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Mystery a/c hum

4377 Views 19 Replies 7 Participants Last post by  ALMFamily, 
O
Good afternoon Y'all'
Im scratching my head on this one and can use your help. I changed my family room around and put my AV set up on the opposite wall. I had the equipment in a vertical tower and TV stand combo and it was working fine. This is where the bizarre ground loop type of hum issue comes in; I recently got an OPPO BDP 103 and decided to eliminate some gear from my rack (and the rack too). I took out a Linn Karik, Marantz Combo SACD/DVD player, and a dvd recorder I seldom used. Mounted my Panasonic Plasma on the wall and used the TV stand to hold my gear. Made for a clean down size, but now I have a ground loop hum, and a pretty good one through all the speakers. I can hear it on the bass & mid amps powering the L&R mains (the treble amp isn't making any noise, due to the Internal Crossover card I think). The center channel amp, and the amp running the surrounds is also transmitting the noise. The noise doesn't increase with volume changes.

Whats odd, is the same a/c outlet is used, same gear minus what was taken out and the added OPPO. I did go to a short S.E. cable set to the main amps from the long set I had b4, but they are all older audioquest cables (forgot the model name). I have it all running through a Cinepro Powerpro 10 balanced line conditioner. The rest of the system is an Active Linn 5140 system with 3) 5105 amps w/ active crossover cards, passive center channel running off an LK100 bi/amped, going through a Marantz 6004 receiver used as a preamp, & a REL Storm sub. Surrounds & outside speakers are running off an Adcom 6000 5 channel amp using 4 channels. Im also using a Directv HD DVR. Video from both the OPPO & the DVR are running through the Marantz and on to the TV by HDMI.

Frustrations:​
When I had everything in the tower in the current location, I didnt have anywhere near as loud of a hum as I do now. still had a hum, but it was consistent with the noise level of the previous location.

What I've tried so far;​
- I insured the single ended cables from the receiver to each amp were not running near the power cords
- I tried running the amps cords through a power strip, taking out the cinepro. No change.
- The OPPO is the only change to the system. took it out, no change in the hum.
- Unplugged all digital sources - No change
- Unplugged each amp one at a time. This improved it incrementally until all amps were out of the system. I plugged them back in one at a time and got the hum back incrementally louder with each added amp.
- Bought a polarity/ground outlet tester from Home depot - outlets tested correct for ground & polarity.
- I finally ran an extension cord from the old outlet across the room to the Cinepro. This had a big effect on the hum reducing it (but not totally eliminating it) by about 2/3rds
:huh: Now Im getting somewhere.

My initial conclusions;​
- The noise is picked up after the source components and receiver.
- I may have something in this circuit that is "dirtying up" the A/C feed. other switches, appliances, etc., bad connections, or some old wiring issues. The house was built in the late 70's, so it may be wiring related
- I am considering running a new, dedicated circuit for the audio sysem.

Any ideas I should check before I go to the trouble of running a separate dedicated circuit?:help: Thanks in advance.
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T
Most line conditioners have a fault indicater that lights up when there is a ground problem. Does yours have an indicator light? Is it on?

You could put the old cables back in & see if the problem goes away.
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G
:rofl2:
Otis857 said:
Good afternoon Y'all'
Im scratching my head on this one and can use your help. I changed my family room around and put my AV set up on the opposite wall. I had the equipment in a vertical tower and TV stand combo and it was working fine. This is where the bizarre ground loop type of hum issue comes in; I recently got an OPPO BDP 103 and decided to eliminate some gear from my rack (and the rack too). I took out a Linn Karik, Marantz Combo SACD/DVD player, and a dvd recorder I seldom used. Mounted my Panasonic Plasma on the wall and used the TV stand to hold my gear. Made for a clean down size, but now I have a ground loop hum, and a pretty good one through all the speakers. I can hear it on the bass & mid amps powering the L&R mains (the treble amp isn't making any noise, due to the Internal Crossover card I think). The center channel amp, and the amp running the surrounds is also transmitting the noise. The noise doesn't increase with volume changes.

