Shure SE30-2E User Manual

MODELS SE30 & SE30-2E

GATED COMPRESSOR/MIXER

OPERATING AND SERVICE MANUAL

Copyright 1981, Shure Brothers Inc.

27A8025 (AK) (90A8103)

Printed in U.S.A.

Table of Contents

List of Illustrations

WARNING

To reduce the risk of fire or electric shock, do not
expose this appliance to rain or extreme moisture.

DESCRIPTION

The Shure Model SE30* Gated Compressor/Mixer is a

high-quality gated memory compressor combined with a
self-contained, portable, three-input mixer and remote
amplifier designed specifically for professional appli­cations in AM, FM, and TV broadcasting, film, tape, and
disc recording, CATV, and sound reinforcement. An acces­sory cover is available (A100A) which covers the front
controls and provides a handle, as well as a support stand
for tilting the front panel upward for easier vision of con­trols during operation. An accessory rack-mount kit
(A100B) is available for permanently installed program
compressor applications.

Features include:

Three transformer coupled inputs, switchable, low im-

pedance microphone or line level.
Individual feedback-type level controls for each input
to provide maximum clipping and minimum noise levels

over a wide dynamic range.
Low-frequency roll-off switch for each input.
Input 1 switchable on front panel to low-distortion, 1 kHz

tone oscillator.
Mix bus jack for adding additional mixers for additional

input capability.

Feedback-type output control (located after compres­sion attenuator) to provide optimum output noise level

regardless of setting.
Binding posts for balanced 600-ohm line output plus

professional three-pin male audio connector switchable
from line to microphone level output.
Two-level headphone monitor jack for 600 to 2,000 ohm

headphones.

Compression range of 40 dB, with a slope or compres­sion ratio of approximately 10 to 1 in the normal oper­ating range.

Gated Memory with a meter indicator to minimize

“pumping.”

True average-responding compression to maximize
output level regardless of peak-to-average ratio of pro­gram material, either music or speech. (Peak responding

circuit to reduce gain rapidly for significant increases in

the input signal.)

Response rate (averaging time constant) adjustment on

front panel to compensate for various types of program

material.
Extremely low distortion, noise, and RF susceptibility,
with wide, flat frequency response at any level of com-

pression.

+18 dB output capability.

Dual-scale illuminated meter for output VU indication
or dB compression.

+4 or +6 dBm range switch for VU meter.
AC or battery operation with built-in battery supply using

readily available 9-volt batteries.

*Unless otherwise noted, information applies to both SE30 and SE30-2E models.

(Model SE30 shown)

Automatic, noiseless switch-over to batteries in the
event of ac line failure.
Battery-check switch to check battery condition with­out interrupting operation of unit.
Detachable ac line cord.
Auxiliary meter lamp operates independently from a “D”
type dry cell for meter illumination when ac power is
not available.
Auxiliary high level input and output on phone jacks for
special applications (approximately --20 dBV).
Microphone and line inputs and outputs phase indi­cated.
Stereo parallel jack for synchronizing the compression
circuits of two units.

Listed by Underwriters’ Laboratories and Canadian

Standards Association (SE30 only).

GUARANTEE

This Shure product is guaranteed in normal use to be
free from electrical and mechanical defects for a period
of one year from date of purchase. Please retain proof of
purchase date. This guarantee includes all parts and
labor. This guarantee is in lieu of any and all other guar­antees or warranties, express or implied, and there shall
be no recovery for any consequential or incidental
damages.

Carefully repack the unit and return it prepaid to:

If outside the United States, return the unit to your dealer
or Authorized Shure Service Center for repair. The unit
will be returned to you prepaid.

SHIPPING INSTRUCTIONS

Shure Brothers Incorporated
Attention:
1501 West Shure Drive
Arlington Heights, Illinois 60004

Service Department

SPECIFICATIONS

Frequency Response:

Flat ±2 dB, 30 to 20,000 Hz.

Gain:

(Below compression threshold, output terminated,
Line 600 ohms, Microphone 150 ohms, Aux. 47 K
ohms.)

