How can I test what's coming out of a headphone port?

I have a Behringer UMC404HD audio interface and I was wondering if there's a way to quantify and test how much power is coming out of its headphone port at full power.
The reason I'd like to find this out, is because I'd like to split that signal to up to 4 headphone boxes I'm going to make each with its own volume control and I need to determine the specs for the potentiometers.
Now, I whole heartedly agree with everybody I ask about this who responds with, 'wow that's a tall order to drive 4 headphones with pots from 1 output'. But, call me crazy, I'd like to have a numeric representation of how tall that order literally is, based on actual readings I'm taking, as opposed to just hypothetically talking about how it may not work.
 

rayma

Member
2011-04-29 8:37 pm
I have a Behringer UMC404HD audio interface and I was wondering if there's a way to quantify and test
how much power is coming out of its headphone port at full power.

I can't find any specs for the Behringer's phone output, but's normal to have a series output resistor in the circuit
that sets the output impedance. You could connect a 1k variable resistor at the output, adjust the 1k for half
the voltage output on a DVM or scope, and then disconnect and measure the resistance to find the output impedance.
If the impedance is less than a few hundred Ohms, there should be no problem driving 4 paralleled 10k pots with buffers.

You need the buffers because a headphone needs a reasonably low impedance source, and the 10k pot's output resistance
(up to 2.5k) is too high. You can't use (say) a 100 Ohm control because these would likely overload the Behringer's output.
There's a chance you could use four 1k pots without the buffers, if the Behringer will drive 250 Ohms, with some effect
on the sound of the phones due to the source impedance.
 
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There's a chance you could use four 1k pots without the buffers, if the Behringer will drive 250 Ohms, with some effect
on the sound of the phones due to the source impedance.

Interesting, I think that's what I'm doing now. I bought 4 volume controls from amazon that read as 1k on my multimeter. I took one apart to try and find its specs to buy just the pot to put in my own DIY boxes, but couldn't find any markings at all. There's no static and they all work when simultaneously plugged into the headphone port with a splitter, but the actual volume control is kinda spotty. Its just not a smooth progression from low to max volume, its very choppy.
Hmmm, I might just stick with the 1k route though. I was looking for cheap and minimal and its starting to sound like I'll need multiple more components and understanding. I was hoping for just a $1 pot. Oh well.
 
Here's my Mark1 prototype btw. It might help to illustrate what I'm trying to achieve.
For strictly a portable podcast setup from the perspective that 'more cords = bad', I decided to use 5 pin xlr cords and connectors to replace 3 pin xlr, so that I can condense mic and headphone cables into 1 run, separating at a breakout box on a desk mic stand. Pictured is the mod I did on my Xenyx 1202 which functionally is working perfectly. I plan on refining the build for MarkII on the UMC404HD.

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[IMGDEAD]http://s14.postimg.org/irykzbwvx/image.jpg[/IMGDEAD]

[IMGDEAD]http://s14.postimg.org/59ron1kql/image.jpg[/IMGDEAD]

[IMGDEAD]http://s14.postimg.org/na0vrfcxp/image.jpg[/IMGDEAD]
 
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I have a Behringer UMC404HD audio interface and I was wondering if there's a way to quantify and test how much power is coming out of its headphone port at full power.
The reason I'd like to find this out, is because I'd like to split that signal to up to 4 headphone boxes I'm going to make each with its own volume control and I need to determine the specs for the potentiometers.
Now, I whole heartedly agree with everybody I ask about this who responds with, 'wow that's a tall order to drive 4 headphones with pots from 1 output'. But, call me crazy, I'd like to have a numeric representation of how tall that order literally is, based on actual readings I'm taking, as opposed to just hypothetically talking about how it may not work.

Something like this will work better than a bunch of pots and their associated issues: Behringer HA400 Microamp 4-Ch Stereo Headphone Amplifier

Mike