Shure AMS4000 User guide

Shure Brothers lncorporated
222 HartreyAvenue
Evanston,
IL 60202-3696 U.S.A.
AMS4000 AND AMS8000 Installer'sManual
The Shure Automatic Microphone System [AMS] turns
microphones on and off [with automatic gating], greatly
reducingthe reverberant sound quality and feedback prob-
lemsoften associatedwith the use of multiple microphones.
The special AMS microphones are gated on only by sounds
arriving from the front within their acceptance angle of
120°. Other sounds outside the 120° angle, including
backgroundnoise, will not gate the microphoneson, regard-
less of level. Inaddition, the AMS adjusts gain automatically
to prevent feedback as the number of "on" microphones
increases.
The resulting sound is clearer than that of conventional
multiple microphone speech reinforcement and recording
systems-and free of the clipped and missed words, clicks
and pops, and noise pumping often associated with other
"automatic mixer" systems. Besides its major advantages
of simple setup and unmanned operation, the Automatic
Microphone System operates over an extremely wide
dynamic range without the possibility of threshold-setting
misadjustments.
AMS Mixers are supplied in 4- and Schannel configura-
tions [Models AMS4000 and AMS80001, each housedin a
single 3lh-inch rack-mount package. Bothcontainlogic ter-
minals [for channelmuting, overridefunctions, and gatingin-
dications], and link circuitry for expansiontoas many as 200
linked channels.
AMS Features:
w Reliable, quick-acting, noise-freegating-virtually insens-
itivetochanges insound source loudness or distance
w Smooth pleasant-sounding turnon and turnoff
characteristics
w Nothresholdsettings to misadjust
w Front-panel microphone channel gain controls and
Master control operateas in conventionalmixers
w Selectable hold time keeps microphones on during short
pauses
w Preset or adjustable Off-Attenuation control for unob-
trusive gating
Automatic gain adjustment as additional microphones
gate on
w Wide, flat frequency response and low distortion up to
+ 18 dBm output
w Logic inputs and outputs enhance systemversatility
w Linking capability for systems of as many as 200
microphonesand 25mixers
LED indicationof gatingoperationand output level
w Automatic muting prevents annoying thumps and
loudspeaker damage when unit isturned on and off
w Four or eight specialmicrophoneinputs[for use only with
AMS microphones]use standardtwo-conductorshielded
cables and three-pin connectors
w Balancedoutput switchableto line or microphonelevel
w Front-and rear-panelunbalancedAux inputs and outputs
w Front-panelheadphone monitorjack
w Direct [non-gated] outputs available from individual
microphones
w Underwriters Laboratories Listed and Canadian Stan-
dards Associationlistedas Certified
..... - ...... -.
Shure AMS4000 andAMS8000 Mixers are designed for use only with Shure AMS Condenser Microphones. Conventional condenser or
other microphones will not operate properly with the AMS4000 and AMS8000.
-
OCopyr~ght1997, Shure Brothers lncorporated
27A8273(QC) Printedin U.S.A.
U.S. Patent 4,489,442; other patents pending

TABLE OF CONTENTS
General ............................................................. 1
Specifications ........................................................ 3
Connections. Controls and Indicators ..................................... 4
.................................................
MicrophonePlacement 6
....................................................
TypicalApplications 6
.................................................
ConferenceRoom 6
Church
.......................................................... 6
Courtroom
...................................................... 6
Legislature
....................................................... 6
LogicFunctions ....................................................... 8
CoughButton .................................................... 8
Chairperson-Controlled Muting ....................................... 8
DisablingtheGating Function [Bypass] ................................. 8
.......................................
RemoteChannel-On Indication 8
...............................................
LoudspeakerMuting 8
.................................................
"Filibuster"Mode 9
Preventing Room NoiseModulation ................................... 9
...............................................
MicrophoneLock-On 9
Diode Isolationof Logic Controls ...................................... 9
.............................................
External Logic Devices 9
15-VoltCMOS .................................................. 10
DigitalControls or Microcomputers .................................. 1 0
............................................
WirelessMicrophones 10
................................................
DirectOut Gating 10
ControllingNon-AMS Microphones .................................. 11
..................................................... OperatingHints 11
........................................................ Phasing I1
...............................................
MicrophoneMuting 11
...................................................... Grounding 11
InternalWiring Modifications ........................................... 11
Troubleshooting ..................................................... 15
Appendix I: Effectsof Acoustic Environmenton Gating ...................... 16
RoomNoise ..................................................... 16
Reverberation
................................................... 16
TalkerDistanceandAngle ......................................... 16
Reflectivesurfaces ............................................... 16
Appendix II: Theoryof theShure Automatic Microphone System
.............. 16
Appendix Ill: AMSMixersand Conventional Microphones
.................... 1 7
1 WARNING
Voltages inthis equipment are hazardous tolife . Referall internal
wiring modifications and servicing to qualified service personnel
.

