Gain Pot Passes Sound in Full CCW Position

[debrad]

Hi everyone!

Hoping you might have some suggestion on how I can resolve a minor issue I'm having with a new build.

I just completed a bass pre-amp build and it works great...with one exception:

As I turn down the GAIN, the output is reduced as expected, reaches "0" before full CCW rotation, and then increases at the fully CCW position.

This is a 500k potentiometer which takes input on the 3rd lug, connects to ground on the 1st lug, and sends the output through the wiper (2nd lug).

One other interesting thing to note is that the pot measures approximately 250k across the outer lugs when it's in the circuit.

Here is the schematic:

 

[debrad]

Following some troubleshooting recommendations for a similar post in another forum, I tried shorting the wiper to ground to see if that killed the output. It did when the GAIN knob was turned up but not when turned fully CCW.

Interestingly, shorting the ground lug to ground when the pot was fully CCW actually DID kill the output. As a result of this test, I added a wire between the ground lug of the GAIN pot and the ground lug on the adjacent output jack and now the GAIN pot functions as it should: LOADS of gain on tap as you turn CW, but ZERO output when turned fully CCW.

What would be causing the bleed from the GAIN's ground lug back into the audio output...and why is it there when turned 100% CCW but not at 90-99% CCW? Is this a sign that the potentiometer's track is damaged and allowing the wiper to find some connection to the 3rd lug when fully CCW?

 

[BuddytheReow]

Sound like a bad pot if you ask me. Or it could be a cold solder joint.

 

[Gordo]

^
+1