dbx 122 User manual

INSTRUCTION
MANUAL
dbx
ll
NOISE
REDUCTION
SYSTEM
124
dbx
ll
NOISE
REDUCTION
syYSTEM
—
7
CHAI
ANNEL
LS
1&3
+»
e

INDEX
FUNCTIONAL CALLOUTS
Front
Panels
2
Rear
Panels
4
BRIEF
OPERATING
INSTRUCTIONS
8
INTRODUCTION
8
DETAILED
OPERATING
INSTRUCTIONS
10
CONNECTIONS
11
OPERATION.
HINTS
TO
GET THE
MOSTOUTOFdbxNOISEREDUCTION
—C
HOW
dbx
TAPE
NOISE
REDUCTION
WORKS
28
SYSTEM
PERFORMANCE
32
TECHNICAL
DETAILS
OF
dbxPROCESSING.
.......————
“SPECIFICATIONS.
OOOO
DISCUSSION
OF
SPECIFICATIONS.
~~—~—~C~—t—“..CCLTOCOOO
dbx
PRODUCT
WARRANTY
i
39
FACTORY
SERVICE
39
“dbx
I22SCHEMATIC..
OO
dbx
124
SCHEMATIC
41
“Quay
©
OS
WARNING: TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS APPLIANCE
TO RAIN OR MOISTURE.

FUNCTIONAL CALLOUTS
NWO
=
SS
=
ma
S
A
s
ws
=
(
A
|
~
la
—
y |
Fig. 1 — Model 122 and Model 124 Front Panels (Descriptions on next page)

NOTES:
To
avoid
repetition,
the
word
‘‘preamplifier’’
is
used
to
mean
preamplifier,
integrated
amplifier/preamplifier,
receiver,
or
the
tape
monitor
loop
of
an
equalizer,
reverb
unit
or
other
device.
if
your
preamplifier
does
not
have
a
tape
monitor
loop*
(tape
record
outputs
and
play
inputs),
substitute
other
suitable
connections.
A. Power Switch
Push
once
to
turn
ON
the
dbx
unit’s
AC
power,
push
again
to
turn it off.
B. Pilot Lamp
When
the
Pilot
Lamp
is
illuminated,
the
AC
power
is
ON.
C. Noise Reduction Switches
REC
Push
this
switch
and
the
TAPE
switch
to
record
a
dbx-
encoded
tape.
BYP
Push
this
switch
to
bypass
the
dbx
noise
reduction
circuitry
(a
“hard-wire’’
bypass).
PLAY
Push
this
switch
and
the
TAPE
switch
to
play
back
a
dbx-
encoded
tape.
Push
this
switch
and
the
DISC
switch
to
play
back
a
dbx-encoded
disc.
NOTE:
For
a
stereo
setup
using
the
124,
leave
channels
1
&
3
switched
to
REC
and
channels
2
&
4
switched
to
PLAY.
For
the
122
in
a
stereo
setup
or
the
124
in
a
4-channel
setup,
it
will
be
necessary
to
switch
all
channels
between
the
REC
and
PLAY
modes.
D. Play Level Match
This
control
allows
you
to
adjust
the
122's
output
level
to
your
preamplifier.
Like
the
RECORD
LEVEL
MATCH
control,
this
adjustment
is
not
critical
and
does
not
affect
the
linearity
of
the
dbx
encode/decode
process.
PLAY
LEVEL
MATCH
is
adjusted
so
that
playback
levels
are
approximately
the
same
when
you
are
decoding
a
dbx
encoded
tape
or
disc
as
when
you
have
the
122
in
BYPASS
mode
for
playing
a
conventional!
source.
Detailed
instructions
for
this
adjustment
are
on
Page
15.
*The
tape
or
record
outputs
and
tape
or
play
inputs
located
on
the
rear
of
most
preamplifiers,
integrated
amplifiers
and
receivers
for
operation
of
a
tape
recorder.
E. Play Mode Switches
TAPE
Push
this
switch
and
the
appropriate
Noise
Reduction
Switch
(REC
or
PLAY)
to
record
or
playback
a
dbx-encoded
tape.
DISC
Push
this
switch
and
the
PLAY
switch
to
play
a
dbx-
encoded
disc.
If
the
124
is
set
up
for
two
channel
simultaneous
record
and
playback,
as
shown
in
Figure
5,
press
the
BYP
switch
on
Channels
1&
3,
the
PLAY
switch
on
Channels
2
&
4,
and
the
DISC
switch.
To
play
a
conventional
(non-encoded)
disc
through
the
dbx
unit,
push
the
BYP
switch
and
the
DISC
switch;
alternately,
switch
the
dbx
unit
out
of
the
circuit
by
placing
the
preamp in SOURCE mode.

