Mechanical variable resistors in audio paths: In practical audio circuits, which audible symptom often reveals a worn or dirty potentiometer (mechanically variable resistor)?

Introduction / Context:
Potentiometers (pots) are widely used as volume and tone controls. Mechanical wear, dust, and oxidation can degrade contact quality between the wiper and resistive track, injecting noise into the audio signal. Recognizing the symptom helps target maintenance like cleaning or replacement.

Given Data / Assumptions:

• A standard carbon or cermet track potentiometer used in an analog audio path.
• Signal present while the knob is being adjusted.
• Room-temperature operation; no exotic failures assumed.

Concept / Approach:

A noisy, intermittent wiper contact modulates the signal and produces a characteristic crackle or “scratchy” noise, especially while the control is being rotated or slid. The noise is due to contact resistance fluctuations and microscopic arcing across contaminated or oxidized surfaces.

Step-by-Step Solution:

Verification / Alternative check:

Cleaning with contact cleaner usually improves or eliminates the noise. Measuring resistance while moving the shaft often shows erratic readings. Replacing the potentiometer resolves persistent issues due to track wear.

Why Other Options Are Wrong:

• Lack of bass or excessive treble: typically due to EQ or coupling capacitor issues, not pot scratchiness.
• Variable volume: expected behavior of a functioning potentiometer, not necessarily a fault.
• Loss of stereo separation: usually a balance/pan or channel wiring issue.

Common Pitfalls:

• Confusing dirty switch contacts with pot noise; both can crackle, but pot noise correlates with knob motion.
• Using inappropriate lubricants that attract dust and worsen the problem.

Final Answer:

scratchy noise