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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Alex Donkle on January 14, 2015, 04:08:48 pm

Title: Distance between electrical and audio cables
Post by: Alex Donkle on January 14, 2015, 04:08:48 pm
More of a poll type question, but has anyone here ever come across sound system hum or buzz that was caused by audio cables running next to power cables? Best practice has always been separate the cable types whenever possible for several reasons (including safety), but I've also never seen it actually cause noise problem problems for the sound system when dealing with balanced cables, correctly wired. Nearly all sound system hum I've come across relates to grounding issues. Has anyone ever witnessed a noise issue that was fixed by just moving audio cables further away from power cables?
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 14, 2015, 05:24:34 pm
More of a poll type question, but has anyone here ever come across sound system hum or buzz that was caused by audio cables running next to power cables? Best practice has always been separate the cable types whenever possible for several reasons (including safety), but I've also never seen it actually cause noise problem problems for the sound system when dealing with balanced cables, correctly wired. Nearly all sound system hum I've come across relates to grounding issues. Has anyone ever witnessed a noise issue that was fixed by just moving audio cables further away from power cables?

When I used to do a lot of political gigs in DC the lighting guys would lay their cables right on top of my mic lines. That would cause a lot of dimmer hash in the pre-amps. I changed to Canare Star-Quad cable for those runs and that problem went away.   

I did have a problem with a stage that had a big 6" AC power conduit running right under where the bass guitar player stood. When he turned on stage his bass would be quiet or hum like crazy, depending on how his pickups lined up with the path of the conduit under his feet. I corrected the problem by having him switch to the opposite side of the stage.
Title: Re: Distance between electrical and audio cables
Post by: TJ (Tom) Cornish on January 14, 2015, 05:24:46 pm
More of a poll type question, but has anyone here ever come across sound system hum or buzz that was caused by audio cables running next to power cables? Best practice has always been separate the cable types whenever possible for several reasons (including safety), but I've also never seen it actually cause noise problem problems for the sound system when dealing with balanced cables, correctly wired. Nearly all sound system hum I've come across relates to grounding issues. Has anyone ever witnessed a noise issue that was fixed by just moving audio cables further away from power cables?
AC mains cables?  No.  Dimmers?  Yes.
Title: Re: Distance between electrical and audio cables
Post by: TJ (Tom) Cornish on January 14, 2015, 05:25:41 pm
I did have a problem with a stage that had a big 6" AC power conduit running right under where the bass guitar player stood. When he turned on stage his bass would be quiet or hum like crazy, depending on how his pickups lined up with the path of the conduit under his feet. I corrected the problem by having him switch to the opposite side of the stage.
All bets are off for single-ended guitar pickups, which are some of the most efficient antennae ever invented by man.  :)
Title: Re: Distance between electrical and audio cables
Post by: Mark Cadwallader on January 14, 2015, 05:58:14 pm
Echoing TJ, I have had induced noise through the Clear-Com when I have been too close to the cables powering conventional stage lighting (i.e., dimmers) when up on the fly rail in a theater.   Moving 2' seems to solve the problem. Mark C.
Title: Re: Distance between electrical and audio cables
Post by: Lee Buckalew on January 14, 2015, 06:04:51 pm
Echoing TJ, I have had induced noise through the Clear-Com when I have been too close to the cables powering conventional stage lighting (i.e., dimmers) when up on the fly rail in a theater.   Moving 2' seems to solve the problem. Mark C.

Standard Clear Com is not a balanced audio signal.

Lee
Title: Re: Balanced Comm
Post by: Mac Kerr on January 14, 2015, 06:08:35 pm
Standard Clear Com is not a balanced audio signal.

Nor is Clear Com TW, or RTS. AFAIK the Teles AudioCom (http://www.rtsintercoms.com/us/rts/products/Audiocom_Balanced_Intercom/81?fam%5B%5D=172) is the only balanced belt pack intercom system.

Mac
Title: Re: Distance between electrical and audio cables
Post by: Mark Cadwallader on January 14, 2015, 06:30:41 pm
Standard Clear Com is not a balanced audio signal.

Lee

Point well taken. I wasn't thinking about it being unbalanced. Duh!  Mark C.
Title: Re: Distance between electrical and audio cables
Post by: Lyle Williams on January 14, 2015, 06:35:17 pm
The 2' suggested is adequate.  If possible power and signal cables should not cross each other, or cross each other at right angles.

