GoldScan-6

[Detectorist#1]

Yes, Altra,
OPA1612 is one of the best OpAmps for front end of PI MD, especially if input stage is non-inverting and input resistor on positive input is under 1KoHm and input resistor in negative input is from 2.2 to 100 oHms.

[Altra]

Okay you didn't mention front end. OPA1612,

[Detectorist#1]

Hi Altra,
LMC6482 is very good choice for sample-hold stage but too noisy choice for input stage.

[Nightryder]

Can not wait. all the best

[Altra]

The LMC6482 is a good choice

[hunter63]

Hello, I am looking for a replacement forLF442-MIL Dual Low Power JFET Input Operational Amplifier in the SMD version

[hunter63]

Hello
I will post the corrected documentation after the PCB is launched, at the moment I am at the stage of ordering the PCB production, best regards

[Detectorist#1]

And what is the final schematic of this beautiful board?

[pigeon]

PCB in 3D GS-6

HI HUNTER63

CONGRATULATION VERY NICE JOB

[hunter63]

PCB in 3D GS-6

[Auto-Mation-Assist]

I took ADA4610 from the KiCad library, ultimately it will be ADA4637-1BRZ

I have been using the ADA-4637-1BRZ since I started my design of the AGD detector years ago with the knowledge that it is a fairly noisy device and as such I have used two in parallel to reduce noise levels which works very well. Thus the ADA-4637-1BRZ can be made workable and I can detect very small gold with my AGD detector design but it is a lot different that your proposed design. As I got my design more and more refined I started working more toward the RX front end front end and since my version AGD24.2 the ADA4637-1BRZ has been replaced with lower noise devices to reduce input stage noise levels to a minimum while using the same basic PCB layout. This however causes a change in the first stage input currents that the lower noise devices have when they don't see the same impedance on its positive and negative inputs. This causes substantial DC offsets at their output which must be compensated for.

If you use a single ADA4637-1BRZ in your application or you may need to set your threshold for detection level fairly high since the ADA4637 generated noise will show up as large jumps in demodulated output voltage levels and modulate your audio tone. I would not use less than two ADA4637 devices in parallel with each one configured to do its own current sharing to the total output. You cannot just solder one on top of the other. When I was crazy about audio work I have paralleled up to eight opamps which gave amazingly low noise noise levels some twenty years ago for moving coil phono cartridges that operate at microvolt levels.

Make sure that during your simulations that you look at the noise generated at mV levels or less at the output of your first two stages with the RX input at your coil connector shorted to ground.
Be careful with the ADA4610 I think I recall that it showed some tendency to oscillate at times if no compensation is used in its feedback loop.

High speed is required of all input stage gain blocks that are before analog gates so that recovery from TX coil recoil voltage is very fast. The input stage must be able to handle anything thrown at it and behave nicely. Clamping diodes will cause loss of speed and other problems which may not be easily identified.

[Detectorist#1]

OPA1611AID is single OpAmp and OPA1612AID is Double OpAmp. The convenient cases are SOIC-8.

[hunter63]

Thank you
OPA1611AID very beautiful parameters, is it only a single one or are there also double ones, if you know the name please tell me, best regards and thank you

[Detectorist#1]

The ADA4637-1BRZ have voltage noise of 30nV/sqr Hz at 2Hz (page 13 of DS) - the same as ADA4610 (page 16 of DS). The OPA1611AID have voltage noise 4pA/sqr Hz at 2Hz.

[hunter63]

I took ADA4610 from the KiCad library, ultimately it will be ADA4637-1BRZ