AV2 and sub woofer and radio interefernce

Posted by: webrat11 on 02 December 2003

Can anyone help with this problem please.

I have a MJ Acoustics Reference 100 sub-woofer in my Naim AV system. It is attached to the AV2 processor high quality QED sub woofer cable into the dedicated sub-woofer output.

The problem is that if I set the frequency contour on the woofer to LFE I get a pronounced (loud) hum when the Low Level Gain is set to about 10'o'clock onwards (1/3rds). At about 2'o'clock onwards (2/3rds) I am getting some sort of radio reception! (sounds foreign - could be short wave?). I have always had some hum but have only just started hearing the radio reception. If I manually set the crossover I get significantly less hum and no radio reception but I need a much higher gain to get the same level of bass
extension.

I really want to set the woofer to LFE but how do I eliminate the hum and radio intereference? Any and all ideas welcomed? WHy do I get interference only when the woofer is set to LFE?

If I unplug the cable from the Naim AV2 the sub-woofer is quiet so I presume the AV is generating the signal and it is not therefore a sub-woofer fault or the cable acting as an ariel.

TIA. Ian

Naim AV2
Naim NAPV175
Naim NAP180
Naim NAP140
2 pairs Kef 104/2s
1 pair Kef 2QDs
Harmon Kardon DVD30
Panny 6.
Posted on: 27 February 2004 by webrat11
Just to complete the story and to record the solution in case anyone else experiences a similar problem. Thanks to the support of the Naim team in Salisbury (thank you Robin) the problem has been solved.

The subwoofer hum and a lesser hum through my other speakers (attached to my 180 and 140) was caused by Radio Frequency Interference (RFI) generated by my plasma screen and picked up by the interconnects. The NPV 175 was not affected. New (black)interconnects reduced the speaker hum to an almost inaudible level. A 8w 20ohm resistor soldered into the AV2 end of the subwoofer cable sorted out the subwoofer.

Apparently because Plasma screens are classified as PC or other equipment rather than a TV they are allowed to generate rather excessive levels of RFI. Radio Hams are non to pleased evidently.