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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
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almarg
9,670 posts
 
To check for a short in the wiring you have to disconnect both the speakers and the amplifier, so that the wires are connected to nothing at either end.

Then set the meter to R x 1, and touch the two leads of the meter to each other. There should be a knob on the meter, perhaps on the side, that is called "ohms adjust" or something like that. While the two leads of the meter are touching each other, adjust the knob so that the meter reads 0 ohms.

Then touch one lead of the meter to either the + or the - conductor of one of the speaker wire pairs, and touch the other lead of the meter to the other conductor in that pair. It doesn't matter which end of the cable you do that on. The meter pointer should not move at all, and should indicate approximately infinity ohms, or whatever it indicates when the meter is not connected to anything. (There is probably a separate screw-type adjustment on the meter to set the reading to infinity when it is not connected to anything).

Making a meaningful reading while the speakers are connected can be tricky, and is probably impossible using the R x 1K or R x 10 scales, because on those scales you won't be able to distinguish between the speaker's resistance and a short. Using one of the higher scales, such as R x 1K, also creates the possibility that you are reading your body's resistance, if your fingers are in contact with the metal part of the test leads or the wires when you make the measurement.

Regards,
-- Al
metro04
222 posts
 
It sounds like only *one* of the speaker wire conductors is shorted to house/earth ground within the wall (either conductor) and would cause the problems he's describing depending how his amps are configured. Note how the Kenwood works fine on the suspect wires. This grounding issue could affect other components feeding the amp via the interconnects and shared AC grounding, thus potentially shorting input circuits.

If the speaker cables were terminated in metal wall boxes (or not), disconnect the speakers and amp from the wires, connect your meter to one of wire conductors and the other meter lead to the nearest AC out metal cover screw, or the outlet's "ground" contact. Note any meter shorting, then try the wire's other conductor to outlet's "ground" conductor. If wall outlets are to far away, use a 3-prong extension cord and repeat the steps above to the cord's "ground", or any other grounded metal piping or electrical conduit.
riasillo OP
12 posts
 
Ding ding ding...
we have a winner.

Thanks to Al and MEtro04
I calibrated meter as per Als instructions, and touched the wires to AC cover screw as per metro.
red wire, the one that arked, reads 0 resistance..
black lead didn't move.

So red wire got nailed or screwed in wall.
and based on what metro said, that could have shorted my receiver input circuits... unreal...

live and learn, should have hired a better low voltage guy that properly protected the wires in the wall... I didn't like the way he left them exposed around studs... I should have covered them with some cheap metal strike plates...or he should have...that guy is getting reamed on Yelp.
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almarg
9,670 posts
 
Metro gets all the credit. All I did was to describe how to use the meter.

Glad the mystery is solved!

Regards,
-- Al
jea48
4,425 posts
 
I found this thread interesting to read.

Riasillo,

I do have a few questions, curiosity I guess.....

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.
Riasillo
Electrician did his job?

What all did the electrician do?

New branch circuits? How many?
Extend from existing wiring only?
Type of wiring used? NM-B, Romex? Conduit and wire?
How did the electrical pass through the studs?
Please be specific as possible.


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.
Riasillo

"plugged into different outlets with nothing else attached, volume on zero = very loud buzz... very loud..."

Outlets on the same 120V circuit?
Outlets on different 120V circuits?


I calibrated meter as per Als instructions, and touched the wires to AC cover screw as per metro.
red wire, the one that arked, reads 0 resistance..
black lead didn't move.

Are the wall studs metal?
A drywall screw through the jacket of the speaker cable and piercing the red conductor wire would indeed bond the wire to the metal stud.

Assuming the electrical receptacle outlet box/es are metal this would bond the safety equipment branch circuit/s equipment grounding conductor to the metal studs.
Thus the shorted reading you got with your meter.

live and learn, should have hired a better low voltage guy that properly protected the wires in the wall... I didn't like the way he left them exposed around studs... I should have covered them with some cheap metal strike plates...or he should have..
Holes for cables, wires, that pass through studs should be back from the surface of the studs
1 3/4" to protect the cable from physical damage from a drywall screw.

Where studs are notched or the holes for cables are less than 1 3/4" from the surface a steel plate of at least 1/16" shall cover cable, wire, to protect the cable from damage of a drywall screw.

Cables, wires, that pass through holes in metal studs shall be protected from damage by bushings or the like.


So red wire got nailed or screwed in wall.
and based on what metro said, that could have shorted my receiver input circuits... unreal...
07-22-12: Riasillo


That still puzzles me...... Output of a power amp ya....

Damage a separate connected preamp? Maybe Al could expand on that.....

One thing for sure I would not connect any new equipment up until everything including the electrical power is checked out. At the very least pick up one of these and check each receptacle for correct wiring and proper AC polarity.
Jim
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