dbx 120A User manual

®
120A
Subharmonic
Synthesizer
with
ModeledWaveformSynthesis™
User Manual

WARNINGFORYOURPROTECTION
PLEASEREADTHEFOLLOWING:
KEEPTHESEINSTRUCTIONS
HEEDALLWARNINGS
FOLLOWALLINSTRUCTIONS
DONOTUSETHISAPPARATUSNEARWATER
CLEANONLYWITHADRYCLOTH.
DO NOT BLOCK ANY OF THE VENTILATION OPENINGS. INSTALL IN ACCORDANCE WITH THE
MANUFACTURER’SINSTRUCTIONS.
DO NOT INSTALL NEAR ANY HEAT SOURCES SUCH AS RADIATORS, HEAT REGISTERS, STOVES,
OROTHERAPPARATUS(INCLUDINGAMPLIFIERS)THATPRODUCEHEAT.
ONLYUSEATTACHMENTS/ACCESSORIESSPECIFIEDBYTHEMANUFACTURER.
UNPLUG THIS APPARATUS DURING LIGHTNING STORMS OR WHEN UNUSED FOR LONG PERI-
ODSOFTIME.
Donotdefeatthesafetypurposeofthepolarizedorgrounding-typeplug. Apolarizedplug
hastwobladeswithonewiderthantheother. Agroundingtypeplughastwobladesand
athirdgrounding prong. The wide blade or third prongareprovided for your safety. If
the provided plug does not fit your outlet, consult an electrician for replacement of the
obsoleteoutlet.
Protect the power cord from being walked on or pinched particularly at plugs, conve-
niencereceptacles,andthepointwheretheyexitfromtheapparatus.
Useonlywiththecartstand,tripodbracket,ortablespecifiedbythemanufacture,orsold
with the apparatus. When a cart is used, use caution when moving the cart/apparatus
combinationtoavoidinjuryfromtip-over.
Referallservicingtotoqualifiedservicepersonnel. Servicingisrequiredwhentheappa-
ratushasbeendamagedinanyway,such as power-supplycordorplugisdamaged,liq-
uid has been spilled or objects have fallen into the apparatus, the apparatus has been
exposedtorainormoisture,doesnotoperatenormally,or has been dropped.
POWERON/OFFSWITCH:ThePowerswitchusedinthispieceofequipmentDOESNOTbreak
theconnectionfromthemains.
ALL-POLE MAINS SWITCH: An all-pole mains switch with a contact separation of at least
3mm in each pole shall be incorporated in the electrical installation of the rack or build-
ing.
FORUNITS EQUIPPEDWITHEXTERNALLYACCESSIBLEFUSERECEPTACLE: Replacefusewith
sametypeandratingonly.
MULTIPLE-INPUT VOLTAGE: This equipment may require the use of a different line cord,
attachmentplug,orboth,dependingontheavailablepowersourceatinstallation.Connect
thisequipmentonlytothepowersourceindicatedontheequipmentrearpanel.Toreduce
theriskoffireorelectricshock,refer servicingtoqualifiedservicepersonnelorequiv-
alent.
ThisEquipmentisintendedforrackmountuseonly.
SAFETYINSTRUCTIONS
NOTICEFORCUSTOMERS IF YOUR UNIT ISEQUIPPEDWITHA POWER CORD.
WARNING:THISAPPLIANCEMUSTBEEARTHED.
Thecoresin the mains lead arecolouredinaccordance with the following code:
GREENandYELLOW - Earth BLUE - Neutral BROWN-Live
Ascoloursofthecoresin themainsleadofthisappliancemay notcorrespondwiththecolouredmarkings
identifyingtheterminals in your plug, proceedasfollows:
•The core which is coloured green and yellow must be connected to the terminal in the plug
markedwiththe letter E, or withtheearthsymbol, or coloured green, orgreen andyellow.
•The core which is colouredbluemustbeconnectedtothe terminal marked N orcolouredblack.
•Thecore whichiscolouredbrown mustbeconnectedto theterminalmarkedLor colouredred.
This equipment may require the use of a different line cord, attachment plug, or both, depending on the
availablepowersourceatinstallation. Iftheattachmentplugneedstobechanged,referservicingtoqual-
ified service personnel who should refer to the table below. The green/yellow wire shall be connected
directlytothe units chassis.
WARNING:Ifthegroundisdefeated,certainfault conditions in the unit or in the system towhich it is con-
nected can result in full line voltage between chassis and earth ground. Severe injury or death can then
resultifthe chassis and earth groundaretouchedsimultaneously.
LIVE
ENEUTRAL EARTH GND
CONDUCTOR
L
NBROWN BLUE
GREEN/YEL
BLACK
Normal Alt
WIRE COLOR
WHITE
GREEN
Thesymbolsshown aboveareinternationally acceptedsymbolsthat warn ofpotentialhazards with
electricalproducts. The lightning flash with arrowpointin anequilateral triangle means that there
aredangerousvoltagespresentwithintheunit. Theexclamationpointinanequilateraltriangleindi-
catesthat itis necessary forthe userto referto the owner’smanual.
Thesesymbols warnthat there areno userserviceable partsinside the unit. Donot openthe unit.
Do not attempt to service the unit yourself. Refer all servicing to qualified personnel. Opening the
chassis for any reason will void the manufacturer’s warranty. Do not get the unit wet. If liquid is
spilledontheunit,shutitoffimmediatelyandtakeittoadealerforservice. Disconnecttheunitdur-
ingstorms toprevent damage.
CAUTION
ATTENTION: RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRIC
SHOCK DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE
RISK OF ELECTRIC SHOCK
DO NOT OPEN
IMPORTANT SAFETY INSTRUCTIONS

