2 RCA to 2 RCA cables: stereo vs mono

kreutz

Standard Member
Hello.

Quick question: are 2 RCA to 2 RCA stereo cables supposed to have 2 or 4 conductors?

I need to wire two 3-pin phoenix connectors from my audio processor (XAP) into two RCA inputs (red and white) for stereo output, similar to below:
2457-23492-001 - Google Search

2 RCA to 2 RCA cables that I have only have red, white and shield, meaning that I can only wire 2 RCA to one 3-pin phoenix connector (red for pin 1, white for pin 2, ground for pin 3), ending up with mono output. The Belkin PureAV audio cable that I have says it's supposed to be stereo, and that's fair enough I suppose as it sends one signal through white conductor and one through red, but how would the above Polycom cable be wired? It seems to have 2 red, 2 white and 2 grounds, yet still ends up with 2 RCA?
 

kreutz

Standard Member
Think I figured this out - 2 RCA to 2 phoenix is wired with ground and negative jumped together in each phoenix contact. So for two conductor stereo cable with red and white cores, one phoenix contact has red conductor and two grounds, the other phoenix contact has white conductor and two grounds.
 

noiseboy72

Distinguished Member
It sounds like you are going from balanced to unbalanced. If this is the case, you should not short the cold (negative) to earth. You only do this when going from unbalanced to balanced. This is because otherwise you are shorting half the output of the XAP to ground, which is not a good idea, as it could either fail or add more distortion.

You should instead ignore the cold and use the Hot (positive) to the centre conductor and connect the grounds together.

So: Red to Channel 1 Hot. White to channel 2 Hot. Grounds connected.
 

kreutz

Standard Member
Hey noiseboy! Hope you're well, good to hear from you.

I was playing around with the set-up today before I read your message - seems like I got it to work? What I did was:

1. Cut a Belkin PureAV 2 RCA to 2 RCA cable into two halves, then I stripped the ends and ended up with two pairs of conductors for each cable, where the 1st pair was red + ground and the 2nd pair was white + ground;
2. On each cable, for conductor pair 1 (red + ground), I connected red conductor to pin 1 of the phoenix contact and ground to pin 2. I then jumped pin 2 to pin 3 (that's assuming that my pin numbering is correct: based on microphone connections, when I say pin 1 I mean the pin where the red conductor of mic XLR cable normally goes, pin 2 is where the white conductor of mic XLR cable normally goes and pin 3 is normally mic ground, it might be that they are officially counted from the other end with pin 1 being ground);
3. For conductor pair 2 (white + ground) I connected the white conductor to pin 1 of the phoenix contact and ground to pin 2. Similarly, I then jumped pin 2 to pin 3.
4. I ended up with two 2 phoenix to 2 RCA cables. I am using this for my video conferencing device, with the help of the following cable.
2457-23492-001 - Google Search

The current set-up is as follows: because mic inputs are all mono, I forward the mics to a single output of the XAP which then goes into line-level input of the Polycom via a single phoenix contact to single phoenix contact mono cable. The Polycom output is stereo, so I use the cable above and the newly made cable to input the sound into the device (line level input 9 (left) and line level input 10 (right) of the XAP). I then map these outputs into output 9 (left) and output 10 (right) of the XAP, which goes to the speaker system in the room via an RCA to ethernet balun.

I did not test the set-up properly, but the sound seemed OK during my 5 minute test (it's Sunday after all!). Are you saying that the input and the output into/from the XAP should be differently wired?

Thanks again!
 
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noiseboy72

Distinguished Member
Yep, Balanced to Unbalanced cables for input and output need to be wired differently. Remove the jumper between the cold and ground, as this is shorting out half of the output buffer amp.

Other than that, this should be good to go!!
 

kreutz

Standard Member
I am posting a diagram of what I've got (with a little picture of how phoenix connectors look like [from the internet] for reference):



Red and white RCA cables have red and white conductors respectively, as well as ground (golden colour in picture). I did this based on the following thread that I found on ClearOne forums:
forums.clearone.com • View topic - Problem with XAP 800 and PC Audio

So all I need to do is to remove the jumper between pin 2 and pin 3, connect ground to pin 3 and leave pin 2 unused? Is that correct? And how would this differ between input and output, as I am planning to use both? Thanks again.
 
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noiseboy72

Distinguished Member
For inputs, you are correct that you short the cold to earth. This "unbalances" the input and ensures that no additional noise gets into the system.

For outputs, just ignore the cold connection and leave it unconnected.
 

kreutz

Standard Member
Seems to be working fine, thanks, great help as always.

As I am not an audio pro and consider myself an amateur, I am yet to understand a few things, so if anyone could help me out, that would be superb. Below are 2 questions about what I still can't quite understand despite reading stuff on the internet:

1. In below diagram (where XAP is balanced output connected to unbalanced RCA audio recorder) left and right audio will be phase and out-of-phase audio respectively, which will cause out-of-phase audio on the recorder. Despite all the theory about phase and out-of-phase audio cancelling each other out, the XAP (and other balanced inputs) 'unbalance' the audio using some specific way which is more than just putting them together. Putting them together like below merely causes out-of-phase audio (rather than silence). Are the above statements correct?



2. When we have a stereo output wired into two XAP ports, I assume we are only really looking to get in-phase audio for both left and right channel as out-of-phase channels don't exist. Why is it recommended to short pin 2 to pin 3 and not just ignore the out-of-phase input (pin 2) completely? What exactly does it do when you short it as oppose to leave it empty?

Thanks!
 
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noiseboy72

Distinguished Member
Think of it like this: Balanced audio has 2 amplifiers. One does the in phase and one the out of phase. But... Apart from the signals being 180 degrees out of phase with each other, the outputs are the same. Therefore, if you short one of the outputs, you are short circuiting the amplifier to ground - which is a bad thing.

The way you have connected it means that you will get a very weird, very wide stereo image, or if you connect it to a mono source, very little output.

You SHOULD short input cables, as otherwise, the balanced input can accept noise on one of the input legs, which will affect the whole signal chain.

So long as it is working for you, fine, but it is not correct to wire left to +phase and right to -phase,
 

kreutz

Standard Member
You SHOULD short input cables, as otherwise, the balanced input can accept noise on one of the input legs, which will affect the whole signal chain.
Didn't know noise could be picked up from an unused pin (pin 2), but I guess it makes sense.

I think I know everything that I need to work with my relatively basic set-up for now, thanks again for all of your help :)
 

kreutz

Standard Member
Yup, the improvement is significant. I have two recorders running simultaneously, one is wired the old (incorrect) way (single XAP output to 2 RCA input as shown in the last diagram), the other is wired the correct way (2 XAP outputs [no middle pins] to 2 RCA input). The voice is louder and clearer on the latter, though the former is actually surprisingly good given that it uses out of phase audio for the left input! Thanks :)
 

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