Its my wild guess, your AKG needs a lot more amplification power to drive them properly and the LD2 may not be a good match.

I'm not concluding your LD2 is not capable of driving the AKG but looking at the impedance specs, the LD2 is having a tougher time driving a heavier load of the AKG. If not mistaken the K701 is rated at 62ohm and Grado at 32ohm. That's hellava difference. The actual AKG studio version is 600ohm..and cannot be used with LD2 or any consumer range head amps.

Its the same with speakers and a tube amp. A 4ohm tap to 4ohm speaker ( or 8 - 8ohm) is best match. If 4ohm tap to 8ohm speaker, it'll be a somewhat softer and with less dynamics and impact. Tube amps require perfect impedance match at the output for music rated power unlike solid state amps which can double the power output when the impedance load is smaller.

This post has been edited by bsl555: Feb 3 2007, 12:47 AM

Yee, Come to think of it..I think there's one lesson to be learnt here if you intend to use the LD2 as your primary head amp. Look for headphones that have a nominal impedance of 32ohms or little less. I think these should suit your LD2 best.
Generally any head amp modestly rated at 100mW will drive any consumer headphones. To most, its just a matter of cranking up the volume knob more or less to give the desired volume, but at what kind of sonic quality..thats the million dollar question.
I'll reiterate, output impedance match is more critical for tube amplifiers for best performance.

Without an actual schematic its futile. The gain may be altered but may bring adverse effects and extra loading on 32ohm headphones which may be disastrous and worsen distortion figures. Nearly all head amps generally quote a load of 32-600 ohm for wide compatibility and convenience. I don't think you'd buy an amp that specifies a narrow range of phones.