Need Advice Re: Potentiometer as a Volume Control

[JLKaplan]

Hello,
I am not even remotely an audiophile, and need advice. Trying to replace a SPST switch that controls a box speaker in a green room behind a stage with a potentiometer so volume can be decreased.

Have been told it is a 70 volt system and an 8 ohm speaker. There is a wall box which inside is a single 22 gauge wire that the switch was spliced into.

I have tried 25 and 500 ohm pots with the wire connected to the wiper and first terminal, with and without the third terminal grounded to the pot's case. The result is - no change in volume.

Would appreciate any advice. Thanks...

 

[Mooly]

If you wired a 25 ohm pot using three terminals then I can't see how it can fail to reduce the volume. The audio is fed across the pot (end to end) with the wiper feeding one speaker terminal. The other speaker terminal returns to either of the pot's end terminals... which if you picked the 'wrong' end simply means the pot works back to front.

 

[Mooly]

Like this:

 

[Galu]

Trying to replace a SPST switch. . . inside is a single 22 gauge wire that the switch was spliced into.

@ Mooly.

If I read the OP's full description correctly, he appears to be wiring the potentiometer as a variable resistor in line with the single 22 gauge wire.

I think we need to locate the other wire (signal ground, so to speak?).

@ OP.

Is the box metal and are there any wires connected to it?

 

[JLKaplan]

Hi, Yes - there is just a single wire inside a plastic box, with nothing grounded.

Do I need to find a ground for the third terminal of the pot?

 

[Mooly]

Yes, you need to find the speakers return lead and connect the pot's third terminal to that so that electrically it is like in the diagram I posted.

 

[JLKaplan]

Eureka! There were two unused conductors from switch back to speaker. Ran one from 3rd terminal on pot to power into Speaker and works. Volume is very linear. Thank you!

 

[Mooly]

That's good