.Mic Preamplifier/Direct Box and Digital Converter

.by Barry Rudolph
 
Art DI/O

(Click image for larger view).
Applied Research and Technology has two new desktop recording units that provide the necessary links from the analog world to your workstation or digital tape deck. Expanding on the original Tube MP, the Tube MP Studio is a single-channel mic preamp/direct box with VU meter and peak limiter. The DI/O is a stereo, 24-bit and up to 96kHz AD/DA converter with 128x oversampling. Both units are packaged in small, 1.5-lbs. desktop boxes measuring 5x5.5x2 inches (DxWxH) and use 12AX7A dual-triode vacuum tubes—powered by 9VAC wall wart supplies.

Tube MP Studio
 The Tube MP Studio has a lighted VU meter for monitoring both the output level and the action of the output peak limiter (OPL) circuit. A bicolored LED glows green with low-level mic signals present and turns red when the tube’s output is either about to clip or when the OPL limits the signal. The MP Studio has XLR and 1/4-inch I/O connections, a phase reverse switch and +48-volt phantom powering for condenser mics.

Using the Tube MP Studio with a Shure KSM44 mic provided good results. This gave a clear, clean sound without harshness in the top end. Plugging an electric guitar into the 1/4-inch jack turned the unit into an instant direct box. The direct sound compared with a FET-based direct box was clean, without coloration or compression. The Input Level Control sets gain from 6 to 40 dB or in High mode, 26 to 60 dB. The Equivalent Input Noise (EIN) is -129 dBu (A- weighted). By deliberately overdriving the input for a little tube distortion, you can still adjust the final output level with the Output Level control. Maximum output level is an impressive 28 dBu into 600 ohms. The Output Peak Limiter uses a FET-based peak limiter to control output peak levels. With the OPL active, the output level is limited to 0 dBu at the 1/4-inch output jack and 6 dBu at the XLR output. The attack time is internally set to very fast, while the release time is set to slow. These presets worked well for most situations and contributed to the overall sound of this cool little box.

The Tube MP Studio is designed to sit next to your computer keyboard for easy access. But I found that in the High Gain mode, I had some increased noise and interference caused by my computer’s monitor. After I moved the MP a little further away, all noise stopped. Using the OPL is simple: Just crank up the Input control and you’ll see the red LED light up more and more. The limiter action is very affirmative: an absolute peak clamp! On one recording, I used it as an effect and loved it. The sound of this “brickwall” limiter is reason enough for me to own the MP.



Reprinted with permission from Magazine, March, 2001
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved


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