Help understanding the wiring of this RCA aux input panel

Thread Starter

john2k

Joined Nov 14, 2019
146
I have an red and white sound aux input panel that is connected to my cars stereo. From my understanding of a red & white aux cable is that essentially there is a max of 3 connections, the ground the left and right. But as you can see from the disassembled pictured of the unit below the PCB actually has a connector with 8 pins. I've labelled the pins in white in accordance to the technical manufactures specs. Although there is 8 pins, there are actually only 4 of those pins that actually connect back to the stereo. 3 of which make sense just like I thought but the 4th connection which is pin number 6 seems to be something called Line In shielded cable. What exactly does that do? I wanted to completely remove this so I can wire in a permenant audio source into the aux input from a left, right and ground cable. What do the other pins on this PCB actually do? Thanks



There is also the following schematic from the manufacturers docs which shows the aux panel pins 2,3,6 and 7 on the left going to the radio. The pins 2,3 and 7 seem to make sense just like a normal audio cable if i was to completely bypass it but the pin 6 I don't understand what does that do? There is essentially a wire coming to pin 6 in the loom of the connector from the radio.

 
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Thread Starter

john2k

Joined Nov 14, 2019
146
Any suggestions? I'm thinking should I not be able to just connect the right, left and ground output from my device to the connector and leave the other connector off completely?
 

djsfantasi

Joined Apr 11, 2010
7,700
Any suggestions? I'm thinking should I not be able to just connect the right, left and ground output from my device to the connector and leave the other connector off completely?
You could do that, but it may sound terrible and have extra noise. The last connector is the cable shield and should be connected to earth
Or chassis ground. Preferably at one end only.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
You could do that, but it may sound terrible and have extra noise. The last connector is the cable shield and should be connected to earth
Or chassis ground. Preferably at one end only.
That last connector originates from the radio player and connects to this aux input panel. So i'm assuming the end at the radio is earthed. So if I was to try and hardwire a 3.5mm output to this using the standard left, right and ground cables where would I connect this earth that is coming from the radio?
 

Thread Starter

john2k

Joined Nov 14, 2019
146
So basically what I am trying to achive is something like the diagram below where I want to connect the audio cable directly to the connector going to the radio and completely remove that aux PCB. But not sure what to do with that pin 6 wire. What exactly is the ground cable doing on the PCB board? I tried to do a continuity test between ground pin 7 and this pin 6 but pin 6 doesnt seem to connect to any other pins.

 

djsfantasi

Joined Apr 11, 2010
7,700
That's a bit difficult to test as I have to remove the radio completely to access pin 5. Whereas pin 6 is on the other end which is easily accessible
Then, I suspect there is no way for me help you. Maybe someone else has an idea... Maybe you can figure out a way...
 

Externet

Joined Nov 29, 2005
1,614
Seen it before; an extra pin on a 'rca' jack senses a plug is inserted to disable or enable something else.
Perhaps is your case.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
Seen it before; an extra pin on a 'rca' jack senses a plug is inserted to disable or enable something else.
Perhaps is your case.
That makes sense because now I've hardwired a 3.5mm connector cable to it directly without the RCA sockets and even if something isn't plugged in it is detecting something is on aux channel.
 

djsfantasi

Joined Apr 11, 2010
7,700
John2k

Where did you get the schematic in your first post? Pins 5 & 6 clearly show connections to the cable shield, as indicated by the ovals surrounding the other conductors. The shield doesn’t directly affect connection of the audio signals. As such it is not necessary to connect. What it does however, is minimize the cable acting as an antenna picking up noise in the air. Like 60Hz power hum. Thus, there may be a degradation of the audio if the shield is not grounded.
 

MisterBill2

Joined Jan 23, 2018
8,808
Here is a suggestion to avoid guesses: With that small board, use a continuity tester and a short cable with an RCA connector and plug the connector into one RCA jack at a time, and discover what pin (center and shield) each of the connections goes to. I am thinking that because some systems have bridging outputs that the two shield connections on the RCA connectors are not solidly connected to the radio ground. That should be simple to verify.
 

MisterBill2

Joined Jan 23, 2018
8,808
Here is a suggestion to avoid guesses: With that small board, use a continuity tester and a short cable with an RCA connector and plug the connector into one RCA jack at a time, and discover what pin (center and shield) each of the connections goes to. I am thinking that because some systems have bridging outputs that the two shield connections on the RCA connectors are not solidly connected to the radio ground. That should be simple to verify.
 
That PCB is a good thing, but I don't like the design.

1, Shielding tend to remove RFI
2. Twisting removes EMI

So, a twisted pair shielded cable is a good thing. For a shield to be effective, it should be grounded at one end. Not connected to the other end is fine. This eliminates ground loops or hum.

the (-) is a reference or common so to speak.

What they should have done is to make it accept a gigabit shielded ethernet (8P8C) cable with the proper pairing and shielding.

Modular connectors are wierd in general.

Fir telephone they can be 6P6C, 6P4C and 6P2C P being poles and C being contacts, So, they can have 1 pair, 2 pairs and 3 pairs. They are also designated pair 1 (the middle 2 contacts), pair 2 (the next outer ones) and pair 3, the final outer pairs.

Straight-thru Ethernet is always paired the same way, but the colors may be different. The shield is messed up.
This https://cdn.amphenol-icc.com/media/wysiwyg/files/drawing/rje591885x01.pdf type of shielde connector would probably been a better choice.


Ethernet has always been 8p8c
 

MisterBill2

Joined Jan 23, 2018
8,808
That PCB is for connecting some source as an external input to an automotive car stereo receiver. It is very short, and probably all located inside a metallic enclosure. So hum and noise pickup on that very short cable is not an issue. It appears that the outer shield connections are DC isolated because some possible sources may be the outputs of a bridging amplifier, with no lead tied to common or frame ground. At least that is the logical explanation that I see.
Modular connectors have no business in car audio systems at all because they can be noisy under mechanical vibration, and also because they demand a special crimping tool and a fair amount of skill.
 
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