How to spot noisy preamps and scratchy pots on a used mixer

1 day ago
3 min read

Myth: A mixer that powers on is fine

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Many people assume that if a mixer lights up and routes audio, it has no hidden faults. **Power alone doesn't tell you about worn pots or noisy preamps.** Those faults show up only when you use the controls and listen carefully.

Reality: Small sounds in silence matter

Turn channels up one at a time. Use headphones or monitor speakers. **Listen for hiss, crackle, or jumps in volume** when you move the gain, EQ, or pan. A steady hum at low gain or sudden spikes when you nudge a knob are red flags.

Myth: Pots only get scratchy from dust

It's common to hear that dirt is the only cause of scratchy pots. That can be true, but it is not the whole story. **Wear, oil breakdown, and corrosion** inside the pot can make noise even if the surface looks clean.

Reality: Movement reveals internal faults

Rotate each pot through its full travel slowly while playing a steady tone. Do this for gain, master, aux sends, and any trim pots. **If the sound flakes, crackles, or cuts out at certain points**, the track inside the pot is worn or dirty. A quick spray cleaner might help, but repeated noise usually means replacement is needed.

Myth: All preamp hiss is normal on older mixers

You might be told that older units always hiss and that you must accept it. That is only partly true. **A little noise is normal, but sudden jumps and uneven hiss are not.** The level and texture of hiss tell you if the preamp is merely warm or failing.

Reality: Compare channels and line-ins

Plug a mic into one channel and an identical mic into another. Keep gains equal. **If one channel is much noisier, the preamp on that channel is suspect.** Also test the same input using a line-level source. If the noise goes away on line input, the problem is likely the mic preamp stage.

Myth: Scratchy faders are easy to hide in a gig

Some sellers say "you can just leave it and ride the fader" like it's a workable fix. That is risky. **Scratchy faders make mixes unreliable and can ruin a set.** Live sound needs smooth, predictable controls.

Reality: Test faders under movement and load

Move each fader up and down while playing music and while sending to an aux (if the board routes post-fader). **Listen for static, channel jumps, or momentary loss of signal.** A fader that thunks or skips is a sign of physical wear or dirt.

Myth: If pots are scratchy, the whole board must be junk

People often think one bad pot means the mixer is scrap. That is too black-and-white. **Sometimes a single pot or channel module is all that's bad.** Replacements or repairs can be affordable compared with buying a new unit.

Reality: Repairs can be simple and cost-effective

Check how modular the mixer is. If the board uses channel strips or replaceable pots, you can often fix one part without replacing the whole mixer. **Ask about parts availability and repair cost before you buy.** Factor that into your offer.

Fast check before you pay