\
SUAS)
dbx
os
©
RECORD
PLAY
©
RECORD
LEVEL
MATCH
INPUTS
OUTPUTS
INPUTS
ouTPuTS
a
Y
MODEL 124
—_
aay
>
Dy YW/I2
>)KOW)
DS
TO TAPE RECORDER AURILIARY OR LINE INPUT TO PREAMP TAPE GR
a
VINA
Fig.
2
—
Model
122
and
Model
124
Rear
Panels
(Descriptions
on
next
page)

A. (Tape) Record Level Match Control
This control allows you to match the dbx Record Output level to
your tape recorder’s input sensitivity. Setting is non-critical, and in
most cases a center-range setting of about 12 o'clock will suffice; for
more exact settings, use a test record or tone generator as described
on Page 15. In no case will the LEVEL MATCH setting affect the
dbx unit’s encode/decode performance. (NOTE: The 122 has
1 control per channel. The 124 has 1 control to simultaneously
adjust 4 channels.)
B. Record Inputs
Connect the cables from your preamplifier’s TAPE OUTPUTS
(REC OUT of the Tape Monitor Loop) to these inputs. These cables
were previously connected to your tape recorder’s LINE or AUX
(Record) INPUTS. (Use only the #1 and #3 RECORD INPUTS for
the 124 in a stereo sound system.)
C. Record Outputs
Connect the cables from these outputs to your tape recorder’s
LINE or AUX (Record) INPUTS. (Use only the #1 and #3 RECORD
OUTPUTS for the 124 in a stereo sound system.)
D. Play !nputs
Connect the cables from your tape recorder’s LINE or AUX
(Play) OUTPUTS to these inputs. (Use only the #2 and #4 PLAY
INPUTS for the 124 in a stereo sound system.)
E. Play Outputs
Connect the cables from these outputs to your preamplifier’s
TAPE INPUTS (Play Inputs of the tape monitor loop). These
cables previously came from your tape recorder’s LINE or AUX
(Play) OUTPUTS. (Use only the #2 and #4 PLAY OUTPUTS for
the 124 in a stereo sound system.)
F. AC Power Cable
Connect this cable to 117V, 50 or GOHz AC power source only.
The Model 122 requires a maximum of 5W of AC power while the
Model 124 requires a maximum of 7W of AC power.
G. Disc Play Level Match Control
This control allows you to adjust the 124’s output level to your
preamplifier when you are playing a dbx-encoded phonograph disc.
This adjustment is not critical and does not affect the linearity of
the disc decoding process. Adjust the DISC PLAY LEVEL MATCH
control so that playback levels are approximately the same whether
you are decoding a dbx disc or have the 124 in BYPASS mode for a
conventional source.
H. Tape Play Level Match Control
This control allows you to adjust the 124’s output level to the
tape play input of your preamplifier. Like the RECORD LEVEL
MATCH control, this adjustment is not critical and does not affect
the linearity of the encode/decode process. Adjust the TAPE PLAY
LEVEL MATCH control so that playback levels are approximately
the same whether you are decoding dbx encoded tapes or have the
124 in BYPASS mode for a conventional source. Detailed instruc-
tions for this adjustment begin on Page 15.

