Demeter VTD82B

Paul White attempts to discover whether the Demeter Tube Direct is really the princess of DI.

Demeter is a name normally associated with tube‑based signal processors, and this DI box must be one of the simpler products in their range. Intended to work both live and in the studio, the Tube Direct is designed to accept a high‑impedance, instrument‑level signal (such as an electric guitar), then convert this to a balanced, line‑level signal suitable for connection to a mixing desk. A second unbalanced jack output is also provided, which may be used to connect a buffered version of the input signal to a back‑line amplifier in live situations.

The unit's construction is solid but hardly elegant. A two‑part folded steel case houses the electronics, which are mains powered via a captive lead. In the studio this is no problem, but for live use the requirement of a mains lead for a DI box is less than convenient. The lead is secured using a self‑clamping plastic grommet, and though these are quite secure, they do tend to place stress on the secured section of the cable; I find they're also quite difficult to remove and insert should the cable need repairing. The voltage rating on the PSU capacitors leads me to believe the valve runs off a reasonable HT voltage rather than in 'starved' mode, and though the valve itself (an ECC83/12AX7 dual triode) doesn't have a retaining clip, it seems quite secure in its ceramic base. Separate PCBs are used for the PSU and valve circuitry, with the balancing transformer bolted directly to the case. All the wiring is discrete and hand‑soldered, and star washers are used to prevent the transformer mounting bolts from working loose. There are input and output connections, and a Boost switch that provides around 10‑12dB of additional gain and a ground lift switch.

What I really like about valve circuitry is how it flatters the sound without adding any obvious coloration...

Though valve DI boxes can't be driven from phantom power, for obvious reasons, they do have certain tonal attributes, not least the way in which valves compress when driven into their non‑linear region. When used with guitars, this produces a more solid, even sound with nice top‑end detail, and acoustic guitars with good pickup systems can sound exceptionally nice. What I really like about good valve circuitry is how it flatters the sound without adding any obvious coloration, though there's always a danger that when you're driving a valve hard with a complex signal as a source, the intermodulation distortion products can confuse the sound, and occasionally produce a dissonant edge.

Tested with my own acoustic guitar (which already has a built‑in preamp), the sound became better integrated and slightly less edgy when DI'd via the Tube Direct; in the Boost switch position with the gains rematched at the mixer end, the sound was slightly warmer and smoother than on the normal setting, I felt. Though the effect is fairly subtle, it's definitely there, and, although some sound sources will benefit more than others, I liked what this box did. Furthermore, the Tube Direct isn't limited to acoustic and electric guitar or basses; it can also be used to warm up synths, samplers, or even vocals if fed from a channel insert point. This is not a pretty box to look at, but it certainly sounds the part.