Strangest problem I've ever had
Quite interesting indeed. Reading Metro/Al's posts helped me understand how to use a meter to test my new cable runs in our garage which was recently wired up for 5.1 channel in ceiling speakers. To your receiver question, an onkyo 3008 or integra 50.3 are both great receivers at great price points right now. Disclaimer: I'm selling one of each |
jea 48. low voltage guy passed wires around studs in the front between drywall. I questioned it, not knowing any better and he said it was fine because the drywall guys could see it and work around it. Hard lesson learned. also cost me a perfectly good receiver. The electrician came in after, ran electric from existing bank of outlets to spot above fireplace for recessed outlet. His wiring went through studs and was to code as best I can tell... thick yellow wire, that's all I can tell you. I also had everything plugged into APC line conditioner/surge protector. Drilled hole today to outside of house, poked wire through and ran it under edge of house out of site, came back in where the cable wire comes. Problem solved ghetto style, I now have a left speaker run... just cost me a $10 for a masonry bit. Hooked up speakers to onkyo direct, drives them fine... pre outs still shot. Now i'm off to get a new receiver...what to buy, what to buy... I was planning on plugging receiver into amp with nothing connected to receiver. fingers crossed when i plug into AMP that the B&K is fine and there is no buzz... then i will connect cable box to receiver and hopefully speakers sign again... any suggestions on way to test amp other than that? I actually have a little Ipod 1/8jack to RCA adapter. I could plug that into amp and see if amp works right? |
To add more fun, and headaches to it, it sounds like Quietrock 530 has metal inside it. It's under "cutting the panel" on page one. I saw this on a home improvement type of TV show. |
Damage a separate connected preamp? Maybe Al could expand on that.....Hi Jim, Assuming that both components have 3-prong power plugs, as you realize the short would result in a direct connection from the "hot" output terminal of the amp to the chassis of both components. What happens from there is obviously hard to predict without knowing the details of the grounding configurations of the components, and other aspects of their design. But depending on the impedances between the chassis of each component and their circuit grounds, some fraction of the current flowing from the amp’s “hot” output terminal will find its way back to the amp’s circuit ground via the Onkyo receiver (being used as a preamp) and the return conductors of the cables connecting the two components. One conceivable scenario would therefore seem to be that a feedback loop is created from the amplifier's output to some upstream circuit point or points, via the Onkyo's grounds, resulting in a large amplitude oscillation, resulting in damage to circuitry in the Onkyo that is designed to handle low level signals. Or something like that :-) Best regards, -- Al |
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.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.
"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?
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.
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 |
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. |
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. |
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 |
when i test the wires they read no resistance. dial swings from infinity all the way to beyod 0 the second i complete the circuit. same as on the non suspect wires... the wires in the wall are perfect as far as I can tell. is there any way to test them with my kenwood amp running juice to the speakers so that I can see if under power they have a different reading? or a difference between speakers and wires. |
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. |
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 |
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. |
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... |
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 |
You have a shorted wire. You can use an inexpensive multi meter set to ohms to check the resistance between the positive and negative of each speaker wire. If there is no resistance it is shorted (it will either have no connection or a 100% connection, 100% connection = short). Quit using your amps to trouble shoot. Once you know which wire it is then it will need to be fixed or replaced. Better to replace the wire than all your amplifiers. |