SPECIFICATIONS
Output Level [at full galn, 1 kHz, one channel gated On,
Off-Atten at -15, wlth AMS26 probe mtcrophone, output
terrnlnatlons: Llne 6000, MIC 1500. Aux 50k. Olrect 50k,
Phones 20001
Frequency Response
Aux lnput to Outputs: 30to 20,000 Hz, *2 dB
Mic IntoOutputs: 70to 20,000 Hz,
* 2 dB [controll-
ed low-frequency rolloff below 50Hz]
INPUT
Mtcrophone
lnput
Senstttv~ty
172 dB SPL tn]
--
Aux
Input
Senstttvlty
1-22dBV ~n]
--
Aux lnput Impedance
70k or greater, unbalanced [designed for use with less
than 10ksource impedance]
Outputs
'Depend~ng on Aux control settlng
OUTPUT
Input Clipping
Leva1at I kHz
128dB SPL
+7to
+ 20dBV'
OUTPUT
Mtc
Llne
Aux
atrect
Phones
IMPEDANCE
Phonaa
-4 dBV
-4dBV
Deaignedfor Actual
Uw With [Internal]
Direct
56 dBV
--
Lina
+ 158 dBV
[+ 18dBrn]
+ 158dBV
-
150R balanced
ltnes
600flbalanced
lhnes
10k or greater
10-50kunbalanced
rno clrcutt
200n
Output
Clipping
bval
Mic
34
dBV
34
dBV
Hum and Noise
Equivalent lnput IYoise: 27 dB SPL, A-weighted, with
AMS26 probe microphone
Aux
+ 17
dBV
+I7
dBV
Output Noise: -62 dBV [master up], -88 dBV [master
down] [300-20,000 Hz, input controls down, Off-Atten
at -1
51
Output Humand Noise: -58 dBV [master up], -79 dBV
[master down] [20-20,000Hz, input controls down, Off-
Atten at -151
Distortion
THD 0.35% or less, 30to 20,000 Hz at + 15dBm
output; IMD 0.5% or less up to + 15darn output
Phase
Positive pressure on AMS microphone diaphragm pro-
duces positive voltage on pin 2 of LinelMic balancedout-
put with respect to pin 3, tip of Aux output, and tip and
ring of Headphones output, and negativevoltage on tip of
Direct output. Aux output is in phase with Aux input.
Gating
Attack Time: 4 rnsec:
HoldTime: 0.5 or 1.O sec [switchable]
Decay Time: 0.3
sec after Holdinterval
Off-Attenuation
F~xed: -15 dB
Varlable -cx, to -8.5 dB
[Slngle mtxer; attenuation Increases as addltlonalmixers
are l~nked]
Overload and Shorting Protection
Shortlng the lnputs or outputs, even for prolonged
perlods, will cause no damage; mc lnputs wlll not be
damaged by slgnals up to 3V; aux lnputs
will not be
damaged by slgnals up to 10V
Logic Terminals [all specifications referenced to Logic
Ground terminals]
lnputs [Override, Mute]
High[inactive]: Greaterthan 1.9V [5.OV typical] [no
input current with 5.0to 20V applied]
Low [active]: Less than 1.9V [OV typical] [sources
80 when grounded]
MinlMax Applied Voltage: + 20V
Outputs [Gate]
High [inactive]: 5.OV in series with 10k resistance
[sources 0.2
mA with 3.OV output] [minlmax applied
voltage: -0.5to
+ 1 5V]
Low [active]: Lessthan 0.5V sinking [I 00 mAmax]
LOGIC EQUIVALENT CIRCUIT DIAGRAM
FIGURE
1
Operating Voltage
105-132Vac, 50160 Hz, 20W [fused internally]. Can
be rewired for 210-264 Vac operation [see 240V
Operation]
Temperature Range
Operating: -29" to 57°C [-20" to 135"FI
Storage: -29" to 71"C [-20" to 160°F]
Dimensions
See Figure 2
OVERALL DIMENSIONS
FIGURE
2
Weight
AMS8000: 6.6 kg [I 4 Ib 8 oz]
AMS4000: 5.8kg [I 2 Ib 1 3 oz]
AMSB000 [packaged]: 7.8 kg [I 7 Ib 4 oz]
AMS4000 [packaged]: 7.1 kg [I 5 Ib 9 oz]
Certifications
Listed by Underwriters Laboratories, Inc.; listed by
Canadian Standards Association as Certified

CONNECTIONS, CONTROLS, AND INDICATORS
[Paragraph numbers that follow refer to pictorial views on
inside back cover.]
