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I build a lot of audio devices - amplifiers, effects processors etc. I've been doing it for about a year and learned a lot of principles. However one thing I still don't understand is wiring pots 1 and or 2 and 3 of a potentiometer together. How is it different from using only pins 1 and or 2 and 3?

I'm talking about this sort of thing (from here):

schematic

simulate this circuit – Schematic created using CircuitLab

Rather than this (from here):

schematic

simulate this circuit

Please ignore resistance values, just examples.

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    \$\begingroup\$ It makes the potentiometer into a variable resistance (circuit 1) rather than a voltage divider (circuit 2) \$\endgroup\$ Commented Aug 26, 2017 at 10:16
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    \$\begingroup\$ @JImDearden That is more an explanation of why one connects a pot as a current limiter (circuit 1) vs a voltage divider (circuit 2). Once you've decided you want a current limiter, the reason for the decision to connect the wiper to the otherwise-unconnected end is as answered by Jasen. \$\endgroup\$ Commented Aug 27, 2017 at 3:38
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    \$\begingroup\$ Yes @RickBrant, Jim is right - the second example is a little misleading as it is for a different function. \$\endgroup\$
    – TCassa
    Commented Aug 27, 2017 at 11:36
  • \$\begingroup\$ @TCassa No. JlM claimed that the connection btw pins 2 and 3 "makes the potentiometer into a variable resistance". No, it does not do that! The pot is being used as a variable resistance in that circuit whether or not there's a connection btw pins 2 and 3. \$\endgroup\$ Commented Aug 27, 2017 at 20:45

2 Answers 2

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It stops the resistance from going to infinity if there is dirt on the potentiometer track. (it just goes to max instead)

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    \$\begingroup\$ So is it more of a safety measure than actually having any effect on the circuit? \$\endgroup\$
    – TCassa
    Commented Aug 26, 2017 at 9:45
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    \$\begingroup\$ yeah, it helps degraded equipment stay within the design parameters. with perfect parts it would have no effect. \$\endgroup\$ Commented Aug 26, 2017 at 9:47
  • \$\begingroup\$ It is well known that the slider of a pot does not make "perfect" contact as it slides (specially wire wound pots). Its make-and-break characteristic could cause erratic behavior in the rest of the circuit. By connecting the slider to the other end, a minimum current is maintained (does not go to zero), as the slider breaks its contact. \$\endgroup\$
    – Guill
    Commented Sep 1, 2017 at 5:25
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As well as the reason in the accepted answer, It also stops the unused part of the pot acting as an antenna and picking up RF noise.

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    \$\begingroup\$ how does it do that? any pick-up is still coupled into the wiper terminal. \$\endgroup\$ Commented Aug 26, 2017 at 20:35

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