Minelab pre-amp

[Solmer]

Hi Gurus, I'm trying to build a Minelab Sovereing coil but I can't locate the pre-amp circuit schematic, I've tried to ask Coiltek and Minelab without reply.
Where I can get the pre-amp circuit?.

Thanks.
Happy finds....

[peter]

Re: Minelab pre-amp




>Hi Gurus, I'm trying to build a Minelab Sovereing coil but I can't locate the pre-amp circuit schematic, I've tried to ask Coiltek and Minelab without reply.
>Where I can get the pre-amp circuit?.

>Thanks.
>Happy finds....

Hi Solmar,

I tried to post yesterday but did not do it right. Trying again. Good luck with your Coil building, I have built a few Coils over the years and constructed a few Metal Detectors.
The best one which was very sensitive was the Heathkit GD345.
This was a simple IB machine but by reducing the frequenct to about 20 kc/s it could disc Foil. A VERY Sensitve machine when running 18 volts through the pre Amp and Transmitter.

I also built two out of the Elector Magazine. These were Phase Shift Detectors.
The first one was the Shadow and I am afraid that on the beaches in Cornwall England it did not work too good. Very sensitive with 10" Coil but not easy to work being very sensitive to ground Effect. The Spectrum is the same.
The other one cannot rememder the name and have not seen it on this Forum. Worked at 6 kc/s and this one was VERY stable on our beaches.
My test used to be to walk quickly across Perranporth Beach in Cornwall raising/swinging and lowering the search head on wet sand. If I could do that without 'Falsing' and could search in salt pools I knew I had a good Detector.
The sand at Perranporth is unique for this as it is very fine,mineralised and holds about 50/50 salt and sand. A course Beach with stones is easier. Ground effect tends to be more Negative. If the Ground effect is 'Floating' equally between Negative and Positive you have the most extreme conditions
Back to your coil.
The Sovereign Coil as you know has a Pre Amp.
The beauty of the design is that to power the Pre Amp it 'Robs' the Power off the Transmit Coil.
Setting up a small coil to get the AC Voltage could be tricky so I suggest aligning the coil with an AC Power Supply to the Pre Amp first then afterwards removing it and setting up the small coil.
Due to limitations I can only send one Photo.
This will show the Pre Amp Board but if you give me your E Mail address I will send you the Photo showing the Coupling Coil.

Happy building.
Peter.

[Peter]

Re: Minelab pre-amp




Hi Solmer,

Here is the Photo of the Sovereign Coil showing the small coil to 'Rob' AC for the Pre Amp.
The Heathkit Detector should have been GD348.
The unknown Phase Shift Detector was called Elector.

Cheers,

Peter.

[Chris]

Re: Minelab pre-amp

Hi Solmer

With the two images of the pre-amp PCB and the datasheet of the LM394 (see application sample page 4) you can make your own Sovereing pre-amp circuit. Exchange the LM112 (appl. note) with a low noise NE5534A and add the power spupply circuit (small coil, protection diodes, bridge rectifirer, cap's).

Check it out!

Chris



LM394

[kt315]

this is not my Home Work i see some progress in the matter and only bring the info to here. enjoy

[kt315]

sprint layout file

[mikebg]

KT315, I think 850C is an NPN transistor (suchlike KT315 :-).

[kt315]

Roger! you are right... 2Gp is BC850C NPN. an author has to fix this, I hope he reads... thanks!