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post #1 of 38 Old 12-04-2019, 07:51 PM - Thread Starter
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Mysterious ground loop hum

So about a year ago when I got my first inuke and DIY sub I had a tremendous hum. It was so bad I almost couldn't use the sub. I tracked down the problem to the coax cable not being grounded. Go figure. I fixed that and and took care of most of the noise. Fast forward to this week and I have a hum returning and I don't know why. I did some basic troubleshooting and the hum is only present when the avr is on. If I mute the AVR or turn it off there is no noise. AVR off with amps on there is no noise. I also disconnected the coax outside the house where it enters the house and the hum is still present. I tried lifting grounds, adding grounds, plugging things into different outlets and no change. I can make it get worse by removing the hdmi from the cable box or removing the ground for the coax but nothing I do makes it better. Do you guys have any suggestions? I ordered a bjc isolation transformer and something else for the coax. I would rather prefer to solve the source if I can. I could run a dedicated circuit for the equipment if I need to.
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post #2 of 38 Old 12-04-2019, 08:51 PM
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Quote:
Originally Posted by LGERIC View Post
So about a year ago when I got my first inuke and DIY sub I had a tremendous hum. It was so bad I almost couldn't use the sub. I tracked down the problem to the coax cable not being grounded. Go figure. I fixed that and and took care of most of the noise. Fast forward to this week and I have a hum returning and I don't know why. I did some basic troubleshooting and the hum is only present when the avr is on. If I mute the AVR or turn it off there is no noise. AVR off with amps on there is no noise. I also disconnected the coax outside the house where it enters the house and the hum is still present. I tried lifting grounds, adding grounds, plugging things into different outlets and no change. I can make it get worse by removing the hdmi from the cable box or removing the ground for the coax but nothing I do makes it better. Do you guys have any suggestions? I ordered a bjc isolation transformer and something else for the coax. I would rather prefer to solve the source if I can. I could run a dedicated circuit for the equipment if I need to.


Try grounding the chassis of the avr to the chassis of the amp.

Chris
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post #3 of 38 Old 12-05-2019, 03:40 AM - Thread Starter
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Thanks. I will give that a try. I thought I tried that last time. Can't hurt to try again!

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post #4 of 38 Old 12-05-2019, 04:16 AM - Thread Starter
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One amp has rca to xlr adapter and another has a 1/4 trs adapter. I thought that could be a cause. Although I know it shouldn't. I did narrow the source a little bit though. When I disconnect the rca from the 3k inuke across the room the noise goes away from the 6k which is right next to the avr. When I disconnect the rca from the 6k nothing changes on the 3k across the room. I think what might have happen was I removed the minidsp that I wasn't using for the moment and it was blocking the hum. Could the y splitter be bad?

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post #5 of 38 Old 12-05-2019, 08:47 AM
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Originally Posted by LGERIC View Post
One amp has rca to xlr adapter and another has a 1/4 trs adapter. I thought that could be a cause. Although I know it shouldn't. I did narrow the source a little bit though. When I disconnect the rca from the 3k inuke across the room the noise goes away from the 6k which is right next to the avr. When I disconnect the rca from the 6k nothing changes on the 3k across the room. I think what might have happen was I removed the minidsp that I wasn't using for the moment and it was blocking the hum. Could the y splitter be bad?


You’re making progress. Bypass the 6k snd y splitter and plug the 3k directly to the avr. See if that changes anything.

Also, I’m assuming the 3k being across the room is on a different circuit and has a long signal cable.
Make sure the signal cable doesn’t run with power cable, that can cause induced noise.


Chris
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post #6 of 38 Old 12-05-2019, 09:33 AM
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I had a bad ground loop hum, but have successfully resolved it. I have the following in my system: HTPC (1000W PSU, GTX 1080, SSD), Crown CTs 8200 (8) channel amplifier, Crown XLS 1502 (2) channel amplifier, and QSC PLX3002 (2) channel amplifier.