x x
PREAMP =] pa)
OUT LEFT tO 6
@) (e)
RIGHT O (@) @)
Sm
y
2
8
=
A
S
Fig. 3 — Connecting the dbx 122 in a Tape Monitor Loop
"
2
=
a
E
=
3
a
=
4
w
x
a
iow
°
io
w
x
<
w
a
a
BACK FRONT
Cs ris rl
Vi
aoe)
Co
mal
ee
ES
=
A
ve
©@
©
Ore
@
\@t®@
AN
A
oe
p
.
©
cl.
Am
R
Z
&
é
a
Fig. 4 — Connecting the dbx 124 in a Tape Monitor Loop
for Four-Channel Operation

or he
2 ai
@
@
®: a
i
1)
@
ROL)
> «#@: 3
a
£®© ©..®
ot ane fans
is.
™
CES. ETE Date
Jomnes AuHLLERY OF WME MELE LAME AME TAN OF ORION MUL
DWI ye
TAPE A
Fig. 5 — Connecting the dbx 124 in a Tape Monitor Loop
for
Two-Channel
Simultaneous
Operation
Preamplifier
having
Two
Tape
Monitor
Loops
rs
aif >
Fig. 6 — Connection of the 124 with Two Tape Machines and a
To simultaneously record and monitor on machine “A,” set
the 124’s channel 1 & 3 switches to REC and channel!
2&4
switches
to
PLAY
mode.
To
simultaneously
record
and
monitor
on
machine
“'B,”’
set
the
124’s
channel
2
&
4
switches
to
REC
and channel 1 & 3 switches to PLAY mode.
NOTE: This setup cannot be used for disc decoding.

BRIEF
OPERATING
INSTRUCTIONS
To Make a dbx-Encoded Tape Recording
1,
Set
the
preamplifier’s
INPUT
SELECTOR
to
the
appropriate
source
(i.e.,
PHONO,
TUNER,
or
AUX).
2.
Press
the
dbx
REC
switch(es)
and
the
dbx
TAPE
switch.
3. Place the tape machine in Record mode, and adjust
the tape machine for peak meter levels typically 3 to 6VU
lower than normal. (With dbx processing, significantly lower
record levels are often required to eliminate tape saturation,
particularly in cassette recording. Experiment during initial
setup to find the appropriate levels.)
4. Do not switch the dbx unit while making the
recording. ‘
To Play a dbx-Encoded Tape Recording
1. Set the preamplifier’s TAPE MONITOR switch to
TAPE.
2. Press the dbx PLAY switch(es) and the dbx TAPE
switch.
3. Place the tape machine in Play mode, and adjust the
preamplifier
VOLUME
and/or
the
PLAY
LEVEL
controls
on
the
tape
machine
for
the
desired
listening
volume.
To Play a dbx-Encoded Phonograph Disc
1. Press the dbx PLAY switch(es) and the dbx DISC
switch.
2.
Set
the
preamplifier’s
INPUT
SELECTOR
to
PHONO,
and
set
the
TAPE
MONITOR
switch
to
TAPE.
3.
Play
the
encoded
record,
and
adjust
the
preamplifier’s
VOLUME
control
for
the
desired
listening
volume.
INTRODUCTION
The
tape
recording
process
traditionally
has
been
one
of
the
major
sources
of
noise
in
recorded
music.
The
dbx
tape
noise
reduction
system
eliminated
tape
hiss
that
would
otherwise
be
introduced
by
the
tape
recorder.
In
addition,
dbx
processing
permits
recordings
to
be
made
at
levels
that
avoid
much
of
the
distortion
which
normally
occurs
in
tape
recording.
As
a
result,
dbx
equipment
not
only
reduces
noise,
it
can
vastly
improve
tape
machine
performance.
With
dbx
processing,
the
only
noise
heard
on
playback
is
that
noise
which
was
present
in
the
original
program.
Taped
records,
upon
playback,
will
sound
just
like
the
original
disc;
taped
FM
broadcasts,
upon
playback,
will
have
no
more
noise
than
was
present
in
the
original
reception
of
the
program;
and
recordings
of
live
music,
conversation,
and
so
forth,
will
be
indistinguishable
from
the
live
event.
These
genuine
improvements
in
the
quality
of
tape
record-
ings
are
due
to
a
phenomenal
increase
in
recordable
dynamic
range
and
the
complete
absence
of
audible
tape-
induced
noise.
The
dbx
Model
122
has
two
processors
for
recording
or
playback
of
a
stereo
program.
The dbx
Model
124
has
four
Processors,
essentially
two
Model
122’s
in
a
single
unit.
The
124
is
switchable
for
recording
or
playback
of
a
four-
channel
program,
or
for
simultaneous
recording
and
off-
tape
monitoring
of
a
stereo
program.
Both
models
share
the
same
high
standard
of
performance,
in
excess
of
30dB
broadband
tape
noise
reduction
with
a
simultaneous
10dB
improvement
in
headroom
in
the
tape
recording
process.
Both
models
may
also
be
used
to
decode
special
dbx
encoded
phonograph
discs.
These
discs,
available
through
many
hi-fi
stores,
are
up
to
40dB
quieter
than
a
conven-
tional
disc
and
can
provide
full
music
dynamic
range.
The
dbx
disc
decoding
circuits
are
not
designed
to
reduce
noise
on
conventional
phonograph
records.
Neither
can
the

