Recording - September 2015 - 44

B Y PA U L V N U K J R .

dbx 676 Tube Mic Channel Strip

A respected maker returns to form with a new all-in-one tracking solution

The 676 is a new tube-based channel strip from dbx. At $999.95
it is a step up from the previously available 376 Tube Channel Strip
and it is one of the company's first pro range pieces in a number of
years. It consists of a 12AU7A (ECC82) tube microphone preamp followed by a 3-band EQ and rounded out by a VCA-style compressor
and limiter. The compressor section borrows heavily from the company's high-end two-channel 162SL Purple Precision compressor.

Front and back
The 676 is housed in a 2U 19" rackmount enclosure. The front
panel is finished in black, brushed aluminum with a large centrally
located backlit dbx VU meter which can show input level, output level,
or gain reduction, the same one found on the 162SL and 160SL. All
of the stylish black aluminum knobs are large and robust, and each of
the pushbuttons features an inset colored LED. Overall it balances a
clean modern look with a healthy hint of vintage style.
Around the back, the 676 features a collection of ins and outs for each
of its effects sections. The mic pre section features XLR ins and outs; when
it's used this way, the EQ is included in the chain. There is also a 1/4" TRS
input that can be used as an insert, placing an external processor between
the mic pre and the EQ. It can also be used as a line input, bypassing the
tube preamp so the 676 can be used as an EQ and compressor during mix
down. The preamp-EQ section also offers a 1/4" balanced output.
In the compressor section there is a 1/4" TRS sidechain jack for true
external sidechaining, as well as both XLR and 1/4" balanced line outputs. There's also a slot for an optional digital I/O card in the future.
Preamp
The 676 signal chain starts with a high voltage gain Class-A circuit
with a 12AU7A tube. Like many tube-style preamps, it offers a dual
gain stage with an input gain control range of -∞ to +55 dB, followed by a knob labeled Post Tube Attenuation with a range of -∞
(silence) to 0 dB (unity gain, no attenuation).
This classic setup allows you to achieve clean and open tones as
well as harmonically saturated and even distorted sound by pushing
the input into the output. A red clip LED is included to let you know
when the circuit is being driven too hard, but note that it can be desirable to hit the red!
44

RECORDING September 2015

The preamp also features a front-mounted, button-switchable 1/4" instrument input with a gain range of -∞ to +40
dB. Additional preamp features include +48V Phantom
power, a -20 dB pad, polarity flip, and a 12 dB/octave 80
Hz highpass filter.
Equalizer

Each of the three EQ bands has a boost/cut range of 15 dB.
The low-frequency shelf is fixed at 100 Hz and the high shelf at
10 kHz, both with a 12 dB/octave slope. The mid band is an
adjustable bell filter with a throw of 100 Hz to 8 kHz and a
choice of wide (0.9) or narrow (2.9) Q at the touch of a button.
The EQ section is completely bypassable via another LEDequipped button. However, unlike some channel strips and
consoles, the 676 EQ is always pre-compressor and cannot
be placed in the post-compressor position.
Compressor and limiter
As mentioned above, the compressor in the 676 is essentially
lifted from the dbx 162SL. Like the EQ, it can be placed in or
taken out of the chain at the touch of a button. Modern dbx compressors are quite full-featured; the 676 has controls for
Threshold (-40 dB to +20 dB), dbx's famous Overeasy (softknee) button, a fully variable Ratio from 1:1 to ∞:1, ±20 dB of
makeup gain or attenuation, and a 3-stage LED meter that lets
you know when the threshold level has been crossed.
There are Attack (400 dB/msec to 1 dB/msec) and
Release (4000 dB/sec to 10 dB/sec) controls, complete
with a full Auto mode which makes both the attack and
release program-dependent. This mode has long been one
of my favorite features on dbx compressors.
The 676 offers both traditional sidechaining and a button
labeled Contour. This button is an 80 Hz highpass filter that does
not change the audio signal path, but does keep the threshold/detector circuit from being triggered by low frequencies. This
gives the compressor a less obvious yet punchier sound.
The 676's last section is the limiter, which makes use of
dbx PeakPlus technology. It has a ratio of ∞:1, a threshold

Table of Contents for the Digital Edition of Recording - September 2015