Lectrosonics AM8, AM8TC Instruction Manual
AM8 and AM8TC
8 Channel Automatic Mixer
INSTRUCTION MANUAL
Fill in for your records:
Serial Number:
Purchase Date:
Rio Rancho, NM, USA
www.lectrosonics.com
AM8
Introduction
The AM8 Automatic Microphone Mixer is an 8 channel, single rack space audio mixer. Using Lectrosonics’
unique Adaptive Level Proportional mixing algorithm,
the automatic action is inaudible and simple to set up.
The AM8 offers remote control of all channel levels and
the master level. In addition, a sophisticated compressor/leveller is included for dynamic range control of
the audio program material. The AM8 has an RS-232
port for remote setup or control by a computer or other
RS-232 compatible controller. More than one AM8 may
be coupled together when applications call for more
than 8 channels.
Table of Contents
Introduction .............................................................................................................................................................................................2
Table of Contents ...................................................................................................................................................................................2
General Technical Description ..............................................................................................................................................................3
Installation ...............................................................................................................................................................................................4
Front Panel Description .........................................................................................................................................................................5
Channel Section ....................................................................................................................................................................................5
AM8 Front Panel ................................................................................................................................................................................5
AM8TC Front Panel ........................................................................................................................................................................... 5
Main Section .........................................................................................................................................................................................5
Rear Panel Description ..........................................................................................................................................................................6
AM8 Rear Panel ................................................................................................................................................................................6
Remote Level Control Connector Pinout ...............................................................................................................................................7
FCC Part 15 Notice ...............................................................................................................................................................................7
Operating Instructions ...........................................................................................................................................................................8
Remote Level Connections ...................................................................................................................................................................9
Troubleshooting ....................................................................................................................................................................................10
Service and Repair ...............................................................................................................................................................................11
Returning Units for Repair ..................................................................................................................................................................11
Specifications .......................................................................................................................................................................................12
Serial Cable Wiring Diagrams ..............................................................................................................................................................13
AMX Programming Notes ...................................................................................................................................................................13
Serial Port Commands Available ........................................................................................................................................................14
General Device Commands ................................................................................................................................................................15
Channel Levels and Attenuation Commands ......................................................................................................................................15
Remote Attenuation Commands .........................................................................................................................................................16
Compressor/Leveller Commands ........................................................................................................................................................17
Auto/Direct Mode Commands .............................................................................................................................................................18
2
LECTROSONICS, INC.
General Technical Description
The AM8 uses a straightforward analog signal path to provide excellent audio performance. This is coupled with a
sophisticated microcontroller to implement both the automatic mixing and the compressor/leveller algorithms. The
Adaptive Level Proportional automatic mixing algorithm
is used by the AM8. This algorithm uses the signal level
pattern at the microphones to derive a pattern of channel
gains. For instance, if only one microphone channel is
being spoken into, its level is dominant and that channel
gets most of the system gain, while all other channels are
turned down. If more than one microphone is active, they
share system gain according to their relative levels. A
“skewing” function gives some advantage to microphones
which are active over time, to minimize interruptions from
transient noise at other microphones. Since each channels’ gain is apportioned continuously based on its relative level, no abrupt gain changes are made. This makes
the automatic action virtually inaudible.
The Compressor/Leveller function uses a combination of the short-term and long-term signal dynamics to
determine the optimum amount of gain reduction in any
situation. The effect of the function is to control both the
average program level (for consistent long-term sound
system level) and to minimize any large short-term deviations. The gain reduction function is gated, which means
that there are no noise ups associated with program
signal pauses.
8 Channel Automatic Mixer
Figure 1 shows the simplified block diagram of the AM8.
The microphone preamp is a low-noise discrete design,
which is extensively RF protected. The preamp has
three gain settings. The 0dB setting allows an input to
accept line level signals, while the +30dB and +50dB
gain settings accommodate both low and high sensitivity
microphones. 15V Phantom power is provided for each
channel, and is switchable. In addition, each channel
may be switched into either the Direct (always on) or Auto
mode.
Following the Channel Level control, the audio signal
passes through a high quality Voltage Controlled Amplifier
(VCA). This VCA, controlled by a signal from the system
D/A converter, is used to implement gain control for the
automatic mixing function, as well as the remote level
function. A Channel On LED indicates which channels
are currently active.
Signals from the Expansion In and Expansion Out connectors allow multiple AM8 mixers to be combined if more
than 8 channels are necessary for the application. In addition, a Mix Minus signal is available which allows easy
interfacing to teleconferencing hybrids.
An RS-232 port is available to allow many of the functions of the AM8 to be controlled either by a computer or
a dedicated control system (such as the AMX or Crestron
systems).
