My suggestion would be to unplug the plasma tv, blue-ray player, and all power conditioners. Then plug all of the stereo gear directly into the SAME ac outlet, on the dedicated ac circuit, using a power strip to provide enough outlets (preferably one that does not include a surge suppressor).
If that does not help, try the same thing but with the undedicated ac circuit.
If either of those steps eliminate the problem, return to the original configuration one step at a time, to determine what is responsible.
Also, if you have a multimeter, measure the voltage between ac neutral and ac safety ground. I'm wondering if one of the ac runs may be miswired.
Also, if any of the components have two-prong plugs, orient the plug to give you the lowest voltage between chassis and ac safety ground, measuring while no interconnects are connected to the component.
Finally, could you describe the exact configuration that was being used when you tried the equipment at your friend's house and heard similar symptoms? That may help to rule some things out with greater certainty.
Hope that helps,
-- Al |
Ok, so it sounds like the plasma, the blue-ray player, and the power conditioner are not responsible.
Behind my other suggestions was the thought that one of your ac runs may be miswired, which at some point in the past may have damaged a part such as a line-filter capacitor in one of the components. Perhaps after 20 minutes of operation it then breaks down further, due to either heat or exposure to voltage, resulting in a leakage path between ac and chassis (which is usually common with signal ground, and in the case of components that have a 3-prong plug, is also common with ac safety ground).
Interconnects for single-ended (rca) interfaces tie the chassis of the connected components together electrically, so disconnecting and reconnecting them would conceivably have a relation to either stored charge or voltage stresses involving capacitance that is in electrical proximity to the ac line.
Also, it's very conceivable to me that a compromised line filter capacitor in one of the components would be the kind of thing that would not show up when you sent the components back to the manufacturers for them to check out.
Obviously I can't quite formulate all of this precisely, but the bottom line is that I am suspicious of the ac wiring and grounding, and that it may have caused effects something like these. I'm envisioning not only miswiring in the sense of interchanged connections, but also, perhaps, the possibility that an ac neutral run is open, creating a round-about return path involving interconnects, safety ground, and/or other components.
Regards,
-- Al |
How do I "use a multimeter to check if one of the AC runs is miswired"? And how do I "orient" a two-prong plug? How do I diagnose, and what do I do about, an "open AC neutral run"? Set the multimeter to read ac volts, on a scale that is greater than 120V, such as the scale that many multimeters have that reads 0 to 300VAC. Then for each outlet measure the voltage between hot and neutral, hot and safety ground, and safety ground and neutral. How to orient a two-prong plug, if any, I explained in my earlier post. I'm referring to the fact that if the two prongs are not polarized (i.e., one is not wider than the other), they can be plugged in with two possible orientations. If an ac neutral run is open, it should become apparent by performing the multimeter measurements described immediately above (i.e., you will not see any voltage between hot and neutral). If you don't have a multimeter, or other ac voltmeter, or you don't feel comfortable doing these things, try my other suggestions first and if they don't lead anywhere perhaps you know someone nearby who has experience making electrical measurements. One more possibility occurs to me: Somehow either a large dc offset or an ultrasonic oscillation may be being sent into the speakers (both would be inaudible), causing speaker driver or crossover elements to heat up excessively, producing the audible symptoms after the 20 minute period. Not sure what might cause that, given that you've apparently tried multiple amplifiers, and I'm not sure how a dc offset would affect the midrange-tweeter part of the spectrum, but I thought I'd mention these possibilities in case they trigger some further thoughts. Regards, -- Al |
"Static buildup in capacitors" sounds to me like a non-technical person trying to be technical. Also, static is most severe when humidity is very low, which is the opposite of what you've got in Florida.
In principle there shouldn't be significant dc offset from your power grid, because if you live in a typical house your ac is coming from a transformer on a nearby pole, and transformers don't pass dc. I suppose improper grounding somewhere in the path nearby could result in an offset, but I would think the other possibilities that have been mentioned are more likely (including the ones I suggested about problems in your house wiring).
Regards,
-- Al |
I agree with the AA person. What he is saying is very similar to what I had suggested. When I said that I felt the likelihood of a dc offset situation was minimal I was unaware of the hot transformer and hum symptoms, although I still feel that a wiring problem is more likely to be the cause.
I think it would be best to have a qualified person check out your ac. He should be able to very easily tell if there are any miswired or open connections, along the lines of what I and the AA person suggested, and he should be able to easily measure dc offset with suitable instrumentation.
Regards,
-- Al |
Good suggestions, Lloyd, but I think the possibility should be kept in mind that the root cause of the problem may be the power wiring or delivery, but that root cause may in turn have already damaged a component (such as by causing excess leakage in a capacitor or transformer), which in turn may be what is causing the audible symptoms.