But people get away with other setups all the time.  I have power taped to my snake along with ethernet and rf coax.
Title: Re: Distance between electrical and audio cables
Post by: Tim McCulloch on January 14, 2015, 06:39:31 pm

But people get away with other setups all the time.  I have power taped to my snake along with ethernet and rf coax.

Done this for longer than there has been ethernet... ;)

As has been said, dimmers fully loaded and running at 50% are the worst things for noise (and newer dimmers are far less of a problem).  Normal AC service has yet to create any noticable induced noise in our systems.
Title: Re: Distance between electrical and audio cables
Post by: Kevin Graf on January 15, 2015, 09:21:30 am
'jneutron' a huge research laboratory systems engineer (has installed over 150,000 miles of wire & cable) is also a weekend pro audio guy.  He runs AC power and signal cables in the same snake.

(http://)
Title: Re: Distance between electrical and audio cables
Post by: Daniel Levi on January 15, 2015, 09:51:37 am
And, of course, a company such as Sommer Cable that make good quality cables would not make combined audio/power cables (and associated multipin plugs) if they thought it was a problem.
Title: Re: Distance between electrical and audio cables
Post by: Steve M Smith on January 15, 2015, 03:30:10 pm
I have power taped to my snake along with ethernet and rf coax.


The only time I have had noise was when I didn't do this.  We had the mixer powered from the same outlet as a follow spot and had some induced noise.  The next day we taped a power cable to our multicore.




Steve.
Title: Re: Distance between electrical and audio cables
Post by: Art Welter on January 15, 2015, 04:54:39 pm
Has anyone ever witnessed a noise issue that was fixed by just moving audio cables further away from power cables?
I remember one set of dimmer cables that were so noisy they induced audible hash into loudspeaker cables run next to them- the high frequency noise could be heard with the amplifiers turned off six feet away from the speakers.
Re routed the speaker cables, turned down amp sensitivity, and the noise dropped to a level below ambient crowd noise.
Title: Re: Distance between electrical and audio cables
Post by: Scott Holtzman on January 15, 2015, 09:21:18 pm
'jneutron' a huge research laboratory systems engineer (has installed over 150,000 miles of wire & cable) is also a weekend pro audio guy.  He runs AC power and signal cables in the same snake.

(http://)

There is so much going on in that picture.  The orange extension core is special but that's been covered so many times we will leave it alone.

The contrast is between the carpet covered speakers, the Tektronix storage (I think but not sure) o'scope and the childrens themed wrapping paper ??  Lot going on in that space.

On a constructive note I have never had an issue with parellel power, snake runs now with DMX, AES50, various wired Ethernet etc.  In fact I have been shipping for some sort of lace up harness so I can group it together.  I tried using telco style wax cord (12 cord) with the running stitch and it looks pretty but doesn't stay together after multiple roll ups.  Individual knows would probably do better but I am not that fast anymore so 150' with 300 knows would be a whole day all said and done.
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 15, 2015, 09:43:58 pm
'jneutron' a huge research laboratory systems engineer (has installed over 150,000 miles of wire & cable) is also a weekend pro audio guy.  He runs AC power and signal cables in the same snake.

Back in my early days of doing live sound, and before I understood all this ground loop stuff, I discovered that powering my mixing console from an outlet in the back of the room, and the power amp rack from a stage outlet would sometimes result in a ton of hum. But plugging the console into the same outlet as the power amp rack would always have very low or even zero hum. So I taped a 100-ft extension cord to my mic snake for convenience and never had a problem. I understood that voltages differences between the two grounds were the culprit, and after being shocked a few times from ground-lifted extension cord, I was dedicated to grounding everything.

Nowadays when I need to run copper between two pieces of gear powered by different electrical outlets, I try to incorporate an isolation transformer whenever there's the slightest hint of hum. And don't count on "isolated" or "technical ground" circuits as the ultimate solution. I find that they're sometimes mis-wired and contaminated by electricians who don't understand audio system grounding, and often not worth all the extra expense. 
Title: Re: Distance between electrical and audio cables
Post by: Stephen Swaffer on January 15, 2015, 10:22:19 pm

On a constructive note I have never had an issue with parellel power, snake runs now with DMX, AES50, various wired Ethernet etc.  In fact I have been shipping for some sort of lace up harness so I can group it together.  I tried using telco style wax cord (12 cord) with the running stitch and it looks pretty but doesn't stay together after multiple roll ups.  Individual knows would probably do better but I am not that fast anymore so 150' with 300 knows would be a whole day all said and done.