DIR OUT
MIC IN +
MIC IN -
MIC GND
Remote Level CH1
Remote Level CH2
Remote Level CH3
Remote Level CH4
Remote Level CH5
Remote Level CH6
Remote Level CH7
Remote Level CH8
Remote Level Master
Auto Mix Log In
DIRECT/AUTO
PHANTOM POWER
+5V
+15V
TO uP
MIC
PREAMP
PREAMP GAIN
0dB (LINE)
+30dB (MIC)
+50dB (MIC)
A/D
CONV
CHANNEL LEVEL
Compressor/
Leveller
Threshold
AUDIO
VCA
SPEECH
FILTER
1 OF 8 INPUT CHANNELS
CHAN
ON
FROM D/A
CONVERTER
LOG
CONVERTER
From CH1
From CH2
From CH3
From CH4
From CH5
From CH6
From CH7
From CH8
TO A/D
CONVERTER
CONV
AM8 Block Diagram
HI
LO
Tone Control
AM8-TC
Only
A/D
To CH1
To CH2
To CH3
To CH4
To CH5
To CH6
To CH7
To CH8
FROM
OTHER
CHANNELS
D/A
CONV
Dir/Auto CH1
Dir/Auto CH2
Dir/Auto CH3
Dir/Auto CH4
Dir/Auto CH5
Dir/Auto CH6
Dir/Auto CH7
Dir/Auto CH8
SERIAL DATA LINK
MIX MINUS OUT
MIX MINUS IN
68HC705
uC
SERIAL
EEPROM
MAIN IN
AUTO M IX
LOG IN
MAIN OUT
AUTO M IX
LOG OUT
MAIN
LEVEL
Compressor/Leveller
Gain Reduction Display
1
2
3
1
2
3
12dB
9dB
6dB
3dB
EXPANSION
IN
EXPANSION
OUT
MAIN
OUTPUT
RS-232 OUT
RS-232 IN
Rio Rancho, NM
3
AM8
Installation
Installing the AM8 properly is simple, and only requires
attention to a few issues. The AM8 should be used in
a grounded metal rack. If only one AM8 is being used,
it should be placed in the Master mode, using the rear
panel switch. Erratic performance will result if the unit
is in the Slave mode, but no damage will be done to the
unit. Proper operation will be restored when the unit
is switched to the Master mode. If multiple AM8s are
used together, the first AM8 (i.e. the one with Expansion
In port used but not the Expansion Out port) should
be switched to the Master mode, while all other AM8s
should be in the Slave mode. Figure 2 shows the correct interconnection for multiple AM8s.
Microphone connections should be made with good
quality braid or foil shielded twisted pair. The shield
should be used for the ground (Pin 1) connection. If an
unbalanced signal is used, the unbalanced signal lead
should be connected to the “+” input terminal, while the
unbalanced ground lead should be connected to both
the “-” and ground terminals of the input connector.
Output connections to the Main Out connector can be
made balanced or unbalanced. If an unbalanced connection is desired, simply connect the unbalanced signal lead to the “+” output terminal, and the unbalanced
ground lead to the output ground terminal. Leave the “-”
output terminal unconnected.
Access to the Remote Level Control port is accomplished using the DB-15 connector (supplied).
PWR
EXPANSION
IN
M
S
A
(CH40)
L
S
A
T
OUT IN
RS232
V
E
20 VAC
E
Switch in
MASTER Position
Switch in
SLAVE Position
Switch in
SLAVE Position
R
PWR
EXPANSION
M
IN
S
A
(CH40)
L
S
A
T
IN
OUT
V
E
20 VAC
E
R
PWR
EXPANSION
IN
M
S
A
(CH40)
L
S
A
T
OUT
IN
V
E
20 VAC
E
R
RS232
RS232
Master
Slave
Slave
Interconnecting multiple AM8s
Switch in
MASTER Position
Switch in
SLAVE Position
Switch in
SLAVE Position
PWR
EXPANSION
IN
M
S
A
(CH40)
L
S
A
T
OUT IN
RS232
V
E
20 VAC
E
R
PWR
EXPANSION
IN
M
S
A
(CH40)
L
S
A
T
IN
OUT
V
E
20 VAC
E
R
PWR
EXPANSION
IN
M
S
A
(CH40)
L
S
A
T
IN
OUT
V
E
20 VAC
E
R
Master
RS232
Slave
RS232
Slave
4
LECTROSONICS, INC.
Front Panel Description
8 Channel Automatic Mixer
Channel Section
CHANNEL LEVEL - Controls the relative signal level of
each channel. Normal operation of the Channel Level
control is from about the 10 o’clock position to the 2
o’clock position.
CHANNEL ON LED - Gives an indication as to which
channels are active.
LF - (TC version only) Adjusts the low frequency response of the channel.
HF - (TC version only) Adjusts the high frequency
response of the channel.
AM8 Front Panel
ON
LEVEL
CHANNEL 1
ON
LEVEL
CHANNEL 2
ON
LEVEL
CHANNEL 3
ON
LEVEL
CHANNEL 4
ON
LEVEL
CHANNEL 5
ON
LEVEL
CHANNEL 6
ON
CHANNEL 7
Main Section
MAIN LEVEL - Controls the overall output level of the
AM8. If multiple AM8s are used together, only the Main
Level control of the last (i.e. Master) AM8 will be operational.
COMPRESSOR/LEVELLER IN/OUT - Enables or disables the compressor/leveller function.
COMPRESSOR/LEVELLER THRESHOLD - Sets the
signal level above which the Compressor/leveller is active. Note that the Threshold level is measured before
the Main Level control. This means that adjustments of
the Main Level control will not affect the amount of gain
reduction.