So moving the system elsewhere may not be conclusive. The same symptoms could appear elsewhere (as they apparently did at the friend's house), suggesting a bad component, but a replacement component could subsequently suffer similar damage when exposed to the defective ac source.
In my (extensive) experience as an electrical engineer, whenever problems arose that were very difficult to isolate, and experiments gave conflicting or confusing results, often it turned out that two inter-related problems were present at the same time.
Regards,
-- Al |
Ok, that's great that you have a friend who is an electrician.
An isolation transformer would eliminate problems with dc offsets, assuming the offset was not so severe that it would cause the transformer itself to overheat or have other problems. But I don't think an isolation transformer would be relevant to the other possible causes that have been mentioned.
Re UncleJeff's comment, yes, undoubtedly something is misbehaving after warming up for 20 minutes or so. But considering the history of similar problems with multiple components over the years, it would seem that something else (such as problems with the ac wiring or grounding) is causing damage to some part or parts, and that damage is in turn resulting in the misbehavior after warmup.
Regards,
-- Al |
I don't get the breaking and re-establishing IC thing, this has nothing to do with power issues. Sns, there are two possible relations that I can envision, albeit somewhat vaguely: -- If a ground is missing somewhere, a component by itself (not connected to anything else except power) would tend to have its chassis and signal ground "float" to a voltage level that is determined by small leakage currents in its power transformer, or elsewhere in its internal circuitry. Connection to other components via interconnects would change that, because the interconnect shields tie together the chassis (and consequently the signal grounds) of the connected components. If multiple components are not properly grounded, they will "want" to float to different levels, but the interconnects between them will prevent that. Temporarily breaking the interconnections will allow the chassis of each component to return to the level that is determined its own internal leakage paths. -- If the proper ground paths and ac return paths are not present (especially if ac neutral is open somewhere), return currents could be flowing through roundabout paths that may include or be affected by the presence of the interconnects. That conceivably could be causing something, such as a power transformer, to overheat and cause the audible symptoms after a warmup period. For instance, if ac neutral is open, the leakage path through a power transformer to ac safety ground could be breaking down and serving as part of the return path (for a component with a 3-prong plug), which would definitely overheat the transformer. For a component with a 2-prong plug, the return path in the absence of ac neutral could be via interconnect shields to other components and through them to safety ground. Or something like that; I obviously can't formulate all of this precisely, but my point is that a relation between disconnecting the interconnects and a power problem is very conceivable. Good point about the overvoltage possibility. Re your suggestions about multiple dedicated lines, etc., those are all excellent suggestions for optimizing sound quality, but I think that what we are dealing with here is a basic functionality and reliability problem, which needs to be resolved first. Regards, -- Al |
Thanks for posting the pics, but they do not trigger any particular thoughts for me.
Did the electrician friend make a comprehensive set of measurements of all 3 of the connections (hot, neutral, safety ground) at each of the relevant outlets, verifying that there is in fact a connection back to the breaker box in each case, and through it to the incoming ac; that nothing is miswired or open; that voltages are correct; and that significant dc offsets are not present? Those are the foremost things that need to be done, imo.
Regards,
-- Al |
Whoa! So the whole system (chassis ground and signal ground of all components, as well as all interconnect shields) are completely floating relative to ac hot and ac neutral.
Seems to me that that is your problem!!
And beyond that, I wonder if ac neutral is connected to a true earth ground near the breaker box and the ac inlet to the house. If not, as you said you may potentially (no pun intended) have worse problems than with your audio system. Such as no safe path to ground for lightning that may hit the power lines. Your electrician friend definitely has some things to check out.
Assuming this more serious potential problem is ok, as far as the audio problem is concerned I would try (as a temporary experimental fix, pending getting the wiring redone) simply connecting a wire from the chassis of one and only one component (probably the preamp) to a known earth ground (such as a cold water pipe, a copper stake driven into the ground, etc). That could very well resolve the problem, it seems to me.
Regards,
-- Al |
OK, thanks Jim. Perhaps I misinterpreted Dave's post, and maybe he meant that the dedicated line does have a safety ground, and one which has a proper complete path back to earth, while it is just in the rest of the house that there are some 3-wire outlets with the safety ground not connected. We'll await Dave's confirmation that that is what he meant.
Regards,
-- Al |
Thanks for the update. I don't think there is anything in what you've reported which changes my basic recommendation -- step one is to have all of the ac wiring, grounding, and voltages thoroughly checked out.
My instinct would be that dc offset is much less likely to be the cause of the problems than a miswire or a missing wire would be.
Regards,
-- Al |