When I first plugged the PLX in I had a horrible ground loop. I tried everything mentioned in every ground loop hum thread on the interwebz - grounded chassis, plugged everything into the same receptacle, etc. I am using (2) 1500VA Pure Sine Wave UPS units, and also have the PLX plugged into an ART CleanBox Pro. The only thing that solved the PLX hum was using a cheater plug. Then I added the XLS and the CTs to the system. Ground loop noise returned, but not as bad as the previous hum. I swapped plugs around on the UPS units and eventually found a combination that eliminated the hum, but left me with a wireless USB crackle every time I moved the mouse for the HTPC. I tolerated it for about two days, as once the cursor disappeared on the screen when watching video the crackle went away, but decided to try to fix it as well. I grounded the chassis of the CTs that is running the majority of my front L/C/R active speakers to the AVR chassis (just a short length of speaker wire underneath a screw on each), and boom, no more USB crackle.

Then, two nights ago the hum returned. I checked the plugs to make sure they were all seated correctly, and in the process, shifted the chassis of the XLS amp that is sitting on top of the PLX amp. It had gotten moved and was sitting at a slight angle. Once I shifted it back to being flush with the front of the PLX, the noise disappeared. Apparently when sitting correctly the contact between the amp chassis is enough to ground the ground-lifted PLX to the XLS. I will probably run a short section of speaker wire between the two at some point, but at least I know what to do if the noise returns.

Now the only excess noise is the slight amount of white noise in the L/C/R tweeters from the high gain of the Crown CTs, but it is only audible if you are right up next to the speaker and does not bother me once seated. If the sensitivity of the tweeters was greater than 93dB I think it would be much more audible.

My thoughts on your situation is to try lifting the ground on the 3k amp and grounding the chassis to the 6k. Ground the AVR chassis to the 6k as well. The elimination of the hum on the 6k when the RCA is removed from the 3k sounds to me like those two amps have an issue. With the AVR off and no hum on either sounds like the AVR is also contributing.
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post #7 of 38 Old 12-05-2019, 01:08 PM
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If you're getting ground loops to balanced equipment, you have a pin1 problem. Stop using junk adapters and make your own cables. Pin1 should be connected on the balanced side and run the length of the cable, but not connected to anything on the unbalanced side. Pin 2 should be connected to the RCA center (signal) and pin 3 should be connected to the rca outer (rca gnd, balanced cold).
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post #8 of 38 Old 12-05-2019, 01:50 PM
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Originally Posted by notnyt View Post
If you're getting ground loops to balanced equipment, you have a pin1 problem. Stop using junk adapters and make your own cables. Pin1 should be connected on the balanced side and run the length of the cable, but not connected to anything on the unbalanced side. Pin 2 should be connected to the RCA center (signal) and pin 3 should be connected to the rca outer (rca gnd, balanced cold).


Isn’t this only for balanced output to unbalanced input? And I thought that pin 1 (s) was connected to rca outer and pin 3 (-) was the one left unconnected?

For unbalanced output to balanced input, don’t you connect both pin 1 and pin 3 to rca outer?

Chris
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post #9 of 38 Old 12-05-2019, 01:51 PM
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Originally Posted by a77cj7 View Post
Isn’t this only for balanced output to unbalanced input? And I thought that pin 1 (s) was connected to rca outer and pin 3 (-) was the one left unconnected?

For unbalanced output to balanced input, don’t you connect both pin 1 and pin 3 to rca outer?

Chris
no. That is exactly the problem. You just connected the rca signal ground to the chassis ground. Bad.

Pin 3 also needs to be connected to rca ground, as this is the 0v reference for the rca signal.
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post #10 of 38 Old 12-05-2019, 01:59 PM
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Originally Posted by notnyt View Post
no. That is exactly the problem. You just connected the rca signal ground to the chassis ground. Bad.



Pin 3 also needs to be connected to rca ground, as this is the 0v reference for the rca signal.


