Looking for some suggestions

[UpTilDawn]

I have been multi-track recording (24-32 ch) a live, outdoor music event for the last six years. The last two years, the radio station that hires me for this has added streaming, live broadcast to the job.

I've managed okay so far, but always have an annoying issue with line hum in the two-track mix I send them that I only resolve partially using line iso adapters. Even plugging into the same leg of the power rig isn't a 100***37; cure for this. I'd really like to come up with a better solution to this problem.

The radio station's tent is setup backstage and I'm about 300ft away, just behind the foh position... which is also where I take my split to record, using a passive 48 ch splitter snake just in front of the foh board. Currently, I send a two-track mix back to the station tent through the same splitter snake on two spare channels.

I don't have anything wireless at the moment and I'm not too sure how well a wireless system will work in this downtown, outdoor environment (surrounded by a University campus and downtown businesses)...
The station IS sending their signal wireless 10-15 miles away (or is it 30+?... don't recall).

I could sure use some suggestions from those of you who have more experience with live sound and outdoor systems. Any ideas?

Thanks,
DanT

Of course, I hope it goes without saying that I'm using SAW-SAC to do all of this.... which is GREAT!, of course. ;)

[Ogmeister]

I use a product made by Gefen http://www.gefen.com/that will allow me to take a SPIDIF and convert it to CAT5 and this worked great for these kind of things. The also make a unit that does analog audio over cat 5 connections.

OGO:)

[Naturally Digital]

Is the hum present on the output of your rig (before the 300' run) or is it being induced somewhere along the run back to the radio station tent?

[dbarrow]

I use a product made by Gefen http://www.gefen.com/that will allow me to take a SPIDIF and convert it to CAT5 and this worked great for these kind of things. The also make a unit that does analog audio over cat 5 connections.

OGO:)
Or the InstaSnake: http://www.etslan.com/pdf%20docs/12.%20PA200%20Series%20InstaSnake.pdf

I may build my own version of the Instasnake once I verify the wiring. I think it is just one side of each of the twisted pair going to XLR pin 1&3 (tied together) and the other side going to XLR pin 2. I just need to borrow my friend's knockout to put some XLR jack holes in a box. The CAT5 connector will be an Ethercon, which fits in an XLR hole.

[Tony Marone]

Hey Dan,

Your problem sounds like ground differential between your mix position and the radio station setup. The best and most economical way to solve this is with a pair of balancing transformers. The UTC A20 is ideal for this, it can handle levels of +20 dbm without saturation and would give you the electrical isolation you need. You break the ground between you and them - the shield is not continuous - the transformer is used to completely isolate you electrically from them. That should solve it for sure. After all, the phone company has been sending audio around for years on copper pairs using the same method, just a balanced isolated line.

Another more expensive idea would be to send your feed to the radio folks over fiber optic cable - no hum over a glass fiber:).

Tony

[UpTilDawn]

I use a product made by Gefen http://www.gefen.com/that will allow me to take a SPIDIF and convert it to CAT5 and this worked great for these kind of things. The also make a unit that does analog audio over cat 5 connections.

OGO:)

This looks like a good low-cost idea.

Unfortunately, the digital version won't work for me unless the station changes out their little 1202 mixer (for these remote location jobs).

The downside of the analog version to me is the 1/8" miniplug.... I suppose I could change that. It'd be nice to have xlr, or at least 1/4" trs... I'd feel safer.

Still, the price is right.

DanT

[UpTilDawn]

Is the hum present on the output of your rig (before the 300' run) or is it being induced somewhere along the run back to the radio station tent?

The hum is strictly being induced.... I would NEVER settle for my rig humming at the output... How rude that would be!:p

It wasn't bad last year, but I know I could do better.


DanT

[UpTilDawn]

Or the InstaSnake: http://www.etslan.com/pdf%20docs/12.%20PA200%20Series%20InstaSnake.pdf

I may build my own version of the Instasnake once I verify the wiring. I think it is just one side of each of the twisted pair going to XLR pin 1&3 (tied together) and the other side going to XLR pin 2. I just need to borrow my friend's knockout to put some XLR jack holes in a box. The CAT5 connector will be an Ethercon, which fits in an XLR hole.