We used to use a nylon fabric sleeve for grouping TIG welding lines (water cooled electrode/return water/gas) came flat-zipper zipped into a tube. These were standard 10' or 12 ' but it seems like I have seen bulk rolls.  Held up well in a weld booth, I would think it would last for sound applications?
Title: Re: Distance between electrical and audio cables
Post by: Jonathan Johnson on January 16, 2015, 01:51:53 am
Normal AC service has yet to create any noticable induced noise in our systems.

Unless you are dealing with 115kV transmission lines, in which case you may want to maintain a separation of a hundred feet or more.

(Sorry, I just had to pick an extreme.  ;D )
Title: Re: Distance between electrical and audio cables
Post by: Nate Armstrong on January 16, 2015, 09:03:41 am
What are your guys thoughts about this device ?
https://www.youtube.com/watch?v=CuvDMjxhE68
if you do not want to watch the video , Here is the an explanation of the video

by  adding large  power rectifier diodes to the ground  it eliminates the 60 hz hum.
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 16, 2015, 09:17:41 am
What are your guys thoughts about this device ?
https://www.youtube.com/watch?v=CuvDMjxhE68
if you do not want to watch the video , Here is the an explanation of the video

by  adding large  power rectifier diodes to the ground  it eliminates the 60 hz hum.

Been there, done that (nearly 40 years ago). Only works for small ground loop voltage differentials (GLVD) up to the forward bias of the P-N junction in the diode. So that's around 0.5 to 0.6 volts for standard Silicon junctions. You can series stack the diodes for a higher GLVD situation, and I used to use really big diodes (40 amp?) for some of my early hum reduction experiments back in the 70's.

I see 1 to 2 volts GLVD all the time, and have personally measured 5 volts GLVD on occasion. My table-top experiments show around 1 amp of current in the shield per volt of Ground Loop Differential, and many types of pro-sumer gear with the pin-1 problem will start ground loop humming at 100 mA of shield current. So even 1/10 volt difference between outlet grounds can make your active floor wedges hum.   
Title: Re: Distance between electrical and audio cables
Post by: Nate Armstrong on January 16, 2015, 09:49:43 am
Mike, I know your the power guy.  What do you recommend for this issue / what do you use ?

it seems the video link i posted is a home made version of this

(http://static.bhphoto.com/images/images500x500/365781.jpg)

Title: Re: Distance between electrical and audio cables
Post by: Josh Millward on January 16, 2015, 12:50:25 pm
Mike, I know your the power guy.  What do you recommend for this issue / what do you use ?

it seems the video link i posted is a home made version of this

(http://static.bhphoto.com/images/images500x500/365781.jpg)

That, right there, is one product that will never, ever receive a UL Certification or UL Listing.

It is but a bandaid for masking the real problems, which are typically things like Pin 1 issues in the interconnected gear, or missing ground connections.

I have been running from the position of ground everything, completely, all the time; and run it all from one source of AC. If this is not possible, use audio isolation transformers to provide galvanic isolation for things operating on different sources of AC. The result is that I never have hum or other weird noises to eradicate from my systems.
Title: Re: Distance between electrical and audio cables
Post by: Nate Armstrong on January 16, 2015, 03:12:38 pm
Often my shows are to small to run a distro. so i use house power.. Most of the time i have zero hum.. but every now and then i do.
It drives me crazy.. CRAZY


it is often
1) different ground potentials on different power outlets though out the venue.  Even when i pull FOH and all PA from the same backline/ stage area power sources. ( example  multiple outlets on the backwall of the stage)

2) older guitar amps like the fender twin reverb
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 16, 2015, 05:14:58 pm
Often my shows are to small to run a distro. so i use house power.. Most of the time i have zero hum.. but every now and then i do.
It drives me crazy.. CRAZY

it is often
1) different ground potentials on different power outlets though out the venue.  Even when i pull FOH and all PA from the same backline/ stage area power sources. ( example  multiple outlets on the backwall of the stage)