Interesting, the wiring I described is the diagrams from the manuals of both the minidsp bal, and my crown dci amplifiers.

I did have to ground my preamp chassis to the amp chassis due to ground noise, maybe I’ll try switching up the wiring.

Chris
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post #11 of 38 Old 12-05-2019, 02:01 PM
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Originally Posted by a77cj7 View Post
Interesting, the wiring I described is the diagrams from the manuals of both the minidsp bal, and my crown dci amplifiers.

I did have to ground my preamp chassis to the amp chassis due to ground noise, maybe I’ll try switching up the wiring.

Chris
I don't think that's the case, if it is, it's wrong.

https://www.rane.com/note110.html

17 and 18 are the correct way to do this.

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Originally Posted by notnyt View Post
I don't think that's the case, if it is, it's wrong.



https://www.rane.com/note110.html



17 and 18 are the correct way to do this.




Interesting.

Minidsp:


Crown DCI:


Might have to mess with my wiring.

Chris
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post #13 of 38 Old 12-05-2019, 02:12 PM
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Interesting.

Might have to mess with my wiring.

Chris

The crown image is showing how to do it with only a 2-conductor wiring in figure 4. Figure 3 is how you'd do it. It's still a pseudo balanced connection. You get most of the benefits of balanced, but only half the voltage. It also doesn't show what to do with the shield on the source side. The MiniDSP image is pretty much same as well.

I try to keep everything balanced, but the pre outs on my AVR are unfortunately RCA. I end up making my own cables for this. I order balanced cables for whichever balanced end I'm using from monoprice, along with some rca ends. Snip one end off and solder on the RCA end properly. Seems to be the cheapest way to do it and know you're getting the right cable.
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Originally Posted by notnyt View Post
The crown image is showing how to do it with only a 2-conductor wiring in figure 4. Figure 3 is how you'd do it. It's still a pseudo balanced connection. You get most of the benefits of balanced, but only half the voltage. It also doesn't show what to do with the shield on the source side. The MiniDSP image is pretty much same as well.



I try to keep everything balanced, but the pre outs on my AVR are unfortunately RCA. I end up making my own cables for this. I order balanced cables for whichever balanced end I'm using from monoprice, along with some rca ends. Snip one end off and solder on the RCA end properly. Seems to be the cheapest way to do it and know you're getting the right cable.


I’ve got the same issue. I will probably just leave mine alone until I get a balanced AVR, since it works noise-free as wired.

Chris
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I’ve got the same issue. I will probably just leave mine alone until I get a balanced AVR, since it works noise-free as wired.

Chris

If only some company made an AVR with balanced outputs - I'd even take phoenix plugs vs XLR if the problem is real estate on the back panel. Pre/Pros, sure, but I'd rather run surrounds/ATMOS with the internal AVR amps and external amplification for the L/C/R and subs (obviously). Such a thing, sadly, does not exist.
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Mysterious ground loop hum

Quote:
Originally Posted by drewp29 View Post
If only some company made an AVR with balanced outputs - I'd even take phoenix plugs vs XLR if the problem is real estate on the back panel. Pre/Pros, sure, but I'd rather run surrounds/ATMOS with the internal AVR amps and external amplification for the L/C/R and subs (obviously). Such a thing, sadly, does not exist.

I run all external amplification, so don’t have this problem. I plan to pick up an AVM-60 or a XMC-2. Subs killed my budget x3 this year though.

Small, many channel amps for surrounds are pretty common. Crown CT875 and CT8150 come to mind.

