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Ground loops and powered speakers.

tonycollinet

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I've seen a lot of question recently on how to solve ground loop noise problems. In a majority of cases I've seen, these have involved powered speakers (either mains or subs) being connected with unbalanced connections. I've thought a little about why in 40 years of owning audio kit, I've never had a problem:

Back in the day a "HIFI" was typically a stack of Amp, Tape Dec, Tuner, CD player etc perhaps with a turntable on top. Everything was connected with short RCA leads and everything was plugged into the same power socket. The only part of the system that was remote would be passive speakers - which being passive have no ground reference. Unbalanced connections were fine in these typical consumer applications, with very little scope for creating a problematic ground loop.

Things have changed - more and more often people are incorporating powered speakers and powered subs into the mix. These are often placed around the room (especially subs) and may be connected to separate power sockets. Even when the power leads are run back to the same power strip, we are still left with a significant ground loop from the preamp (whatever form that takes) via RCA to the speakers then back to a common earth via the power cord. Worse - speakers normally have significant separation from each other, so each one creates a separate ground loop.

Add to that a noisy PC with powerfull energy chomping graphics card and you've a recipe for stray magnetic fields getting into a loop and causing ground noise - even if there is no PC, mains wiring run <1mm from the earth wire can easily induce mains hum into the loop. There are a plethora of other devices that can also get in on the act.

I think the message is - if you are planning to use powered speakers of whatever kind, plan also to use fully balanced (or some other form of noise rejecting connection - eg toslink) interconnect to them.

And if you use a PC as source which is ground referenced - plan to use an optical connection from that to your DAC - or at least have the option to fall back to that if you have issues.
 
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amirm

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I think the message is - if you are planning to use powered speakers of whatever kind, plan also to use fully balanced (or some other form of noise rejecting connection - eg toslink) interconnect to them.

And if you use a PC as source which is ground referenced - plan to use an optical connection from that to your DAC - or at least have the option to fall back to that if you have issues.
These are always my two suggestions so well said!
 

BoredErica

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In my previous setup I had Rokits connected unbalanced to my o2/odac to mypcand the noises coming out of my speakers when I moved my mouse in a videogame was horrifying. A RadioShack ground loop isolator fixed the issue as far and I could tell. Couldn't hear any sound quality degradation but maybe somebody cnanhear a difference

So I decided never again and decided to go all balanced, including the subwoofer. That ended up being very expensive since Rythmik f12+xlr amp+white paint is $1309, or over double the price of L12. All for xlr. But I never want to deal with weird funky noises coming out of my speaker.

I can live with some cheap Logitech speakers with bad spins. I can't live with audible noise coming out of my speakers. I'll slowly go insane.
 

TNPFan

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I have a ground loop hum and have tried everything to fix it. While I did disconnect my powered subs, I never considered the source of the hum may be coming from my powered speakers. Since my speakers are connected only using speaker cable, not sure how I could remedy this. Any ideas?
 

JayGilb

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I have a ground loop hum and have tried everything to fix it. While I did disconnect my powered subs, I never considered the source of the hum may be coming from my powered speakers. Since my speakers are connected only using speaker cable, not sure how I could remedy this. Any ideas?
Why are your powered speakers using speaker wire for their connection ? Normally a rca/xlr/aes/ebu connection is used and their is no need for speaker wire.
If you don't mind, what is the brand/model of your powered speakers and what are they connected to ?
 

TNPFan

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Thanks for the reply. I should have been more specific regarding the “power”. My speakers are GoldenEar Triton One’s with a powered bass section.
 

TNPFan

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And the speakers are connected to a pair of Benchmark Media amps configured in dual-mono. I am using XLR connectors from my preamp to each of the amps. Those, in turn, are connected to the speakers via speaker cables.
 

JayGilb

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If you remove the power cord from the bass amp(s) and just have the speakers connected to the Benchmark amps do you hear the ground loop ?
Just trying to see if having both units (powered subs and Benchmark amps) connected is the cause of the ground loop, which is most likely the case.

Interesting topology on the speaker. I have never seen that particular model before.
 

TNPFan

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The speaker does not work unless the bass module is plugged in. I am guessing it has something to do with the internal crossover. My preamp is an Audio Research with balanced outputs and I have been working with their engineers for 3-4 weeks trying to figure it out. They have been awesome but eventually told me they were out of ideas. I am pulling my hair out trying to figure this out.
 

TNPFan

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Both, and I do it need to be close to the speakers. I can hear it from several feet away. The 50-60Hz hum gets louder as I increase the volume. Luckily, the music is louder than the hum but I can still hear it during soft musical passages and in between songs.
 