U.K.MAINSPLUGWARNING
Amoldedmainsplug thathasbeencutofffromthe cordisunsafe. Discardthe mainsplug
at a suitable disposal facility. NEVER UNDER ANY CIRCUMSTANCES SHOULD YOU INSERT A
DAMAGEDORCUTMAINS PLUG INTO A13AMPPOWERSOCKET. Donot use the mainsplug
withoutthefusecoverinplace. Replacementfusecoverscanbeobtainedfromyourlocal
retailer. Replacementfusesare13ampsandMUSTbeASTA approved to BS1362.
LITHIUM BATTERY
WARNING
CAUTION!
This product may contain a lithium battery.There is danger of
explosion if the battery is incorrectly replaced.Replace only
with an Eveready CR 2032 or equivalent.Make sure the bat-
tery is installed with the correct polarity. Discard used batter-
ies according to manufacturer’s instructions.
ADVARSEL!
Lithiumbatteri - Eksplosjonsfare.Ved utskifting benyttes kun
batteri som anbefalt av apparatfabrikanten. Brukt batteri
returneres apparatleverandøren.
ADVARSEL!
Lithiumbatteri - Eksplosionsfare ved fejlagtig håndtering.
Udskiftning må kun ske med batteri av samme fabrikat og
type. Levér det brugte batteri tilbage til leverandøren.
VAROITUS!
Paristo voi räjähtää,jos se on virheellisesti asennettu.Vaihda
paristo ainoastaan laitevalmistajan suosittelemaan tyyppin.
Hävitä käytetty paristo valmistajan ohjeiden mukaisesti.
VARNING!
Explosionsfara vid felaktigt batteribyte.Använd samma batteri-
typ eller en ekvivalent typ som rekommenderas av apparattil-
lverkaren.Kassera använt batteri enligt fabrikantens instruk-
tion.
IMPORTANT SAFETY INSTRUCTIONS
ELECTROMAGNETIC
COMPATIBILITY
This unit conforms to the Product Specifications noted on the
Declaration of Conformity. Operation is subject to the following
twoconditions:
•thisdevicemaynotcauseharmfulinterference,and
•this device must accept any interference received,
including interference that may cause undesired
operation.
Operation of this unit within significant electromagnetic fields
shouldbeavoided.
•useonlyshieldedinterconnecting cables.
DECLARATION OF
CONFORMITY
Manufacturer’s Name: dbx Professional Products
Manufacturer’s Address: 8760 S. Sandy Parkway
Sandy, Utah 84070, USA
declares that the product:
Product name: dbx 120A
Note: Product name may be suffixed by the letters -EU.
Product option: none
conforms to the following Product Specifications:
Safety: IEC 60065 (1998)
EMC: EN 55013 (1990)
EN 55020 (1991)
Supplementary Information:
The product herewith complies with the requirements of the Low Voltage Directive
72/23/EEC and the EMC Directive 89/336/EEC as amended by Directive 93/68/EEC.
dbx Professional Products
President of The Harman Music Group
8760 S. Sandy Parkway
Sandy, Utah 84070, USA
September 25, 2001
European Contact: Your local dbx Sales and Service Office
or Harman Music Group
8760 South Sandy Parkway
Sandy, Utah 84070 USA
Ph: [phone]
Fax:[phone]

