audio wiring question

[Oscar1613]

i'm making a custom charge + audio cable for my mp3 player to use in my car, and to make it neater, i'm using a firewire cable with the ends chopped off. the cable itself has 2 power leads that i'm using for the power (obviously), then its got 2 shielded twisted pairs that i have available for the audio.

should i put one channel on each pair and just use the shield, or should i put ground on the other wire in each pair or what?

 

[JMWarren]

I'm not sure you'll even be able to hear a difference given most MP3 players output qualities...

 

[Rubycon]

Grounds should always be summed together. Using different ground wires will induce noise through ground loops. It does not matter whether you're listening to 1.54Mbps PCM or 24kbps. Hum is hum. Even worse is high frequency subharmonics from switching power adapters.

 

[Oscar1613]

thats what i figured, but i didnt want to end up with excessive alternator whine. but i guess thats more of a power issue than anything

 

[Oscar1613]

what do you mean summed together? i'm not using a switching power adapter... just a cheapo 5V linear regulator

 

[Rubycon]

Make sure the ground is common with as low as resistance as possible. If you're using something 7805 based you can still have noise passed through the auto electrical system as most are noisy. Just make sure your shields, drain wires, whatever you have are bonded well at both ends and keep the run as short as possible since unbalanced preamp levels will pick up noise easily.

 

[Oscar1613]

well i had it hooked up using the power from the 7805 and rca cable to the stereo and i didnt notice any noise, so i think that'll be fine. i'm just concerned about the audio picking up noise

 

[Rubycon]

Originally posted by: Oscar1613
well i had it hooked up using the power from the 7805 and rca cable to the stereo and i didnt notice any noise, so i think that'll be fine. i'm just concerned about the audio picking up noise

In that case it should be fine.