The Graham Slee Novo is built into a solid metal case that's actually a 'clamshell' design held together by front and rear panels.
Inside is a circuit built entirely from discrete transistors, using (Slee tells us) multi-path feedback, a remarkably painstaking approach to such an apparently simple job as driving headphones.
In agreement with Slee's specifications, we found distortion not quite as vanishingly low as some can offer, though still in practice more than adequate, while frequency response is not entirely flat: treble slopes off perhaps just audibly at some volume-control settings, while bass is a little leaner into low impedances than high, 3dB shy at about 24Hz/15Hz respectively.
In a group which showed subtle, but consistent character differentiation between the contenders, this was very much the beguiling one.
That's not to say that it is perceptibly short of detail or any other particular quality, but it does seem to specialise in a very attractive vocal register in such a way as to seduce the listener, particularly with ballads, gentle instrumental pieces and anything at all sentimental or smoochy.
On the other hand, given something lively like a Mozart symphony or some upbeat jazz, it bops along most cheerfully, with perhaps a little subjective highlighting of middling-range instruments, but also plenty of extension in both bass and treble, the latter being admirably open and 'airy'.
The Graham Slee Novo is excellent choice, we feel, for regular long-term headphone listening.