1. Microphones: The Shure AMS Condenser
Microphones are designed specifically for use with Shure
Automat~c Microphone Systems, AMS4000 or
AMS8000 mixers Do not attempt to connect AMS
microphones to standard phantom-powered or
standard non-phantom-powered inputs; they will
not function properly.
The AMS microphones, inconjunctionwiththe specialcir-
cuitry of the AMS mixers, uniquelydiscriminate between
desired sounds that originate within their
1 20" front ac-
ceptance angle and all other sounds. The desired sounds
from the front of a microphone are detected and cause
the microphone tobe gated on, transmitting its signal to
the mixer output. Sounds outside the acceptance angle
will not gate the microphone on. When a microphone is
"on" [accepting signals], it operates like a cardioid
microphone [or like a hemi-cardioid in the case of low-
profile microphones]. Each AMS microphone operates
completely independently in analyzing its own sound field
and deciding whether a sound source is within the front
acceptance angle.
Among available microphonesare: alow-profilesurface-
mount model [AMS22], a gooseneck model for perma-
nent mounting [AMS24], a probe model[AMS26] with a
front pop-filter grille, and a lavalier model [AMS28]. Due
to the reinforcement of sound waves from the adjacent
boundary surface, the sensitivity of the surface-mount
model is twice as high [6 dB more] as that of the probe
model. The gooseneck modelis suppliedwith a cable, but
less connector.
The microphone connector is a standard 3-pin profes-
sional audio type [XLR]. Under most circumstances,
lengths of 150meters [500
ft] or greater of goodquality
2-conductor shielded microphone cable can be used as
extensions between the microphone and the AMS mixer
microphone input. The same conductor must be wired to
the same numbered pin at both ends of the cable to en-
sure proper functioning of the units. The shield should be
connected topin1 atbothends of extensioncables.Good
practice dictates that microphones and extensioncables
be groundedonly tothe AMS mixer chassis ground.
2. Microphone Inputs: The AMS mixer is supplied with
either four or eight microphone inputs per unit. The
microphone inputs are designed for use only with Shure
AMS microphones; the Mixer will not operate with other
microphones; and Shure AMS microphones will operate
properly only with AMS mixers. The microphone input
connector is a female XLR type.
3. Microphone Channel Gain Control:
When set to
the
"0" posltlon [detented counterclockwise], the
mlcrophone is not
permitted togate on. Turningthe con-
trol
clockwise from this position permits the microphone
to gate on ether for sounds within ~tsacceptance angle
or by a connection to the Override log~cterminal [see
descr~pt~onof Logic Terminals below].
The Microphone Channel Gain control does not affect the
Dlrect Output level unless a jumper change has been
made for post-fader output as
described in Paragraph 4
below.
4 Direct Output: This provldes a non gated
microphone-level s~gnalfromthe mtcrophone Thls output
behaves ltke a conventtonal cardloid h~gh-impedance
mlcrophone output It can be converted to balanced low
Impedance using a line matching transformer [Shure
A95UI An unbalanced low Impedance mlcrophone level
can be obtalnedby loadlng wlth a 100-ohmreslstor [con-
nected t~pto sleeve]
The '/4-1nchphone jack 1s supplled w~redpre-fader so that
the output 1s not affected by the posttionof ether the in-
div~dualChannelcontrolor the Mastercontrol,even when
the Channel control
IS In the counterclockwise detent
["O"] position
Eachchannelcan be wlred post-fader by movingajumper
on the input module board [see section on Internal
Mod~ficationsfor deta~ls]Thls change causes the level at
the Dlrect Output to follow the settlng of the Channel
control
5.
ChannelLED Indicator:
A yellow LED indicator above
the Channel control l~ghtswhen the mlcrophoneis gated
on. The status of the Direct output is not related to the
LED.
6. Hold Time: This swltch determines how long the
microphone stays on after the user stops talklng. Thls
delayedturnoff br~dgespausesIn speechand reduces un-
necessary gatlng action. The 0.5-second posltion
minimizes microphone on-time, while the I .O-second
position bridges longer pauses.
For special applications, the 1.O-second positron can be
increasedto as long as 2 seconds by inserting a reslstor
[see Internal Modifications section for details].
7. Off-Attenuation: This switch determines the at-
tenuatlon of microphones that are not gated on. It is un-
necessary for "off" microphonesto be totally off to galn
the benef~tsof automatic mix~ng.Keepingthem slightlyon
at all times contributes to smooth unobtrus~vegatlng ac-
tlon.
