Low level HUM, driving me CRAZY!

[THX1136]

A brief comment of lifting pin 1 on one end of a balanced cable. Unless you're going from a 3 cond. to 2 cond. connection you should never do that. One comment I read implied that should always be done with XLR (balanced) cables. What you end up with is basically an unbalanced cable so why bother with an XLR connector - RCA/phono or phone would suffice. The other issue is combining pro/+4 gear (usually balanced 3 cond.) with -10 consumer gear (usually 2 cond. unablanced) which causes issues; the biggest - in my mind - being level disparity due to impedance mismatch. Best to stick with either all +4 or -10. This prevents 'jumping through hoops' later to get things to work.

 

[HomerJAU]

Normally in professional studios or systems, the shield of the XLR cable (pin #1) is only connected at ONE END!.

I worked in instrumentation and control systems design and that was standard practise for all screened cables, earth the screen at one end only, insulate at other end.

 

[quadsearcher]

Is there Cable TV hooked up anywhere in the room? Here is an example: CATV went to cable box. Cable box HDMI to TV. Receiver to TV. Hum when all connected, no hum when path between CATV cable ground and receiver is interrupted.

CATV was not properly grounded at the pole or the house.

So if TV with CATV if already connected to PrePro, test again with it out of the picture.

 

[marpow]

Is there Cable TV hooked up anywhere in the room? Here is an example: CATV went to cable box. Cable box HDMI to TV. Receiver to TV. Hum when all connected, no hum when path between CATV cable ground and receiver is interrupted.

CATV was not properly grounded at the pole or the house.

So if TV with CATV if already connected to PrePro, test again with it out of the picture.

Looked into that. I have satellite dish, but a couple of weeks ago, disconnected dish at point of house entry, disconnected all (3) little Genie boxes and ethernet modem at same time. No TV signal at all anywhere in house, no help.
So, sticking with eliminating XLR's and swapping with RCA's.
In regards to my one sub issue I am going to put 3 cheater plugs in place of that trio of setup. One at PC to Fuhrman, One at Ethernet switch to Fuhrman and one at Sub to wall outlet. Plus put in a question to the PC builder to see if they have had any experience.?
Chipping away, that's all I can do.

 

[marpow]

I worked in instrumentation and control systems design and that was standard practise for all screened cables, earth the screen at one end only, insulate at other end.

What does that mean Garry, Earth-----Screened---insulate-----
My XLR's are male at one end and female at other.
Don't know if I want to try anything but certainly interesting to learn the concept.

 

[THX1136]

I've worked in a couple of 24 track facilities years ago (A&R, Ames IA & West Minst'r Sound - now Junior's Motel, Otho IA) and work at a radio station currently. All balanced cables remain intact - all pins connected both ends. No issue with noise in the audio in my experience. I was taught that the only time pin 1 is lifted is if one is connecting balanced to unbalanced gear. I would imagine it would also work if both pieces of gear use a different grounding scheme - one to chassis, the other to circuit. Sincerely with all respect Homer I'm just saying my experience has been different. No worries.

 

[HomerJAU]

I was taught that the only time pin 1 is lifted is if one is connecting balanced to unbalanced gear.

Yes, that's my cables, connecting RCA to XLR.

 

[4-earredwonder]

Markie, maybe if you blast Frank Zappa's Dinah~Moe HUMM through your system ... the offending NOISE will VANISH ZAP!

 

[THX1136]

Here's link to a good explanation of the issue for you folks.
https://tortugaaudio.com/humming-along-to-the-pin-1-problem/
along with this one:
https://www.ranecommercial.com/legacy/note151.html

 

[MarkerB]

Normally in professional studios or systems, the shield of the XLR cable (pin #1) is only connected at ONE END!. Usually the end at the input of the device. This still provides a grounded shield without the possibility of a ground loop in multiple connections or noise currents flowing in the shield. If you have a meter, see if pin one is connected at both ends. If so and you can cut the pin one connection at all of the female XLRs that may solve your problem.

This is exactly right, and might even apply to the shields on unbalanced connectors and cabling. It will open you up to some RF noise potential, but that's not as much of a problem. Using a ground loop isolator keeps you from having to mess with your cables, risk RF interference, and keep track of which ones have the ground lifted.

