Headphone Reviews

Stax SRM-727II ($2200)
This is an all solid-state amp with a zero-feedback output stage. From the Stax USA website:

The new SRM-727II employs semiconductor output drive stage and non-feedback (NON-NFB) output stage for the first time ever in a STAX driver unit. A pure balance DC amplifier configuration is used for the large current emitter follower Class A output stage. A significant increase in dynamic range especially in the upper frequency has been achieved. A high level of sound purity is achieved through the simple two-stage amplification circuit with low-noise FET input stage.

No-feedback sounds like a good idea, but it doesn't seem to pan out well with this amp, which sounded flat, blurred, and boring relative to the rest of the amps auditioned. The low notes are particularly uncontrolled sounding, adding a thick woolliness and subtracting any articulate texture present. The mids are somewhat uninspiring and disjointed, topped off with a slightly shouty upper-mid, low-treble hype. The highest octaves are somewhat rolled-off.

One of the folks I contacted mentioned this amp can be modified to sound quite a bit better, but in its stock form it was clearly the poorest performer of the bunch.

Stax SRM-007tII ($2400)
This is a hybrid amp with a FET input stage and a balanced output stage using two pairs of 6CG7 tubes. A couple of my friends mentioned this was a nicely designed amp, but that the 6CG7 tubes just really can't swing the needed voltage for electrostatic headphones.

I liked the sound of this amp quite a bit. A sweet and delicate presentation. The bass isn't terribly tight, but it's well proportioned. The mids and treble are lush with a slight warm tilt and slightly rolled-off upper treble. There also seems to be a slight glare in the mid treble that more often than not is heard as a bit of treble sparkle, which is nice as it balances out the slight roll-off of the upper-treble.

The problem with this amp is all that goodness goes out the window when turned up to stronger listening levels. The bass doesn't seem to get louder, just woollier, and the mids start to get shouty. But the worst thing is that the somewhat innocuous treble sparkle quickly grew through glare and on into what sounds like significant distortion to me.

After auditioning the above two amps I came to the conclusion that finding an amp for the world's best headphone is a rich man's game. If you're going to get a pair of Stax SR-009 headphones, you need to be prepared to spend big bux on the amp as well. If you're on a budget, but still want to work your way up to it, I'd suggest the Woo WEE energizer and play around with all the power amps you can get your hands on until you can afford the $5000 amp you'll need to get the best out of your SR-009.