dbx 463X Operating manual

Preliminary Technical Service Manual
MODEL 463X
OverEasy® Noise Gate Expander
dbx Professional Products

Manufactured under one or more of the following U.S. patents: 3,377,792; 3,681,618; 3,714,462; 3,789,143; 4,097,767; 4,329,598;
4,403,199; 4,409,500; 4,425,551 ;4,473,795. Other patents pending.
This dbx-branded product has been manufactured by AKG Acoustics, Inc.
©1991 AKG Acoustics, Inc.
dbx Professional Products
adivision of AKG Acoustics, Inc.
1525 Alvarado Street
San Leandro, CA 94577 USA
Telephone: [phone] Fax: [phone]

/j (2 '^rNoise Gate
*J. mExpander
The dbx model 463X is the simplest, easiest-to-use noise-
gate expander on the market. (It's also easy on the budget.)
Modeled after our 904 modular noise gate, the 463X is
designed for the recordist/mixer, instrumentalist, ENG
technician, sound contractor —indeed, for anyone who
needs afriendly processor that gets rid of unwanted noise
between notes or sounds.
The important operating feature of the 463X is the single-
slider action, which enables quick setting of the amount and
severity of gating. There's also aknob for setting the
threshold point where this gating occurs. In an instant you
can change the gating characteristics —and the noisiness
and overall sound of the program —by ear.
The single-ended input and output let the user patch into
the signal path at line level. For the performer, there's a
high-impedance input jack on the front as well. Plug in,
connect the 463X to the amp or board, and you're on your
way. (The Hi-Z input defeats the rear input and has its own
trim for awide range of instrument/ pickup levels.) Finally,
there's a“Key” input for special applications like frequency-
sensitive gating.
Two 463Xes become amaster/slave stereo pair of noise
gates at the push of abutton and asingle connection cable.
However, if you pair a463X with a163X OverEasy Compres-
sor/Limiter, you have achoice of configurations. If the 163X
is the slave and the 463X the master, you'll have astereo
pair of 463Xes —the 163X turns into a463X. And if it's the
other way around (the 163X the master and the 463X the
slave), then the 463X turns into a163X and you have a
stereo pair of 163X Compressor/ Limiters.
Features
Single-slider action
Adjustable threshold
1/4“ front-panel
high-impedance input
Stereo-strappable
600-ohm output to +18 dBv
Key input for special
applications

Circuit Characteristics
4—4— IIII I III i I I I
INPUT
463X
Performance
Specifications
Frequency response
20 Hz-20 KHz ±1dB
THD
0.2°/o (unity gain)
Equivalent input noise
-85 dBv unweighted
(unity gain)
Maximum input
18 dBv to soft clipping
Maximum output
18 dBv into 600 ohms
Input impedance
391 k-ohms, single-ended
Output impedance
22 ohms, single-ended
(designed to drive 600 ohms
or greater)
KEY input impedance
62 K-ohms
Threshold range
+10 to -60 dBv (OverEasy)
Attenuation range
0-70 dB, depending on input
level and slider setting
Gain (no gating)
Unity (rear jack);
0-20 dB, adjustable
(instrument input)
Downward
expansion ratio
Adjustable from none to 6:1,
front slider
Attack time
Approximately 1ms, program-
and slider-dependent
Release time
10-500 ms, program- and
slider-dependent
Power requirements
100-120/220-240 Vac,
switchable; 50-60 Hz; 7W
Notes
1} Specifications are subject to change.
2) Ail voltages are rms (root-mean-square).
3) 0dBv is defined as 0.775 Vregardless of
load Impedance. Subtract 2.2 from the dBv
figure to convert to dBV (i.e., referred to 1V).
When the load impedance is 600 ohms, this
particular dBv is also Known as "dBm."
4) Noise figures are for 20 Hz-20 KHz.
5) Attack time is the time required to restore
the signal to 654b of the input level after It
has gone above the OverEasy threshold;
release time is the time required for the
signal to be reduced to 654b of Its final gated
level.
dbx
Professional Products Division
71 Chapel Street
Newton. Mass. 0219S USA
617-964 3210
Adivision of BSR North America Ltd. naiao
ION 600335 Printed in USA **dbx” and -OverEasy” are registered trademarks

INSPECTION and INSTALLATION
Your unit was carefully packed at the factory in aprotective carton. Nonetheless,
be sure to examine the unit and the carton for any signs of damage that may have
occurred during shipping. If there is such evidence, don't destroy the carton or packing
material, and notify your dealer immediately.
It's agood idea in any case to save the carton and packing should you ever need to
ship the unit.
In the event of initial problems, contact your dealer first; your unit was thoroughly
inspected and tested at the factory.
The carton should contain this owner's manual, a463X, of course, and awarranty/
registration card. Please fill the card out and send it to us. The carton also should con-
tain hardware for rack-mounting both asingle unit (screws, along [half-rack-width] ear,
asmall L-bracket, and ashort rack ear) and two units together (side plates along with a
screwdriven joiner). See below.
No special ventilation is required in any installation; other components may be
stacked above or below the unit provided they don't generate excessive heat.
Here's rack-mounting for asingle unit:
It may help to line everything up on atable as you tighten the screws. The enclosed
sticker with circuit-action graphs may be placed on the long rack ear.
Here's rack-mounting for apair of 463Xes or for a463X and a 163X or other "-63X"
series units:
1<5c 2) Attach side panels;
3) Bring units together, lining up the side panels with the screw-joiner catches,
and then gently tighten the screw to close the catches.

CONTENTS
Rear panel (connections) 2
Front panel (operation) 3
Hookups (plug and cable wiring) 4
Setting up 3
About noise gating and downward expansion 7
Applications note 7
Block diagram 10
SPECIFICATIONS
Frequency response
THD
Equivalent input noise
Maximum input
Maximum output
Input impedance
Output impedance
KEY input impedance
Threshold range
Attentuation range
Gain (no gating)
Downward
expansion ratio
Attack time
Reiease time
Power requirements
Notes
1) Specifications are subject to change.
2) All voltages are rms (root-mean-square).
3) 0dBv is defined as 0.775 Vregardless of load impedance.
Subtract 2.2 from the dBv figure to convert to dBV
(i.e., referred to 1V). When the load impedance is 600 ohms,
this particular dBv is also known as "dBm."
4) Noise figures are for 20 Hz-20 kHz.
5) Attack time is the time required to restore the signal to 63% of the
input level after it has gone above the OverEasy threshold; release time
is the time required for the signal to be reduced to 63% of its final gated level.
20 Hz-20 kHz +1 dB
0.2% (unity gain)
-85 dBv unweighted (unity gain)
18dBv to soft clipping
18 dBv into 600 ohms
391 k-ohms, single-ended
22 ohms, single-ended (designed to drive
600 ohms or greater)
62 k-ohms
+1 0to -60 dBv (OverEasy)
0-70 dB, depending on input level and slider setting
Unity (rear jack); 0-20 dB, adjustable (instrument input)
Adjustable from none to 6:1, front slider
Approximately 1ms, program- and slider-dependent
10-500 ms, program- and slider-dependent
100-120/220-240 Vacj switchable; 50-60 Hz; 7W

1INPUT, OUTPUT. These jacks are for aline-level input and ouput and are the stan-
dard 2-circuit ("mono") 1/4" phone type, where the tip carries the signal and the
sleeve carries the ground.
2KEY IN. Use this jack if you want to control the 463X gating action from an
external source, allowing you to alter the dynamics of one signal with another.
Same plug type as above. Key In will be discussed in detail in the Applications Note.
3Hi-2 trim. This screwdriver control sets the gain of the preamp for the Hi-Z input
only (see front panel). The gain is set at the factory at +20 dB (all the way right, or
clockwise) and shouldn't be changed unless your instrument's output is very hot. All
the way left (ccw) is unity (0 dB) gain.
4STEREO STRAPPING jack and button. Connect this jack to the same jack on
another 463X and you have atrue rms-detecting stereo noise gate. Connect it to a
163X and you have the same thing —astereo pair of noise gates —provided this
first unit remains the Master.But if you connect it to a163X and press the button
in, to Slave, this unit becomes a163X and you have atrue stereo pair of 163X
compressor/limiters. Neat, huh? The jack is a1/4" 3-circuit ("stereo") phone type
(tip/ring/sleeve); use 3-circuit plugs and cables only, for anything else won't work.
Of course, be sure to disconnect everything for independent operation.
Note that you must leave the Master/Slave button out, at Master, for normal
463X (non-stereo) operation as well as for stereo operation as aMaster. Pushing it
in, to Slave (the front-panel LED will light), deactivates the controls and forces the
unit to obey the Master's settings when asecond 463X or a163X is properly con-
nected and switched. (If you push the button in when no Master is connected, it's a
bypass switch for the gate only; the preamp still worksT)
5VOLTAGE SWITCH. This must be properly set for your ac voltage; be sure to check
before plugging in and powering up. For nominal 220-V operation an adaptor plug on
the ac cord will be required.
-2-

HP
1POWER LED. This indicates when the unit is connected to alive ac outlet.
2STEREO SLAVE LED. See previous page; this indicates that the unit has been set by
its rear switch to be the Slave in a163X or 463X team.
3DOWNWARD EXPANSION LEDs. These 12 LEDs show in dB how much the signal is
being gated.
4DOWNWARD EXPANSION slider. For any signal that goes below the threshold point
(see below), moving this slider to the right —MORE —increases the amount of
gating, pushing that signal's level down both farther and faster than the signal's
natural decay rate. The ultimate amount of this attenuation depends on the slider
position, of course, as well as on how far below threshold the signal is in the first
place. We'll discuss this in detail presently.
5THRESHOLD. This thumb knob sets the point where gating begins, the level below
which asignal is attenuated. Set fully clockwise (+10) and the signal will begin to be
pushed down even when it's still loud. Turn the knob counterclockwise and the
signal is not gated until it has dropped to alow level on its own. At full ccw, the
gate is inactivated and the 463X effectively bypassed. Ideally, the knob should be
set such that only wanted signal is above the threshold, and below it is only
unwanted signal or noise.
THRESHOLD LED. This will light whenever the signal level goes above the
threshold point. It's very useful for setting levels and adjusting the 463X to work at
exactly the right times.
6Hi-2 input jack. This connects to the 463X's low-noise FET preamp. There's enough
gain that virtually ail low-level instruments can be plugged in directly —guitars,
basses, keyboards, even high-impedance mikes. As explained, there's again trim on
the rear for ve|7 hot instruments (likely to be useful with some synthesizers, etc.).
Note that this jack overrides the rear line-level input.
-3-

