formica Posted May 25, 2003 Share Posted May 25, 2003 I have recently noticed a hum coming from my Energy ES-12(built in amplifier) subwoofer after I power down my preamplifier. I don't recall it showing this behaviour in the past, and there haven't been any significant system changes prior to hearing the hum. It appears that the "Auto-on/Auto-off" circuit isn't functioning properly... as the built-in amplifier's LED remains green even when there is no signal. The subwoofer is connected via a shielded RCA cable to the LFE output of my Rotel preamplifier and there is no hum when my preamplifier is ON. Here are several tests I have already performed after powering down my preamp: - When I shut the preamp (including unplugging it) the subwoofer hums, and the power amp LED remains "ON" rather than switching to "OFF" - leave the subwoofer plugged in, the hum continues several hours (I got fed up.. so I'm not sure for how long - unplugging it's RCA input results in a slightly different hum, but sub amplifier LED stays "ON" and the subwoofer amp still remains powered up - If I unplug the subwoofer for a period (like overnight) it will not hum when I plug it back in. At this point, the amplifier is "OFF" as it doesn't see a signal as it's supposed to. Have you heard of similar problems? Is there a "sensitivity" switch that may need adjusting or a relay that may need cleaning? Thanks... Rob B. Quote Link to comment Share on other sites More sharing options...
BBB Posted May 26, 2003 Share Posted May 26, 2003 It can't hurt to try a new RCA cable. That fixed a hum I had with my sub under the same circumstances as you described. My subwoofer will hum IF I cut off all the power in the system except for the subwoofer amp but does NOT hum when the receiver is left in standby instead of POWER-OFF. Also check your polarity switch and maybe get a three to two prong adapter if the subs power cord is three pronged. Something may have changed at your electrical outlet. Try switching that too by running an extension cord to another part of the house. Good Luck. Quote Link to comment Share on other sites More sharing options...
TheEAR Posted May 26, 2003 Share Posted May 26, 2003 "Subwoofer doesn't power off..." Ok ...pull the AC plug! Wabbit could be correct,try good shielded cable. Quote Link to comment Share on other sites More sharing options...
formica Posted May 26, 2003 Author Share Posted May 26, 2003 I will do some more tests including the RCA and the extension cord, and see if either helps... I'll post what i find. When i power down my preamp with it's power button, it stays in "stand-by" ... but the woofer hums even if i unplug the preamp. Thanks... Rob PS: it already has a 2 prong plug... Quote Link to comment Share on other sites More sharing options...
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