Lectrosonics LE Series User Manual

*

LE8

LOGIC CONTROLLED EQUALIZER MODULE

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

* Patent No: 5,206,913

INTRODUCTION

Thank you for purchasing the Lectrosonics LE8 Logic Controlled Equalizer. The LE8 represents a significant
advance in equalization technology. The LE8, when used in an automatic Modular Audio Processor system,
provides an economical solution to the problem of multiple microphone equalization and notch filtering. Each of up
to eight microphones may be equalized using a four band equalizer. In addition, three variable frequency notch
filters are available for each microphone. This allows all microphones to be individually optimized for best quality
sound, and the feedback frequencies that are unique to each microphone position may be eliminated.

The heart of the LE8 is a sophisticated microprocessor, which controls all functions of the digitally programmed EQ
and notch filters. The microprocessor also reads all user accessible controls to provide user interface. When a
microphone becomes active, the appropriate EQ curve and notch filter frequencies are loaded, into the digitally
programmed filters in the LE8. Since the filters in the LE8 are "time-shared" between all microphones, very
sophisticated filtering can be provided at a reasonable cost.

TABLE OF CONTENTS

INTRODUCTION .......................................... 1

GENERAL TECHNICAL DESCRIPTION .......................... 2

EQUALIZATION AND NOTCH FILTERING ........................ 3

FRONT PANEL DESCRIPTION ................................ 4

REAR PANEL DESCRIPTION ................................. 5

INSTALLATION ........................................... 6

OPERATING INSTRUCTIONS ................................. 7

MULTIPLE LE8 SETUP ...................................... 8

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

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

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

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

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

The LE8 is FCC type accepted under the following Parts:

Part 15

1

GENERAL TECHNICAL DESCRIPTION

The LE8 is comprised of five major functional subsystems: the balanced input, the programmable four band
equalizer, three programmable notch filters, the balanced and floating output driver, and the microprocessor (see
block diagram below).

The input circuit of the LE8 is a fully balanced, RF filtered differential amplifier. The balanced circuit topology
provides high rejection of common mode signals. It may also be configured to accept unbalanced signals.

The balanced and floating output driver is fully RF filtered, and provides the benefits of transformer coupling without
the low frequency distortion and core saturation that plagues transformers. High current operational amplifiers are
used in the output driver, allowing long cable runs to be driven easily. The output driver may also be easily
configured for unbalanced use.

The microprocessor, a Motorola MC68HC705C8, provides all control and interface functions for the LE8. The
MC68HC705C8 has internal non-volatile memory which stores the control program for the LE8 (note that filter setup
values are stored in a separate off-chip non-volatile memory with data retention that exceeds 100 years). The
microprocessor also provides both parallel and serial ports for interfacing with filters, controls, and indicators. The
high integration density of the microprocessor allows for a much lower parts count design, thus increasing reliability.
All filters are programmed by the microprocessor as appropriate for the particular active microphone. In addition, all
user controls are scanned by the microprocessor to provide the user interface. Link In and Link Out functions are
provided so that more than one LE8 may be used in an installation.

INPUT AMPLIFIER

LOGIC INPUTS

LOGIC IN #8

LOGIC IN #7

LOGIC IN #6

LOGIC IN #5

LOGIC IN #4

LOGIC IN #3

LOGIC IN #2

LOGIC IN #1

LINK IN

LINK OUT

LINK IN/OUT

NOTCH FILTERS AND TONE CONTROLS

4 BAND

PROGRAMMABLE

TONE CONTROL

EEPROM
MEMO RY

3 NOTCH FILTERS

PROGRAMMABLE

50-5KHz

8 LINES

SERIAL/PARALLEL

CONVERTER

NOTCH FILTER DATA LATCH

SERIAL DATA OUT (S DO)

MEMO RY

LATCH

SERIAL CLOCK (SC)

MICROPROCESSO R

MICROPROCESSOR AND NON-VOLATILE MEMORY

Figure 1 - LE8 Block Diagram

TONE CONTROL
DATA LATCH

USER CONTROLS

ROTARY ENCODER

NOTCH/E Q DISPLAY L ATCH

ACTIVE LOGIC IN DISPLAY LATCH

FUNCTION LED DISPLAY LATCH

OPERATE

NEW SETTING

ACTIVE

BYPASS

STORE SETTING

NOTCH

#1

NOTCH

#2

NOTCH

#3

TREBLE

MID TREBLE

MID BASS

BASS

ADJUST

OUTPUT AMPLIFIER

NOTCH

FREQUENCY

EQ LEVEL

DISPLAY

ACTIVE

LOGIC
INPUT

DISPLAY

FUNCTION

LED

DISPLAY

USER DISPLAY

2

EQUALIZATION AND NOTCH FILTERING

FOUR BAND PROGRAMMABLE EQUALIZER

The four band programmable equalizer contains both low and high frequency shelving filters, as well as mid bass
and mid treble bandpass type filters. The low frequency (bass) filter hinge frequency (the frequency at which cut or
boost begins) is 1 kHz. The mid bass center frequency is 300Hz, and the Q of the filter is 0.33. The mid treble
center frequency is 3 kHz, and the Q of the filter is also 0.33. The high frequency (treble) filter hinge frequency is

1.2 kHz. All filters can be adjusted for 10dB of cut or boost. The LE8 uses one filter set with programmable
parameters (instead of eight separate filter sets) to implement the tone controls and notch filters. The filter set is
"time-shared" between up to eight mics. This time sharing is accomplished using the logic outputs from the AP4 or
EP4 module to signal which microphone is active at any time. The filter parameters associated with the active mic
are then loaded into the programmable filter. Needless to say, only one mic at a time may be equalized. When
two or more mics are active, the mic which activates the highest number Logic In on the LE8 will have its filter
parameters loaded. For instance, if mics 2 and 4 were both on, the filter parameters for mic 4 would be loaded.

BASS

+10 dB

+5 dB

0 dB

-5 dB

-10 dB

Hz Hz Hz kHz kHz kHz

MIDBASS

MIDTREBLE TREBLE

201011004010

Figure 2 - LE8 Tone Control Curves

NOTCH FILTERS

The three programmable notch filters are of the fixed depth, variable frequency type. Notch depth is 12dB, and the
notches are 1/7 of an octave wide. The filters are designed to be easily tunable, while being completely inaudible.
The center frequency can be varied from 50Hz to 5kHz. Frequency resolution from 50Hz to 500Hz is 1.76Hz, and
resolution from 500Hz to 5kHz is 19.4Hz.

12

ROOM RESPONSE WITH

RINGING

6

dB 0

-6
REQUIRED NOTCH

FILTER

ROOM RESPONSE
AFTER NOTCH
FILTERING

-12
20 200 2K 20K

FREQUENCY IN HERTZ

Figure 3 - LE8 Notch Filter Example

3