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Ground loops and powered speakers.

JayGilb

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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.
Thanks. That information was very helpful knowing that the company recently refurbished the unit and gave it a thumbs up.
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.
I missed this comment and glad tonycollinet noticed it. Hopefully between several members, we can help figure out your problem.
As he mentioned, either a connection diagram or a text description of the in/out connections to the preamp would be helpful.
 

TNPFan

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I have tried using a cheater plug with no success. The only way I can eliminate the ground loop is to unplug the power from any source that is being fed into my preamp. I have attached a drawing that contains both power and signal connections. Power is black lines and signal connections are red (right) and blue (left). Singles ended and XLR connections are labeled accordingly. All electrical connections are three prong ground being fed from a single 20A source. I REALLY appreciate the help!

Components: Oppo DVD ===> Audio Research Preamp ===> separate Benchmark Audio Amps configured Dual Mono ===> Golden Ear Triton One Speakers with Self-Powered Bass. (I have removed my subs and all other source equipment.)
 

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TNPFan

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For better clarification of the interconnect types...

Components: Oppo DVD singled ended RCA outputs ===> Audio Research Preamp balanced XLR outputs ===> separate Benchmark Audio Amps configured Dual Mono NL2 connectors out of the amps ===> Golden Ear Triton One Speakers with Self-Powered Bass banana plug inputs.
 

Lambda

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Components: Oppo DVD ===> Audio Research Preamp ===> separate Benchmark Audio Amps configured Dual Mono ===> Golden Ear Triton One Speakers with Self-Powered Bass. (I have removed my subs and all other source equipment.)
I see a lot of big loops in your drawing.
in general you need to minimize loop area
index.php


Did you follow this steps?
 

TNPFan

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Wow Lambda, your drawing looks so much more menacing than mine. :facepalm: But seriously, thank you for making time to put it together and pointing out the ground loops. I had no idea I had those and have no idea how to reconfigure/reconnect things to fix it. Plus, I need to add my other sources (turntable, phono preamp, cassette deck and streamer - all using the same electrical inout and single ended connectors). I thought I was doing it right and am humbled to find out I am not. Thanks, also, for providing the link. That looks to be full of great info. Since it may take a while to get through the entire .PDF, can you summarize and recommend what I can try? I don't mean to sound so lazy but I have the work week ahead of me and it will take me a while to find enough time to get through the seminar template. Thanks again!
 
OP
tonycollinet

tonycollinet

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As @Lambda said - you need to minimise the loop area. Start with the loop between source and preamp, as we know that is picking up noise.

try to keep all the connections (Line and power) close together - for both devices. If they are touching all along the length then there is almost no loop area.

You also need to consider the top (long horizontal) loop. Although this is partly balanced, the sheild connection of these still forms a loop with the unbalanced connections, and any currnet in the XLR sheild will also be in the unbalanced shield. So do the same here, keeping the interconnects between pre and power amps close together. (are your two amps in the same place - they should be, and source/pre/power components should be as close together as possible with the shortes interconnects possible.
 

TNPFan

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Are you suggesting I keep all
try to keep all the connections (Line and power) close together - for both devices. If they are touching all along the length then there is almost no loop area.
Are you suggesting I keep the power and signal interconnect cables close together? If so, that may be the issue. I have always tried to keep my power cables as far from my signal cables as possible, in an effort to isolate the two. I may be my own worst enemy. I will definitely be reconfiguring things and let everyone know the results. This forum is awesome!
 

JayGilb

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How do you have your sub powered section of your speakers "GoldenEar Triton One" connected to your preamp ?
I'm assuming it's from your preamp rca output to the LFE rca input on the speaker.
If you disconnect the LFE input on both of your speakers, does the hum level change ?
 

AnalogSteph

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These two statements in combination are giving me pause:
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.
Plus, I need to add my other sources (turntable, phono preamp, cassette deck and streamer - all using the same electrical inout and single ended connectors).
I find it hard to believe that every single one of these sources would be involved in a ground loop. I mean, a tape deck? I would be very much surprised if that had more than a 2-prong mains connection. With a phonopre it's unlikely at least.

Looking at the schematic, it appears the LS3B is an IEC Class I (earthed) device, presumably in order to account for the high internal supply voltages which rival vacuum tube equipment. I am not sure where the common audio ground connects to chassis ground, but I presume it has to because the power supply is referenced to chassis ground. The resistance between audio jack ground and power connector protective earth would be one good thing to ask a multimeter, it should be very low.

I would also verify that the RCA cables are good, especially if they are all the same type. Tarnished connectors, breaks or generally poor construction might ruin your day here. Verify that shield resistance is a fraction of an ohm. Older equipment of the analog era may still have tin-plated RCA jacks, those may appreciate a bit of a polish, too. (Nickel or gold plating generally cleans off fine when plugging and unplugging things, shining them up with a cloth would be quite sufficient.)

Another test: Connect a spare RCA cable to one of the preamp inputs, set volume to a normal listening level and tap the other end of the cable - how much hum do you get? "A bit" is fine, but "overwhelming" may indicate that device ground is floating when it should not be - in which case the fault may not even be in the amp but rather the electrical installation. Repeat test with preamp connected straight to wall outlet in order to rule out the power strip.
 

