The Koss Pro4AA headphones paired with a 6AS7G based amplifier I built.
I built this amp using the chasis and power supply from an old Heathkit A7 amplifier. The output transformer is fine if anyone wants to make me an offer. The schematic is similar to Aren van Waarde's found here. My power supply is different, a 5Y3GT rectifier is used in place of the pair of 1N4007 diodes he specifies. This wasn't done out of a desire for better sound. Rather, I intended a softer start for the high voltage and glowing tubes are a delight so why not use one more eh?
*this was supposed to be an amazon review of the headphones but their site is giving me grief so it gets posted here:
Excellent sound when driven with a decent source. Playing back a FLAC recording through an Audigy 2 seems to be weak on the bass. Using a separate headphone amplifier after the sound card was great without any eq changes needed. I originally bought these for their high input impedance (250 ohms) to be used with a 6AS7/6080 based OTL tube headphone amp I built. I'm happy with how it all turned out.
They're fairly heavy though well built. The headband is not designed for people with large heads so over prolonged use the plastic ridges at the base of each side of the headband do dig in a bit. The ear-cups are great, I like pleather pads and these ones are sized and stuffed the right way. The cord is chunky, this is a good thing for stationary listening but don't expect these to be great on the go. The warrenty service offered by Koss is legendarily good so I'm confident on enjoying these for years to come.