Table of Contents
120A
Introduction
0.1 Defining the 120A.............................................i
0.2 Service Contact Info.........................................ii
0.3 Warranty............................................................ii
Section 1 - Operation and Appendix
1.1 Rear Panel Connections...................................1
1.2 Front Panel Connections..................................1
1.3 Operating Notes ...............................................2
1.4 Basic Connection..............................................4
Appendix
A.1 Block Diagram.................................................5
A.2 Specifications....................................................6
A.3 Wiring Diagrams..............................................7
®
120A User Manual
Table of Contents

INTRO
CUSTOMERSERVICEINFO
120ADEFINED
WARRANTYINFO
®
INTRODUCTION
120A

Introduction
®
120A User Manual
i
120A
Congratulations on your purchase of the dbx® Professional Products 120A Subharmonic
Synthesizer with Modeled Waveform Synthesis™. The 120A has been specifically optimized to
enhance Bass audio material for use in a variety of professional applications, including night-
club and dance DJ mixing, theatre and film sound, music recording, live music performance and
broadcasting.
The 120A’s two separate bands of subharmonic synthesis provide the best combination of
smoothness and control, and the independent low frequency boost circuit is designed to get the
most out of high-performance low frequency speaker systems. Flexible system interfacing is
achieved by providing main outputs which can be full range (including synthesis) or high-fre-
quency ONLY, along with a separate subwoofer output with its own level control.
This manual will be your guide to understanding the full functionality of the powerful 120A.
After you have become familiar with the unit, we encourage you to experiment and find cre-
ative ways that the 120A can help you optimize your specific application.
The 120A’s patented modeled Waveform Synthesis™ process builds a synthesized waveform
using the wave shapes of the original bass material, producing a new Waveform Modeled™ bass
note, exactly one octave below the bass in the original audio signal path. Unlike other attempts
at bass synthesis, the dbx Professional Products 120A process produces smooth, musical low
frequencies that do not interfere with mid and high-band information even when the maximum
synthesis and boost are applied. The result is a low-end punch that people really feel, even at
system levels that won’t destroy sound equipment or damage hearing. The 120A offers the fol-
lowing features:
• Patented Modeled Waveform Synthesis™ Circuitry insures that mid and
high frequencies are not affected
• Individual Controls for Two Separate ranges of Subharmonic Frequencies,
plus Master Synthesis Level Control
• Separate Low Frequency Boost Circuit
• Separate Subwoofer Output
• 1/4” Balanced Inputs and 1/4” Impedance-Balanced Outputs
• RCA Inputs
• LF Synthesis LED Indicators
• Selectable Crossover with 80Hz and 120Hz crossover points
INTRODUCTION

®
Introduction
120A
120A User Manual
If you require technical support, contact dbx Customer Service. Be prepared to accurately
describe the problem. Know the serial number of your unit. This is printed on a sticker attached
to the rear panel. If you have not already taken the time to fill out your warranty registration
card and send it in, please do so now.
Before you return a product to the factory for service, we recommend you refer to the manu-
al. Make sure you have correctly followed installation steps and operation procedures. If you
are still unable to solve a problem, contact our Customer Service Department at [phone]
for consultation. If you need to return a product to the factory for service, you MUST contact
Customer Service to obtain a Return Authorization Number.
No returned products will be accepted at the factory without a Return Authorization Number.
Please refer to the warranty below, which extends to the first end-user. After expiration of the
warranty, a reasonable charge will be made for parts, labor, and packing if you choose to use
the factory service facility. In all cases, you are responsible for transportation charges to the fac-
tory. dbx will pay return shipping if the unit is still under warranty.
Use the original packing material if it is available. Mark the package with the name of the ship-
per and with these words in red: DELICATE INSTRUMENT, FRAGILE! Insure the package prop-
erly. Ship prepaid, not collect. Do not ship parcel post.
This warranty is valid only for the original purchaser and only in the United States.
1). The warranty registration card that accompanies this product must be mailed within 30 days
after purchase date to validate this warranty. Proof-of-purchase is considered to be the bur-
den of the consumer.
2). dbx warrants this product, when bought and used solely within the U.S., to be free from
defects in materials and workmanship under normal use and service.
3). dbx liability under this warranty is limited to repairing or, at our discretion, replacing defec-
tive materials that show evidence of defect, provided the product is returned to dbx WITH
RETURN AUTHORIZATION from the factory, where all parts and labor will be covered up
to a period of two years. A Return Authorization number must be obtained from dbx by
telephone. The company shall not be liable for any consequential damage as a result of the
product's use in any circuit or assembly.
4). dbx reserves the right to make changes in design or make additions to or improvements
upon this product without incurring any obligation to install the same additions or
improvements on products previously manufactured.
5). The foregoing is in lieu of all other warranties, expressed or implied, and dbx neither
assumes nor authorizes any person to assume on its behalf any obligation or liability in con-
nection with the sale of this product. In no event shall dbx or its dealers be liable for spe-
cial or consequential damages or from any delay in the performance of this warranty due
to causes beyond their control.
0.3Warranty
0.2 Service Contact Info
ii

