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

microphone features: it will not sense ambient roomnoise,
gating will
not be direction-sensitive, and gating threshold
adjustment
will be necessary. Figure 23describes the re-
quired circuit. Note that
[I ] microphone-on sensitivity and
effective gatingthreshold are adjusted by potentiometer R5
[level adjustment-but not gating adjustment-is available
usingthe Channel Gain control]; [2] circuit power is supplied
by the mixer; [3] a metal enclosure must be used for
shielding, and
[4] transformer lead P2 is not used.
CONTROLLING NON-GATED MICROPHONES
FIGURE
22
-
0
a-
-
-
OPERATING HINTS
Phasing
Proper microphonecable phasingisessentialtoAMSopera-
tion. If pins2 and 3 arereversedina cablefor a conventional
balanced, low-impedance, microphone-mixer setup, the
microphone will stillfunction properly [although with revers-
ed polarity]. But if pins 2 and
3 are reversed in an AMS
cable, sounds from the
rear of the microphone will gate it
on. The AMS mixer perceives the microphone's rear as the
front and vice versa, andthe microphonegates on only ifthe
rear becomesthevoice entry. In
all AMSinstallations, cable
conductors that start out as pins 2 and 3 shouldend up as
pins 2 and
3, respectively.
MicrophoneMuting
To install an at-the-microphone muting switch for an AMS
channel
without using the logic terminals, the requiredcir-
cuit is slightly different from that of
a conventional
microphone and mixer. Figure 24shows the required corn-
ponents. All resistors are 1/4-watt, and the capacitor is a
metallized polyester film non-polarized type [CDE
MMWA05W5-20, Sprague 431P505X9R51. A low
leakage current capacitor like this is needed to avoid
-
n
0
0
0
-
undesirable switching clicks. The switch must be a snap-
action type, such as a toggle switch.
The circuit must be housedina metalenclosure for shielding
purposes. The enclosure is grounded to pin 1 of the
microphonecable, butmust be insulatedfrom accidentalse-
cond grounding through the enclosure mounting surface.
This avoidsthe formation of a ground loopinthe microphone
circuit.
-
A
0
0
0
Grounding
In AMS wiring, avoidance of ground loops is of the utmost
importance. Good grounding practices must be followed
when using extension cables, junction boxes, and cable
snakes.
Each microphone cable shield must be connected toground
only at the mixer. For instance, if the shielding shell of an
XLR connector is connected to pin 1, and the connector is
plugged into a grounded junction box, the cable shield
becomestied to ground at the junction box
and the mixer.
The result may be a considerableamount of hum and rfin-
terference. Good noise rejection is virtually guaranteed by
eliminationof ground loops.
-
3
0
0
0
-
MIC MlXE R
510fl,5%
f
GATE OUT
LOGIC GROUND
MUTE IN
OVERRIDE IN
MICROPHONE MUTING
FIGURE
24
INTERNAL WIRING MODIFICATIONS
This section describes the internal wiring modifications
previously mentioned. Refer to the specific application or
logic function for detailedinformationon the purpose of each
modification.
NON-AMSMICROPHONE GATING CIRCUIT
FIGURE
23
-
R1
7% 11 C3
02 154F
LO z
NlC. IN
C 4 R6 J2
R2
1 OOK
I)
*
-
INPUT TRANSFORMER
PR p13 1 MARY rRy mas2 Parts
Q2: 2N5087
R1:75K I14 watt
R2: 100K
Ih watt
R3:33K watt
R4: 4.7K '1.1 watt
R5:20K Pot.Audio Taper
R6:4.7K '14 watt
P 2
C1:.22uF 1OV
C2:2.2uF 16V
C3: 15uF 16V
PI-P3 75 OHMS
P3 s 2 P 2
C4:2.2uF 16V
J1:Female XLR
DC RESISTANCE (f 20%) J2:MaleXLR
(31: 2N5210 TI : Shure A95UF or90A8032
S1-S2 4300 OHMS

I
WARNING
I
No user-serviceable parts inside. Refer all ser-
vicing, including modifications, to qualified ser-
vice personnel.
AMS mixers can be disassembled for modification as
follows:
1. Remove line cord from ac power source.
2. Remove screws securing top cover tochassis.
3. Remove individual Channel boards by removing: [a]
Channel board bottom screw; [b] Channel Level con-
trol knob and nut; [c] Channel-On LED leads; and [dl
ribboncable connector.
