djcheung Posted May 30, 2017 Report Share Posted May 30, 2017 Hi all, Just acquired the C-06 and P-10 last week. On first power on, I have noticed that it hums a bit on both channels and the right channel is louder than the left with just the speakers connected. Otherwise it sounds reasonably good. My 3as sound a bit fuller and more solid. When the volume is turned up, the hum is not noticeable. On opening the cover on the P-10 to have a peek, I have noticed that it has been opened before with some screws missing and the support bracket for the RCA inputs missing. I have also noticed that one of the solder pad on the speaker connection board has been lifted off the circuit board, luckily the solder is still holding firm. My skill is limited only on 'like for like' parts replacement. Can this humming noise be fixed or I should just play it and enjoy ? Does anybody here have one of these ? Best regards, David. Link to comment Share on other sites More sharing options...
ar_pro Posted May 30, 2017 Report Share Posted May 30, 2017 Hum at idle - especially in both channels - can be due to a power supply issue, usually aged/defective filter capacitors or diodes. You can download a service manual for the P-10 at the HiFi Engine website: https://www.hifiengine.com/manual_library/acoustic-research/p-10.shtml Honestly, I wouldn't run the risk of damaging your AR-3a speakers with a dicey power amplifier - a lot can go wrong. It's a nice amplifier, and certainly worth servicing for proper performance. Link to comment Share on other sites More sharing options...
djcheung Posted May 30, 2017 Author Report Share Posted May 30, 2017 Thanks ar_pro, I have a copy of the service manual. But not being electronically trained, I wouldn't even know where to start. I have been trying to find a shop locally here in Cambridge,UK but without success. A good shop is quite hard to come by in this corner of the world! I will keep looking. David. Link to comment Share on other sites More sharing options...
ar_pro Posted May 30, 2017 Report Share Posted May 30, 2017 How about this guy: http://www.londonsound.org/repairs.htm His shop lists Acoustic Research as one of the products he handles. Good luck! Link to comment Share on other sites More sharing options...
djcheung Posted May 31, 2017 Author Report Share Posted May 31, 2017 Thanks ar_pro, I just had another quick test to see where the hum is coming from. 1. I connected the speakers with no inputs connected. Power on, only hear hum from within the equipment. No hums from the speakers. 2. Connect the power amp to the preamp with the preamp not connected to anything and not plugged in to the power socket. No hums 3. Connect the power amp to the preamp with the preamp not connected to anything but now connected to the power socket but with power button off - HUMS Any suggestions ? I know this is difficult without seeing the unit physically. Best regards, David. Link to comment Share on other sites More sharing options...
djcheung Posted June 6, 2017 Author Report Share Posted June 6, 2017 I think I have identified the hum is a ground loop hum. I can remove the earth connection on the preamp and the hum disappeared but don't think that is too safe. Any suggestions? Link to comment Share on other sites More sharing options...
mike tarelli Posted June 6, 2017 Report Share Posted June 6, 2017 Hi David, To avoid earth loops I think its usual to earth the pre amp and disconnect the earth on anything connected to it. They are earthed through their leads to the pre amp. Mike Link to comment Share on other sites More sharing options...
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