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Right now, I am using all the pins of a three pin potentiometer, in order to feed a signal into a transistor for amplification.

The leftmost pin is GND, the middle pin is the signal and the rightmost pin is what goes to the base of the BJT.

I want to create a PCB board. How do I trace the signals to the potentiometer? Exaclty just I described?

My fear is that I will design the board, but then I will buy and solder a potentiometer with completely different pinout.

So my question is, is the pinout of all the potentiometers the same?

EDIT: Here is a picture of the topology I am using. enter image description here

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    \$\begingroup\$ The leftmost pin is GND, the middle pin is the signal and the rightmost pin is what goes to the base of the BJT. ... that may be an incorrect connection scheme ... please add a schematic diagram, or a portion of the schematic diagram that includes the potentiometer \$\endgroup\$
    – jsotola
    Commented May 31, 2023 at 20:56
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    \$\begingroup\$ Your pot wiring sounds wrong to me. If the pots are acting like a volume control, adjusting signal level to the transistor, I would put the signal input on one end of the resistor element, other end grounded, and connect the pot wiper (moving contact) to the transistor base. Usually the center pin of the pot is the wiper. \$\endgroup\$
    – Peter Bennett
    Commented May 31, 2023 at 20:58
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    \$\begingroup\$ @PeterBennett Agreed, just think of what happens at the extremes of travel of the wiper. At one end the input is shorted to ground, at the other it is connected directly to the base of the BJT with no apparent current limiting. I imagine the diagram is incomplete. There is no DC biasing for the BJT and no AC coupling for the signal. \$\endgroup\$
    – Peter Jennings
    Commented May 31, 2023 at 21:57
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    \$\begingroup\$ exchange the BJT base and the audio input connections ... the pot forms a voltage divider that way \$\endgroup\$
    – jsotola
    Commented Jun 1, 2023 at 0:03
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    \$\begingroup\$ that only "works" (adjusting volume) by overloading the source signal until it's attenuated. \$\endgroup\$
    – dandavis
    Commented Jun 1, 2023 at 6:04

2 Answers 2

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No. Typically on a three pin potentiometer whichever pin is in the center is the wiper, but you can't count on that.

Look at the datasheets for the type of potentiometer you want to use, they should have the pinout and often a mechanical drawing with dimensions.

If you have several choices of pots with different pinouts and aren't sure which you will use you could layout the board so that it will accept different ones, or have jumpers to change the connections, although this eats up some board space.

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The circuit you show is (probably) wrong, assuming the center terminal of the pot is the wiper.

Normal volume control wiring is like:

schematic

simulate this circuit – Schematic created using CircuitLab

The wiper takes a portion of the input signal to pass on to the transistor.

You may need a bias network or other components between the pot wiper and transistor base for the transistor to work.

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  • \$\begingroup\$ Thank you! I updated the picture with a more complete schematic. \$\endgroup\$
    – user1584421
    Commented Jun 2, 2023 at 11:16
  • \$\begingroup\$ You will probably need a coupling capacitor and bias network between the pot wiper and transistor base for the transistor to work. \$\endgroup\$
    – Peter Bennett
    Commented Jun 2, 2023 at 15:47
  • \$\begingroup\$ Thank you but it works in this configuration... \$\endgroup\$
    – user1584421
    Commented Jun 4, 2023 at 16:50

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