Coil pre-amp schematic wanted

[Neil in Toronto]

Would anyone have a schematic for the coil pre-amp in a Minelab BBS coil (Sovereign/Excaliber)?

[Carl]

Re: Coil pre-amp schematic wanted

See if Coiltek will send it to you. Surely they know. Minelab might even send you a schematic, worth asking.

- Carl

[kt315]

new project from kt315

i am thinking to give promised coil front end to a winter time. what you think?
a base is this board in attach. i plan to do DIP8 and SO8 placement for more universalizm so you can buy/use 'used desoldered american made' opamps from chinese.
those pics made by Foma and board from Tornado coil, i suspect.

[kt315]

schematic

[Skippy]

I would like to see some high-frequency decoupling on the power supply, 100nF ceramic, for example.
Could the bridge rectifier be made from two double-diodes in SOT-23 package, example BAV199 ? There are a multitude of SMD bridge rectifiers, but there's no need to get too exotic.
I think it's wise to keep this board small, so it doesn't upset coil balance. For this reason, avoid using a ground-plane. And I would say use 0805 resistors ... but if you lay it out for 1206, then 0805 can still be fitted onto the big 1206 pads.

[kt315]

thank you Skippy. i do not see advantage of ceramics. i especcialy increased tantalums value from 10 to 47uF and imo thats enough.
ESR of 100nF cap is not low, also ceramic has piezo effect. moving coil transfers all kicks about wood, ground, rocks on the pcb.
i did add BAV199 doing the pcb more universal for everybody.
yes, people avoid ground-plane. pics show that.

[dbanner]

All decoupling capacitors should connect to a large area low impedance ground plane through a via or short trace to minimize inductance.
I saw this document on decoupling techniques. Seems very informative.

[kt315]

schematic

[Skippy]

Just add one 0805 capacitor from +ve to -ve supplies close to the opamp. We don't have to fit the cap if we don't want to.
Regarding circuit ground, try and create a star point at the junction of the two 47uF psu capacitors.

[kt315]

still schematics

[dbanner]

Using a ground plane on such a tiny board may not be so bad for the coils, which will have to be balanced to spec anyhow. I don't know. But a ground plane is recommended for bypass caps and could add some extra sheilding to the components which could be a plus.
Just do the same as was done on the original board, move some components around a little and there you have it.

[kt315]

excaliber 2 coil



taken pic from https://www.reviewdetector.ru/index....wtopic=2259633

[kt315]

Kirill B. gave me pics of the board on request. https://photos.google.com/share/AF1Q...5CUGszR1VjZkdB

[kt315]

- On a side note, I know there was a product called the Sovereign S-Amp that supposedly boosted the TX power being put to the coil and am interested in the circuitry for these also as I understand they are no longer made. http://www.treasurenet.com/forums/te...ier-board.html

[ssama2]

I put a 100 nF 250v capacitor in series on one RX wire, it boosted the signal and decreased ground noise. It might be possible to do without the shielding on larger coils.