Noise:

Equivalent input noise: -129.5 dBV maximum (Micro­phone input, 150 ohms, 20 kHz equivalent noise band­width with lower cutoff frequency of 300 Hz, at full
gain.)
Equivalent input hum and noise: -126 dBV maximum
(same as above, but lower cutoff frequency of 20 Hz.)
Output: (Input controls minimum):

3

SPECIFICATIONS (Cont’d)

Distortion:

Below compression threshold, under 0.5% THD at
+15 dBm output, 30-20 kHz.
At 10 dB compression, under 1% THD at +15 dBm
output, Response Rate set to 7, 50-20 kHz. With Re­sponse Rate set to 0 (fast), under 2% THD at 50 Hz.
At 1 kHz, under 0.8% THD at any level of compres-

sion from 0 to 40 dB.

Compression Ratio:

8:1 minimum from 10 to 20 db compression.
5:1 minimum from 10 to 30 dB compression.

Compression Threshold:

Microphone: -96 dBV at maximum input gain.
Line: -48 dBV at maximum input gain.

Recovery Time:

Time required for gain to reach 90% of its final value
when input is reduced by 10 dB from 20 dB com-

pression is adjustable from approximately 100 milli­seconds to 8 seconds by Response Rate control.

Attack Time:

Same as recovery time for increases up to 12 dB.

Maintains peak to average ratio at 12 dB (sine-wave
equivalent).

Gated Memory:

In “hold” condition, less than 20 dB gain recovery
after 1 minute.

Tone Oscillator:

1.0 kHz ± 10%, THD under 1%.

Input Control Interaction:

Under 0.1 dB with any combination, mix bus jack
open. Under 1.5 dB with mix bus terminated in 50 K
ohms or less.

Lo-cut Filters:

-6 dB per octave, 3 dB down at approximately 150
Hz.

4

Input/Output:

Mix bus:

Impedance 3.9 K ohms. Gain (through 3.9 K ohms)
from mix bus to line output, is 63 dB. Gain from micro­phone input to mix bus is 26 dB (terminated in 3.9 K
ohms). Overall gain drops by 10 dB with mix bus
terminated.

Circuit Protection:

Shorting the outputs, even for prolonged periods, will
not damage the unit.
Microphone inputs will not be damaged by signals
of up to 3 volts.

Temperature Range:

Operating:

-18°C (0°F) to 57°C (135°F).

Storage:

-29°C (-20°F) to 74°C (165°F).

Weight:

9 Ibs., 13½ oz. (4.5 kg) with batteries and line cord.

Operating Voltage:

AC Operation:

108-132 volts, 50/60 Hz (SE30 only).
108-132 or 216-264 volts, 50/60 Hz (SE30-2E
only).

DC Operation:

30 volts ± 20%.

SPECIFICATIONS (Cont’d)

Battery Operation:

27 volts nominal, 21.5 volts minimum. Current con­sumption at 27 volts, 10 ma. at no signal; 12 ma. at
20 dB compression and +8 dBm output.

Battery Life:

Estimated 80 hours at 4 hours use per day.

Battery Complement:

9 volt, 6 Eveready type 222 or 216 or equivalent.

One heavy-duty 1.5 volt “D” size cell, Eveready type
D99 or equivalent to power Aux. Light approximately
8 hours continuously.

CONTROL AND CONNECTOR

DESCRIPTIONS (See Figure 2)

Input Controls: Control gain of individual input stages

(1)

to adjust relative levels between inputs and to adjust

amount of compression. Input 1 (1A) also controls
Tone Oscillator level when used.
Lo-cut Filter Switches: Low frequency response is re-

(2)

duced by 6 dB per octave below approximately 150 Hz
with switch set to IN. Input 1 switch (2A) also activates
tone oscillator.
Output Control: Controls output level when unit is

(3)

used in compression or acts as a master gain control
when compression is disabled. May be used for over­all fading. Does not affect amount of compression.

VU Range Switch: Selects meter sensitivity so 0 VU

(4)

indicates results from either +4 dBm or +8 dBm line

output level.

Gated Memory Indicator: Will be red when Gated

(5)

Memory is “holding” prior amount of compression

during a low input signal. Will be white whenever in-

put signal is above compression threshold, or if either

Gated Memory or compression is disabled. Illumi­nated by ac operated lamps or independent battery
operated auxiliary light.
Response Rate Control: Adjusts time constant of

(6)

compression system to compensate for different types

of program material. Generally, a faster setting (lower

numbers) results in a more constant output level but
a more audible compression effect. Setting this con­trol is a subjective matter, but the following guide­lines may be used:

Meter: Indicates either VU output level (upper VU

(7)

scale) or compression due to input signal above thres-

hold by the amount indicated (lower DB Compression
scale). VU meter isolated from dc on line output. Il­luminated by ac operated lamps or independent bat­tery operated auxiliary light.