The -15 setting of the Off-Attenuation switch is
recommended for most applications. The Variable set-
ting allows continuous adjustment of the Off-
Attenuat~onfrom minus infinityto -8.5dB [-8 setting]
by the screwdriver-slot adjustment directly above the
switch. [See sections on Link Jacks and on Theory of
Operation for further Information on Off-Attenuation.]
8.
Power Cord: A 3-conductor cord and groundedplug
designedfor
connection to 120Vac, 50160 Hz outlets
only. To modifythe unlt for 240V, refer to the section
on Internal
Modifications.
9. On-Off Switch: Push-buttorr switch on the front
panel turns the power to the AMS mixer on and off.
10.
Power-On LED: A green LED on the front panel
lights when the power is on.
11.
Normal LED:
A yellow LED on the front panelabove
the Power-On LED beg~nsto turn on when the line and
aux output levels are above approximately -20 dBV
[I 00 mV].
12. Overload LED: A red LED flashes when the

LineIMic, Aux, and Phones outputs approachclipping. If
this light flasheson, turndownthe MicrophoneChannel
controls of the channels in use or turn down the
Master control until the light stays out.
1 3. Aux Input: A l/4 -inch unbalancedphone jack input on
both the front and rear panel of the AMS mixer,
suitable for Aux level and line level sources, such as
tape recorders or playersor conventionalmrxers. This
non-gatedinput is mixedwith the combinedmicrophone
signals toappear atthe LineIMic,Aux, and Phones out-
puts.
14. Aux Control: The position of this control deter-
mines the level of the Aux Input.
15. Master Control: The positionof this control deter-
mines the level of the combined microphone and aux
signals at the LineIMic, Aux, and Phones outputs.
16.
LineIMic Output: This male XLR audio connector
has switch-selectable levels: either low-impedance
balanced microphone level or 600-ohm balanced line
level. This output provides the combined gated
microphone and non-gated aux input signals.
17.
Aux Output: The '/4-inch phone jack outputs on the
front and back panelsare intended for unbalancedAux
or line levelloads. This output also providesthecombin-
ed gated microphone and non-gated aux input signals.
18.
Phones Output: This %-inch phone jack is suitable
for most stereo or mono headphones with
2- or
3-circuit phone plugs. The signal at this output is iden-
tical tothat at the LineIMic output.
19. Logic Terminals: These four screw terminals are
built intoa female barrier block modulethatplugs into
a male connector on the rear panel below the Direct
Output jacks (Figure
31. The barrier block's plug-in
design ensures proper placement and simplifies ter-
minal wiring by eliminatingthe needfor soldering. Con-
nections tothese terminals arenot necessary for basic
AMS operation, but allow the AMS mixer to perform
additionalfunctions. Unshieldedwire or multi-conduc-
tor cable is adequate for the connectors.
The logic levelsarenomtnally 0 volts [low] and
5.0 volts
[htgh]; they are directly compatible with standard
5-volt logic families [including CMOS and TTL].
GATE OUT: This terminal follows the channel gating
and goes to logic "low'' when the mrcrophone is gated
on. Sufficient current-sinking capability is provided to
l~ghtexternally powered LED'S [see Logic Functions
sectlon for example].
LOGIC GROUND: The Logic Ground terminals of all
channels are connected together internally and are
dist~nctfrom the AMS aud~oground. All logic ground
connections should be made to these terminals. The
power supply ground of external logic circuitry should
be connected to the L.ogic Groundterminal of Channel
8 [or Channel 4 In 4-channel AMS mixers]. To avoid
sw~tch~ngclicks, do not Interconnect the Log~cGround
with the audio, chassrs, or rack grounds.
MUTE IN: Applying a logic "low" to this terminal
[froma logic gate or a switch closure to Logic Ground]
gates the channel off. The channeloutput drops tothe
level set by the Off-Attenuation switch. The Mutefunc-
tion dominates Override when both are simultaneously
activated unless a jumper change is made so that
Overr~dedominates [see Internal Modification section
for details].
OVERRIDE IN: Applying a logic "low" tothis terminal
[fromalogic gate or a switchclosure toground] forces
the channeion. The mixer is supplied so thatwhen both
Mute [described above] and Override of a channel are
activated, Mute dominates.
lnhibit Function: The Mutefunction can be altered
to lnh~bitby an internal jumper change for each
channel [see Internal Modifications section for
details]. After the change, alogic "low" atthe Mute
In terminal prevents the channel from gating on if it
is off, but allows it to remain on if it is already on.
After the Inhibitmodification, for certain specialized
applicationsa logic connectioncan be madebetween
a channel's Gate Out and its Mute In terminal.