Chris
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post #17 of 38 Old 12-05-2019, 03:36 PM
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Originally Posted by drewp29 View Post
If only some company made an AVR with balanced outputs - I'd even take phoenix plugs vs XLR if the problem is real estate on the back panel. Pre/Pros, sure, but I'd rather run surrounds/ATMOS with the internal AVR amps and external amplification for the L/C/R and subs (obviously). Such a thing, sadly, does not exist.
There are AVRs with balanced outs. Personally, I'd rather do all amplification externally. That lets you easily swap out the pre when technology changes.

https://www.stormaudio.com/en/produc...612-elite.html
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post #18 of 38 Old 12-06-2019, 10:29 AM
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There are AVRs with balanced outs. Personally, I'd rather do all amplification externally. That lets you easily swap out the pre when technology changes.

https://www.stormaudio.com/en/produc...612-elite.html
That's a great find, but unless there are any others produced, I'm gonna have to say no one makes them purely based on the price tag. Yes, I realize they DO in fact make them, but for us mere mortal working stiffs, $15k on your receiver is out of 98% of the population's price range. That is - out of the price range of people who don't spend every last cent they make and don't have $300k worth of credit card debt.

Still, thanks for pointing that one out - I looked for a long time and read probably half the internet when I was looking for them. If it was even a semi-affordable product it might force the hand of the major manufacturers to also include similar products in their line-up, which in turn, would drive prices down to a much more affordable range. Even 3-3.5k is in my opinion a lot of dough for a Pre/Pro just to gain the balanced outputs, but at least that is in the realm of possibilities.

Part of the reason I am into DIY is for the hobby enjoyment, and the other part is because I have Patron tastes on a Microbrew (Craft Beer? When did it become Craft Beer? Such a stupid name...) budget.

FYI, no offense is meant by the above comments. <-- obligatory internet signature
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Originally Posted by drewp29 View Post
That's a great find, but unless there are any others produced, I'm gonna have to say no one makes them purely based on the price tag. Yes, I realize they DO in fact make them, but for us mere mortal working stiffs, $15k on your receiver is out of 98% of the population's price range. That is - out of the price range of people who don't spend every last cent they make and don't have $300k worth of credit card debt.

Still, thanks for pointing that one out - I looked for a long time and read probably half the internet when I was looking for them. If it was even a semi-affordable product it might force the hand of the major manufacturers to also include similar products in their line-up, which in turn, would drive prices down to a much more affordable range. Even 3-3.5k is in my opinion a lot of dough for a Pre/Pro just to gain the balanced outputs, but at least that is in the realm of possibilities.

Part of the reason I am into DIY is for the hobby enjoyment, and the other part is because I have Patron tastes on a Microbrew (Craft Beer? When did it become Craft Beer? Such a stupid name...) budget.

FYI, no offense is meant by the above comments. <-- obligatory internet signature
yeah, its priced silly, but afaik, can be had a good deal cheaper. Still, doesn't make sense when you can get a pre and good amplification for less.
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post #20 of 38 Old 12-06-2019, 07:13 PM
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Quote:
Originally Posted by LGERIC View Post
Fast forward to this week and I have a hum returning and I don't know why.
Things don't just magically start happening, something in your system has changed.

You need to start from a basic wiring topology.

Step 1)
Remove all wires and antennas from the AVR, including USB and remove triggers. EVERYTHING!
All you want is the power cord.

Step 2)
Connect the subwoofer output directly to the inuke.
Any hum? Then one of those two devices (or the wiring between them) is the problem.

If no. Step 3)
Connect the other inuke with a Y-Spliter.
Any hum? Then the Y-Spliter is the problem, or the second inuke. Revert to Step 2 and swap the inukes.

If no. Step 4)
Remove the Y-Spliter. Connect the inukes with the miniDSP.

If still all good. Step 5)
Add each speaker wire to the AVR, one at a time.

If still all good. Step 6)
Add all optional triggers and antennas

If still all good. Step 7)
Add each HDMI or RCA or USB or other metal cable ONE at a time. Until the problem connection is found.

-Make sure power wires are not running parallel to speaker wires or interconnects. Perpendicular is ok.
-Do NOT coil ANY wires.
-Keep wires as short as possible.

Most ground loops are caused by one or more components leaking electrons into the chassis and/or grounding wires, and this power finding its way into the signal ground or signal hot (and then amplified to audible levels.)