Whats odd, is the same a/c outlet is used, same gear minus what was taken out and the added OPPO. I did go to a short S.E. cable set to the main amps from the long set I had b4, but they are all older audioquest cables (forgot the model name). I have it all running through a Cinepro Powerpro 10 balanced line conditioner. The rest of the system is an Active Linn 5140 system with 3) 5105 amps w/ active crossover cards, passive center channel running off an LK100 bi/amped, going through a Marantz 6004 receiver used as a preamp, & a REL Storm sub. Surrounds & outside speakers are running off an Adcom 6000 5 channel amp using 4 channels. Im also using a Directv HD DVR. Video from both the OPPO & the DVR are running through the Marantz and on to the TV by HDMI.

Frustrations:​
When I had everything in the tower in the current location, I didnt have anywhere near as loud of a hum as I do now. still had a hum, but it was consistent with the noise level of the previous location.

What I've tried so far;​
- I insured the single ended cables from the receiver to each amp were not running near the power cords
- I tried running the amps cords through a power strip, taking out the cinepro. No change.
- The OPPO is the only change to the system. took it out, no change in the hum.
- Unplugged all digital sources - No change
- Unplugged each amp one at a time. This improved it incrementally until all amps were out of the system. I plugged them back in one at a time and got the hum back incrementally louder with each added amp.
- Bought a polarity/ground outlet tester from Home depot - outlets tested correct for ground & polarity.
- I finally ran an extension cord from the old outlet across the room to the Cinepro. This had a big effect on the hum reducing it (but not totally eliminating it) by about 2/3rds
:huh: Now Im getting somewhere.

My initial conclusions;​
- The noise is picked up after the source components and receiver.
- I may have something in this circuit that is "dirtying up" the A/C feed. other switches, appliances, etc., bad connections, or some old wiring issues. The house was built in the late 70's, so it may be wiring related
- I am considering running a new, dedicated circuit for the audio sysem.

Any ideas I should check before I go to the trouble of running a separate dedicated circuit?:help: Thanks in advance.
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You mention having active speakers. Where do you have those plugged in? If you have gear plugged into separate branch circuits on opposite 120V legs, that could be responsible for your hum.
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O
I have not tried the old cables yet, but that is on my short list to check next. But I dont think that its cable related because some of the same cables were use and the hum is coming through all the amps, not just the L&R mains where i used shorter cables.

The Cinepro has a line of LED's across the front that read system voltage, up to 140 volts, Its at 120 now. It also has a system protection led that isnt lit and a status light thats green. I didnt condemn it because when it was out of the system, the hum was the same.

Thanks for the suggestions, Tonto
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O
Glen B said:
:rofl2:
You mention having active speakers. Where do you have those plugged in? If you have gear plugged into separate branch circuits on opposite 120V legs, that could be responsible for your hum.
Click to expand...
They are active, but dont have the amps built into the speaker cabinets. The crossovers are removed from the speaker cabinets and Im using 3 Linn 5105 amps with Linn's Aktiv crossover cards for treble, mid, bass in each amp that match the 5140's, tri-wired for the corresponding drivers in the speaker cabinet. All the amps are plugged into the Cinepro. The Cinepro has 4 outlets dedicated to digital sources, and that's where I have the OPPO, the DVR and the Marantz plugged into.
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WooferHound
Try disconnecting your Cable TV wire, that has a different ground than the AC system in the home.
Alternatively . . . try connecting the shield/ground of the cable tv wire to the ground of your power conditioner.
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lcaillo
Measure the resistance between the ac neutral and ground, as well as the ac voltage between them. Do the same between the cable or other grounds on any signal lines into the system with those lines disconnected. Listen for a change in the hum when you disconnect.
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P
I am new but I hope this helps.

Try what Wooferhound said, ground loop is a parallel path to earth ground. The fact that it got louder when you ran an extension cord to the other outlet may have deceased the current through the loop.

I believe you got it right when you said you had a hum from a ground loop. You are bi-amping these units I am guessing running the mid and bass off of one amp and the treble off the other.
First check all the bi-amped speakers and insure 1. insure that the shorting plates (metal piece connection the terminals is only shorting the lower two terminals on both +/- sides. This leaves one hole empty on each shorting plate at the bottom. 2. Then make sure you have one set of cables in the top two post and the other set connected to a pair of the bottom 4 post. I am sure you probably found all this in order but you need to check.

