Long balanced interconnect?

whoaru99

whoaru99

Epic Member
Later this summer I'm going to provide the stereo system for a gathering out at my Uncle's place. I'll be using my "garage stereo" that is comprised of sound reinforcement speakers & subs, a stack of pro amps, and a speaker management box for crossovers, tunings, delay, etc.

I will place the amp rack behind the speakers, and all that will be set up not far from the power hookup, away from the main "audience" area. However, I want to run the volume and global bass/mid/treble adjustments from a small mixing console reasonably far from the stacks and racks, so to speak.

I'm thinking I will buy a 100ft length of shielded, stranded Cat5 cable and put some XLR connectors at each end. To, in effect, make a long interconnect for the left and right channel connection between the mixer and the speaker controller.

I'd wire it up in a "star quad" configuration, using (for example)-

White/green & white/blue for Left (+)
Green & blue for Left (-)
White/orange & white/brown for Right (+)
Orange & brown for Right (-)

Certainly this would be a somewhat fragile cable not suited for touring duty, but for temporary backyard party so to speak I think it will work pretty well. Cat5 cable, having low capacitance, mixer with 150 ohms output impedance and speaker controller having 20k input impedance, balanced connection, 100ft (assuming I even use all that) should be no problem, eh?

Thoughts?
 
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Having the mixing board push 100'+ to an amp rack isn't unheard of. I'd say it's pretty common, you'd have a hard time doing sound reinforcement without it. But i think you'll see nasty signal from 24ga solid (they make stranded cat5e?) at that length.

If you've got a balanced in/out that's great, Get some inexpensive in-wall from your local building megacenter. 22ga stranded pair + ground wire. Stuff I have is shielded as well Carol C2516. Got a 500' spool for $65 IIRC.

Don't be surprised if you get a ground hum. snip the ground wire at the amp if you need, or use a ground lifter (power or signal).
 
Come to think of it, there is a pull box of probably 7-800ft of solid, non-shielded Cat5 in the basement. I may just spool out a hundred feet of that and give it a try before buying anything else.
 
whoaru99 said:
Come to think of it, there is a pull box of probably 7-800ft of solid, non-shielded Cat5 in the basement. I may just spool out a hundred feet of that and give it a try before buying anything else.
Click to expand...

sure can't hurt to try.
:lurk:
 
whoaru99 said:
Cat5 cable, having low capacitance, mixer with 150 ohms output impedance and speaker controller having 20k input impedance, balanced connection, 100ft (assuming I even use all that) should be no problem, eh?
Click to expand...
Be careful about your mixer's output Z spec. You want to be very sure that it's specified to actually drive the line impedance in question, which is often quite different from specified output impedance. There is a major difference between these two specifications that is often overlooked by folks without pro audio experience.
 
I know someone who uses 100 ft standard ICs that he makes himself with no ill effects - FWIW.
 
BinaryMike said:
Be careful about your mixer's output Z spec. You want to be very sure that it's specified to actually drive the line impedance in question, which is often quite different from specified output impedance. There is a major difference between these two specifications that is often overlooked by folks without pro audio experience.
Click to expand...

I'm not sure what you mean by driving the line impedance in question vs the specified output impedance?

I mean I can/have looked up those specs but I'm not clear on what you are cautioning about.
 
30 metre send and returns balanced are normal practice with pa stuff .
i keep the amp racks next to the desk and run speaker cables to the speakers i like to keep an eye on the main amps peak lights .. it would be a different story if the speakers were active . then i would simply use the return lines along with active monitors .
 
whoaru99 said:
I'm not clear on what you are cautioning about.
Click to expand...
If the spec for the device driving the line doesn't explicitly state that it's capable of driving a 600R or 150R line, for instance, and only says that its output Z is 150R, then you're on shaky ground. The problem arises because very low apparent output Z values can be achieved via negative feedback, but NFB does nothing to increase power output capability. Think about it --- a SS power amp with damping factor of 80 has an apparent output Z of 0.1 ohm, but it will never effectively drive a 0.1 ohm load.
 
Seems reasonably easy to try it in advance so you're comfortable with it. Try it with the much longer run if that's what you've got so you don't even cut anything now.

EV3
 
evsentry3 said:
Seems reasonably easy to try it in advance so you're comfortable with it. Try it with the much longer run if that's what you've got so you don't even cut anything now.

EV3
Click to expand...

You're saying try it with 7-800 feet?

I just may for shits and grins. :naughty:

Maybe it'll be the longest reported cable on AK.... :rockon:
 
Another interesting, at least for me, question.

Never really paid close attention before but the four pairs in Cat5 have different twist rates. For this project, since I plan to parallel two pair for each channel, do you think -
  • Parallel the two pairs with the highest twist rate and parallel the two pairs with the lowest twist rate?
  • Parallel the highest twist with the lowest and parallel the two middle twist rate pairs
  • Isn't going to matter, just pick some
  • Something else
:idea:
 
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