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Topic: Bass Ground Loop - A Unique Solution? (Read 4684 times) previous topic - next topic
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Bass Ground Loop - A Unique Solution?

Hello,

I've recently upgraded my living room home theater to include a Pioneer Elite SC-36 amplifier, Klipsch Icon VF-36 fronts with the old Bose for center and rear (More Klipsch will be on the way after hearing how incredible their speakers are ... and these are the low end series and are still the best sounding speakers I've ever heard). The sub is decent although the name escapes me at the moment, I got most of the setup from the Best Buy Magnolia store in Rancho Cucamonga, CA.

The Sub Woofer has a built in amp and therefore accepts the single channel 'Sub Out' output from the amp. I convert RCA to F-Type connectors on either end and I use RG-6 coax for the run. The coax is fed through "smurf tube" - flexible conduit that I installed into the house as it was being built. I installed the conduit before the electrician did the wiring, so I'm positive he didnt pay any attention to my conduit layout when wiring up the ceiling and as best as I can tell, there is some high voltage running in parallel to my conduit somewhere because the sub woofer will pick up a lot of noise when there is no signal coming from the amp. If I'm using the amp listening to music or watching a movie, then all is well ... no noise, but if the system is off (and the sub has an auto off feature) ... there will sometimes be enough noise in the RG-6 to induce a "signal" into the sub amp to where it just makes noise and pisses everyone off. The only solution is to turn the sub volume down or pull the cable off the sub. I don't want to do either of those because pulling the cable adds wear to the RCA connector (both on the wire and the female end on the sub) and I don't want to turn down the sub because it was tuned using that auto tune feature with the included microphone ... so its impossible to get the volume back where it should be without going through the tuning process all over again.

SO HERE IS WHAT I WANT TO DO ... PLEASE LET ME KNOW IF YOU HAVE TRIED THIS OR IF YOU KNOW FOR A FACT THAT THIS WILL OR WONT WORK.

I would like to pick up some inexpensive A/D and D/A transceivers that convert signal over to TOSlink fiber and back again, then use my RG-6 as pull rope for a fiber optic cable. Then take the sub level out from the amp and convert it to digital, run it over the fiber, then convert it back to analog and feed it back into the sub woofer. When the signal is in the attic, the electrical wire won't have any affect on the signal since magnetic induction cannot alter light waves with any level of significance so as to bring harm to the sub signal. I think this would clean up my problem. Heck, I don't know why they aren't offering TOSLink out on the sub channels anyways and installing D/A converters right into the sub woofer as a next step in eliminating this problem all together ...the technology is cheap enough, thats for sure.

What say you? Do you think this is a viable (and simple) solution to my problem?

Thank you,

Mike Sims

Bass Ground Loop - A Unique Solution?

Reply #1 –
I guess the F-type and coax have rather made it worse than better, but the digital solution will definitely solve this problem. Professional speaker systems like the Genelec DSP range offer this out of the box.

Bass Ground Loop - A Unique Solution?

Reply #2 –
Quote from: W0rkAH0lic on
I would like to pick up some inexpensive A/D and D/A transceivers that convert signal over to TOSlink fiber and back again, then use my RG-6 as pull rope for a fiber optic cable.
Before pulling the (fragile!) wires, make sure that the system works with the length you need. In general 10m (30ft) is considered the limit although Wikipedia states:
Quote
TOSLINK cables are usually limited to 5 meters in length, with a technical maximum[1] of 10 meters, for reliable transmission without the use of a signal booster. However, it is very common for interfaces on newer consumer electronics (satellite receivers and PCs with optical outputs) to easily run over 30 meters on even low-cost ($0.75/m) TOSLINK cables.
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Bass Ground Loop - A Unique Solution?

Reply #3 –
Is the nose from the sub hum or something else?
A few of issues are worth mentioning.
1) Many people who have hum in their system never notice it until they get a sub, so it may not be due to interference in the line to the sub.

2) The most common culprit for hum is a cable TV line.  If you have one, the FIRST thing to try is disconnecting that.  If that is the problem, you can put an isolating transformer between that and your cable box.

3) Next most common cause is ground loops, which you may have formed (in part) by your sub line (completed by the ground line on the sub's power cord.)  The fibre optic will fix that.  If the distance is too long, you could go with  a balanced line instead of the grounded coax.  You could also (if the sub has a grounded plug) use an adapter to remove the ground connection, but should then power the sub on a GFI (ground fault interrupt) outlet or power strip.

Bass Ground Loop - A Unique Solution?

Reply #4 –
Another approach is to use inexpensive transformers at each end to convert the signal to/from differential, then run some CAT5 or similar cable in between.

Bass Ground Loop - A Unique Solution?

Reply #5 –
Actually, the OP may not even need to go that far - I'd try just throwing a transformer inline right before the input to the sub and going unbalanced in and out with the existing coax...there's a very good chance that will solve the problem.

I'd try something like the Rolls HE18 - it's reasonably priced ($47), and it already has RCA connectors so you wouldn't need more adapters.
"Not sure what the question is, but the answer is probably no."

