ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 3 [4] 5 6 7   Go Down

Author Topic: Distance between electrical and audio cables  (Read 21360 times)

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1569
Girding loins in iron
« Reply #30 on: January 19, 2015, 10:04:10 am »

I think there's lots better ways to stop ground loop current induced hum than a diode ground lift. Audio isolation transformers are my #1 choice, followed by pin-1 lifts on balanced inputs. And if you can get a power distro system in a building properly grounded without contamination from building steel and such, then the previous fixes just aren't needed. Dimmer buzz is it's own kind of hell, and we could (and probably should) discuss that at some point. It's just so messy I don't like to think about it. 

However, electrical things are rarely perfect, so I like to go into battle with my loins girded in steel (how poetic). I take every kind of transformer DI and ISO box I have and put them in any predictable ground loop paths. Most of time I'm smart enough to out-think the gremlins, but I still get surprised at times. Then I put on the thinking cap and try to figure out what's happening to cause the latest hum/buzz/hiss/hash.
Mike,

Being frugal, my first choice is a shield lift at the receive end, then isolation transformers if the shield lift does not work .

A couple weeks ago provided sound for a demonstration against some of the many stupid things the local power company is doing. Since we were not going to be provided AC power, I brought a couple batteries and a modified sine wave inverter which I had previously successfully used to used to power a Christmas "float" with a sound system to power the PA.

I also needed to provide as many as three audio splits from the PA microphones in two separate places, so used what I had, mic "Y" cords through EB-Tech "hum eliminator" audio isolation transformers.

At about 2 AM while prepping for a 8 AM call found the iso transformers output was buzzing when I auditioned them through a Mackie 1402 VLZ mixer powered from the modified sine wave inverter (no earth ground) or regular earth grounded power. The EB-Tech transformers isolate the shield (sleeve) connections as well as tip and ring. I noticed the noise lessened when I touched the Mackie shield and a sleeve connection, found that running a piece of copper baling wire around the six metal in/out TRS shells eliminated the buzzing noise completely.

Having used the iso transformers before to eliminate hum and buzz on gear that was not "cured" with a shield lift I was surprised to find that the iso transformers buzzed, but also pleased to have "solved" the problem so I could get a few hours sleep before the call.

Naturally, none of the video people bothered to get a clean direct feed from me, but at least it was available....

Art
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Distance between electrical and audio cables
« Reply #31 on: January 19, 2015, 10:06:16 am »

Thanks guys, I didn't know about Iso Boxes. only DI's

The Whirlwind ISO-1 is a solid unit that can solve all sorts of common ground isolation problems at line level. I would say that 90% of the time you would have the ground lifted since both pieces of gear you're interconnecting should be earth grounded. WW also makes a stereo (ISO-2) and an 8-channel (ISO-8) version for handling multiple problems. Theory suggests that this should be placed at the receiving end of the line for improved common mode rejection, but lots of times I just put them on the send side of the signal (in the doghouse of the mixing console) and they've always worked from that position. But I've not run actual CMRR tests to confirm the theory. All I know is that putting a good 1:1 600-ohm isolation transformer with the ground lifted stops all ground loop shield current from flowing, and that's the majority of interference I typically hear at remote gigs. If you can stop the shield current, you stop the ground loop hum.
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Girding loins in iron
« Reply #32 on: January 19, 2015, 10:23:07 am »

Being frugal, my first choice is a shield lift at the receive end, then isolation transformers if the shield lift does not work.

That's always a reasonable and affordable way to proceed. I have a couple of short XLR cables with a pin-1 switch wired into the barrel that provides a ground or lift at the flick of a switch. Great for troubleshooting hums and determining how to fix them.

The key thing to remember is that 60-Hz current in the shield causes hum, but high-frequency harmonic content causes buzz. And buzz can sneak in all kinds of other ways besides shield current and requires proper shielding to cure.

I divide noise into four basic categories. You need to determine what you're hearing before you can figure out how to fix it. This is not a complete list, but it's a good starting point.

Hum - Around B flat on a bass guitar in the 60-Hz USA (A slightly sharp Low G for Steve and the rest of the 50-Hz world) without any harmonics usually caused by too many grounds that cause current to flow in the XLR cable shield. Gear with the infamous "pin-1 problem" will hum like crazy. Incorrect building grounds can make hum come and go with changes in panel box current flow from other things such as kitchen appliances, heating, and lighting systems. 

Buzz - same B flat fundamental note but with raspy harmonics typically caused by light dimmers or no shielding or no grounds. Lots of time coupled between parallel runs of XLR and lighting cables with triac dimmers.

Hiss - White noise (actually Brownian Noise) caused the electronics. Everything hisses at some level just due to heat. But noticeable hiss is usually a level mis-match resulting in a gain structure issue.

Hash - Bacon frying noise resulting from switching power supplies in laptop computers and other gear that creeps back into the inputs of your mixer. Sometimes it will change when a laptop computer accesses its hard drive. I've used a WW PCDI to correct that problem 100% of the time.
« Last Edit: January 19, 2015, 10:48:57 am by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Girding loins in iron
« Reply #33 on: January 19, 2015, 10:57:54 am »

Ref - Girding Loins in Steel (or iron) from Singring and the Glass Guitar: 

Fire can never burn me
Flames can not catch me - faster am I
Blazes never faze me
Barefoot I walk hot coals for a mile
My sword is tempered, my loins are girded in steel
Make my way to the heart of the forest of flames
And if I do my best and don't stop to rest
I may pass the test and capture the key that opens the chest
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3210
  • Isle of Wight - England
Re: Distance between electrical and audio cables
« Reply #34 on: January 19, 2015, 12:54:49 pm »

I came across a new one to me on Saturday.  I had set up a couple of speakers and an XR600 for a friend's birthday party - just to play music from his laptop.