dbx tape noise reduction circuits reduce hiss on a tape
which has already been recorded without dbx tape noise
reduction during the recording process. However, dbx
dynamic range enhancers such as our Models 3BX and
118 are capable of reducing noise on a conventional disc,
pre-recorded tape or FM broadcast. These enhancers
(expanders) can be used in conjunction with a dbx Il
tape noise reduction unit. In this combination the dbx 122
or 124 tape noise reduction unit prevents any additional
noise from being introduced by the tape recording process
and the dbx dynamic range enhancer actually increases the
dynamics and reduces noise present in the original program.
The 122 and 124 are fully compatible with all other
dbx II units, such as the 140 series or the Model 128. The
Model 128 combines the functions of the 122 with a dbx
dynamic range enhancer.
The 122 and 124 are not compatible with dbx
Professional equipment, and vice-versa, even though
all dbx tape noise reduction systems offer the same 30dB
of tape noise reduction and 10dB headroom improvement.
The incompatibility is due to signal processing differences,
as described on Page 30 of this manual. Thus, recordings
encoded with any of the dbx 150 semi-professional series
or with the 177, 187, 208, 216, or K9-22 professional series
will not sound “right” when played back through the 122
or 124. Also, while the 122 and 124 are made to decode
dbx-encoded discs, dbx professional series equipment
should not be used for disc decoding.
Alone,
either
the
dbx
122
or
124
will
dramatically
improve
the
quality
of
your
live
tape
recordings.
In
con-
junction
with
any
of
the
dbx
dynamic
range
enhancers,
the
122
or
124
lets
you
make
recordings
of
pre-recorded
material
or
radio
broadcasts
that
can
be
played
back
with
wider
dynamic
range
and
less
noise
than
the
original
source.
When
used
properly,
dbx
tape
noise
reduction
makes
an
extremely
valuable
addition
to
your
music
system
and
to
your
listening
enjoyment.
This
manual
describes
how
your
dbx
122
or
124
functions,
and
how
you
can
obtain
maxi-
mum
benefit
from
its
use.