USB and Coax wires are notorious for this.
Cheap switch mode power supplies can leak enough RF or electrons into the chassis or house-ground to cause this. Also LED lights, dimmers, and motors/fans/pumps.

Even using different dedicated circuit breakers can cause this, due to voltage differences between the ground pins, cause by corrosion and line length. Especially OLD wiring, not so much new wiring.

Unfortunately ground pins and ground wires are required by code, for electrical safety.
In the event of a hot wire or system fault coming in contact with the chassis, without this pin, anyone touching the rack or device could get electrocuted and/or cause other inter-connected devices to be fried (audio & data etc).

This power would flow back to the service panel, across the ground-neutral bonding jumper, back to the pole transformer, and back down the hot wire, tripping the circuit breaker at full rated line-current (say 15a or whatever).

Ideally there would only be a single ground conductor in an audio system, rather than each device having a parallel or star connection.
Each device would be grounded to each other in a straight path back to the wallsocket ground pin, with all other ground pins lifted.

What works best for audio, doesn't work for electrical code compliance; at least in residential structures.
Some exceptions can be made in radio broadcast rigs and professional recording studios, and other such stuff.

If the hum was bad enough, and you had GFCI's on all circuits, I'd imagine the one causing the problem might be sufficient to trip the GFCI breaker. I think those have a 15mA cut-off...
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post #21 of 38 Old 12-07-2019, 04:26 AM - Thread Starter
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Quote:
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Quote:
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Fast forward to this week and I have a hum returning and I don't know why.
Things don't just magically start happening, something in your system has changed.

-Make sure power wires are not running parallel to speaker wires or interconnects. Perpendicular is ok.
Thanks for the tips!

I believe the hum got worse when I removed my mini dsp from the signal chain. I was using it with a commercial sub that did not have any dsp. previously. The 6k inuke was not connected to it. I connected the 3k to it and bypassed the filters and used the internal dsp in the amp. I removed the mini dsp because I didn't feel the need to have extra stuff in the chain that wasn't necessary. Do you think the minidsp was creating some kind of digital break in the circuit and stopping the hum?

When I started this a year ago I was convinced it was the coax. When comcast installed the line the tech didn't ground the line at all. His attempt was to connect the ground to a outside hose spigot. The house is plumbed with pex pipes...
I grounded the coax to the main ground block near the panel. The hum went from unusable to the wife doesn't notice but I do. It is audible from the mlp during quiet scenes or audio.

A couple observations. When I disconnect the coax from the feed line outside the house the hum doesn't go away completely. That would lead me to believe something else is causing the rest of the noise. When I remove the hdmi from the cable box the hum gets louder not better. At first I was able to lift the ground and it solved the problem now lifting the ground on both inukes doesn't make a diffference.

I bought a isolation transformer from blue Jean's cable to see if it made any difference. I didn't have much time to play with it but it created a different problem. I plugged it into the rca between the avr and the y splitter. The low frequency hum was better but a higher frequency hum was now louder. This different noise did not resolve by turning the avr off. It was present as soon as the inukes powered on with no signal. I removed it and will continue troubleshooting.

How far apart should the power and signal lines be apart if they need to be run parallel?

I have easy access to the panel and basement. Should I consider running a dedicated 20a line? Would it help with the noise? I am not so concerned with the 20a part but if I am going to run the line it would be silly not to do 20a. I can easily do it myself and probably have some of the supplies already.

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post #22 of 38 Old 12-07-2019, 05:03 AM
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"When I disconnect the rca from the 3k inuke across the room the noise goes away from the 6k which is right next to the avr. When I disconnect the rca from the 6k nothing changes on the 3k across the room"

the ground loop is likely between the two outlets that you are plugged into.

try putting the isolation transformer in between the Y split and the amp on the other side of the room in order to isolate it from the rest of the system.

