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Strangest problem I've ever had

Ok.
Bought a house.
Paid guy to run wires through the wall for a 3 point system.(too many obstacles & $$ for surround)

Have walls patched and painted. Moved in.
unpacked My Pride and joy B&K 7 channel.

system includes Onkyo sr705, HDMI from cable box to onkyo, connected polk rti12 speakers to B&K with bananas.

turned it all on, incredibly loud buzz snap crackle pop, onkyo shuts off and burnt wire smell fills the air.

Trouble shoot. all wires were hooked up right.
connect speaker wires directly to onkyo one at a time. the farthest one away in the wall shuts off onkyo. I run a new wire on the floor to that speaker. It works.

So it's the wire in the wall, it got compromised some how when the patched wall..?
not so fast.
I have an old kenwood preamp and adcom 2 channel. I hook up "bad wires" in wall directly to kenwood and the speaker works fine. how can bad wire short one amp and work on another???

So then I hook up an RCA pre out channel from the onkyo to the adcom and the same very loud buzz comes on the good speakers.

So the Pre outs on the Onkyo are definitely sending the buzz to both amps... can we assume the Onkyo pre outs are shot.
Million dollar question. Why does the line in the wall short out the onkyo but work on my old kenwood.

So then I test a good speaker line on each output on the onkyo. They all work... I'm doing this with it on, even though I know better... Then I went to connect the bad wires to the onkyo again and I got a spark when I connected the red wire...I've never seen a speaker wire spark off a preamp????!!!!
i've never seen that. I'm going to get a meter and read the line resistance and see if there is a difference with the bad wire.
My concern... If I go get a new preamp, can the bad speaker wire blow it again.
Makes no sense.
That wire was hooked up through the B&K. B&K was connected via RCAs to Onkyo. How could it short the onkyo going back through the B&K.
do we think the onkyo was toasted in the move. If so, how is it that just that 1 line shorts the onkyo and none of the others... too strange
riasillo
almarg's avatar
almarg
9,670 posts
 
Yes, that is a head-scratcher indeed. Some questions and comments:

1)In my experience as an electrical engineer, often when inconsistent and puzzling symptoms are present it turns out either that the problem is intermittent, or there are two different problems that are present at the same time. Not sure what that may specifically suggest in this case, but those are possibilities that should be kept in mind.

2)What kind of speaker cables are you using? Are they by any chance cables like Goertz or Polk Cobra, that have extremely high capacitance which can cause some amplifiers to oscillate?

3)Have you determined where the burning smell was coming from? Was it coming from the speaker wiring, the speaker, the Onkyo, or elsewhere?

Regards,
-- Al
riasillo OP
12 posts
 
Thanks for responses.

On way to get a meter to test wires.
I do think the wire got compromised . Low volatage guy did his thing, then electrician did his, then sheet rock guys. Someone probably hit that wire...but I also think the onkyo pre outs are toasted.

If I hook up speaker to power amp and receiver to either of my amps from any pre out, plugged into different outlets with nothing else attached, volume on zero = very loud buzz... very loud... none of the pre outs are working right.independent of anything else attached.

like al said, it would seem there are 2 different problems present. I think the burnt smell came from the onkyo.

I used in the wall double coated monocable 12 aug.
I just can't wrap my head around a short in the speaker wire plugged into the power amp, back shorting the onkyo plugged into the Power amp with RCAs. is that possible? wouldn't you expect the power amp to go if anything?
also, if there is a short in the wire, how could the kenwood receiver work on that line. is that possible, like if that receiver doesn't have the same level of circuit protection...
theo's avatar
theo
2,706 posts
 
I would say that Onkyo is just more sensative than the Kenwood. But you do have a short. Didn't you put in metal screw plates on the face of the studs before you drywalled?
If not then yes it is most likely a screw thru a wire. Unfortunatley the only fix is to remove the drywall screws which means more expense. Bummer.
riasillo OP
12 posts
 
so i tested with meter.
I dont have much experience with meters, tested some circuits at first job but it was always under direction.

Both set ups respond the same.
i had to crank up ohm resistance on meter to get a reading. First time around both pinged beyond zero...so cranked up resistance dial so reading was right in the middle on good set up. suspect wire, pinged middle.
both respond identical. the wire must be good...right?

2 settings x1k and x10. both respond same
except at x10 setting I hear static from speakers.
?
all other settings detect nada on either.
too bizare...that just that wire shorts out onkyo..

pre out from onkyo still shot..
off to buy a new receiver... open to other suggestions using meter.... anyone that lives in the Los angeles vetura county area and want a suspect onkyo sr705 to tinker with?
thanks to everyone for help
theo's avatar
theo
2,706 posts
 
At this point I would check for the short. Use the "Ohm" section of your meter. This checks for continuity, (briefly: the completion of path of the signal/current between two points)and will confirm if you do or don't have a short. Since you know that your speakerwire in the wall is/was insulated between the negative and positive lead. It should not give you a reading on your Ohm Meter if you touch your meter leads to the both connectors at either end of your speakerwire run.
Don't connect your new receiver to anything till you confirm if you do or don't have a short.
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