10
DETAILED
OPERATING
INSTRUCTIONS
GENERAL NOTES
Level and Impedance
The 122 and 124 input levels, output levels and
impedances are designed for compatibility with most
hi-fi and semi-pro equipment. Because the dbx 122 and
124 input impedance is 50k-ohms, the units can be driven
from high or low impedance sources. The dbx inputs also
will accept a wide range of voltages. The dbx outputs will
drive up to 7 volts into ioads of 5000-ahms or greater.
This
means
that
you
can
connect
the
122
or
124
output
to
almost
any
type
of
equipment
found
in
a
normal
hi-fi
or
semi-pro
system.
However,
thé
dbx
122
and
124
are
not
meant
for
professional
levels
of
+4dBm
(1.23V)
to
+8d8m
{1.95V), nor are they meant for driving low impedances,
such
as
600-ohm
professional
inputs.
Use
the
dbx
150
semi-
professional series or any of the dbx professional series
units for these applications.
Grounding
The 122 and 124 are not grounded to the power mains
through their power cords. They obtain a ground via the
shields of the interconnecting audio cables from the pre-
amplifier, receiver, and/or from the tape machine. No
special ground wires need be connected between the dbx
chassis and any other equipment. If you hear hum, try
reversing the AC plug, and if that does not help, check to
make sure all audio cables are properly installed and that
there are not broken conductors in any cable. Hum and
radio station pickup are sometimes caused by microscopic
dirt particles on the mating surfaces between the chassis
and cable connectors, so clean these areas periodically.
Cable Length
Some installations will tolerate longer cables, but when-
ever possible it is a good idea to keep signal cable runs
under 10 feet. This minimizes hum and noise pickup, and
also
helps
prevent
high
frequency
losses
naturally
caused
by cable capacitance.
dbx and Dolhy®* Together
The
dbx
{[
tape
noise
reduction
system
provides
at
least
20dB
more
noise
reduction
than
Dolby
"B”
tape
noise
reduction
systems,
and
15dB
mare
than
Dolby
“A,”
so
there
is
no
need
to
use
Dolby
processing.
If
your
tape
machine
has
internal
Dolby
processing,
switch
it
Off
and-
use
only
the
dbx
1
encoding
and
decoding.
Dolby
encoded
tapes
are
not
compatible
with
dbx
||
decoding
(and
vice-
versa);
if
a
tape
was
recorded
with
Dolby
encoding,
it
must
be Dolby
decoded.
NOTE:
While
it
is
possible
to
combine
both
dbx
I!
and
Dolby
processing,
we
do
not
recommend
it
because
any
imperfections
in
the
Dolby
encode/decode
processing
will
be
magnified
by
dbx
II
treatment.
Since
dbx
II
processing
alone
reduces
noise
to
inaudibility,
there
is
really
no
need
to
use
dbx
II
with
another
tape
noise
reduction
system.
*'Dolby’ is a trademark of Dolby® Laboratories Inc.

CONNECTIONS
Where to Connect Your dbx 122 or 124
If your preamp, receiver, or integrated amp/preamp has
tape monitoring provisions, the dbx should be connected
within the tape monitor loop. In other words, connect the
TAPE OUT of your preamp to the dbx’s RECORD IN-
PUTS, and connect the dbx’s PLAY OUTPUTS to your
preamp’s PLAY or TAPE INPUTS (Figures 3, 4 & 5).
For preamps, receivers or integrated amps that do not
have tape inputs and outputs, connect the PREAMP OUT-
PUTS to the dbx’s RECORD INPUTS, and connect the
dbx’s PLAY OUTPUTS to your preamp’s AUX INPUTS
(Figure 7). When recording an encoded tape with this setup,
it is very important to keep all preamp filter and tone con-
trols set at ““flat,’’ or whatever setting yields the flattest
frequency response. Any desired tonal adjustments can be
made later, during playback of the dbx-encoded tape.
Where
to
Connect
Your
Tape
Recorder
11
Connect
the
dbx’s
RECORD
OUTPUTS
to
the
RECORD INPUTS, or LINE INPUTS of your tape
recorder. (Do not connect the dbx’s RECORD OUT-
PUTS to the MIC INPUTS of your tape recorder because
the dbx output level is too high for most mic inputs and
could cause distortion.) Connect your recorder’s PLAY
OUTPUTS, MONITOR OUTPUTS, or LINE OUTPUTS
to the dbx’s PLAY INPUTS (Figures 3, 4 & 5).
When Using Two Tape Recorders
The 124 may be connected so that either of two tape
recorders can be used with simultantous recording and
off-tape monitoring, with no re-connections (See
Figure 6).
x
2
>
=
° °
ie)
=O
CAUTION: With the setups shown in
Figure 7, DO NOT switch your tape
machine to “SOURCE” monitor mode
Www pore”
while the preamp is set for “AUX IN”
mode. This would cause feedback that
might damage your equipment.
Fig. 7 — Connecting the dbx Unit When There Is No Tape Monitor Loop