I like the looks of this..... wish it wasn't $250+, especially with a central air repair coming down the pike in a few days.

If I had more than a few partial days, I'd like to try building one too.

DanT

[UpTilDawn]

Hey Dan,

Your problem sounds like ground differential between your mix position and the radio station setup. The best and most economical way to solve this is with a pair of balancing transformers. The UTC A20 is ideal for this, it can handle levels of +20 dbm without saturation and would give you the electrical isolation you need. You break the ground between you and them - the shield is not continuous - the transformer is used to completely isolate you electrically from them. That should solve it for sure. After all, the phone company has been sending audio around for years on copper pairs using the same method, just a balanced isolated line.

Another more expensive idea would be to send your feed to the radio folks over fiber optic cable - no hum over a glass fiber:).

Tony

You want me to WORK?!?:eek:
Man! I'm about worn out after building the splitter snake two years ago... I can still smell the solder. I couldn't even convince myself to swap out some db25 connectors for a single pair of elcos this Spring.

Does spending more really take the place of hard work as you get older? I'm beginning to think so.


why don't a pair of inline iso transformers kill it completely?

I've forgotten 99% of all the electronics I once knew.:o


DanT
I'm gettin' too old or something.:rolleyes:

[UpTilDawn]

Would this work as well? http://www.avovercat5.com/products/avoa2.htm

Or this? http://www.redco.com/shopexd.asp?id=736


It's rca, so I don't know if the unbalanced line creates a problem over the cat5 run (although the Niles specifies the need for shielded cat5 cable).... but at least it's a more solid connection than the 1/8" mini (in my experience).

DanT

[gdougherty]

From a guy who's an old studio wiring hand I got the tip to physically isolate all the gear in your rack, since ground is often tied to the chasis, tie everything to ground through the power cable if it's grounded and then make ground lift cables for all the interconnects. Basically, you snip the ground on the destination side in your standard 3 conductor balanced cable. All the induced noise then drains back to ground through the output instead of the input side. You're doing the physical isolation part already, just clip the shield on the side that plugs into the radio station gear. Make a short adapter if you don't want to do that on a long cable that may need to pass phantom power at some point. Used to have hum and noise problems in my amp rack even with the board, and rack (processing and amps) all on the same circuit. Did this trick across the board, and it's all silent except for some faint noise generated by the speaker processor.

[UpTilDawn]

From a guy who's an old studio wiring hand I got the tip to physically isolate all the gear in your rack, since ground is often tied to the chasis, tie everything to ground through the power cable if it's grounded and then make ground lift cables for all the interconnects. Basically, you snip the ground on the destination side in your standard 3 conductor balanced cable. All the induced noise then drains back to ground through the output instead of the input side. You're doing the physical isolation part already, just clip the shield on the side that plugs into the radio station gear. Make a short adapter if you don't want to do that on a long cable that may need to pass phantom power at some point. Used to have hum and noise problems in my amp rack even with the board, and rack (processing and amps) all on the same circuit. Did this trick across the board, and it's all silent except for some faint noise generated by the speaker processor.

Let me make sure I understand your comment....

So, I'm using a pair of 50ft xlr cables from the rack panel where the sound company's snake terminates on stage (where they plug in their mics to go to foh) to go back to the station's tent.

What you're saying is to snip the shields to the xlr pair where they would plug into the station's mixer?

And to still use the iso adapters as well, correct?

DanT

[Naturally Digital]

The hum is strictly being induced.... I would NEVER settle for my rig humming at the output... How rude that would be!:pAre you using the iso adapters at the radio station end or at the output of your rig? I'm grasping at straws here. I can't remember if those little inline iso adapters lift the ground either.

Is the station taking a feed from anywhere else? Is there any chance of a loop forming?

You mentioned a passive splitter.... Is it transformer isolated? Do you generally lift the grounds?

