AKG AS 8 TC User Manual

AS8/AS8TC

8 Channel Automatic Matrix Mixer

OPERATING INSTRUCTIONS

and trouble-shooting guide

INTRODUCTION

The AKG AS8 Automatic Microphone Mixer is an 8 channel, single rack space audio mixer. Using the unique Adaptive Level Proportional mixing algorithm, the automatic action is inaudible and simple to set up. The AS8 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 AS8 has an RS-232 port for remote setup or control by a computer or other RS232 compatible controller. More than one AS8 may be coupled together when applications call for more than 8 channels.

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

GENERAL TECHNICAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

FRONT PANEL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

REAR PANEL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

FCC PART 15 NOTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

OPERATING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

REMOTE LEVEL CONNECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

SERVICE AND REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

RETURNING UNITS FOR REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

SERIAL CABLE WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

AMX CABLE WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

AMX Programming Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

SERIAL PORT COMMANDS AVAILABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back cover

GENERAL TECHNICAL DESCRIPTION

The AS8 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 AS8. 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.

Figure 1 shows the simplified block diagram of the AS8. 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 AS8 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 AS8 to be controlled either by a computer or a dedicated control system (such as the AMX or Crestron systems).

ΣΣ

MAIN IN 1

MIX MINUS OUT 2

AUTO MIX 3 LOG IN

MAIN OUT 1

MIX MINUS IN 2

AUTO MIX 3 LOG OUT

68HC705

SERIAL

EEPROM

MAIN

LEVEL

Compressor/Leveller

Gain Reduction Display

12 dB

9 dB

6 dB

3 dB

EXPANSION IN

EXPANSION OUT

MAIN OUTPUT

RS-232 OUT RS-232 IN

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

MIC

PREAMP

GAIN

0 dB (LINE) +30 dB (MIC) +50 dB (MIC)

A/D

CONV

TO uP

CHANNEL LEVEL

Compressor/

Leveller

Threshold

AUDIO

VCA

SPEECH

FILTER

CHAN ON

LOG

CONVERTER

From CH1 – From CH2 – From CH3 – From CH4 – From CH5 – From CH6 – From CH7 – From CH8 –

1 OF 8 INPUT CHANNELS

HI LO

Tone Control AS8-TC Only

TO A/D CONVERTER

To CH1 – To CH2 – To CH3 – To CH4 –

A/D

CONV

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

AS8 BLOCK DIAGRAM

INSTALLATION

Installing the AS8 properly is simple, and only requires attention to a few issues. The AS8 should be used in a grounded metal rack. If only one AS8 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 AS8s are used together, the first AS8 (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 AS8s should be in the Slave mode. Figure 2 shows the correct interconnection for multiple AS8s.

Master

Switch in MASTER Position

Slave

Switch in SLAVE Position

Slave

Switch in SLAVE Position

INTERCONNECTING MULTIPLE AS8s

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).

FRONT PANEL DESCRIPTION

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.

MAIN SECTION

MAIN LEVEL - Controls the overall output level of the AS8. If multiple AS8s are used together, only the Main Level control

of the last (i.e. Master) AS8 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 will not affect the amount of gain reduction.

before the Main Level control. This means that adjustments of the Main Level control

COMPRESSOR/LEVELLER GAIN REDUCTION METER - Shows the instantaneous amount of gain reduction applied by the compressor/leveller system.

AS8 FRONT PANEL

AS8TC FRONT PANEL

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.

AS8 REAR PANEL

+ 12 hidden pages