I've seen a number of otherwise properly wired back wall outlets where a few of them had the ground and neutral wires swapped. They test as normal except when under load. Then any voltage drop that should happen on the neutral will now occur on the EGC ground instead. So a big bass note or kick drum which normally causes a few volt drop on the neutral will induce this voltage on the EGC ground, which can produce a GLVD (Ground Loop Voltage Differential) resulting in shield current which causes ground-loop hum that is modulated by the normal current fluctuations of the power amp. I've been messing around with this in my head and on my test bench and call it GLID (G-L-I-D) for Ground Loop Induced Distortion. It sort of sounds like fuzzy bass that has a 60 Hz hum modulating the fundamental note. I can make it happen on my test bench easily enough under forced conditions, but I've been thinking about a simple demonstration that could be done in a room full of listeners with normal powered speakers. GLID can be caused by any miswiring that creates ground loop current and hum under varying amplifier load, but I think the swapped Neutral-Ground wires almost guarantee it will happen.

It seems crazy that someone could swap the ground and neutral wires accidentally, but it's not obvious with casual testing and doesn't create immediately hazardous conditions like an RPBG (Reverse Polarity Bootleg Ground) does.

Sorry for my custom acronyms, but electrical engineering and code books really don't explain how this all works, so I've got to come up with my own definitions sometimes.   
Title: Re: Distance between electrical and audio cables
Post by: Greg_Cameron on January 16, 2015, 05:37:04 pm
I have been running from the position of ground everything, completely, all the time; and run it all from one source of AC. If this is not possible, use audio isolation transformers to provide galvanic isolation for things operating on different sources of AC. The result is that I never have hum or other weird noises to eradicate from my systems.


This is my method as well. I regularly have to run relatively remote powered speakers through the multi-room venue I do most of my work, where running power from my main PA distro is truly impractical. So I use local circuits for those remotes and slap a Whirlwind ISO1 transformer in line. No noise problems, proper AC safety ground, and a high quality transformer that doesn't saturate with hot levels with low frequencies. it's a win/win...
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 16, 2015, 05:50:44 pm

This is my method as well. I regularly have to run relatively remote powered speakers through the multi-room venue I do most of my work, where running power from my main PA distro is truly impractical. So I use local circuits for those remotes and slap a Whirlwind ISO1 transformer in line. No noise problems, proper AC safety ground, and a high quality transformer that doesn't saturate with hot levels with low frequencies. it's a win/win...

That's exactly what I do. I'm a simple man who has to do complicated things, so I use output transformers to feed all remote powered speakers, even if they're just on the other side of the same room. Since the transformers break the grounding path, the shield current drops to zero which means there's no ground loop current. And without ground loop current, there's no ground loop induced hum. 

See, a simple idea that lets you focus on more important things during setup. I HATE hum and buzz in a sound system. 
Title: Re: Distance between electrical and audio cables
Post by: Jay Barracato on January 16, 2015, 06:16:15 pm
The thing is if the dimmers are dumping hash onto the ground it doesn't matter if you are pulling from one source or several. I think back to the hotel room that was giving me fits despite pulling everything from a single 15 amp circuit. Every circuit on the subpanel on that floor had the same problem including the hotels installed system. It turned out to be the dimmers they had installed on the room lights. You could get away with full on or full off but no where in between.

Sent from my DROID RAZR HD using Tapatalk

Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 16, 2015, 07:19:26 pm
The thing is if the dimmers are dumping hash onto the ground it doesn't matter if you are pulling from one source or several.

Dimmers are evil...
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol on January 16, 2015, 07:37:18 pm
Mike, I know your the power guy.  What do you recommend for this issue / what do you use ?

I have a few of the HumX lifts on my test bench, and have tried them in the field. I've even tried a dead short from the hot line to their diode isolated ground a bunch of times which trips my circuit breakers without blowing up the HumX internal rectifiers. That being said, they only work on very small ground differential voltages (less than 1/2 volt AC) and tend to turn moderate ground loop hum into ground loop buzz. That's because the diodes begin to conduct on the peak of the AC cycle when they forward bias.

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.
Title: Re: Distance between electrical and audio cables
Post by: Nate Armstrong on January 19, 2015, 09:10:06 am
Thanks guys, I didnt know about Iso Boxes. only DI's
Title: Girding loins in iron
Post by: Art Welter 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
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol 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.
Title: Re: Girding loins in iron
Post by: Mike Sokol 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.
Title: Re: Girding loins in iron
Post by: Mike Sokol 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
Title: Re: Distance between electrical and audio cables
Post by: Steve M Smith 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.
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol 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. 
Title: Re: Distance between electrical and audio cables
Post by: Steve M Smith 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.
Title: Re: Distance between electrical and audio cables
Post by: Mike Sokol 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?
Title: Re: Girding loins in iron
Post by: Mike Sokol 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.
Title: Re: Girding loins in iron
Post by: Mark Cadwallader 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
Title: Re: Girding loins in iron
Post by: Mike Sokol on January 19, 2015, 05:20:15 pm
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?

