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Discussion Starter · #1 ·
Is it possible that a new subwoofer hooked to a MC-12 that has a ground loop hum will become "broken in" over time such that the hum will go away by itself?


I have a Sunfire Signature sub hooked up to the MC-12 (borrowed from upstairs) that I had for about 6 months. No hum at all. I thought it might have had a hum at some point in the past but it has no hum now.


Loving the sound, I bought the EXACT same sub for the MC-12 such that I could return the other sub back upstairs. This one hums like....well, analogy omitted. Same exact sub. One hums. One doesn't.


So I did the big no-no for a temporary solution (but it works) and broke the ground loop by using a three prong adaptor. BTW, I tried them both upstairs too - the new sub hums and the old one does not.


Is it possible that through a few months of use the new sub will get broken in and loose the hum? I mean - these units are exactly the same, save 6 months down the manufacturing line.


-adam


p.s. Any good isolator suggestions in lieu of the 3 prong non-ul listed approach?
 

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There is no way the ground loop gets broken in. You could but an isolation transformer from Jensen I believe but there is little danger in using the adapter in IMO.
 

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Maybe you should have your house wiring checked? You *could* have a grounding problem in the wiring or at that outlet.


At the least, maybe get one of those testers at the hardware store with 3 lights on it to tell if your outlets are properly wired.
 

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Discussion Starter · #5 ·
It is not the house wiring. Remember, the other identical model sub works fine on the same system. I have an outlet checker, and the outlet checks out.
 

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I don't think you have a ground loop. I bet the new sub is broken.


The only thing I would try before I took the sub back to trade it for a different one is to bind the ground screw on the back of the sub (if there is one- I'm not familiar with that unit) to the chassis of you amp or preamp. If this doesn't fix the problem, the next call is to the dealer.
 

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Discussion Starter · #7 ·
OK guys. My dealer found a new replacement sub and I am going to exchange later today or tomorrow at lunch. I'll post a follow up for those who care what happens.
 

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Quote:
Originally posted by Bill Lummus
I don't think you have a ground loop. I bet the new sub is broken.


The only thing I would try before I took the sub back to trade it for a different one is to bind the ground screw on the back of the sub (if there is one- I'm not familiar with that unit) to the chassis of you amp or preamp. If this doesn't fix the problem, the next call is to the dealer.
If the three prong adapter removes the hum it is most definitely a ground loop issue. This is a common problem and a common remedy with powered subs. It couldn't be defined as anything else.
 

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Sorry- I misread the post and thought he stated that the problem was not fixed by lifting the ground. But just because it is does not absolutely mean it is a ground loop although I agree it is likely.


If the ground wire is noisy, like they all are, and the amp does not properly isolate the safety and signal grounds then you could have a situation where the noise is removed by lifting the ground.


I have a hard time believing that a ground loop would dramatically affect one sub and not affect an identical sub in two seperate outlets in two different parts of the house without one of the subs being faulty. That being said, I guess it is possible that the sub which has no noise has the safety ground lifted internally and it's actually the faulty component. Hmmm...


Try these steps.


1. Disconnect everything from the sub except the AC power and see if it still hums. If it does, it's not filtering the AC power. I would take it back and try again.


2. If it doesn't hum, reconnect it to the preamp but disconnect the entire HT system from any wire except power. Most bad ground loops are caused by the CATV being grounded seperately from the main house ground. Removing the CATV/Sat/Antenna connection may break the ground loop. If this works, you need to fix your grounding scheme. Remember, your CATV/Ant/Sat ground wire is connected to your box/tv which is connected to your preamp which is connected to your sub. Just disconnect the video sources from the wall for testing purposes.


Let me know what happens.
 

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Quote:
Originally posted by Bill Lummus

I have a hard time believing that a ground loop would dramatically affect one sub and not affect an identical sub in two separate outlets in two different parts of the house without one of the subs being faulty.
A ground loop is caused by ground (or return) currents coming back on a path they should not. In this case since the old sub works at both locations and the new sub does not it is plausible that the new sub has AC leakage currents being injected into the audio ground. If that is the case, and if the path of least resistance is thru the audio return line to the preamp/processor, and then the household AC wiring, a hum would result. It does not necessarily take a huge amount of leakage current to cause a hum. Exchanging the sub for another may resolve the problem, or not, depending upon the design of the sub and the problem at hand.


FWIW: The term "ground loop" has always been curious to me...there are many ground loops all over the place in just about every setup yet they cause no problems. The only time there is a problem is when the current takes the wrong (or unexpected) path (for whatever reason) back to it's source, (I guess the more approriate term would be "ground current loop") but I digress.....
 