IMPORTANT: To prevent high-frequencyoscrlla-
tion, never connect a channel's Gate Out to its
Mute In unless the lnhibit modification has been
made.
LOGIC GND
MUTE IN
AMS MIC IN
3
REAR-PANEL CHANNEL PLATE
FIGURE
3
20. Link Jacks: These rear-panel %-inch phone jacks
are usedtolink up to
25 AMS mixers together to pro-
vide an input capability of as many as
200
microphones. To link mixers, use short I -conductor
sh~eldedcables with -inch phone plugs on both ends.
Plug a cable betweenthe Link A Out jack of one mixer
and the Link A In jack of the next mixer;
AND plug a
cable between the L~nkBOut jack of one mixer and the
Link BInjack of the next. Leaveopenthe Link Injacks of
the first mlxer inthe chainandthe Link Out jacks of the
last mixer Inthe chain. Boththe Link A and Link Bjacks
of each mixer must be connected: A Outs to A Ins
and
q Outs to B Ins. Usethe Link jacks for l~nkingonly,
not for audio inputs or outputs.
IMPORTANT: When uslng the logic term~nalson

linkedmlxers, connect the Channel 8 Logic Groundter-
minals of each unit together.
Switching clicks may
result if thts is not done.
When mixers are linked, the combined signals of all the
mlcrophones appear attheoutputs [MicILine, Aux, and
Phones] of ALL the linked mixers. Thus, you can take
outputs from several mixers for a multiple feed.
However, an aux source connected toan AMS mixer is
heard at the outputs of that mixer only, NOT at the
outputs of linked mixers. For this reason, plug the aux
source into the mixer providing the audio output. If
multiplefeeds are being used from linked mixers and it
is desired that the aux source appear in all, parallelthe
aux source [using Y-adapter cables] to the Aux inputs
of all the mixers used for the multiple feeds.
The Master Gain control on each linkedmixer controls
the overail level at its own outputs of
all the linked
mlcrophones and of its own Aux inputs. The Off-
Attenuation controls and the Normal and Overload
LED'Soperate inthe sameway-they controland show
the status of the outputs fromthe mixer on which they
appear. The Hold Tlme switch on each mixer affects
only the microphones connected to that mixer.
TO AMPL,
TAPE REC, ETC
LINKING MIXERS
FIGURE
4
MICROPHONE PLACEMENT
Use Low-Profile AMS22 Microphones on tables and desks;
use permanently mounted GooseneckAMS24 Microphones
on tables, desks or lecterns; use Probe AMS26
Microphones on floor or desk stands or goosenecks; use
Lavalier AMS28 Microphones where the talker must have
freedom of movement.
Locatethe microphones so that intendedsources arewithin
60° of either side of the front of the microphone; that is,
within the
1 20° acceptance angle [see Figure 51. Sources of
undesiredsound should be locatedoutside the
1 20° accep-
tance angle.
Use as few microphones as necessary to pick up everyone.
The closer the microphones are totheir sound sources, the
greater the loudness of the sound system before feedback
occurs. Each microphone should be at least
1 meter [3ft]
from the wall behind it, and at least 0.3meters
[I ft] from
objects behind it, such as large ashtrays or briefcases.
When using AMS28 Microphones, avoid acoustic feedback
from loudspeakers near the microphones.
MICROPHONE ACCEPTANCE ANGLE
FIGURE
5
TYPICAL APPLICATIONS
Conference Room
Refer tothe AMS Operators Manualfor microphone place-
ment at conference tables. Connectextension cablestothe
microphones and tothe microphoneinput connectors on the
rear panel of the mixer. Connect the LineIMic Output tothe
line input of the PA amplifier. To record the meeting, con-
nect the Aux Output to the aux Input of a tape recorder.
Church
Connect extension cables to the microphones and to the
microphoneinput connectors on the rear panelof the mixer.
Connect the LineIMic Output to the line input of the PA
amplifter. To record the service, connect the Aux Output to
the aux input of a tape recorder [see Flgure 61.
Notethat the cholrs are insldethe acceptance angles of the
pulpit and lecternmicrophones. Thus, some choir members
maygate on the pulpit and lecternmlcrophonesoccasionally.
This will not seriously degrade the performance of the
system.
Courtroom
Connect equipmentas described for the church setup. Also
connect each DirectOutput toa separate microphone input
channelof a multitrack tape recorder for easy
identification
of talkers duringtranscription. The Aux Output containing a
mix of all the microphones connects to another channel of
the mult~trackrecorder. Th~schannel can be monitored to
hear the entire
proceedings. [See Figure 71.
