I have had mine for a few days now and I suppose have put about 25 hours on it, so I hope you won‘t mind this newbie giving some impressions:
The front and rear panels are rather subtle, and are made from approx. 2mm thick fibreglass PCB material. Apparently they use a red coloured resin and the routed / milled edges while sharp are probably no more so than a similar panel punched from aluminium. For screening, on the inside of each panel is an etched area of copper foil electrically connected to the case and circuit an earth by wire or by what appear to be plated through holes where the stainless steel socket screws pass through. Both inside and outside surfaces are painted the same white colour. The red switch surrounds are actually the red body mouldings of the PCB mounted switches. The main casing is a pair of anodised ‘clam shell’ alloy extrusions, and the whole unit feels very solid and pretty tough. The miniature toggle switches are positive in action and protrude about 2mm beyond the heads of the panel screws, but I would think you would be quite unlucky to damage them if the unit was dropped onto something hard, but it could happen though.
Internally the circuitry is mounted on an L shaped double sided PCB and is a mixture of conventional and surface-mount components populated above and below the board, The miniature surface mount 8610A op amps are mounted on adapters for conventional 8 pin DIP sockets, and the BUF634Ps are in standard 8 pin DIP packages. Interestingly the BUF634s appear to be doubled up in parallel pairs (one soldered above the other - 4 chips) presumably to double the output current capability. The rechargeable battery pack (two batteries, unknown technology) are charged by a compact 12Volt universal plug top charger. I have found that you need to plug the charger into the MiniBox first before connecting to the mains. Otherwise charging can be unreliable.
Because no instructions were supplied with my unit the various switches are a little confusing to understand at first. This is partly because I am not familiar with the terms ’PtoS’ and ’SFOR’ and the bass boost and SFOR functions operate when the toggles are flicked up, but the PtoS (75Ohm series resistor in the output - I think!) seems to be put in circuit when flicked down. However ’PtoS’ makes a great difference in output when using my low impedance Grado SR125s and hardly any when using my high imp. Sennheiser HD650s. The bass boost is quite effective with my Grados that are fitted with ‘bowls‘. The SFOR function confuses me, as sometimes I think it is just a simple treble boost and at other times I wonder if there is a little cross feed going on there. (I notice that the image has been changed to show ‘3D’ - perhaps the bass boost is to cancel out the treble lift of the ‘3D‘?.) It would be good for the manufacturer to label the unit properly and provide some proper instructions!
The odd little wooden box supplied is of little use. A Remarkable hand made effort, with hand fixed screws for the hinges and the catch, it might serve to underline the ’jewel like’ nature of the amplifier but in my case (sorry) just serves for some ware to store the charger. A nice padded carry case as supplied with the MiniBox D would have been far more useful.
Not having the experience or very much to compare it with, my comments about the sound of the amplifier should be taken with a pinch of salt, as your ears might be younger and more sensitive than mine. I do though have a Graham Slee Solo with about 50 Hours on it. This is a well respected British headphone amplifier that has very good synergy with the HD650s, and I do go to live concerts quite often.
So, compared with the Solo the new MiniBox-E sounds very respectable indeed, and on first swapping from the Solo (using the HD650s) it is surprising (or depressing considering the five times plus cost difference) how similar the little box sounds. No obvious deficiencies with frequency response, distortion or dynamics, and a silent background with both the Sennheisers and the Grados (there is though a switch-on click and a switch-off thump). With well recorded classical music or Jazz, the MiniBox-E does not have the ultimate ‘smoothness’, ‘air around the instruments’ and stage depth that the Graham Slee Solo has. But ‘in the field’ and after a few minutes one just gets on and enjoys the music coming through this little amp. Depending on the source, the MiniBox can also play quite loud without distress or appreciable change in character. My unit has only some 25 hours on it so there may be room for improvement with time (as there will be with the Solo of course).
It may not be a Hornet, and it is not without some quirks: packaging, lack of instructions, switch operation, I am though on balance very happy with this little headphone amp.
It will be interesting to read what the more experienced ‘headphoneists’ have to say about it.
But I hope this was of use in the mean time.
