Audio over Cat% DIY Idea - AVS Forum
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post #1 of 13 Old 07-28-2013, 01:55 AM - Thread Starter
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Hello,

I've had an idea to send the 3.5mm audio jack from my mac over ethernet to my amp. Would it be possible to wire a 3.5mm jack into some pins of an RJ45 plug and then do the opposite on the reverse end, so that I could run one from the headphone jack of my mac to my ethernet port, and at the other end bring the same out of patch panel into amp. It seems to me in theory that it will work, but does any body have any suggestions about this, or have tried this before.

Thanks
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post #2 of 13 Old 07-28-2013, 06:36 AM
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Should work if you aren't using the Ethernet for anything else. I think...?
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post #3 of 13 Old 07-30-2013, 07:01 PM
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I guess if you already had the cat5 cable collecting dust it would be worth it in a pinch. Not the best, but should work.

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post #4 of 13 Old 07-31-2013, 12:34 AM
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Yes it will work if the same cable is not being used for data as well, but you may run into hum issues as it's not (most likely) shielded and you won't be using it balanced.
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post #5 of 13 Old 07-31-2013, 03:16 AM
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I REALLY don't recommend it. You need a coax cable not an Ethernet cable. You will get alot of noise, hum and cross talk from other ethernet connections alongside.

If it costs nothing to try, give it a shot and then post here!
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post #6 of 13 Old 07-31-2013, 04:17 AM
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Actually ethernet cables are all in twisted pairs of conductors already so they cancel noise. Just so long as they are wired properly by using the + and - of a twisted pair then there should be no noise or crosstalk. If he uses shielded cable then it is all the better!
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post #7 of 13 Old 07-31-2013, 04:34 AM
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Quote:
Originally Posted by breney View Post

Hello,

I've had an idea to send the 3.5mm audio jack from my mac over ethernet to my amp. Would it be possible to wire a 3.5mm jack into some pins of an RJ45 plug and then do the opposite on the reverse end, so that I could run one from the headphone jack of my mac to my ethernet port, and at the other end bring the same out of patch panel into amp. It seems to me in theory that it will work, but does any body have any suggestions about this, or have tried this before.

The best way to do this is to use audio baluns at each end. Here's an example:

http://www.newark.com/jsp/search/productdetail.jsp?SKU=96K0889&CMP=KNC-GPLA&mckv=|pcrid|26814758421|plid|



Google is your friend.

Audio baluns are usually composed of transformers that reduce the impedance and make the interconnection like a balanced line. Noise pickup is reduced since the line is does not run at a high impedance and is not unbalanced.
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post #8 of 13 Old 07-31-2013, 09:12 AM
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Quote:
Originally Posted by diaz View Post

I REALLY don't recommend it. You need a coax cable not an Ethernet cable. You will get alot of noise, hum and cross talk from other ethernet connections alongside.

If it costs nothing to try, give it a shot and then post here!

Source of your assertions? Reason why is that nothing I have ever done in my career can back your assertion. In the audio range...UTP/STP and coax have no real difference. One just looks prettier than the other. In terms of noise susceptibility, they are the same (UTP actually has a little edge if put into a balun).

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post #9 of 13 Old 07-31-2013, 10:23 AM
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Quote:
Originally Posted by tsloms View Post

Actually ethernet cables are all in twisted pairs of conductors already so they cancel noise. Just so long as they are wired properly by using the + and - of a twisted pair then there should be no noise or crosstalk.
Only if the amp (receiver) and the source (transmitter) are balanced. Send it single ended, ie like the vast majority of audio sources and you get no noise cancellation.
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post #10 of 13 Old 07-31-2013, 11:06 AM
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Quote:
Originally Posted by A9X-308 View Post

Only if the amp (receiver) and the source (transmitter) are balanced. Send it single ended, ie like the vast majority of audio sources and you get no noise cancellation.

coax has no better noise immunity than TP with single ended signals.

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post #11 of 13 Old 07-31-2013, 12:57 PM
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Quote:
Originally Posted by A9X-308 View Post

Quote:
Originally Posted by tsloms View Post

Actually ethernet cables are all in twisted pairs of conductors already so they cancel noise. Just so long as they are wired properly by using the + and - of a twisted pair then there should be no noise or crosstalk.
Only if the amp (receiver) and the source (transmitter) are balanced. Send it single ended, ie like the vast majority of audio sources and you get no noise cancellation.

The interference rejection takes place at the receiver, so the use of a balanced transmitter is optional. The balanced receiver provides noise rejection based on its common mode signal rejection, while the balanced transmitter provides a 3 dB advantage. There is a 6 dB benefit because of the doubled signal voltage due to the balanced output, but there is a loss of 3 dB due to there being two statistically independent noise sources in the receiver that are in essence connected in series.

There is a type of balanced called "Impedance balanced" where one of the two signal sources in the transmitter is replaced with a resistor equal to the source impedance of the active output.

If you use transformer(s) The CMRR of the receiver is generally higher, and has more bandwidth than active inputs. There is also an opportunity to provide the active stage following the input transformer with a more ideal source impedance.
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post #12 of 13 Old 07-31-2013, 04:00 PM
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Well I design tube amplifiers and use utp for large signals to prevent EMF to other components, and shielded coax type cable for small signals. If I dont use shieled it gets REALLY noisy. However there is a lot of gain
throughout the circuit.

Common sense to me says coax type for small signal requiring amplification at the other end, and utp for any large signal near small signals. Ideally shielded everything.

In this specific application I would cross my fingers that the Ethernet doesn't cross too much AC, or even worse follow long runs of AC..
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post #13 of 13 Old 07-31-2013, 05:11 PM
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Hi Arny,
Quote:
Originally Posted by arnyk View Post

The interference rejection takes place at the receiver, so the use of a balanced transmitter is optional.
This isn't always true, especially if one connection at the source is grounded.

The differential receiver depends on the incoming two signals having equal noise. The wires are twisted so that any noise source induces equal noise in both wires, and the receiver can then effectively subtract out the noise. If the source that is driving the two wires have unequal output impedance, the common-mode noise will become unequal (no longer "common-mode"), and some of the noise will remain after the subtraction.

Transformers inherently have equal impedance at each output line, have equal-but-opposite output voltage and current, and therefore make ideal differential drivers.
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