DS23MAN

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In the old days we had never a problem because all equipment had no mains ground. The stupid idea to start with mains grounding started was that it would sound better....

Almost all audio gear have an isolation class 2, no mains ground compulsory.
 

JayGilb

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Both, and I do it need to be close to the speakers. I can hear it from several feet away. The 50-60Hz hum gets louder as I increase the volume. Luckily, the music is louder than the hum but I can still hear it during soft musical passages and in between songs.
Looks like your preamp is the culprit since the hum increases with the volume. Is there any hum when the preamp is disconnected (xlr to Benchmark amps) ?

What is the model of your preamp ?
Edit: Looks like all models of Audio Research preamps have multiple balanced input/outputs, I'm assuming you have tried all combinations to no avail ?
 
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TNPFan

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If I disconnect all of the single ended sources going into the preamp (LS3B), the hum goes away. Once any of my sources are reconnected, it returns. It has been most frustrating.
 

JayGilb

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And the speakers are connected to a pair of Benchmark Media amps configured in dual-mono. I am using XLR connectors from my preamp to each of the amps. Those, in turn, are connected to the speakers via speaker cables.
According to the Audio Research database, the LS3B does not have balanced outputs and you state that you are using XLR connectors from the LS3B to your amps. I'm assuming the connectors are a rca (unbalanced) to xlr (balanced) ? Are the connectors DIY or purchased, if the latter, what is the brand/model of the connectors ?

Just trying to gather info to help you in debugging.
 

TNPFan

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Audio Research made the LS3 and LS3B, one has only single ended outputs and the other has both single ended and balanced - hence the "B" designation. I assure you mine is a balanced LS3B preamp as delivered from Audio Research. They also made a third, much rarer, version of the LS3 that is balanced and includes a wireless remote and detachable power cord. I have tried both the balanced and single ended outputs of my LS3B and both produce the ground loop hum. I am taking it to my local stereo shop and plugging it into one of their systems to see it does the same thing there. If not, I am also going to borrow one of their balanced preamps and plug it into my system to see what happens. Thank you for your ideas, expertise and the brainstorming session, it is much appreciated!
 

JayGilb

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Audio Research made the LS3 and LS3B, one has only single ended outputs and the other has both single ended and balanced - hence the "B" designation. I assure you mine is a balanced LS3B preamp as delivered from Audio Research. They also made a third, much rarer, version of the LS3 that is balanced and includes a wireless remote and detachable power cord. I have tried both the balanced and single ended outputs of my LS3B and both produce the ground loop hum. I am taking it to my local stereo shop and plugging it into one of their systems to see it does the same thing there. If not, I am also going to borrow one of their balanced preamps and plug it into my system to see what happens. Thank you for your ideas, expertise and the brainstorming session, it is much appreciated!
Thanks for the clarification. It was difficult to find a rear image of the LS3B and the one I did find was labeled LS3B and only had unbalanced outputs. This image does seem to be correct.

2599545-5e42fc6d-audio-research-ls-3b-preamplifier.jpg

Does the LS3B share the same outlet/power source as the monoblocks ?

Pretty straightforward connection setup you have and since the LS3B is an older unit, it might have an internal grounding problem.
If you tap/lightly strike the preamp or wobble any of the xlr connections does the hum level change ?
 
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TNPFan

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While not rare, the LS3B is unique. My wife gave it to me for my birthday back in the mid 1990’s, so it has a great deal of sentimental value and will always be part of my system. I have tried jiggling interconnects and, frankly, they are solidly connected and do not budge. There is also no difference in hum. In February, I sent the unit to the Audio Research factory just to make sure everything on the unit was ok. They replaced a couple of capacitors, due to their age, tested it thoroughly and said it works great. They also spent the past couple of weeks helping me troubleshoot remotely. Even their engineers are not able to find and fix my issue. It may be that this preamp becomes eye candy in the rack and gets replaced with something that was made in the 21st Century. But that would not be nearly as much fun. Ha! Again, I appreciate the help and suggestions.
 
OP
tonycollinet

tonycollinet

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If you only get hum with a source connected, AND It changes with volume setting then the ground loop it between your source and your preamp. What are the sources? Do they have an earth pin on the power line? How are they connected (how far from preamp)?

Can you sketch the connections including power/earth.
 

Tom C

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I use something like this for diagnosis only. It can help you determine where the loop is occurring. When placed between the component involved in the loop and the outlet, the hum will cease. It may be tempting to then say problem solved, but actually a worse (but not audible) problem has been created, because a unit designed to have an earth ground now has the ground eliminated, so that’s a safety issue. Because it’s a loop, there actually has two be at least two grounds involved that are at slightly different potentials, and there may be more than two.
 
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