Lambda

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can you summarize and recommend what I can try?
Page 12 ,13 ,14 capture 2.4 - FINDING THE PROBLEM INTERFACE
Work through the system backwards! As a general rule, and unless clues suggest another
starting point, always begin at the inputs to the power amplifiers (for audio systems) or the input to
the monitor (for video systems) and sequentially test interfaces backward toward the signal
sources. Easily constructed test adapters or “dummies” allow the system to test itself and pinpoint
the exact entry point of noise or interference. By temporarily placing the dummies at strategic
locations in the interface, precise information about the nature of the problem is also revealed.
The tests can specifically identify

 

JayGilb

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Your speakers (Golden Ear Triton One Reference) have a different topology due to the highs/mids being passive and the woofer using a built-in amp.
Not sure if this is part of the problem. Is this what your speakers look like from the rear ?
GETR1.PNG
 

TNPFan

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All great input and suggestions. Thank you.

Referring to the pic above of the back of the speakers... yes, that is the same input on the back of my speakers. I only connect the speaker level inputs with speaker wire and DO NOT use the LFE input. I have two SVS subs that are typically looped in between my preamp and amps via XLR connectors. However, I have removed the SVS subs from the system until I can get the ground loop figured out. Looking at your pic above made me look at the electrical plug on my speakers. What I never noticed, until I saw your picture, is that the speakers are not grounded. There is only a two prong plug in the picture and there is only a two prong plug on my speakers. The supplied electrical cord is a three prong plug. Could that be the missing piece of the puzzle?

As far as other sources being connected... yes, the phono preamp and cassette deck have two prong power plugs but I am still getting ground loop feedback. Earlier this morning, I did connect an old Sony CD/DVD player to my preamp (just to see what would happen) and the feedback was not there. I, then, connected an Rotel CD player (two prong power plug) and it presented the same ground loop feedback I have been getting. So far, the ONLY source I can connect without feedback is the Sony CD/DVD player.

I have swapped out interconnects and it does not make a difference. I am hoping the ungrounded speaker plug is the culprit! If so, is it as easy as just finding an ungrounded cable to connect them to my power strip?
 

JayGilb

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There is only a two prong plug in the picture and there is only a two prong plug on my speakers. The supplied electrical cord is a three prong plug. Could that be the missing piece of the puzzle?
A 3 prong plug would act the same as a 2 prong plug in this situation, since the speaker plugin does not have a physical ground pin, but it might be worth an experiment if you have a 2 prong cord sitting around.

Your speaker was designed to use a separate amp for the mid/highs and a built-in amp for the subs, yet you are only using the separate amp.
Since your LS3B has both xlr and rca outputs, it might be a worthwhile test to connect the lfe input on your speakers to the rca out on your preamp using a rca to rca cable and see if it affects the hum level.

I am interested that you were able to find a piece of gear Sony DVD) that does not cause the hum when connected to the LS3B.
Not sure if it would help, but what is the model of the Sony DVD as well as the Rotel CD player which does induce hum ?
 

TNPFan

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The speaker manufacturer recommends only using LFE (low frequency effects) with a sound processor and not with a standard two channel config. It tried it anyway and still get the hum. I also found a two prong plug for my speakers and it also made no difference. When I disconnect power or interconnects from my Oppo CD/DVD player, the hum goes away. With that unplugged, my phono preamp and cassette deck are working just fine. The problem appears to be tied to my Oppo CD/DVD player.

For what it's worth the Sony CD player is a DVP-NC85H and the Rotel is an RCD-955AX. I have not yet reconnected these.
 

JayGilb

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Thanks for the info. Just trying to find a pattern (2 prong or 3 prong) on sources that cause the hum.
If you put a 3 to 2 prong adapter on your Oppo CD player cord does the hum go away ?
 

JayGilb

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Good idea. I tried that early on and it does nothing.
Looking at the LS3B schematic I see that it has a two relays that pull pin 2 & 3 on the xlr connector to ground when the mute switch is activated.
Does the hum go away when the mute switch is on ?
If the mute switch has no impact, could you toggle the mute switch several times and see if this behavior changes ?

Not too many ideas left...
 

TNPFan

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Yes, when the Mute switch is "on" the hum (and the rest of the sound) goes away. I am beginning to think my Audio Research preamp and Oppo player simply do not play well together. When I replace the LS3B with a Benchmark Media HCG3, there is no hum. I guess I will have to go back to that setup.
 

JayGilb

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Yes, when the Mute switch is "on" the hum (and the rest of the sound) goes away. I am beginning to think my Audio Research preamp and Oppo player simply do not play well together. When I replace the LS3B with a Benchmark Media HCG3, there is no hum. I guess I will have to go back to that setup.
Are you always using the same source input connector with the Oppo Player ? ie CD input. Have you tried either one of the aux inputs or tuner input ?
 

TNPFan

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I have tried using Direct, CD, and Aux and get the same result on each. I have even tried swapping out the interconnects as well. My next step is to reconnect the Rotel and Sony players to see what I get.
 
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