CM-HPX1
Headphone Volume Control, Passive, XLR Input - Jack Output
The CM-HPX1 is a passive headphone amplifier with level control from a stereo balanced line input via 2x female XLRs. It is transformer balanced, and can be used with any headphones above 150Ω impedance.
TAG:
The transformer ratio of 2:1 ensures that any headphone load presented at the output is reflected through to the input at a 1:4 ratio (hence a 150Ω set of headphones looks like 600Ω at the input, a suitable load for most good quality line output stages).