BTW, if you must lift a ground, lift it on the receiving/input end of the cable, not the source/output end.

 

[MidiMagic]

I don't have a meter, but very intersting.

$12 at Lowes. Use ohms scale for continuity of cable. I don't know what I would do without mine.

Thoughts on the XLR hum:

- Is there a transformer at either end of the XLR cable to convert it to unbalanced? It could be picking up an electromagnetic field (e.g. from a wall-wart).

- Is the XLR connection only "impedance balanced"? This offers no hum protection.

- The direct box I mentioned is also a converter between +4 balanced and -10 unbalanced levels.

- Also note that any XLR device with phantom power sends the power between the pin 1 line and the center tap on the pin 2/pin 3 transformer.

- When I lift the pin 1 ground or an unbalanced ground, I put a 10-ohm resistor in the connection instead of entirely opening it. It c;lobbers the ground loop while maintaining a ground if it is needed (e.g. when you unplug another cable that was providing the ground reference). Burt do not do this if phantom power is used.

 

[Steve Schoultz]

Just to clarify the ground shield connection has nothing to do with whether or not a cable is unbalanced vs balanced. The balance refer to the two signal wires in opposite polarity. This allows for common mode rejection (CMR). The shield is for RFI.

 

[jimfisheye]

Just to be extra extra clear with the lifting ground on one end of the shield thing.
This is the shield we're talking about. Not the pin 1 connection itself!

The idea is if some noise is getting caught by the shield, it will be forced to drain off in one direction. That's simplified in a few ways.

Of course pin 1 is still connected and any ground loop would still be literally exactly the same!
Lifting the shield (usually on the receiving end - so that the shield is part of the sending device) addresses noise entering the cable.

For transformer balanced outputs or cross coupled outputs (which will be labeled "balanced/unbalanced"), short pin 3 (ring) to pin 1 (sleeve) ground to connect to an unbalanced input.

Assume anything not labeled "balanced/unbalanced" has op amp outputs that are not designed to short pin 3 to ground! (Most gear nowadays is made for balanced or unbalanced and labeled as such. If it's labeled only "balanced" though, don't just assume! Grab the manual and verify if it's OK to short pins 1&3!) Dropping pin 3 (leaving it unconnected) to make an unbalanced connection with 6db less signal is required to connect op amp balanced outputs to unbalanced inputs here.

 

[jimfisheye]

Just a thought...

What is the "Pre/Pro" device you mention? Is this your crossover unit? Is this the device with unbalanced only connections?

If you have enough outputs on your audio interface (or AVR if that's what you're using), you could try to do the crossover digitally and then send 1:1 prepared outputs directly to the amp channels.

You might find you like the flexibility of that too. You'd need 2x the number of outputs for each channel needing a 2-way split. 3x if it's 3-way. If you were using an interface that had extra outputs you weren't using, this could be a slick "free" solution.

 

[audiomaster]

What does that mean Garry, Earth-----Screened---insulate-----
My XLR's are male at one end and female at other.
Don't know if I want to try anything but certainly interesting to learn the concept.

Isn't grounding FUN! The Rane article is offering, I feel, the best and most complete description. I have used many pieces of Rane over the years and they were very reliable and quiet when installed properly.
They know what they are doing. And they are real ENGINEERS.

But if you are going balanced, you need to be sure the equipment on both ends of the cable is really a true balanced circuit. And remember, almost certainly, the circuitry INSIDE the devices is unbalanced and the signal must go thru extra circuitry on both ends in both devices to balance and then unbalance it. Do you really NEED a balanced connection at all. Unless your devices are more than 5-10 ft apart or you are next door to a radio tower, probably not. Balanced is needed in studios and large installations where hundreds of feet of cable are used to different rooms and then a central ground system is installed, usually at a patch bay.
Are we having fun yet? )

 

[audiomaster]

Is there Cable TV hooked up anywhere in the room? Here is an example: CATV went to cable box. Cable box HDMI to TV. Receiver to TV. Hum when all connected, no hum when path between CATV cable ground and receiver is interrupted.

CATV was not properly grounded at the pole or the house.