12
Graphic Equalizers
If you use a graphic equalizer with your music system,
the equalization must not be introduced between the dbx’s
RECORD OUTPUTS and the tape recorder’s inputs, or
between the recorder’s outputs and the dbx’s PLAY
INPUTS. Ideally the dbx unit is installed in the preamp’s
tape monitor loop, and the graphic equalizer is installed
between the preamp output and the power amplifier input
(Figure 8). Alternately, install the graphic equalizer in the
preamp’s tape monitor loop and place the dbx unit in the
graphic equalizer’s tape monitor loop, but be sure to set the
equalizer so its effect comes after the dbx unit.
Equalized Speaker Systems
If you have an equalized speaker, such as a Bose system
or Electro-Voice “Interface” series, then the dbx unit can
be connected in the speaker equalizer’s tape monitor loop
and the equalizer should be installed in the preamp’s tape
monitor loop (Figure 9).
NOTE: Never connect any other electronic equipment
between the dbx unit and your tape recorder’s inputs or
outputs. This could cause inaccurate encode/decode tracking
and loss of quality in the recorded signal.
CAUTION: Make sure that the power is OFF on all
equipment when installing the dbx unit. As a precaution,
turn down your amplifier VOLUME control prior to
switching
on
the
dbx
unit
for
the
first
time.
Inadvertent
decoding of non-encoded programs (dbx in PLAY mode)
can create surging to high volume levels.
GRAPHIC EQ
or Similar Unit
Fig. 8 — Where to Connect a Graphic Equalizer, Electronic Cross-
over, Reverb, Matrix 4-Channel Decoder, Etc.
(Special signal processing follows the dbx encode/decode
process.) Setup for dbx 124 on next page.

13
GRAPHIC EQ
or Similar Unit
S 0-86
2 « ' a
PNA,
i
Sop
Fig. 9 — Connecting the dbx Unit with an Equalized Speaker System
(dbx processing is done inside the tape monitor loop of the
speaker equalizer, which itself is in the tape monitor loop of the
preamplifier.) Setup for dbx 124 on next page.

14
ae
WDA IES
Simultaneous Stereo Record and Playback (Off Tape
Monitoring) Connections for the 124
If your tape recorder has provisions for simultaneous
recording
and
playback
(off
tape
monitoring),
the
124
can
be connected as shown in Figure 10. This setup allows
material to be recorded in encoded form and monitored
off
the
tape
in
decoded
form
at
the
same
time.
Arbitrarily,
channels 1 & 3 are assigned for recording and channels
2 & 4 for playback. Since the 122 has only two channels,
simultaneous
encoded
recording
and
decoded
off-tape
monitoring
can
only
be
accomplished
by
using
two
model
122's, one for the encoding and one for the decoding.

WWD
Fig. 10 — Connecting the dbx 124 in a Stereo System for
Simultaneous Record and Playback
OPERATION
Setting the Play Level Match and 15
Record Level Match Controls
In many cases, a center range setting on these controls
will be “just right’ (about 12 o’clock), and in no case does
the setting affect the linearity of the dbx encode/decode
process. However, for listening convenience, the following
adjustments can keep record and playback levels the same
and can optimize level matching between your preamp,
recorder and the dbx unit for the best headroom and lowest
noise. The method of setting comparable controls on both
the 122 and the 124 is the same, despite minor differences
in control function and position.
The Model 122 has a PLAY LEVEL MATCH control
on its front panel, a knob that adjusts both tape and disc
playback level at the same time. The Model 124 has a TAPE
PLAY LEVEL MATCH control (screwdriver adjustable),
and a DISC PLAY LEVEL MATCH control (a knob), both
located on the 124’s rear panel.
The Model 122 and 124 both have screwdriver-adjust-
able RECORD LEVEL MATCH controls on their rear
panels. The 122 has two controls (one per channel}, whereas
the 124 has but one control that simultaneously adjusts all
channels that are switched to REC mode.
Record Level Adjustments
1. Connect a source of a 7kKHz tone (such as an audio
oscillator or audio test record) to your preamplifier and
set the preamp’s TAPE MONITOR switch to SOURCE. If
an audio test record or oscillator is not readily available,
you can use musical signals of fairly constant level. Set the
dbx unit as shown below: g.,=. Q-eourtd
doz To cscatce: msi 124
@ 585 085 85

16
2. Setup your tape recorder for tape recording, but do
not record a tape (use the recorder’s PAUSE switch). Play
the source through your system at an average listening level
and adjust the tape recorder’s input level controls; with a
test tone, levels should be set for “OVU” ona reel to reel
recorder or ““-3VU” on a cassette recorder. With program
material, only the peaks should reach these recommended
levels; the average VU meter readings should be —2dB to
—3dB for reel-to-reel and —4dB to —7dB for cassette
recordings.
3. Now reset the dbx unit as shown below:
ey eee 122 dhox M ssarsieuevioxsven 124
e 006 © 68
@ @00 @0° @0
Oe, OsrorLh
4. Without touching any of the recorder’s level controls,
adjust the dbx (Tape) RECORD LEVEL MATCH control(s)
so that your recorder’s VU meters read about the same as
they did with the dbx unit in BYP mode. (For program
material, the average meter deflections can be made to
match those in BYP mode, but the amount the meters move
will be cut in half by dbx REC processing.)
Play Level Adjustment
This adjustment is for listening convenience only, and its
function is to make the average listening levels from your
system about the same whether you are playing conven-
tional sources (dbx in Bypass mode) or dbx encoded
sources (dbx in Play mode).
Adjusting the 124’s Disc Play Level Match Control
1. Set the 124’s front panel switches as shown below:
2. Set your preamplifier as follows: INPUT SELECTOR
Switch at PHONO; TAPE MONITOR Switch at TAPE.
3. Play a dbx encoded disc through your system.
4. Adjust the 124’s Dise Play Level Match control so
that, on moderately loud passages, the levels are approxi-
mately the same when the channel 2 & 4 BYP and PLAY
switches are alternately pressed.
Adjusting the 124’s Tape Play Level Match Control or the
122’s Play Level Match Control
For this adjustment, you will need a source of a 1kHz
test tone or any dbx Ii encoded tape. Since the adjustment
is for listening convenience only, if you do not have a tone
source or a dbx encoded tape, you can delay the adjust-
ment until after you record a dbx encoded tape.
1. Set the dbx front panel switches as shown below:
dbx Wo woissnrovction soso
2. Set your preamplifier as follows: INPUT SELECTOR
Switch at PHONO; TAPE MONITOR Switch at TAPE.
3. Play a dbx encoded tape through your system. You
can use a tape of program material with fairly constant
level. For more accurate settings, you can use a tape
recording of a 1kHz tone (taken from an oscillator or a
test record). If a 1kHz tone is used, the tape need not be
dbx encoded.

4. Adjust the dbx’s (Tape) Play Level Match control(s)
so that on louder passages the levels are approximately the
same when the BYP and PLAY switches are alternately
pressed. (For the 124 in a stereo setup, switch only the
channels 2 & 4 BYP and PLAY switches; in a 4-channel
setup,
switch
both
pairs
of
BYP
and
PLAY
switches.)
dbx Discs
dbx
encoding
makes
it
possible
to
enjoy
phonograph
discs that are 40dB quieter than conventional
discs, with
full dynamic
range and freedom
from distortion.
Since dbx
encoded
discs are cut at lower average
levels, your phono-
graph cartridge
can more easily ‘‘track’”’
the groove excur-
sions, greatly reducing
audible
tracking
distortion.
dbx discs reproduce loud peak levels that are not
practical with standard, conventional discs. Because these
loud peak levels can sometimes cause acoustic feedback,
you may need to acoustically isolate your turntable from
your speaker system; use as much physical separation as
possible, a foam mat, or any workable acoustic isolation
technique.
If dirt or static electricity build up on dbx discs, they
can create noise problems that are not solved by dbx
encoding. Since the other normal disc noises are reduced
by up to 40dB, dirt and static noises may actually become
more distracting. A good quality record cleaner plus an
effective static elimination device should solve these pro-
blems while prolonging disc and stylus life. After listening
to dbx-encoded discs for a while, you'll appreciate and
even demand quieter records.
dbx discs can be decoded with the 122, 124 or with any
other dbx !| system such as the 140 series. However, dbx
discs cannot be decoded by dbx professional models, such
as the Model 216, or dbx semi-professional models, such as
the 150 series. See Page 30 for an explanation of the
difference between dbx professional and dbx II tape noise
reduction systems.
LEFT <O
Lert TO
RIGHT O
Fig.
11
—
Special
Connections
for
dbx-Disc
Decoding
in
Systems without a Tape Recorder
7

