Hi all,
I’m looking for some help diagnosing an issue with an Allen & Heath GL2400-32
Symptoms:
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All output meters (L/R and M) are pegged at peak with no signal present.
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Severe buzzing noise (like motorboating / robotic synth tone) occurs on all outputs (Mains, Auxes, Monitor) when connected to a powered speaker.
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Buzz level increases with fader raise, even with all inputs muted.
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Slight buzz is present even when all outputs are muted, and gets loud when the associated output is unmuted.
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Happens across all outputs, not isolated to a specific bus or aux.
Tests Performed:
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Verified PSU voltages at the board: +15V, -15V, +48V, and +10V all present and within expected range.
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Disconnected and reseated all connectors related to the four Aux buses and three main volume outputs (L, R, M).
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No change in behavior after doing this.
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No obvious visual issues on initial inspection — no burned components, leaking caps, or cracked joints.
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I’ve isolated the board from external input — no signal is present on input, but the buzzing persists as long as an output is connected.
Next Steps Planned:
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Disconnecting the channel ribbons one by one to see if one input strip is backfeeding something malformed into the bus.
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Looking closer at the master section and bus summing.
I’m an experienced amp tech and pedal builder, so I’m comfortable with analog circuitry, probing, and signal tracing. This is my first dive into a live mixing console of this scale, but I’m confident with component-level work.
Request:
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Has anyone seen this specific behavior before?
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Could this be a bus rail short or something in the summing amp section?
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Any known failure points in the GL2400 series I should check first?
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Are there service manuals or schematics floating around for the GL2400-32?
Here’s a video demo of the issue:
Appreciate any help or pointers before I dig deeper!
Thanks,
Kenny
[KR SOUND]