Bass Ground Loop - A Unique Solution?

Reply #7 –
Quote from: mixminus1 on
Actually, the OP may not even need to go that far - I'd try just throwing a transformer inline right before the input to the sub and going unbalanced in and out with the existing coax...there's a very good chance that will solve the problem.


Yes, if it is a ground loop (quite probable), but not if the noise is induced by parallel cabling.

Bass Ground Loop - A Unique Solution?

Reply #8 –
Quote from: DonP on
Is the nose from the sub hum or something else?
A few of issues are worth mentioning.
1) Many people who have hum in their system never notice it until they get a sub, so it may not be due to interference in the line to the sub.

2) The most common culprit for hum is a cable TV line.  If you have one, the FIRST thing to try is disconnecting that.  If that is the problem, you can put an isolating transformer between that and your cable box.

3) Next most common cause is ground loops, which you may have formed (in part) by your sub line (completed by the ground line on the sub's power cord.)  The fibre optic will fix that.  If the distance is too long, you could go with  a balanced line instead of the grounded coax.  You could also (if the sub has a grounded plug) use an adapter to remove the ground connection, but should then power the sub on a GFI (ground fault interrupt) outlet or power strip.


1) Wouldn't I be able to hear some hum in the other speakers as well?

2) I didn't know this ... but I don't have cable, I use satellite and the cable I do use is Intern only. Of course I do know they also carry basic TV service on the same coax. HOWEVER, this service coax feeds in from the South side of the house and it traverses the area in question via 3" conduit that I laid across the vaulted ceiling while the house was still in framing because I knew there would not be enough room up there to crawl around and drag wire from one end of the house to the other, so I laid two - 3" PVC pipes next to each other and looped some rope into the conduit and tied the rope together so it would be easy to cross the house along that long section... anyways, the coax that feed the service is at lest three to five feet away from any point in the smurf tube that carries the sub woofer RG-6 ... although the front and rear left speakers would be considerably closer to that conduit, it certainly would still be at least one or two feet away.

3) I don't think I would need any more than 20 feet of fiber to complete the sub signal circuit. What I AM concerned about is the fact that the sub out from the receiver is actually a low volume signal ... is everyone sure there won't be any loss in that signal during the A/D | D/A transcoding?

Bass Ground Loop - A Unique Solution?

Reply #9 –
Quote from: Martel on
http://en.wikipedia.org/wiki/Galvanic_isolation

Thank you for that post. It's actually a very simple solution and brings me back to my junior college days when I studied electronics.

Now that I think about this, there is nothing preventing me from using a 1 meter TOSLINK cable, then taking the sub side of the RG-6 and plugging it into the A/D converter then back D/A and plugging those copper outputs into the powered sub. But those isolation transformers look awfully inexpensive ... I might just have to give it a try first.

Thank you!

Mike

Bass Ground Loop - A Unique Solution?

Reply #10 –
The 1 m TOSLINK solution does not have any advantages over a simple isolation transformer. You either just have a ground loop, and then a simple transformer is sufficient, or you have induced interference, then either a balanced copper wire and two converters or AD/DA conversion and digital transmission over the whole distance will help (also for the ground loop). A simple AD/DA conversion, when you don't use vintage gear, won't add audible artifacts to your signal (well hidden below the noise floor of even better recordings).

Bass Ground Loop - A Unique Solution?

Reply #11 –
I'll also add that if the OP ends up going the digital route, S/PDIF travels quite nicely over RG-6 coax.
"Not sure what the question is, but the answer is probably no."

Bass Ground Loop - A Unique Solution?

Reply #12 –
Quote from: mixminus1 on
Actually, the OP may not even need to go that far - I'd try just throwing a transformer inline right before the input to the sub and going unbalanced in and out with the existing coax...there's a very good chance that will solve the problem.

I'd try something like the Rolls HE18 - it's reasonably priced ($47), and it already has RCA connectors so you wouldn't need more adapters.


It's hard to beat the Radio Shack 270-054 Ground Loop Isolator at about $17.  Not only does it solve the grounding problem but its actually a very good transformer with good frequency response and low distoriton.

Bass Ground Loop - A Unique Solution?

Reply #13 –
Quote from: W0rkAH0lic on
1) Wouldn't I be able to hear some hum in the other speakers as well?


That depends on how well they reproduce 60 hz (or 50 hz depending on the country).  Many speakers used with subs don't put out much below 80 or 100 hz.  Plus, you are noticing it when the system is off, so the other speakers won't put out anything.

Quote
.. anyways, the coax that feed the service is at lest three to five feet away from any point in the smurf tube that carries the sub woofer RG-6 ... although the front and rear left speakers would be considerably closer to that conduit, it certainly would still be at least one or two feet away.


The big question isn't how far it is from your sub line, it is whether it is connected in any way to your system.  I haven't had hum problems from sat (DirecTV) feed cable, but if it is connected to your system, then disconnecting is something to try.

It might help if you did some reading on ground loops and star grounding.