Replies to Original Minipulse Project Details

[WM6]

Thanks for this NY present, Qiaozhi. Great work done. Did you measure power consumption?

[Geo]

Was there something that was not kaput??

[kt315]

great really home work and the report George. at a link I see not same PCB like you have.

http://www.geotech1.com/forums/showt...ight=Minipulse

[Qiaozhi]

great really home work and the report George. at a link I see not same PCB like you have.

http://www.geotech1.com/forums/showt...ight=Minipulse

I suspect the one from Adam is an earlier version than mine. It's labelled as "MP1" (which presumably means Minipulse 1), the ICs are all in sockets, and there are a few jumper mods on the backside of the PCB. The one I have is labelled "PTL 110" (probably meaning "Pulse Technology Ltd Version 1.10").

Pity I didn't see Adam's post earlier, as the back-engineering might have gone a bit faster.

[Qiaozhi]

Before I finalize the new layout, does anyone have any preference for the size of the PCB? The original is 4" x 4", but I've reduced it to 3.75" x 3.75". I could make it a bit smaller than that, but would prefer to keep the PCB as a square.

[WM6]

Retain DIP trough hole solution, please!

[Geo]

Qiaozhi, i can not see the feedback resistance of U2....

[Davor]

I am interested. If possible I'd like to see UA709 replaced with more common NE5534 and of course some NJR counterparts of it.
I strongly support keeping the PCB through hole, and preferably single sided.
BTW, your schematic is missing a feedback resistor at UA709

[Tepco]

On PCB picture 1M feedback resistor is visible near LM709, capacitors C6 and C14 are 10pF, not nF.

[Qiaozhi]

Retain DIP trough hole solution, please!

That was my intention.

Qiaozhi, i can not see the feedback resistance of U2....

It was in my hand-drawn schematic, but it got missed out when I recreated it on the computer.
Well spotted.

I am interested. If possible I'd like to see UA709 replaced with more common NE5534 and of course some NJR counterparts of it.

OK, I'll do that.

On PCB picture feedback resistor is visible near LM709, capacitors C6 and C14 are 10pF, not nF.

Just rechecked the PCB, and C6 is labelled "3.3", so I assume this is actually a 3.3pF (3p3) cap. I assume you mean C4 (as C14 is an electrolytic) which is labelled as "10", so that's a 10pF.
Again, well spotted.

I will post an updated schematic in a few minutes.

If anyone else sees something wrong, please let me know. Like everyone else, I do make mistakes.

[Tepco]

I already mentioned reverse engineering PCB from pictures on this forum, so this is good reason to put it to the test if I get some time... Why not? People restoring oldtimers, tube radios etc, this is nice part of MD history.

[Qiaozhi]

The project files are now "sticky" (so that they'll remain at the top of this thread) and all the replies have been moved to another thread.
I've also updated the schematic to Version 1.1 to include the capacitor value changes and the feedback resistor for the preamp.

[johnandles]

Does the second sample initiate a sort of GB?
If not I guess this design would not like Australia's mineralised gold bearing areas?
Cheers john

[Qiaozhi]

Does the second sample initiate a sort of GB?
If not I guess this design would not like Australia's mineralised gold bearing areas?
Cheers john

This detector was designed and built in the 1980s, and there is no GB feature.
The second sample is for Earth field elimination.

[Qiaozhi]

Please see the Project Details for an updated schematic (V1.2).
Errors fixed in this version are:
C11 was shown as 10nF. Should have been 100nF.
R39 and C20 were connected to 0V instead of -5V.