pot questions (like potentiometers)

In this context (as a variable feedback resistor around an opamp mic stage), would the gain pot be audio or linear taper? Also, in this configuration (with the wiper tied to one side of the pot), does it have the effect of adding a resistor equal to the value of the pot in parallel with the resistance between the wiper and the other side? (sorry - I don't know how to word this simply) In other words, the resistance between points 1 and 3 would be equal to the resistance of the entire track of the pot (25k) in parallel with the resistance between points 2 and 3.
Thanks, Ben

plumsolly said:

In this context (as a variable feedback resistor around an opamp mic stage), would the gain pot be audio or linear taper?

Click to expand...

Audio.

Also, in this configuration (with the wiper tied to one side of the pot), does it have the effect of adding a resistor equal to the value of the pot in parallel with the resistance between the wiper and the other side? (sorry - I don't know how to word this simply) In other words, the resistance between points 1 and 3 would be equal to the resistance of the entire track of the pot (25k) in parallel with the resistance between points 2 and 3.

Click to expand...

No; the total resistance will be the resistance between the slider (2) and the end to which the slider is not connected (3). The resistance between (1) and (2) is shorted out.

I'd add that this is a somewhat dubious design. If the slider lifts, the feedback resistance defaults to the maximum 25k resistance of the pot, or maximum gain. That pot, therefore, needs to be absolutely pristine.

Unfortunately, it won't stay that way, since it has a small amount of residual DC offset from the opamp passing through it, and all of the current passes through the slider. That pot's going to go noisy in a relatively short time, and when it goes noisy, it will be REALLY noisy.

Also, turning the gain up and down will also turn the offset up and down; do it quickly and you'll hear a thump.

You're stuck with it, unfortunately, since evidently you're doing a rebuild on an existing console. But you need to keep your eyes open to the oddities of the design.

Peace,
Paul

Thanks Paul, that make sense. I guess I don't understand then the purpose of hooking up point 1 at all. why not just hook up points 2 and 3 like we normally see in a variable resistor application?
-Thanks again, Ben

plumsolly said:

I guess I don't understand then the purpose of hooking up point 1 at all. why not just hook up points 2 and 3 like we normally see in a variable resistor application?

Click to expand...

Imagine what happens in both situations when the pot wiper (2) briefly loses contact with the track, which can happen with any real-world pot.

JDB.

Thanks for the reply JDB, I understand now - Ben