I don't know enough yet to make a definite call, but I've got enough for an educated guess. I found the transformer chart for the audio transformer in the Rapco box. It lists the transformer having under 1% distortion from 20Hz to 60KHz at +2dBM. See below.

I've asked Al Keltz at Whirlwind about the transformer in their ISO-1, and they ran a preliminary test for distortion at low frequencies and high signal level. They measured just under 0.5% distortion at 20Hz and with something around +16 or +18dBM level. Don't shoot me if I can't remember the exact numbers since this was just a verbal confirmation with their test engineer.

Now I do know that a transformer's ability to maintian low distortion at low frequencies is largely dependent on the amount of metal in its core. Too little core material and it will saturate/distort at frequencies below 100 Hz. And that's why crappy 70-volt transformers sound so bad with bass frequencies. I'm guessing that the transformer in the Rapco box has to be pretty small to fit in that little case, so it very well could distort at bass frequencies and high signal levels. So maybe at +8 level on a subwoofer it could have significantly more than the 1% distortion listed for +2dBM level. But we need someone at Rapco to give us actual numbers so we can make a proper judgement. Anyone have a Rapco/Horizon connection we can ask?
Title: Re: Girding loins in iron
Post by: Frank DeWitt on January 19, 2015, 08:14:20 pm
One of the many things I like about Jensen transformers is that they publish the test results.  Here is there DI box transformer.
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-db-e.pdf

Here is a line input one made for low frequency use
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-112p-2hpc.pdf
Title: Re: Girding loins in iron
Post by: Mike Sokol on January 19, 2015, 09:29:02 pm
One of the many things I like about Jensen transformers is that they publish the test results.  Here is there DI box transformer.
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-db-e.pdf

Here is a line input one made for low frequency use
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-112p-2hpc.pdf

Remember, we need to consider price as well as performance. If something's not affordable by a large enough base of users, then it won't be available where it's needed. While the Jensen iso-boxes are great performers, they cost at least four times as much as the Rapco units, and twice as much as the WW ISO-1 boxes. For high end installs I would agree that Jensen transformers can be the best choice. But for lots of mid and low-end installations, just getting rid of the hum will remarkably improve the listening experience for the audience, as well as help the musicians who have to deal with humming/buzzing monitors.

I've used lots of Ebtech and WW isolation transformers in hundreds of pro-sound situations to mitigate hum, and never felt I was corrupting the signal. However, I also used to work at radio stations where the transmitter was located within a few hundred feet of the studio, and can remember that Jensen and Lundahl transformers were the only ones that could survive that kind of RF punishment. So for some demanding situations the extra money is worth it. While most of the time you may be able to use a more affordable technology.
Title: Re: Distance between electrical and audio cables
Post by: Stephen Swaffer on January 19, 2015, 11:38:33 pm

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.

The fault may not be the laptop-we have run into situations where same laptop/different power supply made a difference with this issue.  IMO a good USB interface is the best solution here-but not as universal as an iso transformer.
Title: Re: Distance between electrical and audio cables
Post by: Steve M Smith on January 20, 2015, 01:55:49 am
To connect headphone outputs to XLR, a small mains transformer works well.  I have used something like a 10VA 240v to 24v transformer in the past.

Connect left and right to the 240v winding with a couple of series resistors (I think I used 47 ohm) and connect the 24v winding to XLR 2 and 3.

It's a bit bulky and I wouldn't use it on line or instrument level signals but it works fine for headphone level outputs.

The fault may not be the laptop-we have run into situations where same laptop/different power supply made a difference with this issue.  IMO a good USB interface is the best solution here-but not as universal as an iso transformer.

It is more likely to be the power supply.  The pulsing of the noise being the comparator switching the oscillator on and off to maintain the output voltage.

In my case I had a USB interface but still needed to cut the ground.