COMPRESSOR/LEVELLER GAIN REDUCTION METER - Shows the instantaneous amount of gain reduc-
tion applied by the compressor/leveller system.
5
6
4
7
3
ON
LEVEL
LEVEL
CHANNEL 8
8
2
9
1
10
MAIN
LEVEL
GAIN
REDUCTION
12 9 3
THRESHOLD
-40
COMP / LEVEL
-20
-10-30
IN OUT
0
POWER
AM8TC Front Panel
LF
HF LF HF LF HF LF HF LF HF LF HF LF HF LF HF
ON
CHANNEL 1
LEVEL
ON
CHANNEL 2
LEVEL
ON
CHANNEL 3
ON
ON ON ON ON ON
LEVEL
CHANNEL 4
LEVEL
ON
CHANNEL 5
LEVEL
ON
CHANNEL 6
LEVEL
ON
CHANNEL 7
LEVEL
ON
CHANNEL 8
LEVEL
5
6
4
7
3
8
2
9
1
10
MAIN
LEVEL
GAIN
REDUCTION
129 3
COMP / LEVEL
THRESHOLD
-20
-40
-10-30
IN OUT
0
POWER
Rio Rancho, NM
5
AM8
Rear Panel Description
MIC/LINE INPUTS 1-8 - Accepts balanced or unbalanced signal. Fully balanced differential input, RF
filtered.
DIR OUT - Provides a line level signal from each individual channel. The direct output is a post-VCA signal.
Any attenuation from the auto mixing process, compressor/leveler system or remote attenuation will be reflected in the direct out signal. This provides versatility for
different mixing applications such as distributed overhead speaker systems. This 100 Ohm output provides
a +20dBu max signal into a high impedance load.
Note: The DIR OUT shares a ground with the
MAIN OUT.
Don’t use the CHANNEL IN grounds for the DIR
OUT!
When connecting to other equipment, the ground
connection of the MAIN OUT will also be adequate
for all the direct outputs. A separate ground
connection is not needed for each direct out.
FUNCTION SELECTION SWITCHES 1-8 - Allow various functions of the input channels to be set.
Dip switch 1 chooses the channel mode. Auto mode
(down position) sets operation to automatic, with channel gain determined by its signal level relative to other
microphones. When a channel is set to Direct, its signal
will affect the levels of other channels set to Auto, but it
will not be affected by other channels (no NOM attenuation will occur on a channel set to Direct). Note, however, that the Remote Level control feature functions
regardless of the setting of the Auto/Direct mode switch.
Dip switch 2 turns +15V phantom power on (down position) or off (up position).
Dip switches 3 and 4 set the gain of the input preamplifier. 0dB gain, for line level sources, is set when
switches 3 and 4 are in the up position. 30dB gain, typically for high output (electret) microphones, is set when
switch 3 is in the up position and switch 4 is in the down
position. 50dB gain, used for low output (dynamic)
microphones, is set when both switches are in the down
position.
MAIN OUT - Provides a balanced system output. The
Main Out may also be used in an unbalanced mode by
connecting the “+” terminal of the Main Out to the signal
lead of the unbalanced device, and the ground terminal
of the Main Out to the ground of the unbalanced device.
Do not connect the “-” terminal of the Main Out.
REMOTE LEVEL CONTROL - Allows remote control
of both channel levels and the master level. Either 10K
ohm linear pots or an adjustable DC control voltage
may be used. The volume control action is internally
audio scaled in software. This gives an “audio-taper”
characteristic to a linear pot. Approximately 15dB of
attenuation happens for the first half of pot rotation, with
the rest of the attenuation (to full off) happening in the
second half of pot rotation. When using a DC control
voltage, the control constant is .167V/dB (or 6dB/V)
from 0V to 5V. At 5V, the channel is turned completely
off. The control voltage should not exceed 5V. Below is
a listing of the 15 pins on the Remote Level control port
and their functions.
AM8 Rear Panel
PWR
IN
EXPANSION
(CH40)
M
OUT
A
S
S
L
20 VAC
T
A
E
V
R
E
6
DIRECT
OFF
AUTO
LECTROSONICS, INC.
LecNet
(RS232)
REMOTE LEVEL
CONTROL
IN
MAIN OUT
+ –
CH8 IN
DIR
+
–
1 2 3 4 1 2 3 4 1 2 3 4
OUT
CH MODE
CH7 IN
ON
1
3 4
2
PHANTOM
0dB GAIN (LINE) +30dB GAIN (ELECTRET) +50dB GAIN (DYNAMIC)
CH6 IN CH5 IN CH4 IN CH3 IN CH2 IN CH1 IN
DIR
+
–
+
OUT
–
3 4 3 4
DIR
+
1 2 3 4 1 2 3 4
OUT
DIR
–
OUT
DIR
+
–
OUT
DIR
+
–
1 2 3 4 1 2 3 4
OUT
US PATENT NUMBER 5,414,776
DIR
+
–
1 2 3 4
OUT
DIR
+
–
OUT
LECTROSONICS, INC.
Loading...