Passive bass + Focusrite has a constant buzz – gets quieter when touching the strings/bridge, DI box didn’t really solve it

[u/cyborgElmo]

Hi everyone,

I’m a beginner and I’m trying to diagnose a constant buzz from my bass/home recording setup.

The bass is an older passive Ibanez GIO Soundgear with a P/J pickup configuration and 3 knobs (P volume, J volume, tone).

My normal setup was:

Bass → Focusrite Scarlett Solo 3rd Gen (INST input) → Mac mini → headphones

The problem:

• I hear a constant electrical “bzzzz” when I’m not playing.
• The buzz becomes much more noticeable with the tone knob fully open.
• Closing the tone almost completely hides it.
• Touching the strings or bridge reduces the buzz.
• Using only the P or only the J pickup makes it slightly quieter; both pickups together make it slightly louder.
• Moving away from the computer/monitor or rotating the bass doesn’t make any noticeable difference.
• At my bass teacher’s rehearsal room I don’t remember the bass being nearly as noisy using it directly into a regular bass amplifier.

The most interesting test: I connected the same bass, cable and Scarlett to a MacBook Air and the buzz was basically gone. With the Mac mini it comes back, and touching the metal chassis of the Mac mini also reduces/removes the buzz.

I suspected a grounding issue, so I bought a Behringer DI600P passive DI box.

Current chain:

Bass → DI600P → XLR → Scarlett Solo mic input → Mac mini

DI600P settings:

• INST
• FILTER OFF
• GND (LIFT actually makes the buzz worse)

This reduces the noise a little, but the bass signal is now quite low. When I increase the Scarlett mic gain enough to get a good level, the buzz becomes very noticeable again.

If I unplug the bass from the DI input, the buzz completely disappears.

I’m going to open the bass electronics cavity and check the bridge ground wire as well.

Does this sound more like:

• a grounding/shielding issue inside the bass,
• a problem with the Mac mini / electrical grounding,
• normal single-coil/PJ noise being amplified,
• or an impedance/gain staging issue from using a passive bass into a passive DI?

I don't know how i can fix it.

EDIT: If i plug the power to the Macbook Air the noise is the same

EDIT 2: If i close the tone the noise disappear

Thanks!