Langevin AM4A User manual

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mixer system
l2 MJC/UNE equalized inputs
with echo sepd
4 Outputs pfus
Stereo or Mono mix.down outputs
XLR connectors
Complete capability for Recording and Broadcast
· Studio production applications.
CetecNC.
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Bunrling
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Constructjon
The Langevin am4aoffers quality, flexibility and
economy in a sophisticated sound mixer. The
building block concept of the am4a lets you buy
the channel combination you need.Just unpack,
connect your input and output lines, drop in the
modules ... and you're ready to go.
T
Eachblock isa pre-wired, plug-in module. Pre-
amplifier, line amplifier modification groups, and
multi-channel gain control modules are available...
and eachchannel provides true fidelity of sound.
The unique housing assembly is pre-wired and
ready to accept standard Langevin modules ...
offering a variety of functional capabilities tailored
to the individual's requirements.
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am4a HOUSING
The functional low silhouette design of the am4a mixer
equips the operator with a convenient sloping work panel.
Its overall height is 7 inches (17.78 cm) and depth is a
compact 27 inches (68.58 cm). The housing is 45¼ inches
wide (114.93 cm), and will accept 19 modules. Blank
panels are used if the total number of modules does not
completely fill the available housing capacity.
OPTIONS
27"------------------1
CONSTRUCTION FEATURES
Pre-wired circuitry and a solid state power supply within
the mixer assembly provide the necessary interconnections
and power requirements. The standard am4a has twelve
input modules with full equalization and reverb send
facilities. It is equipped with a four-gang board master and
stereo and mono mix-down capabilities. Input and output
lines are permanently wired to XL type connectors in·
stalled in the rear of the housing. Top quality, fou(~inch.
illuminated VU meters are provided.
IMPUT
AM-411AS Standard microphone preamplifier, similar to
AM-401AS, but providing pan pot instead of solo pushbutton.
PROGRAM Output assignment switch is prewired and marked for the fol-
AM-419AC Booster amplifier providing four rotary level con- lowing functions:
trols, has gain of 24 dB for four-channel operation. Primarily Pos. 1 Output assigned to Channel 1.
intended asbooster stage to provide balanced +4 dB monitor Pos; 2 Output assigned to Channel 2.
output of AM-407-type amplifier. Pos. 3 Output assigned through pan pot to Channel 3 and 4.
MG-71 Passive8-to-1 combining network with eight individual Pos. 4 Output assigned to 0-Bus. ·
input level controls, and two groups of four pushbuttons that All switches may be down at the same time, facilitating a
allow selection of input sources. microphone feed to Channels 1, 2, 3, and 4. The pushbutton
NOTE: This module is designed to operate with a nominal in- in position No. 4 is electrically interlocked to disconnect the
put level of +4 dB and hasan insertion lossof 40 dB. ~utput of the preamplifier from the bus system, applying
It must be to1'1ow~ by an AM-407 amplifier, or any signal to the 0-Bus only.
device with similar gain characteristics, in order to -j? AM-449AS Passiveinput module designed primarily for broad-
recover the insertion loss of the combining module. cast applications. Will accept two groups of stereophonic input
MG-81 Passivecontrol module with four rotary potentio- pairs at nominal level of +4 dB. Provided with four bridging
meters. Primarily intended to be used in conjunction with input transformers and input selector switch. Includes dual
AM-419AC booster amplifier in situations requiring separate straight-line mixer and OF F-AUOITION-0 switch.
monitor level controls for control room and studio operations. NOTE: Tv.:o groups of four pushbuttons each are provided to
_..---. assign each of the two output channels to any com-
\IISCELLANECUS
AB-4 Blank panel to fill in unused module space. Mounts
sameas normal modules.
....,,.. bination of four program buses. This module contains
no equalization or reverberation facilities, since it is
primarily used in conjunction with tape or disc play-
back facilities.
