MP3 - signal source in car (unbalanced - balanced - unbalanced?)

[misiacik7]

CAR: low level signal (MP3) to 3 amps (should convert to balanced?)- get lowest noise

hi,

I have this setup in car: 3 amps (front, rear, SW)
I bought theese 'signal' cables:

1)3meter of PROEL HPC 240 (balanced cable used for mics outer dia 4mm) - want to use it as STEREO CABLE with single shield with NEUTRIK MINI JACK

2)5+5 meter of PROEL HPC 230 (balanced cable used for mics outer dia 7mm) (each cable for each channel)

3)from previous cable split each channel to each amp (1+1+1, 1+1+1 meters) of PROEL HPC 210.

My question is, how to wire it to get minimum of noise... The signal source is MP3 COWON D2. It has higher output than ordinary mp3, but still lower than ordinary radio. => higher amplification => more noise.

In the shop i bought all of the amps and speakers told me to use those balanced (symetric) cables and make it double shielded. Question is does it help to wire the WIRE1 + GND together and use the WIRE2 as signal wire? Is it how he meant to it double shielded?

If I make somehow from the unbalanced output balanced somewhere behind the mp3 and convert it back to unbalanced before splitting it into amps, will it help? (the splitting of the signal will cause drop of the level of signal?)

Someone told me to put a filter into, and than someone told me that is a ********.

here is schema of used cables:
**broken link removed**


What is the best and cheapest solution for me?

 

[audioguru]

The MP3 player has unbalanced separately shielded stereo outputs. A car amplifier has unbalanced inputs. A balanced mic cable is for a mono signal. The cables are completely different.

You might be able to change the connections to the balanced cable so that the pair of inner signal conductors are for unbalanced left and right channels from the MP3 player but the stereo separation might be reduced at high audio frequencies by the capacitance between the two conductors.

 

[misiacik7]

I understand both of them (mp3 and the amps) got unbalanced input/output.
You mean the short cable used for MINI JACK NEUTRIK the PROEL HPC240 for STEREO is completely bad? If yes, which kind of cable will you use for this JACK to connect the longer HPC230?

If I use the second wire of the cable as second GROUND.
RED WIRE - SIGNAL
BLACK WIRE - GND
SHIELD - GND
Will it be better shielded?

Or if it will be better to tranform somewhere behind the mp3 the signal from unbalanced to balanced to avoid noise and use RED WIRE as + and BLACK as - and SHIELD as GND and somewhere before amplifiers convert it back to unbalanced and split the signal of each channal into 3 amps.

 

[misiacik7]

I asked now the dealer who sell me the cables and he used this method....

On the side of radio (mp3 my situation) he connect it like this:
RED WIRE - SIGNAL
BLACK WIRE - GND
SHIELD - NC (not connected)

On the side of AMP:
RED WIRE - SIGNAL
BLACK WIRE - GND (with shield)
SHIELD - GND (with black wire)

is this method correct?

 

[audioguru]

The dealer shows a simple Mickey Mouse way for him to sell two expensive balanced cables instead of using one inexpensive unbalanced stereo shielded audio cable.

 

[MikeMl]

Actually, the problem you are trying to prevent is from alternator whine from getting into the audio. This has almost NOTHING to do with SHIELDING; it has EVERYTHING to do with "GROUND LOOPS", which shielding does not prevent.

GROUND LOOPS are created when the signal source is grounded to the car body in one location, while the amplifier is grounded to car body in another, distant location. The normal currents that flow in the car body (because the car body is used as the return conductor for 99% of everything installed in the car) cause a small voltage drop between the two grounding points, and get added to the signal fed into the Amps.

You have only two ways to solve the problem:

Run the MP3 on internal batteries (not on a plug-in vehicle power supply) and only ground the MP3 shielded cable at the input of the amps. Do not allow the MP3 case to touch anything metallic.

If you insist on running the MP3 using a plug-in adapter, then you will have to put a GROUND-LOOP-ISOLATOR, like one of these to break the ground loop between the MP3 and the Amps.