So if TV with CATV if already connected to PrePro, test again with it out of the picture.

The code requires that your incoming cable shield (or an antenna feed) be grounded at the point where it enters the structure. AND that that ground wire be connected directly to the same ground as the electrical service of the building (usually a copper rod in the ground or rebar in the foundation.
But in practice this may require a ground wire to be run halfway around a building, the installers often don't do it. They MAY tie a ground to the nearest thing they think is a ground, a water pipe, nearby receptacle etc. This may actually put more noise on the cable than it removes! And that noise can run back to your cable or sat receiver box and, via audio connections into your system. Lightning surges can also follow this path into your setup. Think ZZZZZZAP!!

 

[audiomaster]

What does that mean Garry, Earth-----Screened---insulate-----
My XLR's are male at one end and female at other.
Don't know if I want to try anything but certainly interesting to learn the concept.

"Earthed" means it is connected to the earth via some path, usually the ground wire in the AC line, but could be a separate wire to a driven rod in the ground or metal bars in the foundation.
"Screened" is another term for shielded, a conductive covering on a wire or metal device cover to block electromagnetic radiation.
"Insulate" means there is no conductive path between two devices or points in a circuit.

 

[marpow]

Thank you @audiomaster.
I have switched to all RCA's. I had to order two 1 meter and one 2 meter to complete.
I am not able to explain why switching from XLR to RCA was the answer.
I have only listened for a couple days now and am happy with a forced decision but a decision never the less.
In the tree of Audioquest cable products, I went two (RCA's) down from the XLR's I had.
Listening now for a couple days, most important hum is gone, but hey, I spent good money on XLR's and now to take two steps down and go to RCA's what about what is most important, music listening.
I can hear a bit of difference, but barely, plus my placebo is probably out of whack.
Bass response is very good, maybe a touch better than before.
Midrange and treble, very good, equal to as before.
Overall: hmm, this is where I am not quite so sure, I want to say for now, some of the brightness is gone? I believe, give me a short amount of time and I will move on. I am still playing with volume levels and definitely listening to hard right now.
I am very happy with this outcome, even though intellectually I don't quite understand.

 

[4-earredwonder]

Thank you @audiomaster.
I have switched to all RCA's. I had to order two 1 meter and one 2 meter to complete.
I am not able to explain why switching from XLR to RCA was the answer.
I have only listened for a couple days now and am happy with a forced decision but a decision never the less.
In the tree of Audioquest cable products, I went two (RCA's) down from the XLR's I had.
Listening now for a couple days, most important hum is gone, but hey, I spent good money on XLR's and now to take two steps down and go to RCA's what about what is most important, music listening.
I can hear a bit of difference, but barely, plus my placebo is probably out of whack.
Bass response is very good, maybe a touch better than before.
Midrange and treble, very good, equal to as before.
Overall: hmm, this is where I am not quite so sure, I want to say for now, some of the brightness is gone? I believe, give me a short amount of time and I will move on. I am still playing with volume levels and definitely listening to hard right now.
I am very happy with this outcome, even though intellectually I don't quite understand.

Great success story, Markie. The chaps at QQ forum have done it again with their wisdom of all things audio!

Well, at least we all know there will never be a HUMVEE ..... IN YOUR FUTURE!

 

[marpow]

Another Success: My interference between PC and Sub. This was a different issue than the Hum in speakers, that was solved by RCA cables.
Took 3 cheater plugs and added as below.
1. Power cord sub to wall.
2. PC to Fuhrman supply.
3. Ethernet switch to Fuhrman supply.
No Noise coming out of sub.
Now disconnect cheater plugs one at a time.
1. Power cord back in wall, no cheater. No Noise.
2. PC back in Fuhrman, no cheater. Noise.
3. Ethernet switch back in Fuhrman, no cheater, PC back in Fuhrman with cheater. No Noise.

Well, that is the answer, PC has a ground something it does not like with Sub being in same something?
Now, I have used cheater plugs my whole life being in construction, never a problem.
So unless someone has something overwhelmingly positive to remove this one cheater plug on PC or some other new fangled device, (maybe I will try my Hum X that failed everywhere else), I will just leave it be and go on so I can forget this months of madness.