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Discussion Starter #1
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
 

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Does not sound like a ground loop (that would usually be a buzzing through the speakers). Could be a defective amp (you never know if you buy it used from a stranger). But try plugging the amp into a good quality power conditioner.
 

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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.
 

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Discussion Starter #4
Yes it happens as soon as I plug it in. It does have large transformed it's 100 watt per channel 12 channel amp
 

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The seller was a gem, he issued a full refund. I am going to try fixing it if I could or sell it for parts and send him the proceeds.
 

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The seller was a gem, he issued a full refund. I am going to try fixing it if I could or sell it for parts and send him the proceeds.
It was probably made in China, but there's a company called Mercury Magnetics and they sell/rewind transformers of many types. A lot of their rewinding business comes from people with vintage guitar amps and audio equipment (the original transformers have a huge affect on the value of vintage equipment) but they may be able to help with this. Look for part numbers on the original transformer- you may be able to cross-reference to a supplier for that part. SpeakerCraft may even be able to help.

IF YOU DECIDE TO REPAIR THIS, MAKE SURE THE POWER SUPPLY CAPS ARE DISCHARGED BEFORE TOUCHING ANYTHING INSIDE!!!!!!!!!!!!!!!!!!
 
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