120A
®

®
120A User Manual 1
Front and rear Descriptions Section 1
120A
A- IEC Power Cord Receptacle
This is the power cord receptacle of the 120A. An IEC cord is included with the shipped product.
B- Subwoofer Output Connector
This output connector sends signal to your subwoofer amplifier, the low bass signal which ranges
from 20 Hz up to the crossover frequency (80Hz to 120Hz). Nominal output signal level is +4dBu
into 600 Ω, and typical maximum output level is +22dBu into 600 Ω. This output is an imped-
ance-balanced output.
C- Crossover Selector Switch
This switch is used to engage the crossover function.
D- Output Connectors
The output section of the 120A offers impedance balanced/unbalanced 1/4” connections with a
nominal output signal level at +4dBu into 600 Ω, and typical maximum output level is +22dBu
into 600 Ω.
E- Input Connectors
The input section of the 120A offers electronically balanced/unbalanced 1/4” connections with a
nominal input level of +4dBu and clipping level is at +22dBu into 600 Ω. The 120A also offers
RCA input connectors with a nominal input level of -10dBV and clipping at +8dBV.
F- Power LED
This red LED indicates that power has been applied to the 120A.
G- Synthesis Bypass
Pressing the SYNTHESIS BYPASS will engage (when lit) or bypass the Synthesis effect of the
120A.
H- Crossover Select
This button is used to the select the desired crossover frequency of the 120A. When pressed
and lit, the 120Hz crossover frequency is engaged. Otherwise, the 80Hz frequency is used.
I- Crossover LED
This green LED (when lit) indicates that the active crossover has been selected. In this case, the
mains outputs (channel 1 and channel 2) contain only the high-frequency portion of the signal,
while the low-frequency portion appears at the mono Subwoofer output.
Subharmonic
Synthesizer
FGHI J K L M
1.2 Front Panel Controls
ABCDE
1.1 Rear Panel Connections

Front and Rear Panel Descriptions
®
120A User Manual
2
Section 1 120A
J- Subwoofer Level Control
This control sets the level of the low frequency crossover signal (original program plus synthe-
sized harmonics) coming out of the SUBWOOFER jack.
K- LF Boost Control
This control is used to even out the total apparent Bass output of the 120A. Use the LF Boost
to gently boost the bass on each channel (after the harmonics are summed in) to fill in the
gap between the synthesized low bass (below 55 Hz) and the mid-bass of the original pro-
gram. Always be careful of using excessive boost, especially if the Subharmonics control is
past its midpoint, or if you are using a speaker equalizer, or any other bass tone control.
LF BOOST can be used with or without Subharmonic Synthesis.
L- Subharmonics Control
This control, along with the individual frequency controls, sets the amount of synthesized bass
that the 120A adds to the program. Its affect depends not only on where it is set between MIN
and MAX, but also on how much bass is present in the original signal to be augmented. Note
that the effect will be most apparent in systems with subwoofers or other speakers that effec-
tively reproduce very low bass tones.
M- 24Hz-36Hz and 36Hz-56Hz Level Controls
These controls individually let you customize the amount of the respective synthesized fre-
quencies to be added in, tuning the ultimate bass response of your system to taste. For
example, if the sound is too woofy or growly, try turning down the 36Hz-56Hz level. If your
woofers are bottoming out (making a ticking, popping sound), or fuses are blowing, or your
amp is clipping, try turning down the 24Hz-36Hz level. You may find that a setting produces
fine results in one room, but produces too much boominess in another. If this occurs, adjust
the controls as needed, (e.g., increase one or the other of the band levels). Experimentation
will pay off with smooth, full, deeply extended bass. Remember, you are not selecting a fre-
quency. You are controlling the overall level of each band.
Setting Levels
Do not use the 120A at its extreme settings with loud volume levels, especially with digitally-
produced audio.
Very low bass frequencies call for considerable amplifier power and for loudspeakers that can
take this considerable power. However, the 120A not only can boost the bass that is present
in the original program, but can simultaneously generate sizable amounts of new bass at even
lower frequencies. If not used with care, the 120A can damage system components (e.g.
woofers can be readily damaged by very loud bass, intentional or otherwise). dbx Professional
Products cannot take responsibility for any damage to the amplifier, loudspeakers, or other
stereo components that results from the 120A.
When using the 120A (or any other component in your system), reduce the system’s output
level. It is also recommended that all of the 120A front panel controls be set to fully counter-
clockwise to minimum (MIN). When installation is complete, carefully return the system to nor-
mal listening levels and adjust the 120A to taste.
If clipping occurs, lower the volume and decrease the 120A settings. Note: Never try to repro-
duce non-musical sounds like artillery explosions or gunfire with the 120A.
1.3 Operating Notes

