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RME User Forum → FireWire & USB series → Headphones out UFX+
Hi, Can anyone please take a look at this:
I use the UFX+ and I experience crosstalk (Leakage - or whatever you want to call it) between the two headphone outputs when I use two headphone pairs.
* I connect two headphone pairs. One pair is muted.
* when playing back on only one pair. I get the same info (but -50dB aproximately) on the totally muted pair as the one that is not muted
* It repeatable both ways.
What is wrong/ or what can I do about it?
Where do you see the -50, and where is the phones out muted?
Where do you see the -50, and where is the phones out muted?
Than you kindly for the answer.
Yeah I hope we get this little space ship to behave 
But, let me explain better.
Two headphone sets are plugged in on 9-12 out.
One is turned down to minimum (muted). This is the one on my heads. The other one I move away to not disturb the test.
I playback a busy mix, right now it was "sea wall" from Blade runner by Hans Zimmer. It stays pretty much around 0dB on the software out 1-2. It's routed to both headphones. I hear the audio in my muted headphones already when the non muted headphones are set to -20dB.
Both sets need to be connected for this to appear. Just a dummy (trs cable) won't provoce this to happen.
Perhaps Ground/Shield related?
-50dB was an estimation. Please ignore that I wrote that..
In a real world situation I get problems when I re-record to spring reverbs through one of the headphones outputs (because it's great at that) while monitoring on the other one. I will most likely crank the reverb output to a maximum and then monitor at approximately -20dB with the other phones. This is where I noticed the problem.
cheers!!
Edit: the headphones are muted at the front panel. I see everything nice and clear.
Edit again: It appears already when the non muted headphones are set to -30dB.
If you use low impedance headphones then the relatively high (compared to Line) currents can cause crosstalk between two locally bundled outputs. That is normal and not easy to avoid in a crowded unit like the UFX+ (it needs a 10 layer PCB design and dedicated headphone amps as in the ADI-2 Pro to get completely rid of it).
This crosstalk might be at -80 dB or so, I would need to measure it with an impedance like your phone to get specific numbers. It's definitely not -50 dB.
If you use low impedance headphones then the relatively high (compared to Line) currents can cause crosstalk between two locally bundled outputs. That is normal and not easy to avoid in a crowded unit like the UFX+ (it needs a 10 layer PCB design and dedicated headphone amps as in the ADI-2 Pro to get completely rid of it).
This crosstalk might be at -80 dB or so, I would need to measure it with an impedance like your phone to get specific numbers. It's definitely not -50 dB.
I use 2x ATH M50 headphones from Audio technica. 38 ohms.
I think the problem especially (if not only) occurs when something has the sleeve connected to the ring (on the receiving side).
The reverb cable is wired like this = TRS to RCA. RCA side ties the Ring and sleeve together.
On the phones it's the same for some reason. The multimeter shows continuity between the ring and sleeve on both headphones.
I'm not engineer but I guess this is normal (due to the low impedance ?).
Also, If I connect a TRS to TRS on one of the headphones out and short the sleeve and ring I get a leak like explained above.
So Ring connected to sleeve is going to make the sound leak over to the muted headphones.
Using the line outputs 3-8, gives me no such problems. This is strange to me because according to the manual they share the same specs.
Perhaps I get back tomorrow, and explain better..
EDIT: there's of course the same resistance between Tip/Sleeve as well as Ring/sleeve on the phones. The coil being the resistance.
> So Ring connected to sleeve is going to make the sound leak over to the muted headphones.
More than obviously. You did not grasp that you short one channel this way? A fully illegal way to connect something. This is not a balanced output, it is two mono channels where you short one with your cable that is intended to be used only for the servo-balanced rear outputs!
> So Ring connected to sleeve is going to make the sound leak over to the muted headphones.
More than obviously. You did not grasp that you short one channel this way? A fully illegal way to connect something. This is not a balanced output, it is two mono channels where you short one with your cable that is intended to be used only for the servo-balanced rear outputs!
I over-interpreated "share the same technical data" in the manual. Cause it never states servo balanced for the headphones as for the rear outputs. Totally right. Still doesnt make it cool that it'd affect the other headphones channel with low impedance heaphones. So, a too low impedance will create crosstalk. Problem solved. I'd advice myself to use higher impedance headphones or just use a dedicated H-phones amp.
I'm not an educated sound guy. There's a lot to keep in mind. I may not always get it right.
But..
This thing being "illegal"? Did you mean that seriously? Faulty yes. Perhaps studpid, once you know.
But any way. Thanks. We'll keep in touch.
If you don't like 'illegal' take 'not allowed'. Whatever, with 32 ohms phones the crosstalk is a lot less than with shorting one channel and hoping it doesn't start smoking...
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