4. When replacing Channel boards, be sure to perform
steps 3[a] through 3[d] in reverse order.
240-Volt Operation
To change the AMS mixer operating voltage from 120Vac
to 240Vac, follow these steps.
1. Locate the Power board [A5].
2. Removethe transformer TIplugfromconnector P501
[marked 120VAC], and carefully insert it inconnector
P502, making sure all four pins are properly engaged.
3.
Remove the 0.25N250V fuse from the fuseholder
marked F502 and insert the TI25 mN250V fuse
[packagedwith the AMS mixer] inthe fuseholder mark-
ed F501.
4. Replace the ac connector with one designed for the
240-volt source. If the mixer is to be used outside the
U.S. and Canada, local regulations may require replac-
ingthe line cordwithone havingwire insulationcolors as
follows:
"Live" or Earth or
"Hot" Neutral Ground
U.S., Canada Black White Green
Europe Brown Blue Green/Yellow
5. Markthe rear panelof the mixer withthenewoperating
voltage.
HoldTime Increase
The 1 .O Sec position of the rear-panel HoldTimeswitch can
be increased to 2 seconds as follows.
1. Withthe top cover removed, locate the Master board
[A21.
2. For AMS4000 mixers, no further disassembly is
necessary; for AMS8000 mixers, removethe Channel
8 board as described above.
3. Solder a 30k,
lh W resistor inthe Master board holes
marked XR201 [see Figure 251.
4. Reassemblethe mixer and mark the HoldTime switch
position "2.0" instead of "1 .Om.
Pre-Fader to Post-Fader
The Channel Levelcontrolcan be rewiredto also controlthe
rear-panel Direct Output levelas follows.
1
. Removethe top cover andthe Channel board to
be modified.
2.
Locate jumper XI01 at the top center of the
Channel board, and jumper holes XI02 at the
bottom center of the board [see Figure261.
3.
Unsolder the jumper at XI 01 and solder itor a
new jumper in the holes of XI02.
4. Reassemblethe Channel boardandtopcover as
described above.
MASTER BOARD A2: XR201
FIGURE25
MutePrecedencetoOverride Precedence
As supplied, if a channel's Mute Inand Override In logic ter-
minals are both grounded, the mute function will take
precedence over the override function and the channel will
be muted. With the following modification [both logic ter-
minalsgrounded], the override function will take precedence
over the mute function and the channel will be forced on.
Note that after modification the Channel Level control will
still turnthechannel off at the full counterclockwise position
[independent of the Override INterminal].
1
. Removethe top cover and Channel boardtobe modified
as described above.
2. Locate jumper XI04 and jumper holes XI03 on the
CHANNEL BOARDA1: XI01ANDXI02
FIGURE 26

Channel boardnear integratedcircuit U105[see Figure
271.
3. ~nsolderthe jumper at XI 04 and solder it or a new
jumper in the holes of XI
03.
4. Reassemble the Channel board and top cover as
describedabove.
MuteAction to Inhibit Action
As supplied, achannelwill mutewhenthe MuteInterminal is
grounded.After this modification,groundingthe MuteInter-
minal will not affect the channel if it is already "on", but it
will prevent the channel from gating "on" from the "off"
condition. The modification is requiredfor the "Filibuster"
modepreviouslydescribed,andfor any logicterminaluse re-
quiring connection of a channel's Gate Out terminal to its
Mute In terminal.
1 . Removethe top cover and Channelboardtobe modified
as describedabove.
2. Locate jumper XI05 and jumper holes XI06 at the
bottom front of the board [see Figure 271.
3. Unsolder the jumper at XI05 and solder it or a new
jumper in the holes of XI06.
4. Reassemble the Channel board and top cover as
describedabove.
EHANNEL BOARDA1: X103-XI06
FIGURE 27
Gated Direct Out
Incontrast tothe externalwiring additions describedunder
Direct Out Gating [see Logic Functions], this modification
applies the internal gated microphone signal to the Direct
Out Jack while retainingthe optimizeddecay characteristics
and avoiding the need for a separate power supply. Itdoes,
however, remove the modified channel's gating from the
mixedoutput, and thus does not provide automatic gain ad-
justment for the number of open microphones.
1. Remove the top cover and the Channel board to be
modified as describedabove.
2. Locateand removeresistor R119and the wire jumper
physically located between R119 and capacitor C118
[see Figure 281.
3. Solder a wire jumper between the hole closest to the
printed marking "R119" and the now-empty jumper
hole closest to it.
