Tube Microphone Preamp Channel Strip


We at dbx Professional Products are proud to introduce the all new 676 Tube Mic Pre Channel Strip. The 676 represents all of the best of dbx’s more than 40 years of dynamics processing.

The 676 offers a pristine high-voltage, Class-A tube preamp section that runs on 250 volts, so your signal can be as crystal clean or dirty as you need it to be. The 676 also incorporates the compressor/limiter design from the highly-sought after dbx162SL, as well as a 3-band parametric EQ with sweepable mids.

The 676 provides audio professionals with the perfect channel strip for recording and live applications alike with its military-grade build and vintage-inspired controls, VU metering and state-of-the-art optional digital output card.


·       Class-A Vacuum Tube Preamp with High Voltage Gain

·       High-Visibility Vintage VU Meter

·       Compressor designed from the dbx162SL

·       3-Band Semi-Parametric EQ

·       1/4” and XLR Inputs and Outputs

·       Front Panel Instrument Input

·       Side Chain Insert


Mic Preamp Connector

Female XLR Pin 2 Hot; Electronically balanced/unbalanced

Mic Preamp Input Impedance

1.9 kΩ


>85 dB from 20 Hz to 3 kHz, >70 dB from 3 kHz to 20 kHz

Instrument Input Connector

Tip-Sleeve ¼” Jack

Input Type

(instrument) Unbalanced

Instrument Input Impedance

500 k Ω

Max Input

(instrument/line) +21dBu balanced or unbalanced

Preamp Insert Connector

Tip-Ring-Sleeve ¼”, RF filtered

Preamp Insert Type

Unbalanced, Tip = send, Ring = return

Line Outputs (Preamp & Compressor/Limiter)


Male XLR and Tip-Ring-Sleeve ¼” (Pin 2 and Tip hot)

Line Outputs (Preamp & Compressor/Limiter) Type


Line Outputs (Preamp & Compressor/Limiter) Impedance

Balanced 30 Ω, unbalanced 15 Ω

Line Outputs (Preamp & Compressor/Limiter)

Maximum Output Level

> +21 dBm (into a 600 ohm load)

Compressor Sidechain Insert Connector

Tip-Ring-Sleeve ¼”, RF filtered

Compressor Sidechain Insert Type

Unbalanced, Ring = output, Tip = input

Compressor Sidechain Insert Impedance

1 kΩ (output), 50 kΩ (input)

Vacuum Tube Type

12AU7A / ECC82

Vacuum Tube Grid Power Supply

+250V DC

Vacuum Tube Heater Power Supply

+12V DC

Frequency Response (Mic Input)

20 Hz to 50 kHz, +0/-1dB, 40 dB gain

Frequency Response (Instrument Input)

30 Hz to 70 kHz, +0/-1dB, unity gain

THD + Noise (Mic In to LIne Out)

0.25% typical at 0 dBu out, 1 kHz, 40 dB gain

THD + Noise (Instrument In to Line Out)

0.2% typical at 0 dBu out, 1kHz, unity gain

Equivalent Noise Level

Typically > -123 dBu with a 150 Ω source load, 22 Hz to 22 kHz

Noise Floor

Mic Insert to Comp Output: <-93 dBu, unity gain, EQ flat and no gain reduction

Preamp Function Switches/Controls: Instrument


Selects between microphone XLR input and front panel ¼” instrument input

Preamp Function Switches/Controls: +48V

Sends +48 VDC through 6.81 kΩ resistors to pins 2 and 3 of the microphone input

Preamp Function Switches/Controls: 20dB Pad

Attenuates the microphone input by 20 dB

Preamp Function Switches/Controls: Polarity Invert

Reverses pins 2 and 3 of the microphone input XLR

Preamp Function Switches/Controls: 80 Hz Low Cut

Enables an 80 Hz, 12 dB/octave high pass filter in the microphone and instrument signal path

Preamp Function Switches/Controls: Gain Control


-∞ to +55 dB for Microphone Input; -∞ to +40 dB for Instrument Input

Preamp Function Switches/Controls: Post Tube


-∞ to 0 dB

Preamp Function Switches/Controls: Peak Indicator

Illuminates RED when the Preamp is within 3 dB of clipping

EQ Low Frequency

100 Hz, Low-pass shelving filter

EQ High Frequency

10 kHz, High-pass shelving filter

EQ Mid Frequency

Sweepable from 100 Hz to 8 kHz

EQ Function Switches/Controls: Narrow

Selects the “Q” of the MID Frequency EQ. “OUT” position Q = 0.9; “IN” position Q = 2.9

EQ Gain

(All Bands) Sweepable from –15 to +15 dB

Compressor Threshold Range

-40 dBu to +20 dBu

Compressor Threshold Characteristic

Selectable OverEasy™ or Hard Knee

Compressor Ratio

Variable 1:1 to ∞:1; 60 dB maximum Compression

Compressor Attack/Release Modes

Selectable Manual or Auto

Compressor Manual Attack Time

Scalable program-dependent; Typically 400 dB/msec to 1 dB/msec

Compressor Manual Release Time

Scalable program-dependent; Typically 4000 dB/sec to 10 dB/sec

Compressor Auto Attack Time

Program-dependent, typically 15 ms for 10 dB, 5 ms for 20 dB, 3 ms for 30 dB

Compressor Auto Release Time

Program-dependent, typically 120 dB/sec

Compressor Output Level Control Range

-20 dB to +20 dB

Compressor Peak Indicator

Illuminates RED when the Compressor/Limiter is within 3 dB of clipping

Limiter Type

dbx PeakPlus™

Limiter Threshold Range

-4 dBu to + 22 dBu (off)

Limiter Ratio


Limiter Attack and Release


Power Supply

Universal switch-mode

Operating Voltage

100 – 240 VAC, 50/60 Hz

Power Requirements

20 Watts


T2.5AL 250V

Turn-On Time

Approximately 2 seconds


3.5”H X 19”W X 8”D (88.9mmH X 482.6mmW X 203.2mmD)


8.1 lbs (3.7 kg)

Shipping Weight

11.0 lbs (5.0 kg) 

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