Listen. It's All Good.
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post #23 of 38 Old 12-08-2019, 04:31 AM - Thread Starter
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Getting closer.

Both amps on everything else off (comcast box is "always on") no noise.

Powered avr on no noise.

Powered TV on and BAM there it is.

Hopefully I have found the source and have the ability to fix it.

More updates to follow.
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post #24 of 38 Old 12-08-2019, 05:58 AM
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Originally Posted by LGERIC View Post
So about a year ago when I got my first inuke and DIY sub I had a tremendous hum. It was so bad I almost couldn't use the sub. I tracked down the problem to the coax cable not being grounded. Go figure. I fixed that and and took care of most of the noise. Fast forward to this week and I have a hum returning and I don't know why. I did some basic troubleshooting and the hum is only present when the avr is on. If I mute the AVR or turn it off there is no noise. AVR off with amps on there is no noise. I also disconnected the coax outside the house where it enters the house and the hum is still present. I tried lifting grounds, adding grounds, plugging things into different outlets and no change. I can make it get worse by removing the hdmi from the cable box or removing the ground for the coax but nothing I do makes it better. Do you guys have any suggestions? I ordered a bjc isolation transformer and something else for the coax. I would rather prefer to solve the source if I can. I could run a dedicated circuit for the equipment if I need to.
The BJC Isolation transformer will probably take the hum out entirely with no ill effects whatsoever. Its the only one that I've ever seen that doesn't also zap away some of your bass. I'd hook that up and consider it solved.

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post #25 of 38 Old 12-08-2019, 08:15 AM
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Just went through that same humm thing. It was my usb cord from my computer to my minidsp, even though I had all my amps, minidsp and computer on ground wires. Someone also said that their fire stick was a cause and when he replaced it with a roku stick the noise was gone.
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post #26 of 38 Old 12-08-2019, 08:35 AM - Thread Starter
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I have been so focused on the amps and coax as the source that I really didn't give a serious thought to the "other" sources. My initial problem was easily fixed by lifting or fixing the amp grounds. Hopefully later I will have some time to work on this a little more.
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post #27 of 38 Old 12-08-2019, 09:12 AM
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Originally Posted by LGERIC View Post
Getting closer.

Both amps on everything else off (comcast box is "always on") no noise.

Powered avr on no noise.

Powered TV on and BAM there it is.

Hopefully I have found the source and have the ability to fix it.

More updates to follow.
The TV was the culprit in my system, also. I ran a wire from one of the TV chassis screws to a chassis screw on the amp.

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post #28 of 38 Old 12-08-2019, 11:05 AM
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Yes you have to look at the entire system as one unit.

Unplug all cables from the TV except the one going to the AVR, and see if the hum returns.

If not, then it ain't the TV.
Then plug each cable back into the TV one at a time, you'll find the upstream device that is causing it.
It is possible it is the TV itself or an upstream device.



Hums can be generated by multiple devices or combinations of devices.
In multiples they are rather sneaky to debug.

A single device isn't so bad, all you have to do is start by unplugging the most-upstream devices and then working down stream. Once you find the hum, you have to go higher up the stream on the problem path and start over, until the source culprit is found.

Most humans cannot comprehend exponential functions, or systematic elimination processes etc.
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post #29 of 38 Old 12-08-2019, 12:36 PM - Thread Starter
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Unplugging the TV from the wall or removing the hdmi does not change anything.
Unplugging the cable box from the wall and coax does not change anything.
Same thing with the bluray no change on or off.

The only thing that produces a change is removing the hdmi to the cable box from the back of the avr. The hum gets louder..
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post #30 of 38 Old 12-10-2019, 12:10 PM - Thread Starter
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Well...grounding both the amp chassis to the avr chassis solved the problem! Thank you to everyone for your input. This place is awesome!
I hope this will help someone else in the future.

On to the 2nd 12"jbl!!!
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Last edited by LGERIC; 12-10-2019 at 12:34 PM.
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