Picked up the brandnew RB-1092 today.
At home I unpacked the unit and put it into my rack. Then I made sure that all RCA and speaker cables were correctly connected. Finally, I attempted to plug in the included power cord and was very surprised. Why?
Well, I could not plug the end of the power cord into the AC connector on the back of the amp. At closer inspection I saw the problem. The amp`s AC connector had a third "pin" for ground connection! The power cord only had two "holes" such that it did not fit mechanically.
I was quite "pissed" at that moment - not because of the useless power cord that Rotel had included, but rather because I knew that in the past I`ve always had an audible ground loop problem (cable TV + higher current appliances with extra ground connection = humming / buzzing). For instance the RB-1080 and RB-1090 are grounded via the power cord and thus produced unmistakeably a humming / buzzing in my system. That is why I ultimately bought an RMB-1075 which is not grounded via the power cord.
Up to today I was absolutely convinced that the RB-1092 is NOT grounded via the power connector. Look here:
http://www.rotel.com/content/backpan.../rb1092-bk.pdf
http://www.florian-wopfner.com/pictu...omehifi_91.jpg
http://www.hometheaterhifi.com/volum...rear-panel.jpg
Obviously Rotel changed this issue over time, or maybe all European models need an extra grounding due to some restrictions / directives? The drawings in my RB-1092 manual clearly show that the AC connector has a third "pin", so this is different from the back panel drawing(s) provided by the international Rotel website.
Nevertheless, I powered up the amp using a PC power supply cord and guess what?!? No buzzing, no humming at all! What is going on here? I have no explanation for that. But believe me, I´m very glad to have no humming / buzzing at all, even if I crank up the volume to insane levels. Any ideas?
Maybe during the manufacturing process Rotel simply used parts that were currently available - in this case an AC connector with a third "pin" for grounding. Unfortunately I cannot see whether there actually is an electrical connection / wire / etc. going from the AC connector´s ground "pin" to another section of the amp...