My usual connection method is a box I put together with a transformer and a couple of resistors to sum the headphone L and R outputs into the primary and XLR on the secondary.  The grounds are permanently connected and have never been a problem before.

However, with channel and master levels at minimum I got a weird noise through the speakers as soon as I plugged into the laptop (actually a little USB plug in output device but it did the same thing on the laptop's headphone out).  Not quite random, more rhythmic yet somehow obviously computer generated.

The cure was to open up the box and cut the ground (yes, I know I should have put a switch on it!). End of problem.

The laptop or quite possibly its switch mode power supply was obviously putting this noise into the ground somehow. Perhaps a fifth category to add to your list!


Steve.
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Distance between electrical and audio cables
« Reply #35 on: January 19, 2015, 01:32:13 pm »

The laptop or quite possibly its switch mode power supply was obviously putting this noise into the ground somehow. Perhaps a fifth category to add to your list!

I believe that should fall under the HASH catagory

Hash - Bacon frying noise resulting from switching power supplies in laptop computers and other gear that creeps back into the inputs of your mixer. Sometimes it will change when a laptop computer accesses its hard drive. I've used a WW PCDI to correct that problem 100% of the time.


You've built what Whirlwind makes and calls a podDI. Does exactly what you describe, plus includes a built-in ground lift switch. Some laptops will couple their internal switching supplies to the audio ground and make exactly the noise you describe, while others will be perfectly quiet. I always try to put a WW pcDI or podDI in any computer feed to a mixing board. There are numerous other brands/models that do basically the same thing. But the one thing they all have in common is a way to combine the stereo headphone outputs of a computer or media player, plus an audio isolation transformer, plus a switch for a pin-1 shield lift. There's just no good way to predict if you're going to have this "Hash" problem from a particular laptop, so I typically put an audio isolation transformer in the line and don't worry about it. 
« Last Edit: January 19, 2015, 01:46:07 pm by Mike Sokol »
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3210
  • Isle of Wight - England
Re: Distance between electrical and audio cables
« Reply #36 on: January 19, 2015, 02:17:31 pm »

There's just no good way to predict if you're going to have this "Hash" problem from a particular laptop, so I typically put an audio isolation transformer in the line and don't worry about it.

I suppose it could come under that category but it wasn't really a bacon frying noise.  If you were to record the sound that a mobile phone sometimes puts into an audio system then played it back at a quarter speed it would be close.

There's just no good way to predict if you're going to have this "Hash" problem from a particular laptop, so I typically put an audio isolation transformer in the line and don't worry about it.

I was just pleased that I took my transformer box which gave me the option of cutting the ground.  I could just as easily have picked up one of my leads which sums and attenuates to a 1/4" jack.

I suppose I should add a switch to mine - although I can't think of a reason why I would need to connect the ground for this application.  Does the parallel 10 ohm resistor and 1uF capacitor as used in active DIs solve this problem?  Only one way to find out I suppose!



Steve.
« Last Edit: January 19, 2015, 02:28:16 pm by Steve M Smith »
Logged

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Distance between electrical and audio cables
« Reply #37 on: January 19, 2015, 03:19:33 pm »

I suppose it could come under that category but it wasn't really a bacon frying noise.  If you were to record the sound that a mobile phone sometimes puts into an audio system then played it back at a quarter speed it would be close.

Perhaps my "bacon frying" noise definition needs work. You're correct, it's more of a mechanical/periodic noise like a cell phone seeking connection. So how about "robot bacon"?  ???  No, that's not it either.

I'm pretty sure that "dimmer buzz" works for most people. And we can all agree on what Hum and Buzz sound like in general. Hiss should be obvious, I would think. So what's a few-word definition of switching power supply hash that will have enough mental imagery to be useful for troubleshooting?
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Girding loins in iron
« Reply #38 on: January 19, 2015, 03:32:53 pm »

Ref - Girding Loins in Steel (or iron) from Singring and the Glass Guitar: 

Fire can never burn me
Flames can not catch me - faster am I
Blazes never faze me
Barefoot I walk hot coals for a mile
My sword is tempered, my loins are girded in steel
Make my way to the heart of the forest of flames
And if I do my best and don't stop to rest
I may pass the test and capture the key that opens the chest

Just in case you're having trouble with a mental image of "Girding Up Your Loins" I've included a graphic.
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

Mark Cadwallader

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1277
  • Helena, Montana USA
Re: Girding loins in iron
« Reply #39 on: January 19, 2015, 04:21:27 pm »

Just in case you're having trouble with a mental image of "Girding Up Your Loins" I've included a graphic.

That's why a kilt is much more practical attire (in non-desert climates).

I have a small handfull of Rapco-Horizon ISOBlox, and a couple of WW podDI boxes. Do you have any knowledge or opinion of the robustness of the transformers in the ISOBlox vs the WW ISO-1 device?

Mark C.
Pipes and Drums of the Black Devils
Logged
"Good tools are expensive, but cheap tools are damned expensive."

ProSoundWeb Community

Re: Girding loins in iron
« Reply #39 on: January 19, 2015, 04:21:27 pm »


Pages: 1 2 3 [4] 5 6 7   Go Up
 



Page created in 0.037 seconds with 23 queries.