Audio/Microphone Phantom Power Hum Question

[Al Hoff]

Question is near the end.

Alright in short, I am using a Focusrite Solo Gen 2 USB Audio Interface. I output to some speakers and headphones and hope to have my PC capture my microphone. I own a ModMic 5. It requires a little voltage to be operational (specifications say 1-10V-ish). So I have a Behringer PS400 phantom power supply and put it into +12V mode. I run a short XLR patch cable from the Behringer to the Focusrite. I picked up a cheapo XLR to 3.5mm plug without much thought thinking it would work.

Well, it _does_ work I tried it out. But the cheapo plug is creating a hum. With or without the microphone plugged in. I don't really know much behind the scenes here with audio equipment. But I do know a reviewer said the cheapo plug had been soldered together on two of the pins. So. What I want to know is why is this plug the problem. Is it because it is unbalanced? Would a balanced solution fix this? Assuming that is the problem..

 

[Wolf_LikeMe]

specifications say 1-10V

Why are you powering it off phantom12 if thats outside of it's rated range?

Can you link to the adapter?

 

[Al Hoff]

Why are you powering it off phantom12 if thats outside of it's rated range?

Can you link to the adapter?

I wanted an elegant solution to power the microphone. And the company that sells the microphone had a post about using 12V phantom power and said it should work fine.

And I couldnt find the product on their website but they have it on their amazon store http://a.co/dg7dlKl

 

[Wolf_LikeMe]

Ah right, thanks, I was just wondering about that.

http://www.plugwiring.co.uk/how-to-wire-an-xlr-cannon-audio-plug/
This gives a decent diagram as to how the connections are made.

http://www.aviom.com/blog/balanced-vs-unbalanced/ - Jump to the section "Balanced Cables and Systems"
This is a good explanation.

In it's most basic terms its utilising the superposition of waves to eliminate noise.
TL;DR

• Balanced consists of 2 Signal channels and GND
• One signal is flipped/inverted at the start. +S1 (Positive Signal 1) -S2 (Negative Signal 2)
• Noise is introduced to both channels, think of (past the shielding (unbalanced relies on just shielding) At this point +S1+N, -S2+N (N=Noise)
• The audio equipment that utilises this then flips Signal2 and superpositions them to give you: (+S1+N)-(-S2+N) = +S1+N+S2-N = +S1+S2
  
• (Note S1 and S2 are the same I just need to differentiate between them.)
• In an unbalanced system you would just get S+N, a high impedance would somewhat negate the noise.

Shout if that doesn't make sense, I struggle slightly to explain it without drawing things, and thanks again for letting me know that the ModMic can run on 12V, should prove useful in the future.

 

[Al Hoff]

Turns out the behringer ps400 is what is making the humming when in 12V mode. Should have tested that.........

 

[Wolf_LikeMe]

I wonder is that a grounding issue then? Worth consulting them, it might just be faulty.