®
AvoidingTransients
Any sharp noises from your sound system can be hard on your system, and since the 120A
amplifies and augments all low-frequency information, extra caution is called for at all times.
To be safe, turn the power amp on last, and off first. and always keep the main volume con-
trol low or off when turning the system or any of its components on.
To further reduce the chance of dangerous transients, make sure your system is operating at its
optimum performance. We recommend you have all switches, button and knobs on your
equipment cleaned by a qualified person (especially if any rasp or crackle is present). If you
are using a turntable, check to make sure that the cueing is gentle.
Speaker Placement
For systems with multiple speakers, we recommend placing each speaker so that the distances
from the center of its woofer to the three nearest boundaries are as different as possible. These
distances are measured along the speaker cabinet sides, not in a straight line. When these dis-
tances are the same, the bass response of most speakers is roughest, with peaks and dips more
than 10dB apart over just a few notes. Putting a conventional box-shaped speaker woofer
down in a corner will make it sound very bassy, but for the evenness of bass, it’s the worst spot
available.
The formula for calculating maximum different distances a, b, and c and least bumpy
speaker placement is: a/b= b/c, or b2 = ac, where a, b, and c are never equal.
The same acoustic laws apply to your listening position: the smoothest bass will result when
the distances from your head to the three nearest boundaries are as different as possible. In
the same manner, the boomiest rooms have all three dimensions the same and the smoothest
have them maximally different.
If you do reposition your speakers, you should also reset any output level controls on the back
of the speaker cabinet. Many speakers offer a slight HF or MF boost with these controls all the
way up, and the new increase in bass might be better balanced by such a maximum setting.
The 120A is not intended only as a device to create wall crumbling low-end. Judicious use with
a pair of full range speakers can create the sense that a pair of speakers with 15” woofers is
being used. An additional benefit of improving the sound of smaller speakers is that a pair of
smaller speakers and a 120A is more portable than a pair of two larger speakers.
Turntable Feedback and Low Frequency Rumble
If you are using the 120A with a turntable, the increased levels of bass may make your turntable
system more susceptible to feedback, wherein the turntable base, platter, cartridge/stylus,
and/or the disc itself actually pickup and replay bass from the speakers. One symptom is an
increasing, flapping rumble as you turn the volume up (severely, the system begins to howl)
that disappears or is markedly reduced when the tonearm is lifted off the record. The cure is
to isolate the turntable, making it immune to low-frequency vibrations. Any LF rumble in the
system from turntable, air conditioning, through mics, etc., will be boosted by the 120A.
To reduce turntable feedback, begin by locating the turntable and the speakers as far apart as
practical. Next, short of replacing the turntable, since some turntables are much more prone to
feedback than others, shock-absorber feet designed specifically for this problem. A massive
base or table under the turntable may decouple it from the cases.
Note for CD Players: High levels of Bass can cause CD players to skip. It is a good idea to
locate CD players away from low-end drivers and loudspeakers, and shock mount them.
Operating Notes Section 1
120A
120A User Manual 3

