Mid-FI dilemma

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maluckey

Platinum Member
Jan 31, 2003
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I have a mid-fi setup by most audiophile standards

  • 2 modded Adcom GFA 555II amps in bridged mono, with cooling fans
  • Adcom GFA 565 preamp
  • Modded Polk Audio Monitor 12 Series 2 speakers
  • Asus Xonar D2X digital source (In the PC of course!)

This issue is that the PC is now in another room in my brand spanking new house, and I'm needing to connect the PC to the Audio from another room (not sharing a common wall).

I was looking at Running almost. 77 feet of solid-core RG11 coax cable with RCA termination ends through the attic to a jack in the wall that now holds a RG6 braided coax. Would this suffice for a low-signal-loss application?

Figured I'd ask before crawling through that gawd-awful hot attic.



 
Modelworks

Modelworks

Lifer
Feb 22, 2007
16,240
7
76
One suggestion:
If you are going to pull coax, go ahead and pull a cat5/6 cable along with it for future use. I say this as someone who ran a cable a long way then a week later needed to run a different one for other things. Now anytime I have to run cable I think of what I might need in the future :)


You can use electrical tape to tape the ends of the cables together and just pull them both as one cable.
 
M

maluckey

Platinum Member
Jan 31, 2003
2,933
0
71
Great info!

Looking at way less loss than would be audible. You lose more in the RCA connectors. (your row is the 1mhz - as audio is 20hz - 20khz)
Click to expand...

That got me on the right track. I did some research this morning on attenuation and found several affordable cables with VERY low signal loss. I also visited a few geeky audio sites and got so much conflicting information that my head almost exploded. These guys must sacrifice small animal by the light of the moon to make their stuff work. Pure VOODOO for their cable selection.

I'm a reasonably intelligent guy, so I disregarded most of what the "audiophiles" had to say and did some more research. I found that ther's really only three things that I need to figure into this issue (in no particular order):

  1. capacitance
  1. propagation delay
  1. signal fidelity

Am I right to figure that within common sense and reason that I need the cable that has the best overall score of these three categories?







 
Modelworks

Modelworks

Lifer
Feb 22, 2007
16,240
7
76
The main issue with long cables and any digital signal is reflections. Reflections are caused by the cable not being at 75ohms the entire length. If the impedance changes too much then reflections are part of the signal that bounce back towards the transmitter. When they arrive at the transmitter they again bounce back towards the receiver and they continue going back and forth until the reflection is gone. That adds noise to the signal.

Propagation time for digital audio is I think 25ns. So a 77foot cable (2ns per foot delay) would mean that you have the potential for 6 different sets of reflections to be on the cable at the same time. That could cause a lot of jitter if the cable impedance is not correct. You are really over the length that the specification allows which is 10 meters. The reason the length is not longer is because of the problem of keeping the impedance matched at long ranges and the transmitter voltages being so low that cable resistance starts to make it so that 0/1 transitions are hard to distinguish. I misread the OP and though it said 27ft.

The only way I would do a run at 50ft + is if I had someone with a oscilloscope that could help me tune the cable and place the correct resistors/capacitors to make sure it was a true 75ohms. That is providing that the transmitter is strong enough to reach the other end without loss. .5V is easy to lose on a cable that long.


 
M

maluckey

Platinum Member
Jan 31, 2003
2,933
0
71
Modelworks,

point taken with running extra cable!! My wife was already scheming to wire the est of the house for the network.

I'm using analog signals, just trying to keep it clean as I can to my amps, so digital jitter isn't an issue. I'm still at odds with myself as to whether any ready-made cables are worth the premium. By the time I buy the tools to cut the cable and connect the ends, I'm at their price. Coincidence? I think not!

 
M

maluckey

Platinum Member
Jan 31, 2003
2,933
0
71
Thanks Thump533,

Forgot all about that option! Time for more homework I guess. If I'm going to end up spending almost 200 dollars... for just 89 clams more, I can listen to music anywhere.

range isn't an issue, because from where I sit, I can see across the room (20' x 35') to where the pre-amp sits.



 
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