Steve.
Title: Re: jensen xformers
Post by: John Roberts {JR} on January 20, 2015, 10:03:21 am
Remember, we need to consider price as well as performance. If something's not affordable by a large enough base of users, then it won't be available where it's needed. While the Jensen iso-boxes are great performers, they cost at least four times as much as the Rapco units, and twice as much as the WW ISO-1 boxes. For high end installs I would agree that Jensen transformers can be the best choice. But for lots of mid and low-end installations, just getting rid of the hum will remarkably improve the listening experience for the audience, as well as help the musicians who have to deal with humming/buzzing monitors.

I've used lots of Ebtech and WW isolation transformers in hundreds of pro-sound situations to mitigate hum, and never felt I was corrupting the signal. However, I also used to work at radio stations where the transmitter was located within a few hundred feet of the studio, and can remember that Jensen and Lundahl transformers were the only ones that could survive that kind of RF punishment. So for some demanding situations the extra money is worth it. While most of the time you may be able to use a more affordable technology.
Not sure what this means for pricing of Jensen transformers but they were purchased by Radial, which seems like a good thing for Radial.

JR
Title: Re: Girding loins in iron
Post by: Al Keltz on January 20, 2015, 12:06:25 pm
Here's what we came up with:

THD @ 20 Hz, +19 dBu = 2.7%
THD @ 50 Hz, +19 dBu = 0.3%


THD @ 20 Hz, +4 dBu = 0.62%
THD @ 50 Hz, +4 dBu = 0.3%


Source impedance = 150 Ohms
Load impedance = 20 kOhms

- Al
Title: Re: jensen xformers
Post by: Frank DeWitt on January 20, 2015, 12:28:43 pm
Not sure what this means for pricing of Jensen transformers but they were purchased by Radial, which seems like a good thing for Radial.

JR

Radial also owns Eclipse.


I have been watching the Jensen web site since Radial bought them.  The only significant change is that Jensen was selling there own single channel DI and a wall mounted DI.  Both are gone.  That makes sense.

They do still sell transformers to the public (me)  and I am grateful that they do.
Title: Re: Girding loins in iron
Post by: Mark Cadwallader on January 20, 2015, 01:45:50 pm
Here's what we came up with:

THD @ 20 Hz, +19 dBu = 2.7%
THD @ 50 Hz, +19 dBu = 0.3%


THD @ 20 Hz, +4 dBu = 0.62%
THD @ 50 Hz, +4 dBu = 0.3%


Source impedance = 150 Ohms
Load impedance = 20 kOhms

- Al

Thank you for the information, Al. Mark C.
Title: Re: Distance between electrical and audio cables
Post by: Chris Clark on January 20, 2015, 02:50:30 pm
The fault may not be the laptop-we have run into situations where same laptop/different power supply made a difference with this issue.  IMO a good USB interface is the best solution here-but not as universal as an iso transformer.

I have to agree with this sentiment. In every instance possible over the last few years I've been pushing for the USB audio interface (in sticking with the WW theme, http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/specialty-interface-solutions/pc-usb ) more and more as a proper solution to computer usage. It solves a number of issues, not only isolating that power supply/hard drive hash, it reduces the possibility of having the laptop volume too high and overdriving the DI, and it also gets rid of the huge point of failure involving the horribly unreliable 1/8" connector. Additionally, most are designed as a standard audio interface that the computer (whether Windows or Mac) sees almost immediately without driver intervention (unless you go back to XP, which I should hope no one is anymore).
Title: Re: Distance between electrical and audio cables
Post by: John Escallier on June 16, 2016, 05:27:02 pm
Sorry to take so long to add to this topic.  I've been sort of occupied..
  The orange extension core is special but that's been covered so many times we will leave it alone.

Can you point me to where it was covered?  It was UL approved and had the ampacity for the task.

The contrast is between the carpet covered speakers, the Tektronix storage (I think but not sure) o'scope and the childrens themed wrapping paper ??  Lot going on in that space.

1.  Yah, I don't like carpet much, but the plywood was cheap..
2.  The oscope was an old toy scope, used because a phosphor screen was needed for my ultrasonic welder PLL adjustments.
3.  What do you have against Power Puff Girls???

The most significant thing was, that snake was used to send UNbalanced line level 100 feet in an auditorium that had 15 Kw of old style solid state dimmers (before the current slew rate limitation was adopted).  The enviro was an E/M mess, especially with two 1.2 Mwatt and one  500Kw 12 pole supply less than a quarter mile away.

