DBX 386 Dual Vacuum Tube Preamp/Analog to Digital Converter
Have you noticed that digital converters are starting to show up in formerly “analog-only” gear about as frequently as high-fructose syrup shows up in formerly “juice-only” beverages? Despite the fact that, as of the last time I checked, our ears and vocal cords are analog, audio consumers are now able to buy “digital microphones”, “digital speakers”, “digital power amplifiers” and “digital microphone preamplifiers.” Sometimes it makes sense; sometimes you just have to scratch your head. One of the places it makes the most sense is in an all-in-one mic/instrument front end like the DBX 386.
Features
I’m going to give away the ending right now: The DBX 386 is a winner. It aims squarely at the ever-growing digital project studio/DAW market, and hits it right on the mark. DBX has crammed so many professional features into this “project studio” box, they could charge twice as much for it (don’t get any ideas, DBX).
The DBX 386, in a nutshell, is a 1-rack unit high dual solid-state mic pre with a tube amplifier stage and built-in analog to digital conversion using the DBX Type IV process. The 386 is housed behind the familiar DBX Silver Series brushed metal faceplate, and features sturdy retro knobs and a wealth of translucent LED buttons. As usual, most input/output jacks are found on the well-laid out back panel. Next to each XLR microphone input is a balanced TRS ¼-inch line input that can also accept an unbalanced ¼-inch TS connector. A post-tube section TRS insert jack is provided for each channel for patching in a compressor or equalizer into the path. The inserts use the familiar unbalanced Tip/Send-Ring/Return scheme. The line outs are available on both XLR and balanced ¼-inch connectors. Again, using a TS ¼-inch connector in the line out will unbalance the signal.
Also on the back panel can be found the digital outputs and word clock jacks. I was happy to see that the digital output is available on both XLR and RCA coaxial jacks. As usual, the XLR connector should be used with 110-ohm cable and the coaxial connection requires 75 ohms. What made me happier was to find out that either type connector can carry an AES/EBU formatted signal or a S/PDIF formatted signal (front panel globally selectable). This extra flexibility is very rarely seen, let alone in a unit at this price point. Also not characteristic of this price range, external BNC word clock input and output jacks are provided. Going the extra mile, the 386 allows jumper-selectable 75-ohm termination—handy for house sync or BNC t-tapped word clock configurations. A standard removable IEC A/C connector rounds out the back panel. Whew! Already a nice complement of features and we haven’t even got to the front panel yet.
So on to the front panel. Each channel is equipped with its own unbalanced high-impedance ¼-inch jack for inserting an instrument directly into the preamp. Plugging a cable into this jack overrides the rear line input automatically (assuming the channel is in line input mode). The first knob we come to on the front panel is the Drive control, which adjusts the amount of gain feeding the vacuum tube section. A peak LED, located above the Drive knob, lights up 3 dB before clipping the input stage. Individually selectable phantom power, 20 dB pad, and phase reverse buttons follow, and only affect the mic input. A low cut button engages a 12 dB per octave shelving high pass filter starting at 75 Hz. Control over the analog and digital output level is accomplished via separate knobs, and a 12 stage LED output meter is selectable between the two outputs.
In between the individual channel controls is the digital converter control section. It consists of five more illuminated buttons, each with a printed key describing the button’s overall function and multiple configurations. The key is necessary because each button changes color with repeated pushes, indicating various settings.
The first button selects the type of dithering to be used for 16 or 20-bit output. Dithering options include the TPDF dithering algorithm, the SNR2 algorithm, or no dithering (for 24 bit output). The next button chooses the noise-shaping curve, selectable between mild (shape 1) and more aggressive (shape 2) to none at all. A sample rate button selects a 44.1, 48, 88.2 or 96 kHz sampling rate. If an external clock source is connected to the word clock in jack, the incoming sample rate will be automatically used and the sample rate LED will glow accordingly. The LED will flash if the external clock should drop out, indicating a lack of sync. Pushing the flashing button automatically reverts to the appropriate sample rate using the internal clock. Word length is selectable between 16, 20 or 24 bits on the forth button. Finally, an output format switch selects either AES/EBU or S/PDIF for both output connectors (e.g. If you choose AES/EBU, both the XLR and RCA jack will spit out that format).
In use
I used the DBX 386 on a variety of sources with pleasing results. I first tried the most obvious application: using the 386 to get a mic signal into a DAW. I plugged a Neumann U87 into the rear mic input, ran an XLR (110 ohm) cable into an AES/EBU input on my Pro Tools interface and ran an external word clock signal into the 386. The clocks locked immediately. I selected a 24-bit word length with no dither or noise shaping, popped in the phantom power and adjusted the drive. Within minutes, I went from boxed up to hooked up and recording. The resulting digital output was clean and warm, with practically no “digital-sounding” artifacts. I’m not proud of this fact but, as a complement to DBX, that was all before unwrapping the manual. I did finally consult the manual to find out exactly what the two dither algorithms choices were (TPDF and SNR2?). Unfortunately, the otherwise well-written and organized manual does very little to inform the curious on the details of these algorithms. Ok, nada.
The manual does, however, include an excellent white paper explaining their Type IV conversion system, which essentially takes high-level transients (that would otherwise create nasty digital overload) and “maps” them logarithmically into the top 4 dB of the converter’s range. This, plus a proprietary Tape Saturation Emulation circuit, yields an impressive analog (dare I say “human”) timbre to the conversion process. For a much more competent explanation of the Type IV conversion process, see the DBX website.
Adjusting the drive level allowed me to control the characteristically pleasing tube saturation, from subtle to affected. I loved subtly pushing the tube circuit on vocal recordings and not so subtly on a bass plugged directly into the unit. As advertised, due to the Type IV system, the converter is practically impossible to clip. In some ways the 386 sounded better at the higher levels where other converters would be cringing from fear of transient (or not-so-transient) overload.
I liked what I heard from the converters so much, I started using the 386 as a front end for my Tascam DA-45HR 24 bit DAT recorder. By going balanced analog into the line in of the 386, and going out digitally into the DAT recorder, I was able to record a hotter, more friendly sounding mix.
Summary
While specs can say a lot about the performance of a particular piece of gear (see bench test), most would agree that what a unit sounds like to a user is more important. While this may not be the quietest mic pre I have heard, the musicality of the DBX 386 won me over. With a wealth of features, good sound and a great price, the DBX 386 is an excellent buy.