VTDB-2B | SPL

SPL (July 1997)
By Hugh Robjons

The mechanical construction here is basically a pair of folded steel plates, the lid being C-shaped into which the U-shaped base slides. The two halves are secured with four self-tapping screws which also provide the attachments for rubber feet. The steel plates are of a pretty thick gauge metal and so should withstand a reasonable amount of abuse without trouble. The whole enclosure measures a slim 140 x 60 x 190 mm (WHD), and all the audio input and output connections are mounted on the front panel. The rear panel carries a captive mains lead, a fuse holder, and the mains power switch and indicator.

Internal electronics are mounted on two well-printed circuit boards: one for the power supply and the other for the Tube preamplifier, the latter is mounted vertically on the side of the case so that the Chinese ECC83 dual triode valve is mounted horizontally, hence the slim look to the box.

The input jack socket is a switched type which has been arranged to short the input signal to ground when no plug is inserted. The input signal is routed directly to one half of the ECC83 so the input impedance should be very high, but unfortunately, the Demeter was not supplied with a handbook so I am unable to quote the exact technical specifications.

A Boost switch is provided on the front panel and this appears to introduce about 12dB of extra gain into the signal path. I am not sure whether this is performed by changing the feedback around the valve, adding the second half of the valve, or by simply adjusting an input or output pad. Whatever the circuitry entails, I found the switch did affect the sonic quality of the box, and I preferred the boosted sound quality over that of the unity gain position in most circumstances!

The sound desk output is transformer coupled (and isolated from) the preamplifier and is made available on a male XLR chassis plug. An adjacent rocker switch provides an earth-lift facility for it and a second jack socket provides a buffered output for onward passage to the backline amplifiers. I was a bit disturbed to discover that the large fuse-holder n the rear panel is wired such that the easily touchable outer contact is directly connected to the live pin on the mains plug. Also, the mains wiring from the captive cable appears to be twisted (and presumably soldered or crimped?) to the transformer cables and protected with a single heat-shrink sleeve. Whilst there is nothing wrong with this per se (the case work is properly and solidly earthed), I would have preferred to have seen a decent mounting on PCB tags n the power supply board. This kind of provision would also make re-terminating the mains cable a lot easier when it needs replacing or repairing, which is an inevitable task after all.

As might be expected, the Demeter adds a classic warmth to most guitars which I found to be very complimentary under most circumstances. Acoustic guitars with piezo pickups in the bridge generally seemed to work well with the Tube Direct, although the complex harmonics of a 12-string fared rather less well, with much of the detail blurred or softened. Solid body guitars worked very well indeed with the Demeter, with very healthy levels of sustain being achieved and, again, that complimentary tube warmth!

The Tube Direct works very effectively but the end results seem to depend to an extent on the source instrument. Experimentation is the name of the game here: with some guitars (particularly decent solid body instruments), it is the perfect partner, yet with others, it actually muddles the sound quality to an unacceptable degree. In practical use, I experienced no problems at all, save for one minor situation where the main transformer (mounted at an angle in the back left hand corner of the unit as viewed from the front) caused a small amount of induced hum in an adjacent digital effects processor, but re-siting the Tube Direct a few inches away cured the hum completely.

Having to find another mains socket to power the device might be considered a bit of a drag and some aspects of the unit's construction are a tad worrying, but the Demeter can be generally recommended for its ruggedness and easy interfacing. Its sound quality and characteristics are such that you will have to audition it carefully with a variety of source instruments, but in the right situation, this is potentially a very musical DI box indeed. I suspect it would be the kind of DI box that a musician would buy for him/herself and insist on using at a gig, rather than being the sort of thing that every engineer would want in their goody bag, but it's worth playing with all the same.