You could check this at home... test your main a/c ground (into your rig) for any potential. I like to use a clamp-on ammeter for tails but on a regular a/c cable you may need to fashion something out of a few pieces of wire and a plug/recepticle.

If you have time to diagnose this during setup at the gig, check the ground right at the distro and make sure there is no current flowing in it when you have your rig plugged in and powered up.

Again, I'm just throwing stuff out there because these 'hum' problems are so unique and difficult to diagnose remotely.

What are you using for a DAC to feed the station? Are you sure it's properly balanced and capable of driving the cable length between you and the tent?

[Yogi]

The iso transformers I've seen tie the grounds together. If you open one of them up look and see if the grounds from both plugs are joined together. If so lift one of them (by unsoldering it or clipping the lead). The most common schematic I've seen for these is transformers on leads 1 & 2 with pin 3 being common to both plugs. That could be your problem. I know the ones sold by Radio Shack have this problem.

[UpTilDawn]

The iso transformers I've seen tie the grounds together. If you open one of them up look and see if the grounds from both plugs are joined together. If so lift one of them (by unsoldering it or clipping the lead). The most common schematic I've seen for these is transformers on leads 1 & 2 with pin 3 being common to both plugs. That could be your problem. I know the ones sold by Radio Shack have this problem.

A quick test with an ohm meter shows pin 1 must be ground in these adapters. Pin 1 is indeed connected at both ends.

It obviously wouldn't be as versatile, but would unsoldering the end that plugs into the station's mixer be essentially the same as purchasing a unit that has ground lift siwtches, such as the whirlwind iso-2 http://www.whirlwindusa.com/spcint.html#iso2

Are the transformers in this Whirlwind, or say, the Jensen unit, etc. likely to be better than those in the typical inline iso adapter?

I don't recall where I got mine a few years back as they simply have a yellow rubber jacket on them that says "Isoline"... I think they were a store brand from someplace like Redco, or something, but I haven't been able to find them after numerous google searches.

Not that I wouldn't like to go the cat5 route and avoid this whole issue, but it's more than I can spend at the moment, considering the added cost of a few hundred feet of durable cat5 cable and Neutrik ends and possibly extenders.

DanT

[UpTilDawn]

Are you using the iso adapters at the radio station end or at the output of your rig? I'm grasping at straws here. I can't remember if those little inline iso adapters lift the ground either.

Is the station taking a feed from anywhere else? Is there any chance of a loop forming?

You mentioned a passive splitter.... Is it transformer isolated? Do you generally lift the grounds?

You could check this at home... test your main a/c ground (into your rig) for any potential. I like to use a clamp-on ammeter for tails but on a regular a/c cable you may need to fashion something out of a few pieces of wire and a plug/recepticle.

If you have time to diagnose this during setup at the gig, check the ground right at the distro and make sure there is no current flowing in it when you have your rig plugged in and powered up.

Again, I'm just throwing stuff out there because these 'hum' problems are so unique and difficult to diagnose remotely.

What are you using for a DAC to feed the station? Are you sure it's properly balanced and capable of driving the cable length between you and the tent?

I had a nice, organized answer to this one all typed up this morning and then the computer decided it was break time or something.:rolleyes:

I think I've tried the isos at both ends before (it's a year between this particular gigfest, so I forget). I think it worked best at the radio end.

The station is running the output of a larger mixer into this same submixer (the 1202), but other than that they are not getting or giving any other feeds.

No groundlifts on the passive splitter and no transformers... although I wish I had the room for the grnd lifts... I've thought about it many times anyway.:o

Using the xlr output of the ada8000 to send the mix to the station... I don't know if it's designed to send signal over this long of a run.... It may not be, but it's what I have at the moment.

I sometimes wish I could set up backstage, but then I can't see what's going on. That's a major problem because there's 11 bands in 2 1/2 days and I don't get word of the channel assignments until the last minute most times. I try my best to get channels assigned, armed and labeled by the time a group starts playing.... I don't really want to record a dozen blank tracks, or have to re-name the files if I don't have to after the fact. It's also pretty tough to make live mxing decisions without being able to see the stage.