4.
riel t iuue resistor R101 [near the Direct Out jack] and
replace itwith a 5.6k, 5%resistor.
5. Reassemble the Channel board and top cover as
describedabove.
6. NOTE: Withthis modification,the Direct Out jack now
providesa gated signal for that channel only. The signal
ishighimpedance[2.8k to5.6kland unbalanced,witha
nominalsignal levelof -24 dBV [60mV] for 74dB SPL
with the Channel Gain control centered.
It will vary
directlywiththe Channel Levelcontrol. This isequivalent
to a typical aux level signal. To obtain a low-impedance
balanced, mic-leveloutput, pluginan impedance match-
ing transformer [Shure A95U or equivalent]. The
nominal level then becomes -48 dBV [4mV].
BEFORE AFTER
DIRECTGATED OUTPUT CONVERSION
FIGURE
28
Direct Out to SendlReceive Jack
AMS Direct Out jacks can be modified to function as
sendlreceivejacks for use with equalizers, limiters, voltage-
controlled amplifiers, or other external devices. With the
modification,the microphoneoutput signal is present on the
tip terminal of J101, and the return input signal is on the
ringterminal. The modifiedoutput signal has a nominal level
of -37dBV at 74dB SPL [I7 dBhigher thanthe unmodified
DirectOutsignallevel], withamaximumlevelof
+ 17dBV at
128dBSPL. The patchpointisbeforethe Channel Gaincon-
trol [pre-fader]and beforethe microphonegating[ungated].
The external device should be a nominally unity gain circuit,
with an input impedance of 10k or greater. The load im-
pedance it sees at the ring terminal will be 5k to 1
Ok, de-
pendingonthe ChannelGaincontrolsetting. Consultthe pro-
cessingdevice manufacturer's literature for proper applica-
tions within these level and impedance limits.
1. Removethe top cover and Channel boardtobe modified
as describedabove.
2. Locate, unsolder and remove resistors Rl01 and
R104 and jumper XI07 on the Channel board [see
Figure 291.
3. Solder a wire jumper between the XI07 solder hole
farthest from the edge of the board and one of the
solder holes
between the now-removed Rl01 and
R104resistors.
4. Locate point
Z on the Channel board [ring terminal of
J101 1, and solder ajumper betweenitand the remain-
ing [board edge] solder hole of XI07.
5. For circuit continuity when a processing device is
not
connected to the modified Direct Out jack, wire the
jack's tip and ringswitchingterminalstogether. [These

are the two terminals on the opposite side of the jack body
from RlOl and R104.] Wiring can be made at the top
[component] side of the board, or to the foil side
after the
bottom plate is removed. Note that the jumper should be
run
around the area that will be covered by the bottom
platetoassure proper bottom platefitting. Replacethe bot-
tomplate after wiring. Notethat a similar effect is obtained
by plugging a stereo phoneplugwiththetip and ring shorted
into the Direct Out jack; this must be done if the modified
Direct Out jack istobe usedas a standard Direct Out jack.
24-Volt Relays
To use the AMS Gate Out logic terminal to drive 24-volt
relays for loudspeaker muting, each channel must be
modified as follows:
1
. Removethe topcover and Channel boardtobe modified
as described above.
2. Unsolder and remove diode Dl13.
3. Reassemble the Channel board and top cover as
described above.
4. To prevent circuit damage caused by inductive
"kickback" when the relay is de-energized, make cer-
tain a diode is placed across the relay coil as shown in
Figure 13.
AMS4000: Input Expansion
Model AMS4000 mixers, suppliedwith four input channels,
can be expanded to accommodate up to eight AMS
microphones through the installation of additional Channel
boards [RKCI 88; order one for eachadditionalchannel] and
a nine-connector cable [RKCI 89; one cable provides for up
to eight inputs].
1. Remove the top cover as described above.
2. Remove the five-connector cable between the Channel
boards, andremovethe blank rearplateof eachchannel
to be added.
3. Usingthetemplate suppliedwiththe Channel board, drill
the front-panel nameplate holes for the LED [0.254"
&0.005"] and Channel Level control [0.296"
&0.005"] for eachchannel tobe added. [NOTE: Itis
not necessary to
drillthefront panelfor therectangular
locator pin.]
4. lnsert the new Channel board from the rear, making
sure the rectangular locator pin is properly centeredin
its mounting hole.
