Whites Surf PI schematic

[nonkapo]

Current progress

The current progress...Did not manage to get 5mm raster capacitors here:-(. Order them back in Bulgaria and they arrive in one day:-)). Will continue when the vacation started.

[nonkapo]

Another question. Do you think it is allright to use wire winded potentiometers all over the circuit? I'm just woriyng a bit cause they may have some induction or it is neglectable? Thanks.

[dbanner]

Do not use wires wound pots. They essentially present themselves as having inductances ( self inductance)which are prejudicial to these circuits. They are for high power applications, and other things.
It also depends on what type of wire wound pots you have, there are various types made for specific applications.

[dbanner]

On the other hand, if this is what you have already, then try them to see results. Below 1khz might be ok to use them.

[nonkapo]

I have both. Definitely they are not suitable for dumping. I get multi turn pots for better tuning, not realising they are wire wounded. Will measure their inductance, compared to standard pots and let you know. As my pots are not on the board I can easily swap them.

[dbanner]

It has been noted here on forum that they are perfect for damping tool. I have use a 500ohm wire wound pot in series with 390 ohm resistor on my surf pi self build to adjust damping for different coil and I just left it in permanent. I have noticed that on beach in tropical climate(36 degrees Celsius) where I live, the sensitivity of coil is different than at home, so I have variable damping pot on panel, can you believe it. All the experts work with spice simulations and say this and that and whatever, but the proof is in the eating.

[Polymer]

It has been noted here on forum that they are perfect for damping tool. I have use a 500ohm wire wound pot in series with 390 ohm resistor on my surf pi self build to adjust damping for different coil and I just left it in permanent. I have noticed that on beach in tropical climate(36 degrees Celsius) where I live, the sensitivity of coil is different than at home, so I have variable damping pot on panel, can you believe it. All the experts work with spice simulations and say this and that and whatever, but the proof is in the eating.

I agree with all your observations and have yet to implement this one myself.
How do you notice that you have hit the optimal damping resistance out in the field without an oscilloscope?
Thanks!

[6666]

I agree with all your observations and have yet to implement this one myself.
How do you notice that you have hit the optimal damping resistance out in the field without an oscilloscope?
Thanks!

good question

[Tim]

The way I understand it is the few uH of the wirewound pot would not be enough to throw your coil out.
Over-damping is more acceptable than under-damping. Having a sample of the metal you are searching for, and either placing it on the ground or burying it will give you a far better indication of appropriate damping than any simulation or calculation.

[nonkapo]

Thanks everyone. It sounds as a good news. However i did not buy one for damping, so must do :-). One more thing. Is there a point to replace the offset trimmer with potentiometer? Just curious. I gues small voltmeter must be put on pin six as well to do the implementation the proper way?!? Same reason as with the damping - there might be difference on the field, compared to home?

To Polymer: These days there are portable osciloscopes one can take on the field at least for the lower frequencies. It is another question how accurate they are ;-).

[Tim]

If you are referring to the voltage offset on 5534 no. The optimum zero offset for 5534 may however be slightly positive (or negative) from zero. As with any practicality, it is best to test this in the field/on bench rather than rely on simulation or calculation.

[dbanner]

I agree with all your observations and have yet to implement this one myself.
How do you notice that you have hit the optimal damping resistance out in the field without an oscilloscope?
Thanks!

I just adjust the pot while swinging a gold ring across the coil, looking for greatest depth( distance).
Every time I go to beach I do this adjustment. The pot is on back panel of my box for easy access. It's that simple.

[dbanner]

I have noted the difference in temperature between my workshop at home and out on the beach is sometimes as much as 12 degrees Celsius. For some reason it affects the circuit. This has been my experience. Maybe for others it will be different. Maybe my coil is temperature sensitive.

[nonkapo]

I have noted the difference in temperature between my workshop at home and out on the beach is sometimes as much as 12 degrees Celsius. For some reason it affects the circuit. This has been my experience. Maybe for others it will be different. Maybe my coil is temperature sensitive.

Thanks. For you issue it is not only the coil but all the elements have some temperature tolerance.
T

[6666]

I just adjust the pot while swinging a gold ring across the coil, looking for greatest depth( distance).
Every time I go to beach I do this adjustment. The pot is on back panel of my box for easy access. It's that simple.

ok thanks, is there much variation ?