Amplifier power supplies are very good at removing 60 Hz or anything near it from the AC lines. Amplifiers are not really built to remove any ac from there ground plane. Somewhere tough you are getting a parallel path to your earth ground. Start by shrinking your problem to a manageable number of boxes. Isolate 1 amp and its speakers. RCA cables between amps and components are usually shielded to chassis ground so disconnect them all. Power up the amp. If the speakers do not hum any more you are going to find either the hum returns when you plug in one other unit or the hum returns when you plug in anything else to the amp.

If the speakers hum while the amp isolated and you tried what Wooferhound said. (Wow) I would have to think a little more.
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WooferHound
Here is how I understand it . . .
If you have two different pieces of equipment that are grounded in two different locations
you may get a voltage difference between the two grounds that will appear on the unbalanced signal
DC voltage is filtered out
But AC radiated from the grid power wiring that is around us can cause an AC voltage difference on two different grounds which will appear on the unbalanced signal
that is the 60 hz buzz you hear, and sometimes you can hear a radio station
it's a Ground Loop

-- Ground Everything --
I've done this with great success
I got alligator clips that were large enough to clip onto a Phono/RCA jack
connect the alligator clips at 1.5 foot intervals on a long wire
one end of the wire should connect to the Power Ground
all the alligator clips connect to each piece of equipment: on an unused phono jack, a chassis screw, the chassis it's self, the cable wire, the TV ...Everything...
it's a common ground tied to the power ground
this greatly decreases the chance of ground loops and the hum it causes
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P
Here is how I understand it . . .
If you have two different pieces of equipment that are grounded in two different locations
you may get a voltage difference between the two grounds that will appear on the unbalanced signal
DC voltage is filtered out
But AC radiated from the grid power wiring that is around us can cause an AC voltage difference on two different grounds which will appear on the unbalanced signal
that is the 60 hz buzz you hear, and sometimes you can hear a radio station
it's a Ground Loop

-- Ground Everything --
I've done this with great success
I got alligator clips that were large enough to clip onto a Phono/RCA jack
connect the alligator clips at 1.5 foot intervals on a long wire
one end of the wire should connect to the Power Ground
all the alligator clips connect to each piece of equipment: on an unused phono jack, a chassis screw, the chassis it's self, the cable wire, the TV ...Everything...
it's a common ground tied to the power ground
this greatly decreases the chance of ground loops and the hum it causes
Click to expand...
Agreed,
Good commercial electronic installations always begin with a grounding strategy and most will feature a copper ground buss bar with all equipment starred from that bar. A ground buss bar makes a lot of sense for home installations also but, I will admit that I do not use one or know anyone who does. It makes a lot more sense than some pieces of equipment for noise prevention.
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O
Thanks for the replies, everyone. I was out of town for the weekend, and am just catching up. I thought I'd try the easy things first, and VIOLA!! I disconnected the cable from the Directv DVR and the hum was gone INSTANTLY!!! :clap: Next question, how do I ground this cable to the common ground I'm using for the rest of the system? Do I run a chassis ground wire to an unused ground terminal in my power conditioner? The DVR does not use a 3 wire grounded power cord.
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ALMFamily
Otis857 said:
Thanks for the replies, everyone. I was out of town for the weekend, and am just catching up. I thought I'd try the easy things first, and VIOLA!! I disconnected the cable from the Directv DVR and the hum was gone INSTANTLY!!! :clap: Next question, how do I ground this cable to the common ground I'm using for the rest of the system? Do I run a chassis ground wire to an unused ground terminal in my power conditioner? The DVR does not use a 3 wire grounded power cord.
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I got a power strip that had an in/out cable connection on it - completely solved mine.
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O
Thanks ALMfamily, I'll give that a try. I tried an alligator clip jumper wire from the DVR case to the ground socket on the wall plug that my power conditioner is plugged into and it made the hum even louder. So Im going to have to try something else.
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P
Not fun. The test you performed with the alligator clip kind of indicated that the power conditioner is lengthening your distance to earth ground. I do not own one so I cannot comment on how they should work. It also sounds like the dish antenna is most likely installed properly. You might try putting something like this surge protector on the output of the power conditioner.
http://www.amazon.com/Monster-MP-AV-800-PowerCenter/dp/B00003CWDH/ref=sr_1_9?s=electronics&ie=UTF8&qid=1378231914&sr=1-9&keywords=surge+protectors.

