Partial Sovereign schematic

[David]

This is not the finished version or format that I am going to put this in but as long as I have been taking about finding time to do this I thought I should go ahead and post what I have. This is the section from the pre-amp output to the microcontroller input,it shows most of how this detector functions as far as hardware goes. I will try to complete some more of it soon but right now I am focusing on DSP studies as DSP methods perform extrodininary compared to analog circuits. If the Sovereign with its little 8 bit microcontroller works about as good as anything out there I know that something with a true 32 bit DSP could really perform. I had to re-asign designators to the resistors because to good folks down in kangaroo land put the R numbers DOWN UNDER the resistors. I included an X,Y chart for the resistor locations on the board.

[PhilippeM]

Re: Partial Sovereign schematic

WOW !
VERY GOOD JOB DAVID!!!!
CONTINU !!!!
BYE BYE
PhilippeM

[Beachcomber]

Nice Job!!!

But I have always wondered about something and no one has ever been able to give me an answer that seemed right. That is that in Minelab Coil for the Sov there is a preamp in the coil...yet none of the aftermarket coils by Sunray or Coiltek have the preamp in them and thier coils seems to work fine. So if the preamp isn't necessary why does Minelab have it there in the first place?

Again good job on your schematic....where are you located? Here in the USA we normally use "R" numbers for resistors, "C" numbers for capacitors, "Q" for transistors and "IC" or "U" numbers for Integrated Circuits.

HH

Beachcomber

[David]

Re: Nice Job!!!

As I said this is not the final format I intended to use. The normal R numbers for the resistors are silk screened under the component and impossible to read on the close spaced ones. I created a quick X,Y chart with 1-9 running horizontal and a-w running vertical so I could keep track of what I was doing, thats why the designators on the resistors are non standard. No I am not in the USA, I am in Texas and we all do what we want to down here. The final format will be in PC-cad, I was going to use eagle soft but I don't feel like taking the time to make another career out of a software package.

[Beachcomber]

I always heard Texas was like a country unto itself

n/t

[David]

Re: I always heard Texas was like a country unto itself

Houston is really a combination of all countries in itself, it's probably one of the biggest melting pots in the world and we all seem to get along togeather quite nicely except during rush hour.

[sevzirfo]

Very much interest!

Very well ! Make it full !

[Beachcomber]

I live in NJ just outside Philadelphia and no one gets

along at rush hour around here either

HH

Beachcomber

[PhilippeM]

Re: Partial Sovereign schematic

HI David,
After some search in the forum i found this:
1) Drawing from David
http://www.thunting.com/cgi-bin/geotech/forum/view.cgi?action=message&forum=tech&message=3791

2) Photo From Peter
http://www.thunting.com/cgi-bin/geotech/forum/view.cgi?action=message&forum=tech&message=2575

3) Macro photo of the preamp from Peter
http://www.thunting.com/cgi-bin/geotech/forum/view.cgi?action=message&forum=tech&message=2569

Between David drawing and Peter's Photos there is some difference like device name /
Does this refer to the same circuit or does this circuit different in concept but egal to fonctionality?
What is the good drawing to do this ?
Thanks for your reply.
PhilippeM

[Gary]

Re: Nice Job!!! (Preamp in Coil)

The Reason for putting a Preamp at the coil is usually done to obtain a Higher signal, as well as impedance matching before sending it through the Coax Cable. This results in less losses and better noise figures. This is particularly advantagous when the coax is a long length.

[bbsailor]

You raise a good point...no aftermarket coil preamps?

Beachcomber and others,

If, as you state, that no aftermarket coils use internal coil preamps, this would suggest that one could improve the sensitivity of these aftermarket coils by simply constructing an outboard preamp add-on similar to the one shown in the link below.

http://www.thunting.com/cgi-bin/geotech/forum/view.cgi?action=message&forum=tech&message=3791

This outboard could be powered by either a single 9V or dual 9V batteries, depending on the headroom needed to capture the range of signals. It should be built in a small metal case, with internal batteries. It should have a power switch to turn it on/off, a bypass switch to pass the signal through unamplified, and an adjustable gain control to maximize usable gain. By using a short pigtail with a connector, similar to the one on the coil cable, only one chassis mount is need. This preamp device could be easily clipped on to the shaft.

All these parts could be easily obtained from Radio Shack (IC and other electronic components) and Thomas Distributing (6 pin wire connector and chassis mount) and not require any modifications to the Sovereign or coil.

If you could find a four-pole-double-throw switch, you could turn on/off both batteries as well as provide a signal bypass when in the off position using a single switch. Otherwise, an individual DPDT should be used for switching battery power and another DPDT could provide the preamp bypass function.

This is just a little food for thought for those who might want to hot-rod their Sovereign detectors at low-risk and little cost.

bbsailor

[David]

Re: Partial Sovereign schematic




Here is the picture of the pre-amp circuit post. This came from the original Sovereign about 1992. It looks like they changed it somewhere down the line, the original uses a LT1028.

[David]

Re: You raise a good point...no aftermarket coil preamps?

It looks like the first stage of U1 only has a gain of about 12 and the second stage with a gain of 1 is just for inverting. I sure would not want to use a coil without a pre-amp. The Sovereign coil pre-amp dose have gain and the output impedance is low to reduce noise on the cable. The cable is very soft and apears to be unshielded twisted pairs.

[PhilippeM]

Re: Partial Sovereign schematic

Hi,
Many thanks David.
Your picture doesn't seem so focus but we can see what you said and draw.
Can you send us a total picture of the coil?
It will be interresting.
Can you give us also the material use for the cover?
Thanks for your reply
Regards
PhilippeM

[David]

Better coil/pre-amp pictures