Potentiometers

[Koala]

Had some stability issues on a homemade Bandido. Moving near the potentiometers switches would have an affect on distance or threshold tone. Tried tying all potentiometers cases to ground still the same. Change to a different type with a nylon shaft and the issue has gone.

Has anyone else found the nylon shaft potentiometers better or was it just a bad quality originals

[chemelec]

I used Metal Cased Pots, and had No Problem with them on my Bandido.

[Koala]

Thanks for the feedback


Both are metal cased

The ones I was having problems with have a metal splined shaft and the new ones have a solid nylon shaft.


Just wondered if it was the quality of the smaller splined POTS or there design that caused the problem. You Don't even have to touch them. No big deal as everything is working fine with the replacements.


On my Barracuda I have not had a problem with a metal shaft potentiometer but then again I only have threshold adjustable from the outside.

[WM6]

The ones I was having problems with have a metal splined shaft and the new ones have a solid nylon shaft.

What sort of buttons you use on metal shafts, Alu-metalic or synthetic?

[Koala]

Cheap eBay ones brass middle and rubbery plastic outside cover. See where you are going with this LOL. Think you could be right. They are tiny. A bigger size button would give a greater isolation distance. Don't like the small size anyhow as threshold adjustment is too coarse.


The ones I am testing with now you can pick up and move around and the threshold stays constant. You could hear the threshold change with the originals even without touching them just needed your hand very close.

Funny thing is the same thing happened if you picked up the switches threshold would alter. Not altered the switches but after changing the threshold, discrimination and sensitivity POTS this has gone????

[kt315]

you have to learn a way how firms are shielding MDs housing. i did especial excurse for delta pulse users,
with much pics. you do not wish to notice a relation between electrostatic charge on your body what constanly
is and accumulate up. if you touch a metal something the charge goes out - a discharge getting out.
value of the charge may be reach easily even to 10kV (kilovolts). try to learn this matter.
if you use nylon shaft pots - no the discharge there, just cause the nylon is only perfect isolator. and you then tell about
'issue has gone'. NOT gone. you have to take steps - open Fisher housing - learn the shielding,
open Minelab housing - learn the shielding. they use a foil, simple and effective way. HARD TO LEARN SOME LESSONS?

[kt315]

notice the discharge has a IONIZED channel - sparkover - it is PERFECT CONDUCTOR for the current.

[kt315]

[kt315]

you have to see - electrostatic charge is on cat body and on a boil. so the field is EVERYWHERE AROUND YOU.

[Koala]

Many thanks Kt315

The cat video

[golfnut]

some form of couplling of you and any signals on your body to the wiper thru the shaft. Ive had mains hum on some audio kit when Ive touched the metal pot shaft.

A plastic control knob may have been enough of an isolation?

[Koala]

Yep. Changed all for nylon shaft ones probable could have used a different / large top.

Have the same issue with the retune switch. Fine if I operate it with a bit of plastic.

[golfnut]

sounds like something else going on - is the Tx gnd and the preamp ground dc isolated - joined only with a cap.

[Koala]

TX is grounded on the PCB. Preamp is grounded via a resistor as per original. Detector is running fine. Tried tying the shield to the TX only and TX and RX there is no difference.

[daihatsu]

Talking about potentiometer like in guitar amps if not grounded properly when it touched the amps is so quiet and when it loose from finger make noise, I chose plastic shaft over the steel type, if budget are low I use 5x 10k pot in series to replace 50k ten turn and make sure it needs grounded well