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Old 9th September 2007, 05:10 PM   #1
lews is offline lews  United States
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Default Shocked by Subwoofer thru Speaker Outlets of Main Amp

I have a JBL PSW1000 powered subwoofer. I just finished wiring a whole house audio system and when I hooked up the subwoofer using coaxial cables with rca hook ups on the end into my Denon AVR-887, amp, my home theater speaker connectors became line voltage. I've pulled the back off the sub woofer and nothing seems amiss, like a paper clip or something bridging a connection. No evidence of any problem. Any ideas?

I had this in Subwoofer but I've isolated it to the subwoofer amp. There is 110 voltage from the RCA inputs for connection to the regular amp. I noticed this morning that the fuse that in it is rated high amp than it should be I can't imagine that causing this problem.

Also I see that the wider spade of the plug (to the wall outlet), which I thought was the ground spade is the wire that unioned to the transformer wire at the circuit board. Is that right? (though it doesn't look like anyone re-soldiered it.
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Old 9th September 2007, 10:21 PM   #2
jaycee is offline jaycee  United Kingdom
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Does the subwoofer have a safety ground (3 pin plug) ? If not.. check for continuity between the transformer primary and secondary. There is no way in hell you should have line voltage on the RCA's

I guess this is a no brainer, but I'll say it anyway - do NOT use the sub until you figure out wtf is wrong!
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Old 9th September 2007, 10:45 PM   #3
Nordic is offline Nordic  South Africa
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I had a new shock experience tonight.. well I burned at the same time too...the damn thing was pipeing hot. This through the caseing of one of those long rectangular white ceramic resistors, nothing serious though, but I thought that stuff was isolated...
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Old 10th September 2007, 11:04 AM   #4
lews is offline lews  United States
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Thanks Jaycee. The Sub doesn't have a 3 prong plug, just the grounding type 2 prong. It does seem like it's not being grounded somehow.
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Old 10th September 2007, 11:13 AM   #5
jaycee is offline jaycee  United Kingdom
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Well it is normal that it has no safety ground especially if it has no metal casing.. but if you are getting line voltage on the connectors then that means that the transformer's insulation between windings has failed.

I would either get this repaired professionally, or junk it.
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Old 10th September 2007, 11:17 AM   #6
lews is offline lews  United States
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I see. I wonder why the transformer does burn or melt or spark or something if the winding's insulation are compromised. So in other words, you think the insulation (the plastic covering of the little wires that wrap around to form the transformer) has failed somewhere and voltage is leaking from the windings?
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Old 10th September 2007, 03:11 PM   #7
AndrewT is online now AndrewT  Scotland
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Quote:
Also I see that the wider spade of the plug (to the wall outlet), which I thought was the ground spade is the wire that unioned to the transformer wire at the circuit board. Is that right? (though it doesn't look like anyone re-soldiered it.
Is this saying that mains is connected to the low voltage side?
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Old 10th September 2007, 03:43 PM   #8
lews is offline lews  United States
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No Andrew. At least I don't think so. I was just pointing out that when I took the back panel off to see if there was any noticable short of some kind, I traced the power wire and the squared spade plug (which I thought was supposed to be the neutral) was connected to the transformer in the amp of the subwoofer. That seemed strange.
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Old 10th September 2007, 05:53 PM   #9
jaycee is offline jaycee  United Kingdom
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The hot and neutral both connect to the transformer. Typically the hot wire should go via a switch and a fuse.

I can't think of another reason for line voltage appearing on your RCA jacks. This definitely needs looking at properly.

I assume the rest of the system operates normally without the sub being connected? Does the Denon amp have a 2 or 3 pinned plug?
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Old 10th September 2007, 11:57 PM   #10
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Are you sure you are describing the symptons properly? I have no problem believing that the sub out RCA's have AC on them, or that the receiver speaker outs have AC on them, but that putting AC into the receiver and getting AC out on the speaker connections without something frying seems far fetched to me.
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