5. Usethe suppliednut andwasher tosecurethelevelcon-
trol to the front panel.
6. Secure the new Channel board bottom plate with the
screw previously removed.
7. lnsert the new Channel-On LEDthroughthe front panel
[leads first] and use a 3/16" nut driver against the
bezel to secure the LED flush with the front panel. At-
tach the white and red LED leads to the marked ter-
minals at the upper front of the new Channel board.
8. Attach the newnine-connector cabletothe Masterand
all Channel boards [unused channels will have unused
connectors].
9. Attach the new Channel Level control knob and replace
the cover.
CHANNEL BOARD Al: X107, R101, R104, "2"
FIGURE29

TROUBLESHOOTING
To Diagnose or Correct
Make indicatedcorrection.
Listento headphonespluggedintothe AMS front-panel Phonesjack.
To check microphone: replace suspect microphone with another. If
there is sound, replace microphone cartridge and PC board
assemblies, or returnthe unit tothe Shure Service Department for
repair; if there is still no sound, check cable.
To check cable: replace suspect cable with another. If there is
sound, repair or discard defective cable; if there is still no sound,
check input module.
To check input module: connect microphone and cable to another
channeland follow initialsetupprocedure. Ifthereissound, replaceor
repair defective input module; consult Shure Service Department.
If there is sound on headphones but no sound from system, check
other components and cables.
If there is no sound on headphones, consult Shure Service Depart-
ment.
If there is a reflective surface near microphone, and neither micro-
phone nor surface can be moved, cover surface with a sound-
absorptive materialat least 100mm [4 in.] thick. Iftalker is on edge
of acceptanceangle, movemicrophoneor talker. If loud, steadyroom
noise [typically from air-handling equipment] swamps out quiet
speech, reduceroomnoisetoreasonableconferencelevelsor reduce
talker-to-microphone distance. If none of above, check microphone,
cable, channel, and system as in NO SOUND section. Check
teleconference equipment for malfunction.
Check that red OverloadLED is not on: if on, turndown Channel or
Master control until LED goes out. If overload LED is not on, check
whether one or all microphones sound distorted. If only one is
distorted, check microphone, cable, and channel as in NO SOUND
section. If all microphonesare distorted, remove AMS mixer from
system, and connect undistorted signal source to system inputs. If
final sound isstill distorted, check systemcomponentsand recording
level. If final sound is
not distorted, consult Shure Service Depart-
ment.
Move source or microphone if possible.
Repair or replace cable. If microphone still gates on, check micro-
phone and channel as in NO SOUND section.
Make sure microphone cable shield and 3-pin connector shells are
not connectedto earth or grounded metallic objects. Shield ground
connection should only be made at AMS mixer input connectors.
15
Symptom
No sound
Erratic micro-
phone gating
Distorted sound
Micmphonegates
on for unintended
sound
Excessivehum
from one or more
microphones
[proper gating
"
may be affected]
Probable Cause
Channel control or Master
control turned too far down;
microphone not connected; mix-
er not connected to power
source; Power switch not on.
Defective microphone, cable,
channel input module
Defectivepower amp, tapedeck,
speakers, etc.
Defective AMS mixer
Reflective surface near
microphone (closer than 200 to
300 mm
- 8 to 1 2 in.] not in-
cluding table top for surface-
mount models);talker positioned
on edge of microphone accep-
tance angle; excessive steady
room noise; defective
microphone,cable, or inputchan-
nel.
Master or Channel control set
too high; defective microphone,
cable, or channel; defective
amplifier, recorder or speaker
Source is within
1 20° accep-
tance angle
If source is outside
1 20° accep-
tance angle: microphone cable
defective or wired out of phase;
input module defective
Microphoneinput ground loop

EFFECTSOFACOUSTICENVIRONMENTONGATING
Room Noise:
The louderthe roomnoise,the greater the
talker's sound pressurelevelmust be at the microphonefor
ittogate on reliably. Generallythis is not a problem because
people tendtotalk louder in noisy environments. In addition,
thesensing circuitry has beenequalizedtoreduce sensitivity
to room noise. If room noise is causing erratic gating, in-
struct the talker to stand or sit closer to the microphone.
The quieter the room, the farther thetalker can be fromthe
microphone before gating becomes erratic.
Gatingaction is degraded most by continuous noise [such
as from air-moving equipment]. Noises of a transient
nature, includingoutside-acceptance-angletalking, havelittle
interfering action.
