Author Topic: potentiometer with solder blob  (Read 1751 times)

0 Members and 1 Guest are viewing this topic.

Offline hammy

  • Supporter
  • ****
  • Posts: 436
  • Country: 00
potentiometer with solder blob
« on: May 10, 2016, 03:45:03 pm »
Why do musicians connect a ground wire to the case of a potentiometer with a big solder blob?
Any reasons? Why is the ground pin not used? What is the benefit?

Cheers
hammy
 

Offline Grzegorz2121

  • Contributor
  • Posts: 13
  • Country: pl
Re: potentiometer with solder blob
« Reply #1 on: May 10, 2016, 03:52:03 pm »
Where you have ground pin on the potentiometer?

Potentiometer have 3 pins- two connected to sides of the resistor and one to slide on the resistor to vary the resistance of this pin.

I think that musicians connects case of these (because is not connected to anything) to shield signals in potentiometers from noise.
 

Offline Audioguru

  • Super Contributor
  • ***
  • Posts: 1508
  • Country: ca
Re: potentiometer with solder blob
« Reply #2 on: May 10, 2016, 03:55:07 pm »
Pots usually do not have the case connect to one of its pins then its case can pickup mains hum that is all around us. If you connect its case to the circuit ground then it shields the pot terminals.
 

Offline Coulombic_Irrigation

  • Newbie
  • Posts: 2
  • Country: england
Re: potentiometer with solder blob
« Reply #3 on: May 10, 2016, 04:56:21 pm »
You need somewhere to connect a bunch of ground wires to and the back of a pot provides a decent amount of area to work with. There is no reason why you have to do it that way, but it's standard practice because it's so convenient.
 

Offline hammy

  • Supporter
  • ****
  • Posts: 436
  • Country: 00
Re: potentiometer with solder blob
« Reply #4 on: May 10, 2016, 06:33:41 pm »
You are correct Grzegorz2121. There is no dedicated ground pin. :palm:
I had a quck check with all metal potentiometer I found . The case is not connected to any pin.

I see, this makes sense: To prevent hum you ground the case.

Thanks for refreshing the basics.  ::)  :palm:
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15318
  • Country: za
Re: potentiometer with solder blob
« Reply #5 on: May 10, 2016, 07:10:28 pm »
Do not forget that that nice big heat sucking metal case is generally right next to a lovely low melting point plastic wiper, so soldering on a few wires to the case might just make your pot a Dali-esque object. Instead use a solder lug under the mounting nut, it generally is also connected via the alloy casing to the back metal shield.
 

Online Cerebus

  • Super Contributor
  • ***
  • Posts: 4035
  • Country: gb
Re: potentiometer with solder blob
« Reply #6 on: May 10, 2016, 08:59:27 pm »
Pots usually do not have the case connect to one of its pins then its case can pickup mains hum that is all around us. If you connect its case to the circuit ground then it shields the pot terminals.

And also for simple safety. If the case is grounded then any metal parts of the pot that might be touched are at ground potential. It isn't unknown for live mains to make it's way onto signal lines on stage equipment especially with old valve amps that get chucked into the back of a van each night. It's lead to some well known and well documented deaths.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Online rstofer

  • Super Contributor
  • ***
  • Posts: 6943
  • Country: us
Re: potentiometer with solder blob
« Reply #7 on: May 10, 2016, 09:58:36 pm »
Pots usually do not have the case connect to one of its pins then its case can pickup mains hum that is all around us. If you connect its case to the circuit ground then it shields the pot terminals.

And also for simple safety. If the case is grounded then any metal parts of the pot that might be touched are at ground potential. It isn't unknown for live mains to make it's way onto signal lines on stage equipment especially with old valve amps that get chucked into the back of a van each night. It's lead to some well known and well documented deaths.

Right!  In theory, all non-current-carrying metallic parts are supposed to be grounded.  Even though there may be a plastic knob, often the knob is missing and the metallic shaft and nut are exposed.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf