dbx 2BX User manual

db:>X Model 2BX
two band dynamic range enhancer
INSTRUCTION MANUAL

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S^A A?DvPi\N0T ^OSE THIS APPLIANCE
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INDEX
BRIEF OPERATING INSTRUCTIONS
INTRODUCTION
CONNECTIONS
OPERATION
EXPANSION
SIMPLE PRECAUTIONS WHEN USING ANY PROGRAM EXPANDER
HOWdbx EXPANDERS WORK '
SPECIFICATIONS "
dbx PRODUCT WARRANTY
FACTORY SERVICE "
SCHEMATIC "'
GLOSSARY "

BRIEF OPERATING INSTRUCTIONS
PILOT This L.E.D.
(light emitting diode),
above the POWER
switch, glows when the
2BX is ON.
GAIN CHANGE L.E.D.'s These
two rows of L.E.D.'s indicate
the amount of gain change
created in each of the 2BX's two
frequency bands. The red L.E.D.'s
indicate upward expansion
(volume increase), the yellow
L.E.D.'s indicate downward
expansion (volume decrease).
TRANSITION LEVEL When an
incoming signal is above the level set
by this control, the 2BX expands up-
wards; when an incoming signal is
below the level set by this control, the
2BX expands downward. Set the
control so that red GAIN CHANGE
L.E.D.'s glow during loud portions of
the program and yellow GAIN
CHANGE L.E.D.'s glow during the
quiet portions of the program.
SOURCE Push this
switch and the PRE
switch to expand
programs coming
from your phono-
graph, FM tuner or
other auxiliary
equipment.
TAPE Push this
switch and the
POST switch to
expand programs
coming from your
tape recorder. If
you do not have a
tape recorder, push
the SOURCE switch.
PRE Push this switch
to expand aprogram
before recording it.*
POST Push this
switch and the TAPE
switch to expand a
program played back
from your tape
recorder.
POWER Push this switch
once (IN) to turn the 2BX
ON; push again (OUT)
for OFF.
EXPANSION Adjust this slide
control for the desired amount of
expansion. A"1.4" setting means
that an input signal with a40dB
dynamic range will be expanded to
56dB, or that an input signal with
a50dB dynamic range will be
expanded to 70dB. A1.2 setting
would result in a20% increase
in dynamics; a1.4 setting would
result in a40% increase in
dynamics, etc.
(PRE/POST Summary) The PRE switch expands the signal before the tape recorder
input (PRE places the expander before the tape recorder input); the POST switch
expands the signal from the tape recorder's output (POST places the expander after
the tape recorder output). Pushing both PRE and POST switches simultaneously
bypasses the expander functions.
"Expansion will, in most cases, increase the dynamic range of aprogram beyond the
capabilities of your tape recorder. To capture this increased dynamic range on tape
requires adbx noise reduction system, which a/lows recording at levels below the
tape or tape head's saturation point To expand aprogram and then record it, we
recommend using any dbx tape noise reduction system and carefully setting record
and expansion levels. If you do not have adbx tape noise reduction system, we
recommend expanding aprogram upon playback (place the 1bx in TAPE and POST
mode).

RECORDER OUTPUTS* Connect
the cables from these outputs to the
Line inputs of your tape recorder.
If you do not have atape recorder,
do not connect any cables to these
outputs.
RECORDER INPUTS* Connect
the cables from your tape
recorder Line or Monitor outputs
to these inputs. If you do not
have atape recorder, do not
connect any cables to these inputs.
INPUTS Connect the cables from
the Tape Outputs of your receiver,
preamplifier, or integrated amplifier
to these inputs.
OUTPUTS Connect the cables from
these outputs to the Tape Inputs, or
Monitor Inputs of your receiver, pre-
amplifier, or integrated amplifier.
AC POWER CABLE In the U.S.A.
connect this cable to a117V AC, 50 or
60Hz AC power source. The 2BX
requires amaximum of 20 watts of AC
power. Models for use with power
sources outside the United States
are available. Contact the dbx factory
for information.
*/f you have adbx tape noise reduction system (such as any of
our 120 or 150 series) see Page 9for connection diagrams.

