The HRS-10, HRS-8 and HRS-12 amplifiers are practically identical, and they share six small, weak electrolytic capacitors in the power supply board. They are located in pairs. The cheap, original capacitors dry out after several years, and cause the hum. Upgrading them to high quality (e.g., Panasonic) low-ESR capacitors will typically solve the hum, and will last longer than the originals used by Sunfire.
Take a look at my video to get an idea of how to open the Sunfire MK2 properly and also get an idea what sort of dangers live inside the box. There are several fixes that have worked for me in the past and one that is not working now.
It sounds like you are describing an earth loop problem. I won't go into detail in this post, but try an isolation test first. disconnect everything from the reciever except the sub and try connecting say a BATTERY powered mp3 player or cd player to minimise connections to the electrical mains earth. you could also isolate things by taking your sub to a friend's house and trying it on their system. If it is an earth loop use a process of elimination to find out which two pieces of equipment causes the earth loop. then apply filtering. you can buy earth loop isolation transformers for about AU$26 and I've used one on my sub myself. Theyhave RCA (phono)plugs on each end and they connect inline with the signal cable to the sub amp.
as for the thumping sound it might be the speaker protection circuitry cutting off the amp to protect the subwoofer speaker from damaged. This might be triggered if the earth loop sound is causing the sub amp to overload and clip.
Failing this there might be a dried out overheated electro capacitor in the amp circuit causing the hum. Hav a chat to your local electronics person, who should be able to spot it! Hope this puts you on the right track Happy Hunting!
Hi, I had the same problem as this, the fix was quite simple and the hum never came back.
If you pull straight out on the sub amp's volume knob it will slide off, then to fix the hum, tighten the nut that is behind the knob on the potentiometer and your hum should go away. My hum went away and never came back after this fix. Hope this helps you.
Easy. Your home theatre amp will have a sub or LFE output ( RCA plug ). You simply connect this output to the input ( usually the left side, or use a Y splitter and use left and right inputs, or the LFE input if your sub has it ). Then, you must turn the sub on in your recievers setup menu, and your sub should work.