Often a tape playback 1s used for evidence or for transcript
ver~f~cation.Connectthe tape player's aux output tothe Aux
lnput of the mixer.
Legislature
A typical legislature setup is shown in Figure 8.
[Chairperson-Controlled Muting-see LOGIC FUNC-
TIONS-is also shown.] Two or more mixers are linked via
the L~nkA and Link
B jacks. The Channel 8 Logic Groundter-

ALTAR
ma
RECORDER
CHURCH SETUP
FIGURE
6
r*i PLAYER $GK-~
COURTROOMSETUP
FIGURE
7
minalsof the linkedmixersareconnected. One mixer feeds a
PA system, and another mixer feeds a tape recorder and
equipment for a television broadcast.
Notethat the Off-Attenuation can be set differently for the
PA mixer than for the
TV mixer. The Ti/ feed and recorder
may sound morenaturalif the Off-Attenuation is set at
-8 if
the room noise is sufficiently low. On the other hand, for
highest gain before feedback in the PA amplifier, the Off-
Attenuation shouldbe set at
-1 5 or, insome cases, atminus
infinity. The Master Gain control is set differently on each
mixer to obtain proper levels feeding each system. The aux
source feeds both mixers via a Y-adapter cable but the Aux
control on each mixer may also need to be set differently.
ol MUTING SWITCH
0
CHAIRPERSON*^
CHANNEL
LEGISLATURE SETUP
FIGURE
8
LOGIC FUNCTIONS
Cough Button
The user canturnoff his or her microphone [tothe selected
Off-Attenuation level] during coughing or private conversa-
tions. To establish this function, wire an SPST pushbutton
switch betweenthe Mute In and Logic Groundterminals on
each channel requiring a cough button. See Figure
9.
0 GATE OUT
LOGIC GROUND
MUTE IN
COUGH BUTTONS
FIGURE
9
Chairperson-ControlledMuting
By activating a switch, the chairperson can silence all the
other microphones and be heard without interruption. To
establish this function, connect together all the MuteInter-
minalsof all the mixers, but make no connection tothe logic
terminals of the chairperson's microphonechannel. Wirean
SPST pushbuttonor toggle switch between the Mute In and
Logic Ground terminals of any one channel except the
chairperson's channel. See Figure
10.
TheChairperson-Controlled Mutingfeature isalsoillustrated
[see Figure
81 as part of a large system for a legislature.
Note that the Logic Ground terminals of both mixers are
connected, andthat the chairperson's logic channelsareun-
connected.

0 / GATE OUT
0 LOGIC GROUND
01 MUTE IN
OVERRIDE IN
CcHAIRPERsoN7.s
CHANNEL
Loudspeaker Muting
In some applications, a loudspeaker is located near each
talker toprovide audio reinforcement or toallow monitoring
of a telephone conversation or conference. Each
loudspeaker can cause feedback unless it is automatically
switched off whenever the talker near itspeaks. To provide
this function, connect the Gate Out terminal of eachchannel
to a separate loudspeaker muting relay as shown in Figure
1
3. Recommendedrelays are Guardian 1345-15120or
1475-1C-120, or Potter
& Brumfield R50-E2-YI-l2V or
R10-El-Y2-V185, or equivalent.
CHAIRPERSON-CONTROLLEDMUTING
Each loudspeaker should be placed behind its associated
FIGURE 10
microphone to prevent the loudspeaker from gating on the
microphone. The loudspeaker volume should be low; other-
Disablingthe Gating Function[Bypass)
wise the microphone may not gate on reliably when the
To keep all the microphones on, wire all the Override In ter- talker speaks.
minalstogether to a Logic Groundterminal [see Figure 1I].
This isusefulif itisdesiredtobypassthe automaticfunction- If theexisting soundsystemuses 24-volt relays, theycan be
ing and use the AMS mixer as an ordinary mixer. drivenwith theAMS Gate Out usinginternalwiring modifica-
tions described inthe Internal Wiring Modifications section.
GATING BYPASS
FIGURE
11
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
RemoteChannel-On Indication
The LED's aboveeach Channel control light when that chan-
nel is gated on. These indicators can be usedto identify the
talker or to indicate to each talker when his or her
microphone is on. To provide Channel-On indicators at loca-
tions remote from the mixer, connect LED's and a 5-volt
power supply tothe Gate Out terminals as shown in Figure
12.NOTE: To avoid switching clicks in the audio outputs,
do not ground the power supply negative terminal to the
audio system ground or rack ground.
