RCA -> XLR produces no sound - what can cause this?

[Daze]

Hello everyone,

I have recently gotten a new amplifier (NC122MP based) which comes with XLR inputs only. I want to connect it to the RCA outputs of my pre-amp. To do that I also ordered a male RCA to male XLR cable. When I connect everything together I don't get ANY sound at all.

The pre-amp itself is working just fine. I have also used a multimeter to measure the cable wiring and it seems to be wired correctly (according to this thread https://www.audiosciencereview.com/forum/index.php?threads/xlr-to-rca-cables.7843/). That amp itself is also working when I connect it to my XLR DAC.

I am not very experienced in this field. However, from my observations it seems that everything until the amplifier is working as intended. My suspicion is that the manufacturer screwed up the internal wiring of the amplifier (switched the two signal pins of the XLR connector). Could that explain my problem? Or could it be something entirely different?

 

[Wayne A. Pflughaupt]

In addition to checking continuity (RCA tip to XLR pin 2, et.), check the cable for a short. That would be done by connecting the meter across the RCA tip and sleeve, or the XLR pins 2 and 3. If that shows continuity, then there is an internal short in the cable.

If that checks, and you’re confident that the pre-amp is good (i.e. you’ve been using it prior to getting the amp), then I’d assume the amp has an issue. The only way to verify that would be to plug it into a balanced source.

Regards,
Wayne A. Pflughaupt

 

[PaulD]

I would suspect the cable before either of the components. You said the amplifier works properly with your DAC via XLR-XLR cable (is that how you connected them?).

As Wayne said, check the cable for a short. If you have the bare connectors, make yourself a quick cable to test it.

Here's another of the wiring:
https://www.mediacollege.com/audio/connection/xlr-rca-1.html


Or you could try one of these adaptors.

 

[Daze]

Thank you for your replies. I have received a response from the manufacturer and they confirmed that the polarity of the amplifier is reversed.

 

[dasdoing]

Do ths cabels work from unbalanced to balanced?
I mean, balanced to unbalnced is simple, a device expecting two inverted signals and recieving only one is diferent. iarc you would need a converter

 

[Speedskater]

With a balanced input, why would polarity reversal matter?
* * * * * * * *
But with a balanced output to an unbalanced input it might.

 

[Daze]

Do ths cabels work from unbalanced to balanced?
I mean, balanced to unbalnced is simple, a device expecting two inverted signals and recieving only one is diferent. iarc you would need a converter

This is my understanding and I can in no way guarantee that everything is correct:
With balanced input the inverted signal is again inverted at the amplifier and added to the original signal. The sum is then twice the original signal. That's why output voltage for balanced DAC's is typically given as twice the unbalanced output.
Now if you are coming from unbalanced output you can simply connect the inverted signal input to ground. That way when it's inverted and added to the original signal nothing really happens. The sum is simply the original signal. It will be quieter compared to a balanced source but it will work.
For more details take a look at the thread that I already linked: https://www.audiosciencereview.com/forum/index.php?threads/xlr-to-rca-cables.7843/

With a balanced input, why would polarity reversal matter?
* * * * * * * *
But with a balanced output to an unbalanced input it might.

To be honest: I don't fully understand that. The thing about the unbalanced -> balanced cables is that one of the balanced inputs is shorted to ground. And if it's the wrong one (because the internal amplifier wiring is inverted) your signal "gets lost" there. Maybe someone with more detail knowledge can explain exactly what's happening there.

 

[Speedskater]

Actually an XLR balanced input stage only looks at the difference signal between pins 2 & 3. That pin 1 connection is not needed and just clutters the drawing.
* * * * * * * * *
now about XLR outputs to RCA inputs, things are different. There are three and a half types of XLR output stages:
1] transformer. the signal is only between pins 2 & 3. Pin 1 is not involved.
2] passive/impedance. the signal is only on pin 2. so the RCA pin must connect to XLR pin 2.
3] (type A) active/ powered there is a signal on pin 2 & 3 but pin 2 or 3 may NOT be connected to ground.
3] (type B) active/ powered there is a signal on pin 2 & 3 but pin 2 or 3 may be connected to ground.
So there is no one XLR to RCA adapter that will work in all cases.
However I believe that many of the most recent digital components have a type 3B output.

 

[Daze]

You are right, polarity doesn't have anything to do with it. Somehow the idea got into my brain that the signal pins may have been miswired (which would mean reversed polarity).

In reality pin 1 and 2 were switched. Those are not the signal pins but signal and shield. That obviously explains everything that was going wrong with the amp. After re-soldering the wires to the correct pins on the connector the amp is now working fine.