Connecting toYour System
®
3120A User Manual
4
Section 1 120A
Basic Connection
The 120A can be used with any line-level device. For more specific cabling information, refer
to the Cable diagram on page 7.
1. Turn off all equipment before making any connections.
2. Mount the 120A in a 1U Rack Space (optional)
The 120A requires one rack space. It can be mounted above or below anything that
doesn’t generate excessive heat, since it requires no special ventilation. Ambient tem-
peratures should not exceed 1130F (450C) when equipment is powered.
Note: Avoid over-tightening of rackmounting screws as this could damage the front
panel.
Caution: Never remove the cover. there are no user-serviceable parts inside, and you
run the risk of an electric shock.
3. Make connections via 1/4” phone jacks or RCA jacks according to your requirements.
Subwoofer Operation: Set the OUTPUT switch to FULL RANGE and connect the ampli-
fication for the main speakers to Channel 1 and Channel 2 Output Jacks.
Operation without a Subwoofer: Set the OUTPUT switch to FULL RANGE and connect
the amplification for the main speakers to CHANNEL 1 and CHANNEL 2 Output.
Typical patch points include: a mixer’s channel or subgroup inserts when using the
120A on individual instruments or tracks; the mixer’s main outputs when mixing an
instrument preamps’s effects loop when using the 120A for guitar or bass; main outs of
a submixer as the signal is sent to main mixer. The 120A can be used either before or
after an external electronic crossover. When using a chain of processors, the 120A
should generally be placed as far down the chain as possible. We recommend you use
common sense and experiment with different setups to see which one provides the best
results for your needs.
4. Plug in the AC power cable to power On the unit.
Note: Check the line voltage. The 120A is shipped for 115V or 230V, 50Hz or 60Hz
operation. Refer to the unit’s rear panel to verify your unit’s precise line voltage.
1.4 Connecting the 120A toYour System

Block Diagram Appendix
120A Appendix
24-36Hz 36-56Hz
A.1 Block diagram
®
5

Appendix
Frequency Response: 20Hz-20kHz ±0.5dB, (no synthesis, full-range mode)
15Hz-90kHz +0, -3dB
Input Impedance: ≥40kΩBalanced or 20kΩunbalanced (1/4”) 20kΩ(RCA)
Maximum Input Level: +22dBu (1/4”) +8.5dBV (RCA)
Output Impedance: 100Ω, Impedance balanced
Maximum Output Level: +22dBu into 600Ω
Connector Type: 1/4" TRS Jacks (Inputs and Outputs) RCA (Inputs)
THD: 0.05% (no synthesis, either output)
Output noise: -88dBu, controls@max., 22Hz > 22kHz unweighted (full range output)
Front Panel Controls: 26-36Hz and 36-56Hz Band Synthesis Level, Subharmonics, Low Frequency Boost,
Subwoofer Output Crossover Frequency, Select, Crossover in/out
Indicators: Power, Crossover, Bypass
Metering: Synthesis activity (3 LEDs per band)
Dynamic Range: 112dB
Synthesis Frequency Range: 26-56Hz (from 54-110Hz input signal)
Crossover: 12dB/octave high pass (-3dB @ 80 Hz or 120Hz); 6dB/octave derived low pass.
Phase-coherent (unity-sum)
Power Requirements: 100-120VAC; 50/60Hz DO Version, 220-240VAC; 50/60Hz EU Version
Dimensions: 1.75"x19"x6.2" (4.5cm x 48.3cm x 15.75cm)
Rack Space: 1 Rack Unit
Weight: Net/Shipping: 4.75 lbs/8 lbs, 2.2kg/3.7kg
A.2 Specifications
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120A User Manual
Specifications
®
6
120A

®
120A User Manual
®
Wiring Diagrams Appendix
120A
7
The 120A has 1/4”, balanced/unbalanced inputs and is designed for nominal +4dBu levels. The 120A also offers RCA
connectors, and is designed for nominal -10dBV levels.
Input Cable Configurations
The 120A will accept either balanced or unbalanced sources as long as cables are wired according to the following
diagrams. In an emergency, 1/4” mono cables will work. Connect the sleeve to the cable’s shield. Note: for maxi-
mum hum rejection with a balanced source, avoid common grounding at the 120A’s input and output. The best start-
ing point is to ground the shield of the input cable at the source device (leaving it unconnected at the 120A).
Output Cable Configurations
The 120A will drive either balanced or unbalanced loads as long as the cables are wired according to the following
figures. The output’s impedance at 100Ω, allowing operation with virtually any load. Nominal operating level is
+4dBu into 600Ω. If using 1/4” mono plugs, at the output, the 120A will be grounded to the load device. This can
cause a ground loop. By using 1/4” balanced phone plugs, the grounds of both the 120A and the load can be isolat-
ed to reduce hum. Leave the shield unconnected at the load device.
A.3 Installation Considerations andWiring Diagrams

®
8760 South Sandy Pkwy.
Sandy, Utah 84070
Phone: [phone]
Fax: [phone]
Questions or comments?
E•mail us at: [e-mail]
or visit ourWorldWideWeb home page at:
www.dbxpro.com
A Harman International Company
18-2217
®