I may ask the sound crew to help me out to make a test off the distro as you suggest. They're thoroughly familiar with it and my skill with test equipment has gone south with my brain.

I understand what you're saying about testing the a/c ground for any potential, but you'll have to give me the dummies version of setting up a way to test it.... a step-by-step... I've forgotten so much!:eek:

Anyway,
thanks for all the suggestions..... it's really helping.

DanT

[Yogi]

The transformers are probably fine. Lift one end of pin 1 and the hum will probably go away. I've done this with several Radio Shack xlr adapters and they all work much better afterwards.

[mycorn]

Are the transformers in this Whirlwind, or say, the Jensen unit, etc. likely to be better than those in the typical inline iso adapter?

whirlwind- maybe
jensen- yes

i'v heard the difference

do i own any?
no

i want to rebuild all my DI's with jensens

as soon as i have a couple hundred bucks laying around...

a good DI with as ground lift may do the trick

just keep the unbalanced input short
[i unbalance my ada8000s outs pin 2 hot]

fwiw
mh

[UpTilDawn]

whirlwind- maybe
jensen- yes

i'v heard the difference

do i own any?
no

i want to rebuild all my DI's with jensens

as soon as i have a couple hundred bucks laying around...

a good DI with as ground lift may do the trick

just keep the unbalanced input short
[i unbalance my ada8000s outs pin 2 hot]

fwiw
mh
I noticed Whirlwind didn't post the distortion spec... doesn't necessarily mean it's bad, but Jensen certainly does state it up front.

I've got a few hundred feet of mic cable and a mackie 1202, so maybe I'll try some experiments at home this weekend while I finish testing my SAC/SAW setup.

Thanks for all the great ideas all!

DanT

[Ogmeister]

Ianyway.:o


I understand what you're saying about testing the a/c ground for any potential, but you'll have to give me the dummies version of setting up a way to test it.... a step-by-step... I've forgotten so much!:eek:

DanT

The way that I test for ground loops in power supply mains is this.
First you can clamp on and amp meter to the system ground and this should have a reading of zero amps. All of the current in your distro should be flowing in one of the legs to the neutral and not the ground. The neutral and the safety ground need to stay separated and should only be tied together at the service entrance. If current is flowing to ground than we need to start one by one checking of each branch circuit on the power distribution panel. My quick way is to switch off all of these circuits and then turn them on one at a time until I catch the offender. No we can trouble shoot on this branch. For this I first check continuity of the ground circuit in the equipment connected and correct wiring of the neutral. If this checks out then I take off all of the audio cables ins and outs and see if I am still putting current to ground. This can be in the milliamps range so you may have to insert your amp meter in series with this ground to find it. If I find that the removal of audio connections to other devices in the signal chain improves the reading then I can trace to exactly the problem. Most likely the loop is not in this branch but is coming from the connected gear. This is where you need to start removing the ground connections from the cables (not the signal ground) but the shield because the connected devices are trying to get to ground thru this device instead of its own ground. Especially if this device is connected to another power panel or branch circuit with a different ground reference.
This can be a real pain to trace out but in general I have all of my XLR's and most of my balanced audio cables with the shields disconnected . That is any XLR or balanced in has the shield connected and on the other end where it comes out of a mic etc it is disconnected. This will go a long way to eliminating loops and will completely insure that all safety grounding is happening in the power cables and not your audio shields.
I have had to open up gear and find that the inputs that are supposed to be balanced are not designed correctly (Can we say Servo Balanced Mr. Behringer). This is what makes the difference in a low cost mixer and say a Midas. Once you get all of the ground loops out of your signal chain you should hear a remarkable difference in the sound. Often times the looping can cause signal degradation that is not immediately apparent but you will notice it once you have it fixed.

Hope this helps :)
OGO

[gdougherty]

Let me make sure I understand your comment....

