I have made some interesting tests using a couple of ordinary level/volt meters and a couple of "standard" studio headphones: AKG K240 Studio, AKG K141 Monitor, AKG K420, Yamaha HP-3 The following observations and measurements are the same and repeatable with two different PCs, two different UMC404HD units and two different level/volt meters. Also, everything checks out using Studio One and VLC too, and of course with all the headphones already listed. 1) Feeding the UMC404HD with a 440Hz sine wave at "full" level, generated in Audacity, all headphones start to clip with the Phones level knob at about 1 o'clock. 2) When feeding music with peak levels near 100% the "audible" clipping occurs at the same setting of the Phones level knob, at between 1 and 2 o'clock. 3) When measuring the output of the headphone jack, with no load (no headphones connected) the max level before clipping is about 1,48V RMS. 4) When repeating the above tests and measurements with my old PreSonus Firestudio Mobile, the headphone output stage does NOT clip even with the Phones level knob at "full", and the output level then is about 6,5V RMS. WAY too loud for human ears, but this clearly shows that the PreSonus FireStudio has a headphone amp that is "loud enough with power to spare". Conclusion - PreSonus Firestudio Mobile: Max headphone output power with a 55 ohm load (AKG K240 Studio) is AT LEAST 800 mW before clipping. Conclusion - Behringer U-Phoria UMC404HD: Max headphone output power with a 55 ohm load (AKG K240 Studio) is about 40 mW before clipping. As you can surely agree, the UMC404HD headphone amp is severely underpowered!
Just replaced my old Presonus FireStudio Mobile with a brand new Behringer U-Phoria UMC404HD. Everything seems to work pretty well, but the headphone output is too weak. Using the Firestudio Mobile, all my headphones can play more than loud enough, AKG K141 Monitor, AKG K240 Studio, Beyer Dynamic 770 and a couple of other 'standard' studio headphones. With the Behringer, the headphone amp is clipping long before I can get a loud enough output. The output level is inadequate for headphones with a sensitivity below 110dB, which most studio cans are. I've tried with another UMC404HD connected to another computer, and this confirms that the headphone output clips in exactly the same way as my own. Very disappointing to say the least. Where can I get the schematics for the UMC404HD ?