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Curves for AM-401 AS Equalizers
/ol&IIMU.. oau1NUL£ lQUALIIATION
JD IDO
AM-401AS
I.OOD
'RIIIUINC:YIN CYCLH ~IR UCOND
OUTPUT ASSIGN (push-push). Not
interlocked .
SOLO (push momentary). For rehearsals.
Whendepressed,all channelsgo deadex-
cept the one with the depressedbutton.
INPUT ATTEN dB {interlocked) ·
One-down-at-a-time. Preventsoverdrive.
HF (interlocked) SelectsHF equalization ·
boost peak frequency. 3, 5, 10 kHz.
DEGREE OF HF EQUALIZATION
(rotary) 12 dB boost or attenuation
boost peak frequency. 50 Hz, 100 Hz,
(rotary) 12 dB boost or attenuation /
REVERS POINT, Band A (interlock)
Before or after mixer control.
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arn"la mixar modules
OUTPUT ASIIGN
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~:~~EE OF LF EQUALIZATION 1/;
REVERB SEND (stepless)NOTE: OUT- ca•
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PUT ASSIGN switches, top of panel,
switch reverb and program.
MIX (stepless)for channel gain. •
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IIASTCII
AM-401AS AM-407AS AM-439A AM-4298
AM-407AS Program Module
Line amplifier with nominal program output of +4 dB;
maximum output +22 dB. Amplifier hastransformer
coupled input and output and is provided with straight
line submastercontrol and reverberation receive circuit.
Reverbcircuit hasrotary level control and three.position,
interlocked pushbutton switch. In the first position, it is
possibleto disable the reverb receivecircuit; in the second
_position, to feed the reverb signal to the monitor circuit
only; or, in the third position, to feed the reverb signalto
the monitor and program channelssimultaneously.
NOTE: A small feedback amplifier is provided asa booster
for the reverberation-send line. The AM-407 AS
hasa fixed gain, thus requires no control. If
applicable, the board's master control is connected
to the AM-407AS amplifier circuit and performs
T3-.:l04
in conjunction with the sub-mastercontrol, which
is located in the module's front panel.
Talkback module. Fits into left trim panel of console.
Permitsslating, with or without tone, and talkback into
studio monitor system.
1
AM-439A
A combining module designedto provide astereo mix·
down derived from the four main output busesof the
am4a. Push-button switches allow the operator to select
from any combination of the four main busesand four
pan pots are used to place the selected signalsto any posi-
tion between the stereo outputs. Left and right stereo
amplifiers provide unity gain output when the pan pots
are in full left or right position.
AM-4298 Mono Mixdown Module
Amplifier with 4-to-1 combining network primarily for
useasmonophonic feed from the four-channel output of
console. Provided with rotary mixer for each input channel
and four-position pushbutton switch, allowing for the
selection of feed points. Provided with rotary output level
control aswell asoutput indicating meter.
~'ilG-G1/4 Mas1er Control
Passiveboard master control module that isdesignedto
control output level of four AM-407-type line amplifiers
on one control.

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TYPICAL OF FOUR - - - - - - ;rVU ON CONSOLEl
AM-407 AS : ..: '
I~ •4 PROGRAM I
C: OUT .
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1 r-""l.---- AM-439A I
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Jm4a TECHNICAL SP!:CI FICAT:ONS
INPU1.
Source Impedance Microphone, 250 ohms nominal.Balanced Line lSK ohm.
Level 60 dB signal to noise can be maintained with input level as low
as ·62 dBm. Proper operation of input attenuation buttons
prevents overload with levels as high as +27 dBm. Any signal
ranging from low level microphones to outputs of lines or tape
recorders may be accommodated.
Power Requirements 45 to so voe at 35 ma for each AM·401AS module.
OUTPUT
Impedance 600 ohms balanced.
Level Normal +4 dBm.
Maximum +22 dBm
Frequency Response Without LF or HF equalization,± 1.0 dB, 20 Hz to 20 kHz.
Distortion Not over .5% over the range 30 Hz to 20 kHz at output level of
+20 dBm. Not over .1% kHz at +22 dBm.
