Channels 2 and 20: what we know and what's next
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The symptom
Channels 2 and 20 in the Live Room are buzzing.
On the Trident and the Allen & Heath, with no mic plugged in.
What tonight's tests proved
Tonight's tests: the buzz needs the Cat6 link and the ch 2 XLR into the GX.
It survives the GX off, SLink pulled, SQ-7 off, and a new XLR and Cat6.
A source plugged straight into the GX is clean.
Lights off made it quieter, but it didn't go away.
The system
One passive Radial Catapult Y-split feeds two consoles in two rooms.
Their grounds float apart. The isolated-ground outlets don't reach an earth electrode.
Radial says to use transformer modules for this.
Best read
Our best read, moderate confidence: a mains voltage between the two rooms' grounds.
It rides the ch 2 and 20 pairs, and something on those channels makes it buzz.
The lights push that voltage up.
The bad channels move
The GX4816 is now the weakest suspect. A box fault can't move channels.
And this buzz moved. After the 2024 install, it was channels 9 and 10.
Top suspects
Top suspects: Trident phantom on for 2 and 20, and the hand-wired screw terminals.
Next steps
Next steps, in order.
Phantom off on ch 2, both desks. Thirty seconds.
A battery recorder in place of the GX.
Swap Catapult out 2 into GX input 1.
Meter AC volts chassis to chassis, lights on and off.
A temporary 12 AWG bond between the racks.
The permanent fix
The permanent fix: bond the isolated ground and the lighting transformer to the service ground,
and put RX4M transformer modules on the mic-closet leg.
The checklist
The 12-item checklist is at buzz.gregspero.com.
Three answers cut 48 hypotheses to about five.
Narration is a synthetic voice (Kokoro, local TTS), not Greg's. The full 12-item checklist and the evidence behind every claim are on the main page.