goldscan IV problem

[Alexismex]

Hello Reg,
Yes i have built 3 o 4 time the goldscan IV but my pc boards was experimental and hand made ....sorry i do not have, I still have the original , now i do not have time to make photos but next month i will upload goods photos of the board up and down ....
Also for the error you say i will check up these resistance ....because when i redraw a detector i check 3 minimum time ...i did not like to give errors to people ....see for example the two diodes in my schematic in the front end ...this is like that not inverted like usual !!!!
Thank for your explanation,
Alexis.

[dom44]

I was wondering out of the two circuit diagrams of Goldscan going arround there is one error i have just noticed! the GND pot on one is shown as 50k and on the other shows 10k does some one know which is correct? as well as the input op amp nulling circuit ne5534 are wired diffrently? one shows 22k on the wiper and the other 220k.

[Jose]

Hello everyone
I have a question please if I can answer, with no OA95 diodes (germanium) or similar to arm the G4, I can use the 1N4148 in its replacement?
thanks
Jose

[mikebg]

Hello everyone
I have a question please if I can answer, with no OA95 diodes (germanium) or similar to arm the G4, I can use the 1N4148 in its replacement?
thanks
Jose

Jose, I think small Shottky diodes are more suitable than 1N4148.

[Jose]

Mikebg Thanks, I agree with replacing the diodes 1N4148 by shottky.
The question is how to replace OA85 diodes gemanio?, Which has a lower junction voltage (0.2, 0.3 volts) compared to silicon (0.7 volts).
Apparently, these diodes gemanio are used as a voltage limiter or overload in some parts of the scheme of GS4.

[Altra]

Jose,

Use BAT85 diodes as replacements.

At 1ma forword voltage drop is 240mv

[Jose]

Altra Thanks for responding, try to get the BAT85.
regards
Jose

[Altra]

Jose,

If you are building the GS4 from that schematic and did not know. You need to add a ground connection. Between the J113 drains and the 100n capacitors on both channels.
You can find details in the main GS4 thread.

Regards
Mark

[Jose]

Thanks Mark
I'm building the GS4 and encounter many questions, is it your observation.
In addition to ground drainage, which is the value of the resistors in parallel between drain and source on both channels?. In addition, the drainage would be connected on the side of integrated, land-side would be connected to the source, according to the attached diagram.
In the J113 data sheet reads that drain and source are interchangeable, this is real?
Deputy scheme I found in another forum for better illustration.
Your help is greatly appreciated.
Thanks, Jose

[Altra]

The original design did not have resistors in parallel with the fets. If you want to experiment, typical values for adjusting the SAT speed, 220K to 1M with a 470n capacitor. The original schematic is by PaPa Alex and is supposed to be correct, except
for the grounding of the fets. Posts by Alex and Reg should be studied. In general you can reverse the drain and source on small signal fets assuming no built in diode. In my last post I mentioned "drain" because Alex's schematic is marked that way.

Where did you get the above schematic?

Regards Mark

[Jose]

Thanks Altra
The image was copied Forum Thunting, metal detectors, Design IP, pag.3 Goldscan Pulse IV, pag.11.
At the same forum pag. 8, you can see a single phase PCB (not SMD) for the G4, is that I'm putting together.
URL address here
http://i50.tinypic.com/wjb588.jpg
Regards, Jose