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Noise Without LF or HF equalization, not to exceed a level of ·122 dBm
Input equivalent.
Power Mains 105/130 or 210/260 volts
50/60 Hz (Specify Voltage)
Dimensions Height - 7 incnes (17.78 cm)
Width - 451/• inches (114.93 cm)
Depth - 27 inches (68.58 cm)
Weight - Approximately 125 lbs. (56.70Kg)
CeteclNC
o suosidia,v ot Computer Eou1pmentCoro
13035 Saticoy Street
North Hollywood, California 91605
Phone: [phone]
TWX: 9104992669
N>l.Si-lVI LLE OFFICE
Route 4, Devens Drive
Brentwood, Tennessee 37027
Phone: [phone]
::UROPEAN OFF,CE
Cetec U.K.
Shaftesbury Street
High Wycombe, Bucks, England
Phone: High Wycombe 37326
Telex: 837329
CL·006•1173
PRINTED IN U.S.A.
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WARRANTY
Langevin guarantees this p~oduct to be free from defects of
material and worloianship for a pe:riod of one year from date
of manufacture.
Exceptions : 1) Langevin assumes no responsibility for any
shipping damage•
2) Carbon-composition controls aTe guarant~ed
for ninety days after first use.
3) VUmeters are warranted for four weeks from
date of shipment.
4) Warranty is void if unauthorized repair or
modification has resulted in d~~age or in
deterioration of performance. ,_
Within the guarantee periods, Langevin will replace or re-
pair·any part of the AM4Asystem at no cost to the purchaser
or user except for his payment of one-way transportation to
the factory at Santa Ana, California.
SHI PP i NG DAM AG'E
No containeT that shows visible external damage should be
unpacked, except in the·presence of an official of the car-
rier (who should sign a statement as to nature of d~~age).
If concealed damage is discovered within any unpacked con-
tainer which showed no visible external damage, the carrier
should be notified illL~ediately. An official should inspect,
and sign a statemeht as to the nature of the d~~aga.
The Interstate Con,m~rce Commission has indicated that a
carrier is as much responsible for concealed damage as for
visible damage.
Please notify Langevin of any shipping damage.
REGI STRATI ON OF PURCHAS E
If you have purchased this equipment through a dealer (or
through any supplie.r other than the Langevin factory), please
notify the factory of your purchase in letter form. This will
place youT name nnd address on the list for receipt of chanio
notices and additions to this booklet.
AN4.4 pegs 1 of 4

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FuS ES
Thare are two fuseholders on the chassis of the power supply
(which is under the top covar of the housing). They are
marxed AC and DC.
If the AC fuse fails, all power will be removed from ths entire
assembly.
If the DC fuse fails, amplifier power will ba removed
but the meter lamps will stay on.
B~ sure and replace fuses with values as indicated on tha supply
chassis. Turn off power befora removing or replacing a fuse.
Although years may go by before any fuse fails, it is well to
keep spares handy. Whynot tape boxes of fuses to the inside
of the housing cover?
PORTABLE US E 0 F T HE AM 4 .4
Although compact, the AM4Awas not designed to be a truly port·
able unit. In particular, the frame of the housing is not suf-
ficiently braced to withstand rough handling.
It is suggested that, if an AM4Ais to b~ made p~rtable, a
carrying case be constructed. ·This case shpuld. totally· enclose
the housing and should have padded supporting sections. The ·
cover should have padded inserts that bear against the panels
of the plug-in modules so that they will not loosen with vibra-
tion.
When using the AM4Aon location, small portable reverbaration
generators can be connected for monitoring purposes only, and
recQrdings made "dry". (See specifications for tha Output
Modules.) Proper reverberation can be added during remixing
back at tha studio.
FACTORY 'SERVICE
The Langevin factory will repair and/or refurbish any part of
an AM4Aat moderate cost.
It is recommended that you save one or more of the packing
cartons fo~ the modules so that this material can be used ~hen
returns are made.
