Chance PI coil...

[baum7154]

Baum7154,

This reduced delay is due to the lower gain (about 33 X per stage vice 1000 X for a single stage) of amplifier each stage allows the opamp to come out of saturation faster. Another way to get a slightly lower time out of saturation is to increase the supply voltage to the preamp.

Nice work!

bbsailor

Thanks for the comments Joe.

The original CHANCE PI amp has 470 gain so I built this amp with a first stage gain of 18 and the second stage gain of 28 for a total gain of 504. I can easily change stage gains to other values as performance needs may dictate. However changes to the feedback resistance values will necessitate changes to the Low Pass Filter Cap values as well, but that too is not a big deal. It will be tempting to see how far the gain can be pushed and how it affects performance.

Thanks again,

Dan

[bbsailor]

bbsailor what would be the maximum supply voltage to the preamp that you would use ?
thanks

6666,

Check the opamp specifications and don't exceed the maximum voltage. There are common +/-8V regulators that will increase the headroom over the common +/-5V supplies. Ensure good filtering to keep noise low. The quicker the opamp comes out of saturation, the faster you can begin to sample. The input clamping diodes allow the input voltage to the opamp to clamp at 0.7V. This voltage times the opamp gain equals the max output voltage just below the +/- supply voltage. Higher gain opamps take longer to come out of saturation, thus two low gain stages come out of saturation faster and a little more fast with an increased supply voltage.

bbsailor

[baum7154]

If you have not already done so take a look at the more detailed description of the amp I posted in the CHANCE PI Build thread of the TECH FORUM. 2nd stage output is voltage limited to 11 volts, still below the 12.5 volt rail voltage and in line with the minimum operating battery voltage of 11 volts.

Dan

[6666]

Thanks for the voltage info bbsailor and dan, good to know.

[geoscash1]

I know this will sound a little off the hook, but I consider myself a fairly intelligent guy, can do most anything or figure out how to do it even if it takes a bit...


Problem here, I cannot for the life of me figure out how you guys are wrapping this dogon spider/basket coil.. I have now wrapped, unwrapped and rewrapped this thing on its form a half dozen times and it comes out looking NOTHING like baum7154's pictures or others I have seen.


Dont get me wrong, for whatever reason it works as is, 88.9mm inner radi, 0.42672mm wire with 25 turns, approx 327mH and it gets 7 inches on a quarter with my cuda in air as it sits but I want to wrap it like it is in the images (baum7154's) in this thread, does anyone have a video of how they are weaving this? I'm starting to feel like an idiot.....


I know its better to use the teflon coated silver stranded wire (got some coming in the mail) this is just a test coil first to see how it does before I get to involved with it.. But now it seems it has become a dogon mission and its really startin to tick me off...



Anyone have a "Hooked on Phonics" tutorial for this poor Un-enlightened dummy, or atleast an explanation on How To wrap this dam thing.....

[6666]

Having a look at these pictures should put you on the right track.

[geoscash1]

Hey 6666,
I have all of those images but I had not seen the one with the english translation, thank you..

Now I see where my mistake is, its on doing the second layer of 5 turns at the crossover (blue to green in pic), I had just kept going on the same side...


Ok, will be unwinding and doin it again, hope it comes out right this time...;lo

[6666]

Practice with some string or thread first.

[geoscash1]

Good Idea....

[kt315]

Having a look at these pictures should put you on the right track.

all right, but big mistake there the winding is drowned by epoxy. right way at first to use some tape 1-2mm gauge, then to cover by scotch, then
to drow by epoxy. ie winding will be free in air. that decreases interturn capacitance.

[mschmahl]

Having a look at these pictures should put you on the right track.

Is this the coil with some self-shielding? I have wound it for my mirage and don´t know should i shield it or not.

[baum7154]

Yes, this is the coil with some self shielding. My 334uh 8" coil in the pictures posted earlier does not see my hand fully encircling the coil with the detector set at 8us sample delay and 'wide open' in all other settings. I would try your coil first without additional shielding as it can easily be added later. Make sure to put the outermost winding wire end at system ground. Don't flood the coil with anything or it will slow down. I use cloth adhesive medical tape as the overwrap of the windings and the form and polyethylene foam per the previous pictures I posted. Then 2 layers of fiberglass are applied as armor.

Good luck,

Dan

[mschmahl]

Thank´s a lot. Than i will try it without shield. I thought this coil is the selfshielding coil. Sorry.

[baum7154]

Thank´s a lot. Than i will try it without shield. I thought this coil is the selfshielding coil. Sorry.
[ATTACH]29920[/ATTACH]

The coil picture you have attached is the original CHANCE PI coil and I have built 2 of them and they are fast but do not self shield and they will not optimize performance of the CHANCE detector. The original coil also requires shielding for short sample delays and because of its geometry it loses much of it's speed even with graphite shielding. It is possibly the worst coil I have used with CHANCE for finding small gold. You are far better off with spider wound coil of this thread.

Dan

[baum7154]

I know this will sound a little off the hook, but I consider myself a fairly intelligent guy, can do most anything or figure out how to do it even if it takes a bit...


Problem here, I cannot for the life of me figure out how you guys are wrapping this dogon spider/basket coil.. I have now wrapped, unwrapped and rewrapped this thing on its form a half dozen times and it comes out looking NOTHING like baum7154's pictures or others I have seen.


Dont get me wrong, for whatever reason it works as is, 88.9mm inner radi, 0.42672mm wire with 25 turns, approx 327mH and it gets 7 inches on a quarter with my cuda in air as it sits but I want to wrap it like it is in the images (baum7154's) in this thread, does anyone have a video of how they are weaving this? I'm starting to feel like an idiot.....


I know its better to use the teflon coated silver stranded wire (got some coming in the mail) this is just a test coil first to see how it does before I get to involved with it.. But now it seems it has become a dogon mission and its really startin to tick me off...



Anyone have a "Hooked on Phonics" tutorial for this poor Un-enlightened dummy, or atleast an explanation on How To wrap this dam thing.....

----------------

Very nice work on the form…it looks like someone has access to machine tools!

A suggestion on the form slot width, if you are using about 1/8" thick material the slots should be about 1/8" wide as well. This causes the wires to cross in the slots perpendicular to each other and to stack up in the slot. The object is to avoid close parallelism of the wires and thereby capacitance. If the slots are too wide they do not cross perpendicular to each other in successive layers. Each layer of windings must cross through the slots reasonably perpendicular to the previous layers winding.

Hope this helps

Dan