The in house system guy was unable to get his balanced system to be as quiet as my el cheapo unbalanced one.

John
Title: Re: Distance between electrical and audio cables
Post by: Stephen Kirby on June 17, 2016, 05:43:29 pm
Sorry to take so long to add to this topic.  I've been sort of occupied..
Can you point me to where it was covered?  It was UL approved and had the ampacity for the task.
Code for temporary entertainment use is extra hard service cable, typically SOOW is used.  Consumer vinyl extension cords are not rated for our industry.  Besides being a bear to manage all the kinks and bends compared to rubber jacketed cable.  The typical orange vinyl extension cord is a standard tell for amateur production.
Title: Re: Distance between electrical and audio cables
Post by: Jonathan Johnson on June 17, 2016, 06:20:57 pm
Code for temporary entertainment use is extra hard service cable, typically SOOW is used.  Consumer vinyl extension cords are not rated for our industry.  Besides being a bear to manage all the kinks and bends compared to rubber jacketed cable.  The typical orange vinyl extension cord is a standard tell for amateur production.

Or any color other than black, for that matter.

SOOW and SJOOW are almost always black. When cared for and coiled properly, they will easily lay flat on stage.

Black is the preferred color for what should be an obvious reason: the cables should be as visually unobtrusive as possible.

Yeah, I've got some fluorescent orange cords that I've used. I don't use them in any visually-sensitive area such as anywhere near a stage. The bright orange cords I have are all 12AWG and made of a high-flexibility vinyl. I have black SOOW/SJOOW cords for stage use.

Most of those pumpkin-orange cords are only 16AWG and the connectors are flimsy garbage. They are designed for electric weedeaters and holiday lights, not serious work. Even when cared for and coiled properly, they get stiff and kinky.
Title: Re: Distance between electrical and audio cables
Post by: Lyle Williams on June 19, 2016, 04:53:21 pm
I agree that orange on stage isn't the best look.  But some of the high current cables rated for outdoor use (and their IP66 connectors) only come in orange in my corner of the world.
Title: Re: Distance between electrical and audio cables
Post by: John Escallier on June 20, 2016, 09:02:30 pm
Code for temporary entertainment use is extra hard service cable, typically SOOW is used.  Consumer vinyl extension cords are not rated for our industry.  Besides being a bear to manage all the kinks and bends compared to rubber jacketed cable.  The typical orange vinyl extension cord is a standard tell for amateur production.
Ah, thanks.

I'm a cable tray kinda guy (article 392), with lots of grounding experience as well as EMC problems, not full time audio.  Can you point me to the article that specifies that?  thanks.

Honestly though, I built that snake 15 years ago, that pic was when it was 7 or 8 years old.  The orange cord hasn't kinked or bent.  I've seen that on other job site cords, but they really get abused.  I simply reel it out, reel it in after use.  And the load draw is one mixer and a dual cd player, a denon 600 IIRC, so maybe an ampere or two max.

If I really need to make a new one, I'll go with a code wire....that was made in 15 minutes to address an immediate system issue, and I never looked at it again.

Thanks, John
Title: Re: Distance between electrical and audio cables
Post by: Tim McCulloch on June 20, 2016, 09:21:01 pm
Ah, thanks.

I'm a cable tray kinda guy (article 392), with lots of grounding experience as well as EMC problems, not full time audio.  Can you point me to the article that specifies that?  thanks.

Honestly though, I built that snake 15 years ago, that pic was when it was 7 or 8 years old.  The orange cord hasn't kinked or bent.  I've seen that on other job site cords, but they really get abused.  I simply reel it out, reel it in after use.  And the load draw is one mixer and a dual cd player, a denon 600 IIRC, so maybe an ampere or two max.

If I really need to make a new one, I'll go with a code wire....that was made in 15 minutes to address an immediate system issue, and I never looked at it again.

Thanks, John

The applicable parts of NEC Chapters 2 & 3, the parts of Chapter 4 that deal with flexible cords, then 520, 525, and 640
Title: Re: Distance between electrical and audio cables
Post by: Steve M Smith on June 21, 2016, 02:44:23 am
Or any color other than black, for that matter.

In the UK, blue is fairly standard for 16A cables.  Black for 13A stage power.


