest me a point for starting.
I don't know which of Delay, Frequency, Sample width pulse and TX pulse width plays key role in detecting thin metals.
I forgot to tell you about my sample width, i tested it with 20uS and 50us (maximum) but its max. detection for foil smoke box is still 45cm distance.
If possible, please tell me which of the above options is better i play with it?!
Or it's better to increase gain of 5534 opamp?!
I hope you forgive me for my amatory questions.

[Carl-NC]

Higher pulse rate always helps but also increases power consumption (things get hot).
Lower sample delay always helps but will quickly overload due to the flyback.
Wider sample width only helps with high-tau targets.

For low-tau targets (thin foil and such) you can reduce the TX width, 100us is too much. This reduces power and allows you to increase the pulse rate. It also will reduce the flyback and should allow earlier sampling.

Try this:
Pulse width = 25us
Pulse rate = 4kHz
Delay = 6us

The higher pulse rate will require you to figure out new delays for the ground channel and EFE pulses. I don't know the solution for that. Keep in mind that these changes will reduce depth for high-tau targets. There is no free lunch.

You can also increase R12 to reduce flyback overload if you want to get really aggressive with sample delay. However, it also increase thermal noise. Save this for last.

[h9361]

Higher pulse rate always helps but also increases power consumption (things get hot).
Lower sample delay always helps but will quickly overload due to the flyback.
Wider sample width only helps with high-tau targets.

For low-tau targets (thin foil and such) you can reduce the TX width, 100us is too much. This reduces power and allows you to increase the pulse rate. It also will reduce the flyback and should allow earlier sampling.

Try this:
Pulse width = 25us
Pulse rate = 4kHz
Delay = 6us

The higher pulse rate will require you to figure out new delays for the ground channel and EFE pulses. I don't know the solution for that. Keep in mind that these changes will reduce depth for high-tau targets. There is no free lunch.

You can also increase R12 to reduce flyback overload if you want to get really aggressive with sample delay. However, it also increase thermal noise. Save this for last.

Very thank you dear Carl for your valuable information.
About decreasing delay, i changed R42.a from 1.5K to 1K. For reaching 6us, do you think i should decrease it to 560R?
According to your information, so GPX is using low TX width, is it true? I remember that the gpx frequency is 5kHz.