Please correspond with Langevin before raturning equip~snt.
AN4A page 2 of' 4

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THE A>~.;,;MI~ct< IS .A. MODULARASSEMBLYthat ca;; b-2 pu~ tJgather-
in a great number of different ways. It is unfortunate thdt
no concise set of instructions can possibly be written that
remains readable while covering all the variations that can
exist.
In lieu of an instructions book, it is requested that you
read the enclosed material which outlines the characteristics
and specifications for the individual modules.
Also enclosed is a section for the housing of the AM4A. It
is the variations in housing wiring that makes one system
different from another.
If your system has any special modules ... or any modifica-
tions that are not considered to be 11standard" ••. you will
find the pertinent sections enclosed.
Regardless of th~ possibly unique properties of your parti-
cular AM4A,there are certain comments that will apply.
Indeed, most of these comments hold good for mixing systems
in general •.. not just for the Langevin AM4A. Please read
the section below:
0 PERATI ON
IMPUTOVERLOAD Input Modules and Preamplifiers ar~ often
overdriven, resulting in distortion. The
AM401Input Modules have inbuilt Input Attenuators, a 4-key
interlocked push-switch (0, 20, 40 and 60 dB). The proper
key should be selected so that overdrive does not occur.
The II norma111 posi ti ons of al 1 mi xer co ntr o1s , ~ 1.1h-fii r) ~ t.er ~.j
masters and board (grand) masters on the AM4Aare with the
knobs each set at about 010". Any time that a mixer control
on an Input Module must be run further CCHthan about 113011
in order to maintain proper Vu meter level, over-drive is
probably occurring ... and the next higher Input Attenuator
button should be pressed.
Input over-driva will be accompanied by a sliqht upward
f 1a$ hi ng Q f t he. H St at USII l i ght Q n aj'\ · rnpU C :,,Q d:.JrS •
VUMETERS Do not allow Vu Meters to bang their pegs con-
tinuously, as this will only result in distor-
tion being generated. The proper l2vel for pro9ram exists
when th,~ pointers approcch 110a 0:1 th2 seal es fa i rl: 1 of ten J
but go into th~ r9d portioil3 only about on-:c p~r tP.n :~c(:ir.ds.
(In public-address work, output level monitoring s~ou1d be
primarily by the level cf tha sound in the house4 Vu met2rs
are secondary-standard indicators.)
pag:B 3 of f

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EQUALILERS The best way to use variable equalizers is:
A3 Zittle as possible. They should be consid-
ered as crutches that are resorted to only if proper choica
and positioning of microphones fails to achieve the desired
end •
The equalizers in the AM4Ause no inductors, and are fr2e
from ringing.
A studio that is equipped only with 11 flat 11 microphones pro-
bably cannot avoid use of the. equalizers. In this case, the
following comments may be of interest:
1) Try to avoid use of high-frequency equalization
that boosts at 10 kHz or above. If possible,
add brightness only in the 3 or 5 kHz region.
2) Some bass jnstruments that fall off in acoustic
output at the extreme low end of tha spectrum
may benefit from boost at 50 or 100 Hz. In
particular, small bass fiddles often require
low-frequency augment~tion. Also, rolling off
the highs on a bass fiddle mike may help to
reduce string slap.
3} 1000 Hz equalization boosting may help to main-
tain uniform speech and dialogue characteristic,
and should be introduced as the actors distances
from the mike decrease.
N~TE: The 1000 Hz peaking equalization on the
AM401 Input Module cannot be used with any
other peaking frequency. In other words, do
not attempt to boost at 1000 Hz and 3, 5 or
10 kHz.
4) The six push-keys mar~ed 3, 5, 10, 50, 100 and
1000 on the AM401have nothing to do with tha
response of an equalizer 1n the roll off mode.
They select boost peaks only.