Reverberation:
If the talker is far enough from the
microphone so that the sound field at the microphone is dif-
fuse, the microphone will not stay gated on. For example, in
highly reverberant environments the microphone may gate
on initiallyfor a distant soundsource, thengate off when the
reverberant sound field builds up.
The less reverberantthe room, the farther the talker can
be from the microphone before gating becomes erratic.
Typically, a source will gate the microphone on reliably up to
2 to 6 meters away [6 to 20 ft], depending on the
reverberation time and noise level of the room.
Talker Distanceand Angle:
As the talker moves away
from the microphone and his speech becomes weaker in
comparison to room noise and reverberation, the accep-
tance angle for reliable gating narrows.
If the talker speaks just outside the acceptance angle, the
microphonewill gate onoccasionally. Itwill notgateon atall if
the talker is well outside the acceptance angle.
Reflective Surfaces: Soundreflections froma hardsur-
face behind the microphone can hamper proper gating. The
microphone should be at least 1 meter
[3 ft] from a wall
behind it, and at least 0.3meters
[I ft] fromobjects behind
it such as large ashtrays or briefcases. For this reason, do
not place the AMS mixer on the table near the rear of the
microphones.
Earlyreflections from nearbywalls maytrigger occasional
microphone gating for sound sources outside the accep-
tance angle. This ismorelikelytooccur insmaller roomsex-
citedby narrowfrequency range loudspeakers.This effect is
minor and should not cause any operational difficulty.
Operation ontheverge of feedback [ringing], with sustain-
ed feedback or with test tones, can be expected to cause
some gating due to standing wave patterns in the room.
APPENDIX II
THEORY OFTHE SHURE AUTOMATIC MICROPHONE
SYSTEM
Two problems associated with conventional multi-
microphone installations result from unwanted sound pickup
from temporarily unused microphones. These microphones
contribute excess room noise and reverberation, reducing
clarity and intelligibility.They also increasethe total gain of a
sound reinforcement system, pushing the system close to
feedback [howling] and reducing the gain-before-feedback
available to individual microphones.
An idealized multi-microphone installation would have the
microphones spaced in a uniform, diffuse sound field, and
operated at identical effective gains. Under these condi-
tions, the increase in system gain compared to a single
microphone is given by:
G[dB] = 10log1 n
Where G is the system gain increase in dB over a single
microphone and n is the number of "on"
microphones.
In a sound reinforcement application, total system gain
must be adjusted below the feedback threshold with all
microphones operating. In a conventional mixing system,
each microphone would have G decibels less gain-before-.
feedback available than it would operating alone. G also
represents the increased pickup of room noise and
reverberation compared to a single microphone.
A solution to these problems is to gate on only the
microphone or microphones immediately in use. The Shure
AMS does this effectively and reliably by gating an individual
microphone on only inresponse to a sound source within its
acceptance angle. A microphone will not gate on for diffuse
roomnoise and reverberation, or for sound sources outside
its acceptance angle. While gated on, the AMS microphone
has a standard cardioid [unidirectional] pickup pattern[half-
or hemi-cardioidin the surface-mount AMS221.
With multiple talkers, or a talker within the acceptance
angle of more than one microphone, a number of
microphones may be gated on simultaneously. In a sound-
reinforcement application,if the system gain isset belowthe
feedback threshold with a single microphone gated on, the
increase in system gain with additional "on" microphones
could cause feedback. The AMS prevents this by
automatically reducingall "on" microphone gains by at least
G decibels as additional microphones are gated on. This
maintains constant total systemgain, avoiding feedback and
permitting the maximum microphone gains at all times.
This constancy of system gain means that pickup of room
noise and reverberation alsoremainsconstant atthelevelof
a single microphone. Except for transitions between zero
and one "on" microphone, gating action does not result in
audible modulation ["pumping" or "breathing"] of the room
noise. In applications where room-noise modulation caused
by the gating action of the first microphone is objectionable
[e.g., critical recordingor broadcasting], the logic terminals
can be usedtoensurethatatleastone microphoneisalways
gated on. An Override In terminal can be used to keep a
commonly usedmicrophonegatedon. Alternatively, thecon-
nection shown in Figure 16can be used to force one of the
microphones on only when all the other microphones are
gated off.
As mentioned in the description of the Off-Attenuation
controls, partially rather than fully attenuating the "off"
microphone makes the gating action significantly less
noticeable. However, if insufficient attenuation is used, the
increased system gain from the unused but not fully off
microphoneswill result inroomnoise andfeedback problems
approachingthose experiencedwith all microphonesfully on.

