DBX 676 Tube Microphone Preamp Channel Strip - DBX676FX

Product Overview

The DBX 676 tube microphone preamp channel strip is the professional recording studio standard for engineers who demand both pristine transparency and character-laden warmth from a single unit. Featuring a Class-A vacuum tube preamp section running at 250 volts, the 676 delivers up to 55 dB of gain through a military-grade chassis that handles the demands of broadcast studio, live recording, and house of worship applications. Integrated dynamics from the legendary dbx 162SL compressor/limiter design and a 3-band semi-parametric EQ make this channel strip a complete front-end processor for any microphone or instrument source.

Product Description

The DBX 676 tube mic preamp channel strip consolidates the signal chain into one rack-mount unit without compromising at any stage. The 12AU7A/ECC82 vacuum tube operates at +250V DC on the plate and +12V DC on the heater, giving engineers the ability to dial in anything from a clean, linear gain structure to subtle harmonic coloration using the post-tube attenuation control. Input gain spans from -infinity to +55 dB on mic and -infinity to +40 dB on instrument, accommodating passive ribbon microphones through to high-output condenser mics without the need for external equipment beyond the onboard 20 dB pad switch.

The compressor section draws its circuit topology directly from the dbx 162SL, offering selectable OverEasy or Hard Knee operation, variable ratio from 1:1 to infinity:1, and the PeakPlus limiter for absolute peak protection. Attack and release modes are switchable between manual and auto, giving the engineer full control in tracking applications or fast, program-dependent response for live broadcast. The 3-band semi-parametric EQ provides a 100 Hz low shelving filter, sweepable mid from 100 Hz to 8 kHz with selectable wide or narrow bandwidth, and a 10 kHz high shelving filter, each with +/-15 dB of cut or boost.

The front panel instrument input accepts unbalanced 1/4-inch sources up to +21 dBu with a 500 kOhm impedance, while the rear panel provides balanced XLR and TRS outputs simultaneously from both the preamp and compressor/limiter output stages. A side chain insert allows external processors into the compressor detection path, an essential feature for broadcast de-essing and parallel compression workflows. The vintage-style VU meter with high-visibility illumination allows fast, intuitive level monitoring in dim studio and live environments. Available at Creation Networks for broadcast studio, recording studio, and house of worship installations.

Key Features

• Class-A Vacuum Tube Preamp (250V) — 12AU7A/ECC82 tube running at high voltage for real tube character, from clean transparency to harmonic saturation.
• Up to 55 dB Mic Gain — Wide gain range accommodates ribbon, dynamic, and condenser microphones without external equipment.
• dbx 162SL Compressor Design — Selectable OverEasy or Hard Knee compression with variable 1:1 to infinity:1 ratio and manual or auto attack/release.
• PeakPlus Limiter — Hard brick-wall limiting with program-dependent attack and release protects downstream converters and signal chain.
• 3-Band Semi-Parametric EQ — 100 Hz low shelf, sweepable mid (100 Hz to 8 kHz) with dual Q settings, 10 kHz high shelf, all +/-15 dB.
• Compressor Side Chain Insert — RF-filtered TRS insert point for external frequency-conscious detection, ducking, or de-essing.
• Dual Output Format — Simultaneous balanced XLR and TRS outputs from both preamp and comp/limiter stages for flexible routing.
• Front Panel Instrument Input — 500 kOhm impedance unbalanced input handles guitar, bass, and keyboards directly.
• Vintage VU Metering — High-visibility analog VU meter with peak indicator LED for accurate level monitoring.
• 80 Hz High-Pass Filter — 12 dB/octave rolloff reduces low-frequency rumble, HVAC noise, and mic stand vibration.
• Universal Power Supply — Operates on 100-240 VAC, 50/60 Hz worldwide without manual voltage switching.

Typical Applications

• Broadcast studio
• Recording studio
• House of worship
• Auditorium
• Multi-purpose room

Technical Specifications

Frequently Asked Questions

Q: What type of vacuum tube does the DBX 676 use?

The 676 uses a 12AU7A/ECC82 dual triode tube operating at +250V DC on the plate. This high-voltage operation is central to the unit's tone character and distinguishes it from preamps that run tubes at starved-plate voltages.

Q: Can the 676 be used as a standalone preamp without engaging the compressor and EQ?

Yes. The compressor/limiter and EQ sections each have dedicated bypass controls, allowing the 676 to operate purely as a tube mic preamp. The preamp and compressor outputs are also available on separate jacks simultaneously.

Q: Does the 676 provide phantom power for condenser microphones?

Yes. The +48V phantom power switch sends 48 VDC through 6.81 kOhm resistors to pins 2 and 3 of the XLR input, meeting the standard phantom power specification for condenser and active ribbon microphones.

Q: What is the purpose of the post-tube attenuation control?

The post-tube attenuation control allows the engineer to drive the tube stage hard for harmonic saturation and then attenuate the output level, controlling output without reducing the drive into the tube itself.

Q: Is the DBX 676 suitable for broadcast applications?

Yes. The 676 compressor, derived from the dbx 162SL, provides program-dependent dynamics control and side chain insert functionality required for broadcast voice processing. Its +21 dBm output is compatible with professional broadcast routing.

Q: Does the 676 have a polarity invert function?

Yes. A polarity invert switch on the front panel reverses pins 2 and 3 of the microphone XLR input, useful when combining the 676 with other microphones in multi-mic recording scenarios.