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Author Topic: Snake termination, punch down or?  (Read 10571 times)

Karl P(eterson)

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Re: Snake termination, punch down or?
« Reply #10 on: July 09, 2004, 11:55:36 pm »

Rick Johnston wrote on Fri, 09 July 2004 21:58


Let's face it: The trend in our industry is moving toward unshielded twisted-pair for line-level signal wiring. Who knows that stuff better than the phone company?




There are a few problems with your message.

First off - Who is recommending to use unshielded wire for line level audio signal? Maybe I am behind the times, but my first reaction to that statement is a resounding hell no.

Second - When the previous poster said about Whirlwind/ADC using punch down blocks, he meant the specialized ones, _not_ 66 blocks.


Third, and lastly - 66 Blocks are designed for telephone wire, which is of course, solid copper. Are you suggesting as well that line level audio not only be moved to unshielded wire, but solid core wire at that?

Karl P
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Vince Byrne

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Re: Snake termination, punch down or?
« Reply #11 on: July 10, 2004, 10:09:12 am »

Rick Johnston wrote on Fri, 09 July 2004 20:58

Let's face it: The trend in our industry is moving toward unshielded twisted-pair for line-level signal wiring. Who knows that stuff better than the phone company?



Yup. The phone company moves around analog 300Hz-3KHz bandpass signals with about 3dB dynamic range on UTP by the billions. Who knows that stuff better? About the equivalent of 8-bit digital sound quality, and you still get crosstalk and other transimission noise ...

Peace,
Vince <><
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Philip Roberts

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Re: Snake termination, punch down or?
« Reply #12 on: July 10, 2004, 05:25:22 pm »

The church where I do sound has a system that is setup with lots of  66 punch blocks. Passing through blocks four times on the way from the stage to the mixer, and 2-3 on the out put side. All this times ~40 lines from the stage.

We have had no issues with it, as its in a climate controlled environment. There is also no cable movement except for servicing.

It makes things easy to reconfigure, just pull the wires off the block and rerun or repunch, yet keeps everything looking neat and clear to understand. It so neat because serious thought was put into planing the original system. Especially as any system gets larger I'd recommend giving plenty of planing and thought to exactly how things are connected.

For adding to the system I've considered using the Whirlwind/ADC punch blocks, however they are _much_ more expensive. $6-15 for 50 pair on 66's, 100-200 for the ADC style blocks. Though if you need it they are denser.

If you'd like I can get some pictures of the whole panels of punch blocks.

_____________________

Philip Roberts
Sound Technician
Pioneer Memorial Seventh Day Adventist Church
Berrien Springs MI
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Philip Roberts
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Pioneer Memorial Seventh Day Adventist Church
Berrien Springs MI

steve g

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Re: Snake termination, punch down or?
« Reply #13 on: July 11, 2004, 05:17:33 am »

OK GUYS!  You're all right and wrong!  There we go... No seriously, of course you can use them and they most likely will work and give you no trouble.  However, you COULD run into problems in some situations, such as real RF heavy areas or where theres a lot of AC nearby.  Look very close at the "audio" patch panels...

1) The special units like ADC have a specially designed punch down "bite" that grabs the wire differently from a 66 or 110 block, which is for solid wire PRIMARILY, as I believe Karl so well put it.  More solid connection... good for weak signals.  Line or speaker level stuff might not notice a less solid connection as much.

2) They also don't keep the connection out in the open long--just enough to get past that 1/8" or so back panel, then it's back into the 22-24 ga shielded cable again till it hits the 1/4" jacks.  The 66 blocks line up every conductor in parallel with each other and right out in the open, like "Hey interference, gimme your best shot!"

Also, 66 block guys, please understand that a "speaker level" and "line level" signal are way different than an unamplified "mic level signal".  If I'm not mistaken, we're talking a very weak signal here (mere millivolts? for a mic) that has to travel several hundred feet sometimes before it hits a preamp for the first time.  An exception would be a keyboards, etc... which should be driving the line a lot harder to begin with (~line level).  In addition, you are already relying pretty heavily on Mr. CMR to do his job and get rid of noise as much as possible.

So, I guess you just have to know the surrounding environment real well... If you know for sure thet you have an RF/EMF free area and can't afford the ADC stuff, then give em a shot.  I DO understand where you're coming from, because the 66/110 stuff terminates in a breeze.  Then again it usually only takes us up to a couple of hours to terminate and test a 48-point ADC bay using our current tooling.

On a simlarly-related subject, I heard that the Furman IEM systems get away with using twisted pair by driving the line extremely hard and then dropping the level back down at the receiving end... if somebody knows different, please let me know.  Anyways, it is my understanding that this is how they are getting away with using UTP with "telco" connectors on their big IEM system and "RJ45" connectors on their smaller systems.

Well, hope you enjoyed my rant.  Twisted Evil   Twisted Evil Sorry if I offended some of you by stating so much of the obvious, but hey, to some people it may not be so obvious.

