Pro Audio Review (October 1999)
By Russ Long
Demeter STDB-1 Tube DI and H Series Stereo Tube Direct/Line Driver
Demeter is the first name that comes to mind when the subject of tube direct boxes arises. In more than 12 years in the engineer's chair, the only criticism of the Demeter tube DI I have encountered is the price. With a list price of $1,100, the 1U rackmount STDB-1 stereo direct box is beyond the price range of many interested buyers.
Now there is a second option. The acclaimed Demeter H series line of hybrid tube equipment has been expanded to include the new H series stereo tube direct/line driver. The H series piece has a list price of $899, which makes it one of the most financially accessible Tube DIs on the market.
The H series stereo tube direct/line driver is more than just a tube direct box. In addition to featuring the same tube driven ultrahigh impedance input from the STDB-1, it includes a balanced line-level output section. The unit can be used as either a line level direct instrument input or as a line level driver to add tube warmth to line-level audio sources.
The STDB-1 and the H series tube direct/line driver look almost identical. Although the STDB-1 is black and the H series unit is blue, both machines offer similar features.
The front panel of the STDB-1 features identical controls for both channels. Each channel features a 1/4" jack for signal input, a tube buffered unity gain 1/4" output jack for amplifier connections (up to 40' of cable can be run without signal loss), a ground-lift switch to eliminate ground loops (very handy), a phase switch that flips the signal's phase at output and a boost switch that activates the boost circuit.
The boost circuit increases the output level of the unit. The front panel also offers a continuously variable volume control on both channels to adjust output level (up to 20 dB in boost mode). In unity gain mode (when the boost mode is not activated) the volume control is not active.
The rear panel of the STDB-1 is equipped with separate 1/4" unbalanced line level tube, buffered output jacks and male microphone level XLR connectors for both channels. The 1/4" output jack's signal is buffered through the tube circuit. The jack has a source impedance of <2 kohms. This makes the signal perfect for driving long cable runs (up to 40') between the STDB-1 and a guitar amp. The male XLR makes use of the Jensen JE-DB-E direct box transformer for its exceptional sound.
The front panel of the H series machine also has identical controls for both channels. Each channel features a 1/4" jack for signal input, a tube buffered unity gain 1/4" output jack for amplifier connection, a ground-lift switch to eliminate ground loops, a phase switch that flips the signal's phase at output and a boost switch that activates the boost circuit. The front panel offers a continuously variable volume control on both channels to adjust output level when in boost mode.
The rear panel of the H series machine is equipped with separate 1/4" TRS and male XLR connectors for both channels. On the H series unit the signal is Y- connected to the 1/4" and male XLR connectors. There is no difference between the two outputs.
I always believed the only way to record acoustic guitar is with a microphone, never with a direct box. A few years ago a client convinced me to use the Demeter DI instead of a second mic. It sounded fantastic. The track actually became the primary acoustic guitar track for the song and the track recorded with the Neumann KM84 became a secondary track. To this day, the Demeter tube DI is the only direct box I've encountered that actually records acoustic guitar at a high enough quality to use on a record.
Both machines make use of the 12AX7A vacuum tube for the input stage. Using a tube circuit instead of a transistor circuit lets the machines provide extremely high input impedance, preventing pickup loading. This also gives considerable headroom, which allows a wide dynamic range without distorting.
I have been mixing a project for new artist Dave Pardue at Woodland Studios over the last few weeks. The record was tracked on a variety of formats including 2" analog, RADAR and ADAT. For mixing, we transferred the entire project to Sony 3348 using the Otari UFC. Many of the tracks that were recorded to ADAT have a harshness difficult to overcome using EQ.
I found that using the H series tube direct/line driver adds tube warmth to the problematic tracks and helps overcome this problem. After setting the H series machine on unity gain it can be inserted on the problem tracks resulting in a smoother, punchier and warmer sound with no gain change. The improvement is quite amazing. My only complaint is I can only use it on two tracks at a time.
Using the H series machine as a line driver on the stereo bus insert also yields brilliant results, especially for material that has never been attached to analog tape. The mix becomes punchy and warm without losing any high end and, in most cases, without adding any noticeable noise.
The only difficulty in using the H Series machine in this manner is that there are no audio inputs on the back panel. A pair of cables for audio input must run to the front of the rack while a pair of cables for audio output must be run to the back of the unit. It's a bit of a pain but the results make it worthwhile. (Demeter notes that the H series tube direct can be special ordered with input jacks on the rear panel.)
In today's recording environment, having a tube direct box has become almost mandatory. With the release of the new H series stereo tube direct/line driver, the choice becomes which tube DI to buy, rather than whether to buy one or not.
Applications: Recording studio; project studio
Key Features: 1/4" jack for signal input; ground-lift switch; phase switch for 12AX7A input stage
Price: STDB-1: $1,100; H Series: $899
H Series Tube Direct Box
The STDB-1 and the H Series Stereo Tube Direct/Line Driver are both exceptional sounding units boasting their own unique personalities.
Russ Long, a Nashville-based producer/engineer, owns The White House and The Carport recording studios. He is a regular contributor to Pro Audio Review.