Definitely not a ground loop hum, as that would be from the speakers. Here's a good read about transformer hum,
http://www.altavistaaudio.com/hum.html#trafo
Also, here is an owners manual for the 5503,
http://www.users.interport.net/a/d/adcom/manuals/gfa5503.html
The troubleshooting section has a little about amplifier hum. The manual also states that the amplifier is OK to use with 4 ohm speakers, and is stable to 2 ohms and less, so the 683's should not be a problem.
Swampwalker, sorry to disagree, but continuous power is RMS power. Adcom inserts the word "average" because in the manual they make a reference to the FTC, and a lot of times in the FTC documents, the terminology "continuous average power" was used to explain the standard. Most of the time it is just stated as "continuous power".
This series of Adcom amps do have a history of running hot, but what is too hot may be hard to determine without putting it on a test bench. Maybe Adcom tech support could help with these issues.
http://www.altavistaaudio.com/hum.html#trafo
Also, here is an owners manual for the 5503,
http://www.users.interport.net/a/d/adcom/manuals/gfa5503.html
The troubleshooting section has a little about amplifier hum. The manual also states that the amplifier is OK to use with 4 ohm speakers, and is stable to 2 ohms and less, so the 683's should not be a problem.
Swampwalker, sorry to disagree, but continuous power is RMS power. Adcom inserts the word "average" because in the manual they make a reference to the FTC, and a lot of times in the FTC documents, the terminology "continuous average power" was used to explain the standard. Most of the time it is just stated as "continuous power".
This series of Adcom amps do have a history of running hot, but what is too hot may be hard to determine without putting it on a test bench. Maybe Adcom tech support could help with these issues.