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Author Topic: Subwoofer is humming...help! Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-28-2003 07:54 AM                     A ground loop is in no way shape or form an antenna. It is as the name implies an electrical loop formed by "grounds" of different potential. It has nothing to do with an induced hum. If the grounds of a system are not of the same potential then current flow will result (on the ground wires themselves) and the hum is the by product. Now there are other noise (including those that take the form of hums) that can be induced but they are not groundloops. Steve  |  IP: Logged Jim Alexander Film Handler Posts: 71 From: Greenwood, Nova Scotia, Canada Registered: Nov 1999 posted 07-29-2003 09:30 AM                        Well Duh! What do you think an antenna is. An chunk of wire attached to a capacitive/inductive tank or filter. The length of the wire or antenna is matched to the center frequency of choice and the tank selects the frequency you want. All you you have described is the tank function...inductive capacitive loop. Mine was the simplisitc explaination, meant to make understanding a little easier. And you are right, their are may other forms of hum, just as I said, the problem here sounds like an hum coming from an active component and not a ground loop.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-29-2003 12:27 PM                       Jim's right. I had a grounding problem in a theatre that was causing it to pick up a local radio station. Fixed the bad ground, no more receiver.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-29-2003 09:34 PM                     Tim, A bad ground (overall), is also not the same as a ground loop and yes, a bad ground can allow your system to act as an antenna...but again, different than a ground loop. Ground, for audio takes on several purposes. One is for safety...most professional equipment is grounded via the ground pin on the power plug. In a well designed piece of equipment this will ensure that the frame of the equipment is at ground potential and often now also provides RFI/EMI protection (either emitting out or receiving in). Ground also allows us to effectively use shields since the "shield" is tied to ground and drains away induced noise. Ground is also a reference. While it is not necessary that ground be the reference in an audio system, it often is and as such is often the reason a ground loop can come up. That is, if both pieces of equipment use ground as its reference but if both pieces don't connect to the same ground then a potential difference can exist between each piece of equipment's ground reference. Addionally, if ground is used as the reference, any noise impressed onto the ground buss can show up in the sound (or video) system as well. Steve  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 07-30-2003 10:10 AM                     I'm just curious if Aaron was able to troubleshoot this yet. We've taken bets on the cause here and I'd really like to collect my earnings! Seriously, though. One needs closure.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-30-2003 10:20 AM                       quote: Tim, A bad ground (overall), is also not the same as a ground loop I never said it was. I was talking about Jim being right about the antenna. de, KJ5KX  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 07-30-2003 05:44 PM                    Something just came to mind that I don't think we mentioned. Is the hum present no matter what you put the format card in. Does it do it in nsync, mono, stereo, and digital. Does it do it with the format card removed. If the hum is only present in the stereo and mono selections it could be a solar cell wiring issue. If you are using a Jax light setup the line amp could be introducing the hum into the system. Could be a loose ground on the solar cell imputs. I'm affraid to say it could be many things. Sound problems can turn a man grey and cause him to loose a lot of hair.  |  IP: Logged Aaron Garman Phenomenal Film Handler Posts: 1470 From: Toledo, OH USA Registered: Mar 2003 posted 07-30-2003 07:21 PM                     Hello all. Just got in from work, and I tried some stuff today. First of all, I did the old switcheroo with another power supply. This did not solve the problem. I guess the plot thickens. I'm going back in tonight to see the film in that house and then I work tomorrow morning. Any more advice guys? Thanks for all the help. EDIT: I'll see if it hums tonight in DIGITAL Darryl. I didn't even think of checking that this afternoon, as I was busy enough as it is. AJG  |  IP: Logged Jim Alexander Film Handler Posts: 71 From: Greenwood, Nova Scotia, Canada Registered: Nov 1999 posted 07-30-2003 08:49 PM                        Quote Steve Guttag: A bad ground (overall), is also not the same as a ground loop and yes, a bad ground can allow your system to act as an antenna...but again, different than a ground loop. Ok, now we are talking apples and oranges.... A bad ground, something like a "floating Ground" will normally follow the potential of the line signal that it is attached to. In which case the audio signals will resultantly follow, which equates to hum at the speaker...you are right it is different, but not as you elude to. Quote Steve: Ground, for audio takes on several purposes. One is for safety...most professional equipment is grounded via the ground pin on the power plug. In a well designed piece of equipment this will ensure that the frame of the equipment is at ground potential and often now also provides RFI/EMI protection (either emitting out or receiving in). Ok, let's start by separating this discussion. Sheilds and grounds. Grounds, as you state have many purposes. Safetly, potential reference, etc... Sheilds are a different matter. They serve one purpose, and one purpose only, and that is to electrically isolate the audio signal lines from any extrenuous electrical noise. They originate from grounds and cover certain wires known to be sensitive to interference. Some call it EMI protection, others call it shielding, but the end result is it prevents induction of electrical noise onto the signal lines that may be sensitive... like audio. Contrary to what you've said, ground loops do not need equipment at different potentials to form. A prime example of this is aircraft wiring. A great deal of engineering goes into ensuring equipment is, not only grounded, but grounded to the exact same reference and potential. However, should a loop be formed by grounding both ends of the shields, EMI interference will result. And, in the cases on aircraft, this can manifest its self is a wide range of problems. Radar systems that will not receive returns. Audio intercom systems that receive VHF transmissions where no radio is connected to them (I even had one aircraft that received the local AM radio station on the intercom, even though there was no AM receiver on the aircraft!). Engine monitor displays that fluctuate whenever a Transmitter is keyed. Sheilding, if not done properly will cause problems...EMI (Electro-Magnetic Interference) and ground loops is a complex theory that is difficult to understand at the best of times. The easiest solution to explaining it to most non-electronic, or people who have not been trained in EMI prvention, is to use the antenna example. People can understand that. They have a difficult time comprehending an indepth EMI discussion.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-31-2003 10:09 PM                     I tend to avoid the antenna explanation as it is also misleading A ground loop is not an induced noise that is similar to antenna or magnetic coupling Star Grounding of sensitive equipment is the best solution  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-01-2003 11:29 PM                     Somehow, I don't think I'm communicating my thoughts very well...especially as Gord seems to be agreeing with me Suffice to say, I wouldn't use the antenna analogy in ground loop situation and clearly others would and had success with that....I can live with that. Steve  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 08-02-2003 10:17 AM                     Steve Brad says I am allowed to agree with you once a month  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-03-2003 01:38 AM                     Hmmm and you agreed with me on the last day of last month...I wonder what it will be this month...anticipation... Steve  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 08-04-2003 06:05 AM                        and disagree, never!  |  IP: Logged Clint Koch Phenomenal Film Handler Posts: 1435 From: San Luis Obispo, CA, USA Registered: Feb 2002 posted 08-07-2003 06:45 PM                     Was this ever fixed?  |  IP: Logged

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