So, I'm using a pair of 50ft xlr cables from the rack panel where the sound company's snake terminates on stage (where they plug in their mics to go to foh) to go back to the station's tent.

What you're saying is to snip the shields to the xlr pair where they would plug into the station's mixer?

And to still use the iso adapters as well, correct?

DanT

No need for the isolation boxes in my experience.

[UpTilDawn]

The way that I test for ground loops in power supply mains is this..........
Hope this helps :)
OGO

thanks for the detailed post ogo..... copied and printed.

DanT

[UpTilDawn]

Well, so far my attempts to test some of these ground loop ideas has hit a brick wall.... I can't get a hum generated through the system at home.... yet.:rolleyes:

DanT

[Ogmeister]

thanks for the detailed post ogo..... copied and printed.

DanT

You are welcome.
I have taken a complete setup in the shop and had it working perfectly only to get on site and have a stupid buzz or hum.. It drives me crazy when this happens. It is really worth the effort to track this stuff down as you will have great benefits in the clarity and response of your PA once these kinds of things are taken care of. A lot of my associates around here can't even imagine how I can get my C rig full of marginal Behringer and Mackie gear sounding decent.
The key to it is getting connections and gain structure setup right and knowing what the real design specs are of the devices. It is a real shame what passes for so called PRO Gear these days. I would be ashamed to put my name on some of this garbage. Once you understand its real specs you can make it sound decent.

Good Luck in you quest for better sound.... at least you care enough to know the difference and look for a solution. It frustrates me to no end when I walk in on a job with the band that is not my PA and the sound co does nothing to get this stuff taken care of.

OGO

[UpTilDawn]

...Good Luck in you quest for better sound.... at least you care enough to know the difference and look for a solution. It frustrates me to no end when I walk in on a job with the band that is not my PA and the sound co does nothing to get this stuff taken care of.

OGO

I've experienced and dealt with it from many perspectives over my life in music... from a guitarist playing a strat through tubes with no ground, to a (very low-level ;)) soundman chasing lighting-induced hum, to trying to rid tracks of the nasty stuff in live recordings.... and more. It's one of the most horrendous sounds there is to my ears (unless you're using it as a special effect, which I might be found doing when the mood strikes :) ).

I've spent all weekend testing at home and no problems at all.... I'm expecting that will be different next weekend at the gig. At least now I'll be more prepared with some other tricks to try.

DanT

[gdougherty]

I've experienced and dealt with it from many perspectives over my life in music... from a guitarist playing a strat through tubes with no ground, to a (very low-level ;)) soundman chasing lighting-induced hum, to trying to rid tracks of the nasty stuff in live recordings.... and more. It's one of the most horrendous sounds there is to my ears (unless you're using it as a special effect, which I might be found doing when the mood strikes :) ).

I've spent all weekend testing at home and no problems at all.... I'm expecting that will be different next weekend at the gig. At least now I'll be more prepared with some other tricks to try.

DanT

Have you lifted grounds on the destination ends? If not, it's quick and easy. I don't carry as much power cable as I should so I occasionally end up needing to place FOH and stage power on different grounds. In the past I've had hum problems in various locations and even hum internal to the rack. No problems since. This also eliminates the need for the horribly unsafe practice of lifting ground at the outlet. Everything stays properly grounded, noise properly drains to where it should, everything's naturally isolated.

[UpTilDawn]

Have you lifted grounds on the destination ends? If not, it's quick and easy. I don't carry as much power cable as I should so I occasionally end up needing to place FOH and stage power on different grounds. In the past I've had hum problems in various locations and even hum internal to the rack. No problems since. This also eliminates the need for the horribly unsafe practice of lifting ground at the outlet. Everything stays properly grounded, noise properly drains to where it should, everything's naturally isolated.


Lifting grounds on the destination ends is going to be big on my list for sure. I already know that using the iso-bars gets me part way there (from past shows)... and now I know that the adapters are wired with the shield connected at both ends. I've put together a couple adapter cables with the shield lifted rather than cutting or desoldering the iso adapters themselves.

DanT