IMPORTANT: Ifasinglecable is tocarrytheAMSmicro-
phoneaudio signal
and thedc powerforthe LED, separate
shielded pairs
must beused. Failuretocarrythedc power
on a shielded pair may result in audible clicking due to
capacitive coupling between the dc power lines and the
AMS microphone lines.
i
GATE OUT
LOGlC GROUND
MUTE IN
0VERRIDE.IN
R=150-300n
SUPPLY
POWER
OVERRIDE
IN^
LOUDSPEAKERMUTING F:gR
FIGURE 13 AMPLIFIER
"Filibuster" Mode
In normal operation, when several people talk, all their
microphones gate on so that no speech is missed. But with
the mixer wired for "Filibuster" action, a microphonethat is
gated on prevents other microphones fromgating on. Once
a microphone is on, other microphones cannot gate on until
the talker has paused long enough so that his or her
microphone has gated off. Thus, the person talking has the
floor and cannot be interrrupted.
To establish this function, perform the internal Mute to In-
hibit jumper change [see Internal Modifications section for
details]. Then connect all the Mute In terminals of the
modified channels together; connect all the Gate Out ter-
minals of the modified channels together, and connect the
Gate Out terminal of one modified channel to the Mute In
terminal of another modifiedchannel [see Figure 141.
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
REMOTECHANNEL-ON INDICATORS
FIGURE
12
FILIBUSTER" MODE
FIGURE
14

NOTE: To preventhigh-frequencyoscillation,do notwire a
channel's GateOutterminaltoitsown MuteInterminaluntil
the Muteto Inhibit change has been made.
Preventing Room Noise Modulation
This connection keeps at least one microphone on to
eliminatevaryingbackgroundnoiseor "pumping" [see Figure
151. The channel to which the transistor collector is con-
nectedwill be turned on whenever all other microphonesare
gatedoff [see AMS Theory section].
GATE OUT
LOGlC GROUND
MUTE
IN
OVERRIDE IN
ROOM NOISE MODULATION PREVENTION
FIGURE
15
MicrophoneLock-On
The circuit described in the preceding paragraph can be
expanded using diode isolation to perform a new function.
Evenwiththe advantagesofferedby the AMS, there may be
installations where it is desirable that the last microphone
gated on should remain on until another microphone turns
on. Forinstance,thesoundreinforcementrequirementsof a
church may dictate that an altar microphone remain on as
the minister moves outside the acceptanceangle. Normally
the AMSwouldnotremaingatedon afterthe initialholdtime
elapsedif the ministercontinuedtospeak outsidetheaccep-
tance angle.
With the circuit shown in Figure 16,the last microphone
to gate on remains on indefinitely. When a new microphone
gates on, it will release the lock-on for the previous
microphone,andthe new microphonewill lock on. The result
is the ultimate in automatic mixing: each logic-wired
microphoneis capable of remaining on until no longer need-
ed. Note that if two or more AMS microphones are
simultaneouslygated on, normalAMS action will take place.
Since at least one microphone is always on, this circuit also
prevents room noise modulation. Bath the Mute In and
Override In remainusable for additional functions.
For eachmicrophonetobe given lock-oncapability,the cir-
cuit uses a 2N2222 general-purpose amplifier NPN tran-
sistor [Motorola], a I-megohm, %-watt resistor, and a
numberof 1
N4148diodes [GE] equal tothe total number of
AMS channels involved. For instance,if the installation has
five AMS channelsto be wired, a circuit containingone tran-
sistor, one resistor, andfive diodes mustbe constructedfor
each channel [a total of five transistors, five resistors, and
25 diodes]. The circuit in Figure 16shows only one lock-on
circuit; similar circuits must be constructed for all lockan
channels.
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
MICROPHONE LOCK-ON
[ONE CHANNEL SHOWN]
FIGURE
16
Diode Isolation of Logic Controls
Two or more control functions using the same logic ter-
minals can be isolated with diodes. Here a channel can be
mutedby an overall group mute switch, or by its own cough
button [see Figure 171.
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
D= IN4148
OR EQUIVALENT
GROUP
f
MUTE
COUGH BUTTONS
DIODE ISOLATION OF LOGIC CONTROLS
FIGURE
'I7
External Logic Devices
The AMS logic levels are directly compatible with TTL and
5-volt CMOS logic families. The following example [Figure
181uses logic gates to perform the same function as the
diode isolationof logic controls. Suggested TL, LSTTL, or
CMOS NANDgatesinFigure 18 are I/2-7420,74LS20 and
74C20. Suggested AND gates are 7408, 74LS08 and
74C08. In the example, the output of the Channel-On in-
dicator goes tologic Highif any channelgateson. [For infor-
mation on logic gate use, see the
TTL Cookbook and
CMOS Cookbook, both by D. Lancaster, Howard Sams
PublishingCo.]
c3
+3
-
--
GATE OUT
NAND GATE
0
MUTE IN
0 0
EXTERNAL LOGIC DEVICES
FIGURE
18

15-Volt CMOS
The logic terminals can be usedwith 15-volt CMOS if a pull-
up resistor is usedwith each Gate output [see Figure 191.