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LANGEVI N AH2 1 / 1 3
A II 2 1 / 1 9
HOUS I rJGS
BASIC HOUSINGSFOR THE Af':14/\MIXER SYSTEMS,TWOLENGTHS,WITH
RESPECTIVE CAPACITIESOF THIRTEENANDNINETEENPANEL MODULES.
POSITIONING['10DULES To place a plug-in module in its panel
position: 1) Loss en thumbscrew at
top. 2) Engage nylon bushing at lower end of module with the
short retaining stud i~ the housing. 3) Carefully lower the
module into position, meshing the module connector with the
housing connector. Never force a module.
To remove a module: 1) Loosen retaining thumbscrew at top
of module. 2) Using the thumbscrew as a pull handle, raise
the top of the module until the connectors disengage complete-
ly. 3) With your other hand, grasp one of the knobs on the
module panel. 4) Remove the module with motion upward and
toward the meter panel.
Do not remove or insert modules with power on the system.
HOUSINGSIZES The walnut end-sections are identical for
. both sizes of housings ... and are slightly
larger than the cross-section of the metalwork. They measure
approximately 27 1/2" (from front of armrest to rear of side-
piece) by 7 1/8'' (overall height of side-piece, not including
distance the entire housing is raised off supporting desk by
its feet).
The AH21/13 Housing (thirteen panel modules) is approximately
32 1/8" wide, overall.
The AH21/19 Housing (nineteen panel modules) is approximately
45 1/4" wide, overall.
MOUNTINGTHEHOUSING
The AM4Amay be placed on any suitable
desk, table ·or ped~stal. Rubber feet
support the housing approximately 1/4" above the mounting surface
to prevent scratching furniture-type finis11es. Should you desire
to recess the AM4A into a specially constructed console, you
may want ~o remove the front trim to realize a flush assembly.
This trim is fastened by 4 or 6 machine screws accessible after
removal of all modules.
AH21/ Page 1 of 13

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If you are planning to use the bottom access holes for
cable lines, or if you have XL-Connectors installed in
these positions, a table cut-out ~s required to reach
these points. It is also possible to have the housing
assembly protrude 3 inches past the rear edge of the
table to gain access to the bottom connectors.
CONNECTir~THEAM4A If you ordered your Mixer Assembly
without XL-Type connectors, all
laads are brought to the applicable terminal boards.
MICROPHONEINPUTS are always in multiples of 8 inputs per
terminal board. The terminals marked "l '' and "2·" are
balanced transformer .inputs, "CT" .is the transformer center,
and ''S" is the cable shield. The ''S" terminal is grounded to
chassis at the terminal board location.
The "INCO~IINGLINES" terminal boards accomadate 4 lines per
~oard. Two sets of terminals are provided for each 1ine.
The ampljfi.ers are always connected to the terminal pair
toward the VU-Meter Panel, leaving a set of 4 terminals
available for a level pa<l.
If your Hsscmb1y is wired with XL-TYPE CONNECTORS,the
term in a l p a i rs are ·connect cd s tr ai g ht th rough , but th c $ e
jumpers may be removed and a resistor level reduction
network can be installed to obtain a €:ompatible input· leve].
The "OUTPUT'' and ":,IONITOR'' lines arc connected to the
appropriately mark0d terminal boards. Unused terminals
are not connected, and may be used by the installer for
possible a<l<litional networks, or as tye-points. In a 4-
channel assembly, for example~ terminal groups 1 thru 4
are connected to the lines, and termina.ls 5 thTu 8 are
free.
If your AM4A is eq u ipec.l with a ''~IONITOR GAIN CONTROL",
terminal groups 1 thru 4 arc BEFOREthe control, and
terminal groups S thru 8 are AFTER the· control. The
monitor amplifier fl should be connected to terminal #5;
amplifier #2 to terminal #6, and so on.
REVERBERATION SEND ANDRECEIVE termin·aJ.s are located on
the same board, and all terminals are used.
For Power-Line Connection, see PS4ROO Section.
/\P·:, 1 /
.'"\..1 - .I. Page 2 of 13