This BUF03 is class A unity gain zero feedback buffer and is a real sleeper, pity it's not being made anymore, NOS is all that's availible, and it runs very hot, big heatsinking is a must.
I use this buffer for the output stage of a heavily modded i/v stage R2R Multibit cdp. And it blows away any (feedback based)opamp there is, very dynamic, powerfull tight bass, rich mids full of body, and sweet extended highs. And can be dc coupled.
It will drive just about anything, 2ohm output impedance with bags of current even drives 300ohm HD650's better than any headphone amp I've listened to.