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Old 23rd November 2006, 08:19 PM   #1
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Default line out signal wire question

Any suggestions on the type and size of wire for line out from a computer headphone output to tube preamp, tube power amp, etc?

I am finishing out a basement and want to place stereo jacks on the wall with signal cable to the preamp running through the walls.

Suppose there could be a lower high frequency roll off due to wiring impedance, no?

Thanks,
Rick
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Old 23rd November 2006, 10:05 PM   #2
lineup is offline lineup  Sweden
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I use rather normal stereo cable.

It is a black pair about 2 meter length.

There are at least 3 groups of quality.
~1.5-2.0 mm. Very thin and badly shielded,
Type often attached in cheap stereo gears packages.

2.5-4 mm.(1/10inch-) Shielded of a better quality.
This is what I use for my 3.5 mm stereo jacks connections.
For good normal hifi applications.


5-8 mm. Very thick and a bit more expensive hifi cable.
This is most often used together with RCA Phono plugs.
It is difficult to mount smaller 3.5 mm stereo plugs onto such thick cable.
==================

Best solution is maybe to use a very short
ready made 3.5mm stereo .. to 2 RCA Female sockets.
This is what I use from my Computer to my stereo inputs.
It is less than 20cm(8 inch) long.

From these two Female RCA to my stereo two Female RCA inputs,
I can use any quality of stereo RCA cables, with RCA plugs in both ends.

The influence of a cable is in proportion to the length.
If using very short 'normal quality' cable + a much longer high quality cable,
As my RCA cables are 150cm (1.5m) and the other only 20cm
the overall performance will be like the better longer one.

See picture here:
Click the image to open in full size.
Quote:
3.5mm Stereo Plug to Two Phono Sockets Information:
Nickel-plated connectors
Fully screened cable
Durable PVC jacket
Cable strain relief
20cm (approx) cable length
Link to product at www.maplin.co.uk
Maplin: 3.5mm Stereo Plug to Two Phono Sockets

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Old 23rd November 2006, 10:49 PM   #3
moamps is offline moamps  Croatia
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I'd like to point out two potential issues with the type of installation in Rick's post. Firstly, connecting the computer and the piece of audio equipment separately to power outlets in different parts of the house may give rise to ground loop problems. Secondly, if the connecting cable is too long and unbalanced, there is a danger of inducing various noises, regardless of whether the cable is shielded or not. In such cases, the best solution IME would be using audio transformers to get the balanced signal with separate grounds between the PC and the audio eqipment. These transformers are connected directly to the PC output and the signal is brought to the audio equipment via balanced cables.

Regards,
Milan
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Old 23rd November 2006, 10:55 PM   #4
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I second balanced signal runs.
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Old 24th November 2006, 12:08 AM   #5
dangus is offline dangus  Canada
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I'll vote for S/PDIF... you'll get cleaner sound out of the 'puter if you use a separate DAC. Regular CAT-5 twisted-pair may be good enough, or else cable TV coax should work since it's the correct impedance. There must be some deals out there on used DACs, or there's the Behringer SRC-2496 for around $130. You can spend more than that on a pair of audio transformers without trying too hard. http://www.jensen-transformers.com/prices.html
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Old 24th November 2006, 02:20 AM   #6
lineup is offline lineup  Sweden
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hi again

I don't know how long cables you will need.
-> But first thing is to try keep them as SHORT as possible.

Going into balanced is probably the most perfectionist approach.
But if you do not want to try that road
which will require more than only cables,
-> you should use very good quality unbalanced RCA cables.

At least if length is like 5 meter or more.
At audio outputs/inputs you may have to consider some counter measures against capacitive loading.
Typical unbalanced, even of very good quality, can have 200pF per meter.

Done in the best way, I don't think you will have be too afraid using long cables.
Performing artists on stage and public sound systems
can have several 10's of meters cables for signals.
Even if many of these are balanced,
I would guess many times they also using unbalanced high quality.
At least for line level signal outputs.


But first thing is to figure out the shortest possible way
to fit your cables in your house.

I say you can make an unbalanced cable test first.
Using same length, but not put them into walls, yet.

My opinion is there is a good chance it will work well.
If not, there are people here that can help you design a balanced alternative.
If you would need such assistance.


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Old 24th November 2006, 01:51 PM   #7
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Default great info and good discussion

Thank you! Very useful info!

Rick
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