Steve.
Title: Re: Distance between electrical and audio cables
Post by: John Escallier on June 21, 2016, 10:01:03 am
The applicable parts of NEC Chapters 2 & 3, the parts of Chapter 4 that deal with flexible cords, then 520, 525, and 640

You code guys crack me up.  The "applicable parts"...sheesh..

I was looking more for something like this:
640.42 Use of Flexible Cords and Cables.
640.42(E) Between Equipment Racks and Branch Circuit Power
The supply to a portable equipment rack shall be by means of listed extra-hard usage cords or cables, as defined in Table 400.4.

I'll have to look at the cable stamping and tag, as quite a few cables do meet the criteria of extra-hard usage ini 400.4


The chances the cord I used meets that?  Probably zero...

Again, thanks.

John
Title: Re: Distance between electrical and audio cables
Post by: Tim McCulloch on June 21, 2016, 10:21:12 am
You code guys crack me up.  The "applicable parts"...sheesh..

I was looking more for something like this:
640.42 Use of Flexible Cords and Cables.
640.42(E) Between Equipment Racks and Branch Circuit Power
The supply to a portable equipment rack shall be by means of listed extra-hard usage cords or cables, as defined in Table 400.4.

I'll have to look at the cable stamping and tag, as quite a few cables do meet the criteria of extra-hard usage ini 400.4


The chances the cord I used meets that?  Probably zero...

Again, thanks.

John

I'm available for weddings, bar mitzvahs, and NEC consultation beginning at $250/hour.

The language in 400.4 and the tables that accompany it isn't particularly clear, but the take-away is that any cable type with a "J" in it is NOT extra-hard service.  "J" is for Junior hard service; without the J the cable is "hard service" under 400.4 and is actually "extra hard service" as referred to elsewhere in the Code.

Usage indoors puts our work under 520, "Theaters, Audience Areas of Motion Picture & Television Studios, Performance Areas, and Similar Locations."  This Article is where much confusion comes from regarding allowed cable types for certain types of assemblies (break outs, break ins, etc).  Outdoors, our work is under 525, "Carnivals, Circuses, Fairs and Similar Events."

Special Equipment (Chapter 6) potentially modifies or excepts certain uses from other aspects of the Code or places additional conditions/requires different materials or methods.

It takes time to figure this stuff out and just when you think you have it down, an Inspector will come along with a Code interpretation that will make your head spin... doesn't happen so often in our work but I've had that happen in residential electrical wiring...
Title: Re: Distance between electrical and audio cables
Post by: John Escallier on June 21, 2016, 12:04:19 pm
I'm available for weddings, bar mitzvahs, and NEC consultation beginning at $250/hour.

"You may kiss the bride....but first, this excerpt from Annex C..."
The language in 400.4 and the tables that accompany it isn't particularly clear...

A part of code that isn't particularly clear..  Shirley you jest...
, but the take-away is that any cable type with a "J" in it is NOT extra-hard service.  "J" is for Junior hard service; without the J the cable is "hard service" under 400.4 and is actually "extra hard service" as referred to elsewhere in the Code.

Usage indoors puts our work under 520, "Theaters, Audience Areas of Motion Picture & Television Studios, Performance Areas, and Similar Locations."  This Article is where much confusion comes from regarding allowed cable types for certain types of assemblies (break outs, break ins, etc).

520 seems to be limited to portable stage equipment.  I suspect a mix rack of the type I use falls out of that, but 640 does cover it.
Outdoors, our work is under 525, "Carnivals, Circuses, Fairs and Similar Events."

Special Equipment (Chapter 6) potentially modifies or excepts certain uses from other aspects of the Code or places additional conditions/requires different materials or methods.

Yup, definitely agree.
It takes time to figure this stuff out and just when you think you have it down, an Inspector will come along with a Code interpretation that will make your head spin..
Tell me about it.  We not only have an AHJ, we have an entire committee.  When one gets a bee in the bonnett, it gets shall we say, "interesting".  Try shoe-horning a very large "science" machine into 392, when most of the equipment doesn't come close to code applications.

Thanks for taking the time to explain to me..I really appreciate it.

John

Title: Re: Distance between electrical and audio cables
Post by: richard_cooper on June 21, 2016, 01:15:01 pm
In the UK, blue is fairly standard for 16A cables.  Black for 13A stage power.


Steve.

But, however widespread it is, blue 3183A/"Arctic" type cable is not supposed to be used according to BS7909, unless for reduced low voltage systems..........