INTRODUCTION
If you're amusic lover or an audiophile (or both) you
have probably noticed that much of the excitement of a
live performance is missing in arecorded or broadcast per-
formance. The primary reason for this loss of excitement is
that the dynamic range of the recorded or broadcast per-
formance has been purposely restricted to fit the dynamic
range limitations of the recording or broadcast medium.
The 2BX is asophisticated expander that can restore the
dynamic range and excitement to arecording or radio
broadcast, adding considerably to your listening enjoyment
By expanding dynamic range, the 2BX lowers the
characteristic noise levels of atape, phonograph record or
FM broadcast. It restores the "punch" of loud passages and
the whisper of quiet ones. It can add new life to an old
record collection, and make FM broadcasts worth listening
to. The use of a2BX with adbx tape noise reduction
system (such as our 120 or 150 series), lets you make tape
copies of records, FM broadcasts or other tapes that actually
sound better than the original. With these capabilities, the
2BX will become one of the most valued components' in
your home music system.
CONNECTIONS
AC POWER
Connect the 2BX to a117V AC, 50 or 60Hz power
source only. The 2BX requires 20 watts of AC power
(maximum). As aprecaution, do not connect the AC
power cable until all signal connections have been made.
(Models for use with foreign power sources are available
Contact the dbx factory for information.)
SIGNAL CONNECTIONS
NOTES:
1. If you do not have atape recorder, do not connect
anything to the TO TAPE RECORDER, or the FROM
TAPE RECORDER jacks.
2. With the setup in Figure 2, changes in preamp volume
will require adjustment of the 2BX transition level.
3. If you do have atape recorder and wish to expand
before you record, use the connections shown in Figures 1
2or 3. *
4. If you have adbx tape noise reduction system see
Page 9.
Connect the 2BX to your system according to one of
the following diagrams:

LOCATION
FOR OPTIONAL
REVERB
LOCATION FOR
-OPTIONAL
GRAPHIC EQ
*NOTE: 2BX will
reduce reverb noise,
but will also shorten
decay time.
——OPTIONAL RECORDER —i
Fig. 1—How to Connect the 2BX to Your Receiver, Preamplifier
or Integrated Amplifier. This is the preferred hookup assuming a
tape monitor loop is available.
LEFT
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PREAMP
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MAIN AMP
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(.LOCATION OF
^•"^OPTIONAL REVERB
|OR GRAPHIC EQ*
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*NOTE: 2BX will
reduce reverb noise,
but will also shorten
decay time.
OPTIONAL RECORDER .
Fig. 2-How to Connect the 2BX if atape monitor loop is
unavailable and you are using aseparate preamp and power amp
(or between preamp out and main amp in jacks).

Fig. 3-How to Connect the 2BX in the Tape Monitor Loop of
aGraphic Equalizer or Speaker Equalizer.

OPERATION
NOTES:
1. For adescription of control functions, see the BRIEF
OPERATING INSTRUCTIONS at the front of this manual.
2. If you do not have atape recorder connected as shown
in Figures 1through 3, press IN the SOURCE and PRE
buttons.
3. To avoid repetition, we will use the word "amplifier"
to refer to your receiver, preamplifier or integrated
amplifier.
EXPANSION
To Expand an FM Broadcast or aConventional Phonograph
Disc
1. With your amplifier's master volume control all the
way down, turn on the AC Power for your entire system.
2. Select the desired source (FM or disc) on your
amplifier's selector switch.
3. Place 2BX in SOURCE and PRE mode (SOURCE
and PRE buttons IN).
4. Set the EXPANSION RATIO and the TRANSITION
LEVEL (threshold) controls to approximately mid position.
5. With the music playing, readjust the TRANSITION
LEVEL control until red L.E.D. GAIN CHANGE indicators
glow on loud passages, and the yellow L.E.D. GAIN
CHANGE indicators glow on quiet passages*.
*The L.E.D. GAIN CHANGE indicators show the relative amount
of expansion produced by the 2BX in each of its two frequency
bands. When one or more red L.E.D. 's light in agiven band, the
2BX is raising the program level in that band. When one or '
more
of the yellow L.E.D. 's light, the 2BX is lowering the program
level in that band. The number of L.E.D. 's that light correspond
to the relative amount of expansion up to the maximum dis-
playable range. More upward or downward expansion can be
achieved than is shown on the display.
6. Slowly bring up your amplifier's master volume
control to the desired listening level.
7. Readjust the EXPANSION control for the desired
amount of expansion. This will depend on the program
being expanded. For agood classical phonograph disc, an
expansion ratio of 1:1.1 or 1:1.2 (settings of 1.1 or 1.2)
may be optimum. For ahighly compressed FM broadcast,
an expansion ratio of 1:1.4 or 1:1.5 (settings of 1.4 or 1.5)
may produce better results. If you're not sure where to
set the EXPANSION control, start at alow setting, and
move it higher until it sounds extreme, then move the
control back so the sound is natural again.
The degree of expansion desired also depends on the
mood of the listeners. Generally, you will desire larger
amounts of expansion when you are totally involved with
the music.
To Expand aTape During Playback
Follow the instructions above for expanding an FM
broadcast or conventional phonograph disc, except place
the 2BX in TAPE and POST mode (TAPE and POST
buttons IN). It is not necessary to expand adbx-encoded
tape after decoding (during playback) if the tape has already
been 2BX-expanded prior to recording.
If you have two tape recorders only one TAPE input, and
you use one recorder primarily for playback, plug it into your
amplifier's AUX INPUTs; then follow the directions for Ex-
panding an FM Broadcast or aConventional Phonograph Disc
(as already described).
How to Expand and Tape Record aProgram
NOTE: Expanding aprogram and then recording it may
cause the dynamic range of the program to exceed the
dynamic range of your tape recorder. This could add
distortion and/or excessive tape noise to the recording.