HOOKUPS
Inputs and Outputs
The line-level inputs and outputs are single-ended (unbalanced) and should be con
nected to other such equipment with single-conductor shielded cable, as shown here.
TS
Cl TvAntST
_SvU—itri rL>
2-Circuit ("Mono") Plugs and Single-Conductor Shielded Cable
This will work fine for balanced inputs, too, but if the 463X input is connected to source
equipment with balanced outputs, the next hookup should be used. Most balanced sources
will work without the dotted connection between the ring (-) output and the sleeve (the
ground -- this is true for "active-balanced" and "ground-referenced" outputs). This float-
ing condition unbalances abalanced source, which is usually okay. However, some
sources require the dotted connection, e.g., "transformer-isolated" balanced outputs. We
recommend making the connection only if necessary for your installation, because some
active balanced and ground-referenced outputs may be damaged by doing so. Consult the
owner's manual.
cnz
FROM SOURCE
OUTPUT MAKE THIS COMSECTIOW
Only if necessary—see text
ZD
TO 463X
INPUT
Balanced Outputs and the 463X Line Input, Single-Conductor Shielded Cable
To take advantage of the balancing capability provided by the balanced inputs, the
following connection may be used when the 463X output is connected to adevice with
balanced inputs.
TS
csz~
FROM 463X
OUTPUT ONLY IF NECESSARY—SEE TEXT
SRT
ZED
TO BALANCED
INPUT
Balanced Inputs and the 463X Line Output, Two-Conductor Shielded Cable
The connection between the shield and the sleeve at the 463X end of the cable should be
made only if hum develops in your installation.
The Key input jack provides adirect connection to the 463X's "brains" —its
level-sensing circuitry, or rms detector —without disturbing the normal audio path. This
feature lets you control the gating from an external signal source, or lets you add
processing (e.g., equalization) to the control path only. This jack overrides the
detector's normal connection to the main input signal (see the block diagram, p. 9).
Plugs and cabling are the same as in the two illustrations above.
The Hi-Z (instrument) input is single-ended (unbalanced) also and should be connected
to instrument outputs with single-conductor shielded cable as shown at the top of this
page for line-level jacks.
-4-

SETTING UP
Which Input?
Use the rear-panel (line) input in recording when the instrument to be gated is
already preamplified, such as through adirect box or mixing console. Synthesizers
sometimes can plug in here, too. And of course when mixing or submixing, the signal
from the deck (or mixing console) goes here as well.
In performance, this input again is useful for connection to synthesizer high-level
outputs or line-level outputs of guitar and bass preamps (before the feed to the power
amp).
Use the front-panel Hi-Z input in the studio for adding quick (direct-input) overdubs
and for the convenience of carrying aguitar or bass into the control room (no hassle of
lugging an amp). In performance, any instrument can plug directly into this input (synths
included), as well as most high-impedance microphones.
Setup
Start with the slider fully left, and while the music (or whatever) is playing adjust
the Threshold knob so that the Threshold LED turns on —flashes —with the sound you
want to keep.
Then slowly push the slider right until the desired amount of attenuation is
achieved. Moving it right increases not only the amount but also the speed of the gating.
Then readjust the Threshold knob.
Vocals and instruments like bass guitar call for mild settings, toward the middle of
the range, which yield smooth results. Percussive sounds like kick or snare drum want
more severe (deeper and faster) gating, with settings toward the right. Since hearing the
point where gating begins is easier than seeing it (with the Threshold LED), zero in on
exactly the sound you're going for by fine-tuning the Threshold knob. There are no
"typical" settings, because an exact one necessarily depends on widely varying levels and
program material.
The Hi-Z trim
This screwdriver trim is rarely necessary in practical applications; most of the time
it won't need to be adjusted. It should be reset ONLY if you hear distortion (over-
driving) while using the Hi-Z input. The mike or instrument signal is probably over-
driving the Hi-Z input and the gain must be changed (by means of the trim).
To adjust it, play your instrument or mike through the 463X with the slider to the
far left. Listen to the output of the 463X. Turn the Hi-Z trim down (ccw) until the
distortion disappears. If distortion is still audible with the trim all the way down, the
problem is not in the 463X.
Stereo Gating
True stereo gating, as opposed to dual-mono gating, which you can achieve with two
independent units, is important when astereo signal is to be attenuated and its channel
balance and imaging preserved. Dual-mono gating won't do this; instruments and their
reverberation (decay tails) can wander or jump around, because the two channels may
have different levels at different times. As mentioned, apair of 463Xes or a463X and a
properly connected 163X will give you true rms stereo-tracking gating; your sound and
your mixes will readily show the benefits.