I bought this a few years ago to drive my HD650s and it works great. Sold the headphones and no longer need this. It is in great condition.
Maximum amplification factor 3.0 (+ 10 dB)
Maximum output voltage Vp
12V at 4V analog input
2.8V at USB digital input
Maximum output current 250 mA
Crossfeed filter (stereo, low)
Gold-plated input jacks.
Silver plated headphone jack (Neutrik).
Silver plated heavy duty switches.
Alps Blue Potentiometer.
7 Watts toroidal transformer.
110V and 220V selectable.
Power uptake 4 Watts
Built-in groundloop breaker.
Low impedance electrolytic buffer capacitors. Total Buffer capacity 22.000 uF.
Polyesterfilm bypass capacitors in the power supply.
Polystyrol and polypropylen capacitors in the signal path.
Metalfilm resistors in the signal path.
Double sided PCB with 70 um copper.
LM6171 opamps biased into class-A using LM334 current sources.
BUF634 buffer amplifiers at each output channel.
Built-in USB-DAC (PCM2704, 16 bit, 32/44/48 kHz)
Ultra short signal paths.
Signal paths and signal path components at the bottom side of the PCB for maximal shielding.
Sturdy aluminium enclosure.
Weight: 2.2 kg.
Size: 23.1 x 18.7 x 8.7 cm.
Edited by chezhed - 4/14/14 at 11:52am