With a single microphone fully "on", the increasein system
gain duetoincompleteattenuationinthe "off microphones
is given by:
Where:
G' is the system gain increase in dB comparedto
full attenuation, Att is the Off-Attenuation in dB,
and m is the total number of microphones.
For an eight-microphone system:
The recommended setting of
-15 provides the benefit of
finite Off-Attenuation while degrading available gain-before-
feedback by less than
1 dB. The Variable positionset to -8
[actually -8.5 dB, fully clockwise] provides very smooth
gating in applications where an increase in room noise and
degradation of gain-before-feedback of up to 3.0 dB is ac-
ceptable.Automatic adjustmentof the Off-Attenuationlevel
maintains these relationships when additional microphones
areaddedthroughthe linkingof additionalunits.The
-00 set-
ting is usefulwhen a muted microphone should be fully off.
The above discussion assumed an idealized installation
with allthemicrophonesoperatedunderidenticalconditions.
Inpractice, of course, the microphonesmay notbeoperated
at identicalgains, and the acoustical environment will vary at
different microphone locations. Because of its acoustical
location or the need for a higher gain setting, one
microphone will usually reach its feedback thresholdbefore
the others and will establish the limit on system gain. The
AMS will act to prevent an increasein system gain beyond
that of the worst-case microphone operatedalone.
The formulas previouslygiven in this section, whichdeter-
mine the system gain controlling action, assume random
phase relationships among the sound fields at the
microphones.The approximationis valid for a large number
of microphones, but not for just a few. The sound fields at
two microphoneswill be in phase at some frequencies.The
combination of the two microphones will tend to increase
system gain by
6 dB at these frequencies, insteadof the 3
dB for whichthe AMS compensates.Feedbackcanoccur at
one of these frequencies with the gating on of the second
microphone,if the gain and phase criteria for feedback are
met. Although unlikely, this possibility should encourage the
installer to check different combinations of "on"
microphonesbeforedeclaringthe systemtobe free of feed-
back.
APPENDIX Ill
AMSMIXERSANDCONMNTIONALMICROPHONES
If a conventionallow-impedance microphone is connected
tothe inputof an AMS mixer, that channelwill operatelikea
normal mixer channel with the following exceptions:
1 . Normallyno gatingactionwilloccur;the gatewill be per-
manently off.
2. The channel signal will be (compared to the properly
operating AMS channel] somewhat degraded through
loss of low-frequency signals [bass rolloff of about
6 dB/octave below 500Hz], increasein noise, and loss
insignal level.
However,the conventionalmicrophonesignal
will be passed
if:
1 . That channel's Level control is sufficiently high.
2. The Master Gain control is sufficiently high.
3. The Off-Attenuationcontrol is
not set for minus infinity
[-a].
Since the channel remains gated off, the Off-Attenuation
control determines the level at which the conventional
microphone signal will be passed.
A more desirable methodof using an AMS mixer channel
with aconventionalmicrophoneistousethe OverrideInlogic
terminal to force the channel on. In this mode, the
microphonesignal istypically
1 5 dB higherthan inthe gated-
off mode. Only the Channel Leveland Master Gain controls
affect the microphone signal; the Off-Attenuation control
does not affect the signal because the channel is gated on.
Notethat the use of a conventionalmicrophoneinone chan-
nel will not affect other AMS mixer channels. They will con-
tinue to operateproperly with AMS microphones.
.Many phantom powerable condenser microphones may
operatewith the low dc voltage supplied by each AMSmixer
channel. For instance,Shure's SM85will operate; however,
the microphone's clipping level is significantly reduced
because the powering voltage is lower than the minimum
rated voltage.
As this section indicates,
a conventional microphone can
be used in an AMS mixer channel. However, it must be
notedthat signal degradationand lossof all automaticaction
for that channel are the price paid for not using an AMS
microphone.

MODELS AMS4000ANDAMS8000
FRONT PANEL
I OFF-ATTEN "oLoki;a
o
0.5 SEC 1.0
Om0
LINE MIC
OUTPUT
MODELSAMS4000 AND AMS8000
REAR PANEL
8
..
GATE OUT
LOGIC GND
MUTE IN
OVERRIDE IN
0
- -.

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Shure Brothers Incorporated
222 HartreyAvenue
Evanston, IL60202-3696U.S.A.