18
How to Decode a dbx-Encoded Disc
1. Set the front panel switches as shown below:
dbx We wose tocrion orsten 122 dbx B woise neous
© 068 © 88 °
@-n— O-zord
2. Set your preamplifier as follows: TAPE MONITOR
switch to TAPE, and INPUT SELECTOR SWITCH to
PHONO.
3. Play the disc.
Making a dbx-Encoded Tape
1.
Set
the
dbx
unit's
front
panel
switches
as
shown
below:
%
dix E imac 122
e 06 Ce
Ax Done neouction svsrew 124
@ 06 pes e
Press REC instead of Play
if 4 channel recording
for {or
NOTE:
Do
not
change
the
settings
of
the
Noise
Reduc-
tion
switches
while
recording
since
this
would
ruin
your
recording.
CAUTION: Never depress the 122’s REC and PLAY
switches
simultaneously.
Similarly,
never
depress
the
REC
and
PLAY
switches
on
either
pair
of
the
124’s
adjacent
channels
(1
&
3
or
2
&
4).
The
resulting
output
could
damage your sound system.
2. Using an input signal that is similar in level to the
Program
to
be
recorded,
or
using
the
program
itself,
place
your
tape
machine
in
Record
Ready
mode
(PAUSE
mode)
and
set
the
machine’s
recording
level
for
maximum
VU
meter
readings
typically
3
to
6VU
lower
than
normal.
(With
dbx
processing,
significantly
lower
record
levels
are
often
required
to
eliminate
tape
saturation,
particularly
in
cassette
recording.
Experiment
during
initial
setup
to
find
the
appro-
priate
levels.)
These, or even lower recorded levels may be used with
success
because
the
dbx
processing
prevents
audible
tape
noise.
3. Restart the program and start the tape recording. If
your
system
is
set
up
for
off-the-tape
monitoring
with
the
Model
124,
you
can
monitor
the
program
in
decoded
form
while
it
is
being
recorded
by
switching
your
preamplifier’s
TAPE
MONITOR
switch
to
TAPE;
switching
between
SOURCE
and
TAPE
gives
an
“A-B”
comparison
of
original
program to the dbx-processed program.
Playing Back a dbx-Encoded Tape
1. To play back a dbx-encoded tape in decoded form,
© 007 008 8
for
Press PLAY instead of REC
if 4 channel playback
2. Place the tape machine in PLAY mode, and your
preamplifier’s
TAPE
MONITOR
Switch
to
TAPE.
Play
the
tape normally.
NOTE: If you listen to an encoded recording without
decoding,
the
sound
will
seem
shrill,
lacking
in
bass,
and
will vary little in loudness. Hiss, hum and other noise will
fill momentary pauses in the music. The unpleasant sound
of
an
encoded
program
is
normal,
but
when
decoded,
the
recording
should
sound
excellent
—
clean,
exciting
music
against a background of silence.

Bypass Mode
To listen to a conventional disc, tape or FM broadcast
without dbx processing, simply set your preamplifier’s
TAPE MONITOR Switch to SOURCE. If your system has
no tape monitor loop, or if you wish to bypass the dbx
rrocessing for any other reason, set the front panel
switches as shown below:
$i ee A, AS ae na
22. 2 at salted ead 124 2
C@ 32 @ 0@0 C@0 Ce 2B
—2e a
Dubbing (Copying) an Encoded Disc onto a Tape in
Encoded Form
1. Set the front panel switches as shown below:
AEM iwcaieienisectocie 122 e Zo dx cates e casas 124
: é
e 006 © 06 ae d@6 O60 66
ta
2. Set your preamplifier as follows: TAPE MONITOR
switch to TAPE, and INPUT SELECTOR switch to PHONO.
3. Set your tape recorder to Record, and record
normally.
4. The tape copy will be dbx encoded. With the 124,
you will hear the program in decoded form while mon-
itoring this operation off tape.
Dubbing an Encoded Disc onto a Tape in
Non-Encoded Form
This process is for transferring a dbx-encoded disc in
non-encoded form onto a tape for future playback without
dbx processing (such as in an automobile tape player).
1. Connect the 122’s PLAY OUTPUTS (or the 124’s
Channels 2 & 4 PLAY OUTPUTS) to your tape recorder’s
Fig. 12 — Connections for Recording an Encoded Disc
onto a Tape in Non-encoded Form.
19