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It is possible that the sub has a cold solder joint, loose wire, or other bad connection internally that is causing the ground loop.
 

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because amplifiers almost never ever hum, and that is the only thing in a sub that could hum. I have never heard of that in my life, and because it is so strange and illogical, I would simply return it and get another since it makes no sense.


On another topic but related to a sub you should consider trying some audio points for that sub because they really do wonders for the imaging and cost less then a 100 bucks with the ability to return them if you don't like them.
 

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There is something odd with the Sunfire subs. I have a mark II sunfire which worked fine with a Sony ES receiver. i upgraded to a Denon and resulted with a very loud hum. Disconnected everything from the Denon (all inputs and speakers) except the sub and got hum. Called Sunfire and apparently there is a anomaly with the sub and its volume control. The sunfire rep told me to jiggle the volume knob and see if the hum changes. sure enuff, the hum would change volume but not completely go away. They said to tighten the nut which holds the volume pot to the sub. Tried that and it somewhat lessened the hum but not eliminate it. They said the only way now would be to send in the sub for repair.
 

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Quote:
Originally posted by Addicted Help!!
because amplifiers almost never ever hum, and that is the only thing in a sub that could hum. I have never heard of that in my life, and because it is so strange and illogical, I would simply return it and get another since it makes no sense.


On another topic but related to a sub you should consider trying some audio points for that sub because they really do wonders for the imaging and cost less then a 100 bucks with the ability to return them if you don't like them.
amps almost never hum, subwoofers image


:confused: :confused: :confused:
 

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Quote:
Originally posted by Swampfox
It is possible that the sub has a cold solder joint, loose wire, or other bad connection internally that is causing the ground loop.
Yes indeed, there are a number of possibilities that could cause the problem. I hope sample #2 is free of such issues.....
 

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Discussion Starter · #16 ·
A quick note that I now have the replacement sub in my car (where it is not currently humming :D ) and I will hook it up tonight and post the results. Thanks for all the input so far.


-adam
 

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Geof said if exactly right, When currents return on an unintended path, for whatever reason, noise is the result. Two things can happen. The first is that audio returning over the household saftey ground becomes contaminated with 60 Hz for obvious reasons.


Secondly, because the all of the audio signal current did not return over the shield of the interconnect, the shield becomes less effective and more noise is the result. It is important to remember that center conducter and shield currents be equal in order for a coax shield to effective. Few people realize this. Try inserting a interconnect halfway so only the center pin makes contact and you will see what I mean.


I agree that the root problem could be in the new sub with an unintended leakage between the audio circuits and saftey ground. As Geof said it dosen't take much and they are difficult to control in the design. This is why most audio equipment does not have a safety ground pin connection.
 

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>>Secondly, because the all of the audio signal current did not return over the shield of the interconnect, the shield becomes less effective and more noise is the result. It is important to remember that center conducter and shield currents be equal in order for a coax shield to effective. Few people realize this. Try inserting a interconnect halfway so only the center pin makes contact and you will see what I mean.
 

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Quote:
Originally posted by Roger Dressler
Actually, a current in the shield does not affect the shield's effectiveness. However, that current, if it is AC, can induce a signal into the center conductor, but that's beside the point. The reason you may hear a loud buzz when connecting a signal lead without the shield contact is not because of the current difference, but because that shield is the only path which establishes a common signal ground reference potential between the two components being connected. You can verify this by noting that once one such signal/ground path is fully connected, the buzz no longer occurs with subsequent signal lines between the same two components.
Mr. Dressler;

I must disagree. What I stated is clearly outlined in Noise Reduction Techniques in Electronic Systems by Henry Ott. It is corroborated in Electron-Magnetic Interference Reduction by JefferyP Mills. Both texts explain that the coaxial shield is not really a shield at all (unlike a Faraday shield), but a concentric conductor that induces a equal and oppisite voltage into the center conductor and effectively cancelling inductively coupled interference such as would be the case of 60 Hz power lines. Any imbalance in the two currents results in a reduction of shield effectivness. Unless I completely misunderstand the text this seems to prove my point and makes sense empirically. If I do misunderstand this, I would love to hear a better explanation.
 

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Discussion Starter · #20 ·
UPDATE: The new sub also hums. The original sub still does not hum. Thus, scorecard: Out of 3 Sunfire Signatures, 2 hum, one does not.


Starting tomorrow I will get into the next steps of troubleshooting.


-adam
 
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