LOGIC GROUND I GI'
MUTE IN
OVERRIDE IN
15-VOLT CMOS
FIGURE
19
Digital Controls or Microcomputers
The AMS mixer logic terminals can interface with custom-
designed digital control circuitry or even a microcomputer
for unlimited possibilities of system control functions.
Wireless Microphones
A wireless microphone can be usedwith the AMS [without
automaticgating], but itsconnectionmay be madeinseveral
ways. Ifthe microphone has aline-leveloutput, connectthat
output to the AMS mixer auxiliary input. An alternate
method is to connect a short jumper between the Logic
Ground and Override In logic terminals of the channel that
will containthe wireless microphone.Withthis channel per-
manently gated on, the balancedmicrophone-leveloutput of
the wireless microphone receiver can be connectedto the
channel input. [If the receiver has only a balanced line-level
output, the same connections can be made, but a line at-
tenuator such as Shure's A15LA should be used in the
receiver-mixer line.]
The wireless microphone can be switched on and off re-
motely by grounding both the Mute In and Override In logic
terminals, and puttinga switch in the circuit from the Mute
In terminal to ground. Since the Mute In circuit has
precedenceover the Override Incircuit, the microphonecan
be controlled by this in-line switch.
If the wireless microphone receiverhas a balancedline-level
output, a circuit can be constructed to use the wireless
microphone and still retainthe automaticgatingfunction. In
the diagramshown below [Figure 201, the value of resistor
R can be determined as follows. Start with a 2-megohm
resistor; at this value, the channel will not gate on until it
receivesa signalof at least 0.016 volts [-36 dBV]. All AMS
logic terminalsoperatenormallywith this circuit. The gating
thresholdcan be varied by usingadifferent resistorvalue ac-
cording to the needs of the installation. Note that the
thresholdis raisedby ahigher resistorvalue [more voltageis
requiredto overcome the threshold].
FROM WIRELESS RECEIVER TOAMS MIXER
LINE LEVEL OUTPUT MIC INPUT
Direct Out Gating
The AMS mixer Direct Out jacks can be convertedtodirect
gated outputs so that the level and equalization of each
microphone can be controlled by a studio mixing console.
Automatic gain adjustment [based on the number of gated-
on microphones] is out of the circuit-the decay time is
slightly decreasedbelow the normal 0.3-second interval.
The logic circuit for direct out gating is shown in Figure
21 .
All resistors are 114 watt, and the opto-isolator can be a
Vactec VTL5C2 or VTL2C2, or a Shure 86A8900. The
50k to 100k resistor is optional; itwill provide a finite Off-
Attenuation capability.
Note that if a gated mixed output is not needed for the
modified channel, that channel's internal circuitry can be
modified rather than using the logic terminals. Inthis man-
ner, the level control and decay characteristics can be re-
tained, andthe need for aseparatepower supply eliminated.
[IMPORTANT: This conversion removes each modified
channel fromthe AMS mainmix bus, so that it operates in-
dependently of the unmodifiedchannels. Inother words, the
automaticgatingfunctionisretained,but the automaticmix-
ing isnot.] Refertothe InternalWiring Modificationssection
for further information.
DIRECT
OUT
GATED
300 OUT
(AUX/HIZ
+5v
MIC LEVEL)
POWER
SUPPLY
GATE OUT
LOGIC GROUND
MUTE IN
OVERRIDE IN
DIRECT OUT GATING USING LOGIC
FIGURE
21
Controlling Non-AMS Microphones
If it becomes necessary to use a conventional [non-AMS]
microphone in an AMS system and the non-gated
microphone must be turned off whenever an AMS
microphone is gated on, the wiring shown in Figure
22 ac-
complishesthis easily. Connectthe non-AMS microphoneto
the desiredinput, and other AMS microphonestothe other
AMS mixer inputs.
Connect the selected channel Logic Ground to its Override
In. Wire the Gate Out terminals of the remainingchannels
together and connect them to the Mute In of the selected
channel. Now, whenever an AMS microphoneis activated,
the Override In and Mute In on the non-AMS microphone
channel are grounded, and the Mute Intakes precedence.
MICROPHONE INPUTTO GATING LlNE INPUT
FIGURE 20
An external,or "outboard," circuit can also be constructed
touse aconventional[non-AMS] microphonewith on and off
gating. However, itwill
not have some of the primary AMS