Steve
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Vince Byrne

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Re: Snake termination, punch down or?
« Reply #14 on: July 11, 2004, 03:56:53 pm »

globalaudiovideo wrote on Sun, 11 July 2004 04:17

On a simlarly-related subject, I heard that the Furman IEM systems get away with using twisted pair by driving the line extremely hard and then dropping the level back down at the receiving end... if somebody knows different, please let me know.  Anyways, it is my understanding that this is how they are getting away with using UTP with "telco" connectors on their big IEM system and "RJ45" connectors on their smaller systems.



Steve,

With voltage rails at 22V, I can believe they hit the signal levels hard.

The wire that Furman sells for long runs (I made a 150 footer for my church) is 25 twisted pair with a braided shield. The connectors are Centronics type, with the the shield grounded to the connector shell.

- pr 1-8 pr are mono signals,
- pr are 9-16 are 4 stereo signals,
- pr 17 is ground/solo control
- pr 18-19 are +22V
- pr 20-21 are -22V
- pr 22,24 are ground
- pr 23 is talk back bus
- pr 25 is talk back microphone.

BTW, I wouldn't recommend this system for anything more than routing phones in a low grade studio environment.

The 25 foot molded cordsets that come with the units are pretty good quality, but the Centronics printer connectors that they use are not up to and were not designed for hard usage.

The connectors they sell to use for long runs are cheap-ass stuff (Is there such a thing as a "robust" Centronics connector?) that doesn't really support the diameter of the wire, is a royal PITA to solder up, and is fragile when you are done.

Peace,
Vince <><
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steve g

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Re: Snake termination, punch down or?
« Reply #15 on: July 11, 2004, 04:33:51 pm »

Vince,

Thanks for the info on the IEM stuff... Yes, you are very right about the Centronics connectors.  They are a terrible choice for a regular-use environment.  Hopefully sometime in the future they will look at replacing it with a more rugged connector.  Maybe a nice locking circular multipin or something similar.  I know most of them are very expensive (Link, Veam, Cannon), but maybe they could try some cheap Amphenol.  I would think that would do the trick.

I have had pretty good luck with the smaller 4-channel system that they make.  For church installs that have a very tight budget, I've specd and installed them with very good results.  Another plus is, since it uses standard Cat 5/RJ45, they can easily migrate to the Aviom system later.

Steve
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Vince Byrne

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Re: Snake termination, punch down or?
« Reply #16 on: July 11, 2004, 10:37:33 pm »

(Regarding the Furman analog personal monitor mix system)

globalaudiovideo wrote on Sun, 11 July 2004 15:33

Maybe a nice locking circular multipin or something similar.  I know most of them are very expensive (Link, Veam, Cannon), but maybe they could try some cheap Amphenol.  I would think that would do the trick.



I really doubt they will bother. With the success of the Aviom, etc. digital systems the market window for an analog personal monitor system is pretty much closed.

These things were really intended for studio use where the Centronics wouldn't be plugged and unplugged all the time like they are for live use. I think Furman was actually a bit suprised at the live sound market interest they saw for a while. Clearly their solution for long runs was an afterthought and wasn't nearly as well engineered as the rest of the system. In any case, the Avioms do more and cost the same or less.

Wanna buy a gently used six mixer Furman system with a 150 foot snake run?    Laughing  

Peace,
Vince <><
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Rick Johnston

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Re: Snake termination, punch down or?
« Reply #17 on: July 12, 2004, 07:40:58 am »

The problem is that there is no standard for the Pin 1 connection. Chassis ground? Building Ground? Audio ground? Any or all can be present in an installation, depending upon the mix of manufacturers. Pin 1 connections are causing more issues than they solve (ground loops, primarily ... but connecting Pin 1 to only the high-impedance input side creates an RF antenna). So generally, the "Pin 1 problem" is being solved by simply ignoring that connection and allowing the common-mode rejection of twisted-pair wiring to do its job on EMI. RF issues, if any, can be solved by adding a cap to the signal line.

Exposed connections, such as those on a punch block, can be shielded by placing the block inside a grounded metal back box or inside an enclosed rack away from electrical power sources. The shield doesn't care how close it is to the signal connections.

Although I've seen solid 22 and 24 used for line level signals on PBs and inside racks, the most common cabling is WP #452 or its equivalent.
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Geoff Doane

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Re: Snake termination, punch down or?
« Reply #18 on: July 18, 2004, 05:33:44 pm »

Leaving the relative merits of different punch blocks aside,  I'd take the opportunity to turn the junction box into another connection point.  Assuming it's in an appropriate location, and there's enough slack on the various wires inside, mount 32 female XLRs in the cover, and then use them as your splice points.

Although lots of people do it, and get away with it, I'm still rather old school in liking to see mic connections soldered.  Since you need to provide for a phantom power return path, unshielded is out of the question, even if it didn't pick up noise.  The most recent install I worked on made extensive use of AVP punch blocks, and they really have their stuff together.

http://www.avpmfg.com/

You can even mix gauges on the same terminal (within limits).

You can also get very good performance from UTP cable (CAT 5) for line level audio.  The system needs to be all balanced, but the twist in CAT 5 is so good, crosstalk figures can be down in the -100 dB range.  Shielding really only does something at RF frequencies, and some broadcasters (with co-located transmitters) use the shielded CAT 5 for this reason, but it's usually not needed.

Geoff Doane
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