(An exception would be for very highly compressed
programs, where expansion prior to recording adds only a
modest margin to the dynamic range.) To avoid these
problems, dbx recommends the use of adbx tape noise
reduction system when expanding before recording
(see next page for how to connect your system).
1. With your amplifier's master volume control and your
recorder's input level controls all the way down, set your
recorder to the "record ready" (RECORD and PAUSE).
2. Select the desired source on your amplifier's
selector switch.
3. Place the 2BX in SOURCE and PRE mode (SOURCE
and PRE buttons IN).
4. Play the source (start the phonograph disc or listen to
the FM station you will be recording). Set the TRANSI-
TION LEVEL control so that the red L.E.D. GAIN
CHANGE indicators glow on loud passages, and the yellow
L.E.D. GAIN CHANGE indicators glow on quiet passages.
Set the EXPANSION control for the desired amount of
expansion. If you're not sure where to set the EXPAN-
SION CONTROL, start at alow setting, and move it higher
until it sounds extreme, then move the control back until
the sound is natural again.
5. Bring up the amplifier's master volume control to the
desired listening level.
6. Now adjust the input level controls on your tape
recorder for normal VU meter readings. You may find that
slightly lower record levels are necessary when recording
an expanded program in order to avoid tape saturation.
7. Restart the program and record it normally.
If your tape recorder has tape monitoring provisions
(a three-head machine), and you wish to monitor the
recording as it is being made, place the 2BX in TAPE
mode (TAPE button IN). This Monitors the signal coming
from the tape recorder's outputs without changing the
expander's input to the tape recorder.
SIMPLE PRECAUTIONS WHEN USING ANY
PROGRAM EXPANDER
The 2BX (or any expander) places greater demands,on
your power amplifier and speakers. Whether or not agiven
amplifier is of adequate power rating is not always easy to
determine; it depends partially on the sensitivity of the
speakers, and partially on the distortion characteristics of
the amplifier.
Set for 1:1.5 expansion, the 2BX will expand agood
60dB classical recording to about 90dB of dynamic range.
Full realization of the benefit of this dynamic range
requires both ahefty power amplifier and speakers that
can take the high power. If you have such equipment, the
results will be breathtaking. Fortunately, such components
are not mandatory for full enjoyment of the 2BX.
The most important point is this: if the speakers and
amplifier cannot handle wide dynamic range, and if the
expander "tries" to drive them to awide dynamic range,
excessive clipping distortion (overdrive) may occur. To
avoid this unpleasant effect, use good speakers and areason-
ably large amplifier. If distortion still occurs, it will probably
be noticed only with programs that have agood dynamic
range to begin with, and which do not need expansion to
much greater dynamics. In such cases, areduction in the
transition level and the expansion ratio setting will avoid
distortion. Agood expander is apowerful tool, and, as
with any powerful tool, it can be used to excess. Used
properly, the expander can turn an old record collection
into atreasure of new listening enjoyment, and it can turn
aboring selection of compressed and limited FM broad-
casts into an exciting new source of listening pleasure.