A&H GL2800: Submaster Ground Hum

[StradivariusBone]

So on this console I've recently noticed that two submasters will generate ground hum seemingly independent of what's patched through them (4 and 7 if that makes any difference). We use submasters heavily to group a 7-9 piece band plus spoken word and all the other typical church service stuff into a user-friendly mix, but I can't figure out why only two specific sub outs would generate noise. Is this a typical failure? I tried unpatching everything from the subs and seeing if it was one channel causing it and nothing was suspect. It seems very much linked to the submasters themselves.

The board is 10-ish years old and there is some noise when moving certain faders as I've seen with other boards as they age gracefully or not. The building itself has some grounding issues and we're accustomed to a modicum of hum due to how they configured power for the audio system, but this is very much linked to these submasters and not much else seems to affect it.

 

[FMEng]

The internal grounding of sections of analog consoles is complex. Depending upon how the GL2800 is constructed, all it would take to have a grounding problem would be a loose screw to the chassis or a copper buss, or a little oxidation on a ribbon cable connector. Some makers use heavy wire and slip-on connectors that get loose or dirty. Another brand grounds to the chassis via pot shafts, which can loosen a little. Clean connections with DeoxIT D5, then follow with DeoxIT Gold preservative.

I remember taking delivery of a high end, analog console. I opened it up to set some jumpers and discovered a missing screw for bonding a ground buss to a channel module. It would have led to trouble eventually.