I am not sure it will work while the power conditioner is still installed because the shield of the could still be a shorter path to ground. Unless the surge protector isolates coax ground form other grounds you could be grounding your whole system through the coax shield. This situation makes me wonder why the GFCI is not tripping in the power conditioner.
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O
WHAT a pain!! I finally figured out what was going on and a way around it. What I found was the analog cables from my DVR to the Marantz receiver was the source of the hum. I went on a Directv forum and they suggested a grounding terminal for the coax, mine had one that wasnt hooked up. I hooked it up to earth ground at the electric box and that didnt help either.

I stumbled on the analog cables I was using from the DVR to the receiver was the source of the hum. I went with a toslink (no digital coax on the DVR) to the receiver and the hum was gone !!! Completely!!! The toslink isolated the DVR from the analog circuits in the receiver.

That left me with a new issue. I need an analog feed to use my zone 2 on the Marantz receiver and was using the DVR to play pandora on my outside speakers. OPPO to the rescue!! Im now using the analog L&R jacks to go to my zone 2 and Im up & going again, Without the HUM. Plus the Pandora interface on the OPPO is better than the DVR too. Too bad the equipment Directv and cable provide isnt better quality, but what do you want for $125/month without movie channels?

:sweat::paddle::dumbcrazy::scratch::help::huh::help::dontknow::ponder::hsd::boxer::dumbcrazy:
Pretty much spells out the roller coaster I went through on this one!!
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O
Premature celebration. I woke up early this morning to hear my ground loop hum is back. :scratch: Now its going through through the HDMI cable. If I unplug it or the coax going into the DVR, my hum goes away. I really think Directv needs to address grounding issues better with their equipment. While I have a more complex home theater than many people do, I cant be the only one fighting this type of ground loop hum.
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P
I am sure you are not the only person facing this dilemma. It is more of an installation issue than an equipment issue but yes, DirectTV needs to better train their installers. I work large non-A/V electronics venues an current between the grounds is a constant issue to be dealt with mostly during the design of the venue. It even gets worse when you separate logic and equipment grounds.
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O
As suggested on the Directv forum, I picked up a polarity checker at Home depot and tested all the outlets I can get to, which represent all the 110 breakers in the panel. This unit tests for correct circuit, open ground/hot/ neutral, reversed hot/neutral, reversed hot/ground with a simple plug in to the outlet. All tested correct, unless I missed a hidden outlet that isnt correct.

Stranger yet, I came home from work to find a MUCH quieter hum,but still present hum than my 5am post. The house was quiet, maybe not as quiet as 5 am, but it was obviously a lower volume hum than before. Go figure.

As a Directv forum member suggested, I swapped out the HD DVR from the bedroom to check the equipment and the hum was the same with both DVR's. This tells me it isnt an equipment issue.

Question, does a power strip/surge protector with a coax in/out have coax cable grounding? This was suggested by ALM family on this forum as a cure for his ground loop hum. And if so, wouldnt grounding the case or coax fitting of the DVR straight to the wall outlet ground or power conditioner ground outlet do the same thing?

Still hunting the mystery hum.
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O
95% success!! I ended up making a grounding buss that ties all the ungrounded components including the DVR to the power conditioner ground. This has dramatically reduced the hum, not completely, but to a very low and acceptable level. My guess is that grounding the coax cable at the distribution box outside and the ground buss has eliminated as much of the hum as I can w/o running a dedicated a/c circuit.

Well that was fun!!

Guess I will be happy with this very low level hum for now. Thanks all for the ideas
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ALMFamily
Otis857 said:
95% success!! I ended up making a grounding buss that ties all the ungrounded components including the DVR to the power conditioner ground. This has dramatically reduced the hum, not completely, but to a very low and acceptable level. My guess is that grounding the coax cable at the distribution box outside and the ground buss has eliminated as much of the hum as I can w/o running a dedicated a/c circuit.

Well that was fun!!

Guess I will be happy with this very low level hum for now. Thanks all for the ideas
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Good to hear you got it straightened out mate - happy listening!
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