I recently acquired speaker craft 12 channel amp over ebay. The amp starts making annoying low pitched noise as soon as I plug it in and it does not matter where in the house it is plugged in. My other receiver amp combo does not make any noise. It does not change whether speakers are connected or not. Otherwise it works fine for what it is supposed to do. Can someone guide me. I tried to look into ground loop issue but not sure if that is my issue. Thanks
This hum occurs when nothing is connected to the amp, other than the power cord? If it has a large transformer, it seems to have loose windings in the primary section. This isn't necessarily a problem, but it will probably be annoying. Contact Speakercraft about this, but I doubt they have replacement parts like this. If not, and you want to keep it, you may be able to have the transformer repaired/re-wound, but it will cost more than you want to spend on it.
If nothing but the power cord is connected to the amp, a ground loop isn't possible- that occurs when it's connected to another piece of equipment and one of them is on a different circuit and/or phase on the same circuit but resistance is measurable between their respective neutral and/or ground connections.