Meter Switch: Selects function of meter for VU out-

(8)

put level or DB Compression.

Battery Check Switch: Spring-return switch overrides

(9)

Meter switch, allows checking battery condition with-

out affecting operation of unit. A reading of 0 VU indi-

cates end-of-life.

(10) Aux. Light Switch: Spring-return switch allows illu-

mination of meter and Gated Memory indicator from

internal battery.

*Designed to mate with Cannon XL series, Switchcraft A3 (Q. G.) series. or equivalent connector.

Power Switch: Controls ac, external dc and internal

(11)

battery power applied to the unit, but will not prevent
power from being drawn from the internal batteries by
a load connected to 30 Volts DC jacks (26) when
switched to OFF.

REAR PANEL

Mix Bus Jack: Phono pin jack allows adding inputs by

interconnecting to a similar jack on another SE30

or M67 Mixer.
Input Connectors: Female professional three-pin au-

(13)

dio connectors* accept balanced low-impedance mi­crophone or high-level line inputs. Wired with pins
2 and 3 “hot” and pin 1 ground.
Mic/Line Input Switches: Select either microphone

(14)

or line level input sensitivity for each input.
Aux. Line Input Jack: Three-conductor (tip, ring,

(15)

sleeve) phone jack provides a second balanced line
input for Input 1. May be used in conjunction with, or
instead of, three-pin input connector when input
switch (14A) is set to LINE. Inserting a two-conductor
phone plug will automatically unbalance the input
without otherwise affecting operation. Tip and ring
are “hot,” sleeve is ground, and tip is in phase with

pin 2 of input and output.
Output Connector: Male professional three-pin audio

(16)

connector* provides balanced output at either line
level or microphone level (50 dB below line level).
Wired with pins 2 and 3 “hot” and pin 1 ground, in

phase with input connectors.
Mic/Line Output Switch: Selects either microphone

(17)

or line level output at output connector.

Aux. Output: Two-conductor (tip-sleeve) phone jack

(18)

provides isolated unbalanced aux. level (20 dB below

line level) output, for use with tape and cassette re-

corders and power amplifiers with high level, high
impedance inputs. Tip of jack is in phase with tip of

Aux. Line Input jack (15).

Headphone Jack: Three-conductor (tip, ring, sleeve)

(19)

phone jack wired to provide two different output levels

for 600 to 2,000 ohm headphones. If a two-conductor

(tip, sleeve) phone jack is inserted partially (to the first

detent), output will be approximately .18 volts into

1,000 ohms at +4 dBm output. If the plug is inserted
fully, the voltage will be approximately .38 volts. If
stereo headphones are used, signal will appear in both

phones. The tip and ring are in phase with pin 3 of
the input and output.

Line Output Terminals: Thumbscrews for direct wire

(20)

connections to balanced line, wired in parallel with
three-pin Output connector (16) in LINE position of

switch only. Phase is indicated by pin number ref-

erences, and a ground thumbscrew is provided.

Gated Memory Switch: Will disable Gated Memory

(21)

function without affecting other operation.

Compression Switch: Will disable compression and

(22)

Gated Memory functions of the SE30, converting it to

a high-quality linear mixer and remote amplifier.

Stereo Parallel Jack: Phono pin jack allows two units

(23)

to be synchronized to compress equally the channel

sum (L + R) signal. See Service section.

Battery Compartment: Requires six readily available

(24)

O-volt batteries (Eveready type 222 or 216 or equiva-

lent) wired in series-parallel for 27 volts dc and one

heavy-duty D cell (Eveready type D99 or equivalent)

5

FIGURE 2

CONTROLS AND CONNECTORS

(25) AC Power Receptacle: Special internationally ac-

cepted connector for detachable ac line cord, three­wire with safety ground pin.

(26) 30 Volts DC Jacks:

unit from an external 30 ± 20% dc source, or for
powering external equipment (up to 5 ma) from the
batteries or ac operated power supply of the SE30.
Controlled by front-panel Power switch (11) except
that an external load will discharge the batteries with
the unit OFF. In this case, remove the Battery Com­partment (24) when unit is turned off.

(27) Voltage Selector Switch: Selects operating voltage

range of 108-132 V or 216-264 V (SE30-2E only).

May be used for powering the

GENERAL OPERATION

POWER CONNECTIONS:
AC Line Operation: Insert female end of ac line cord into

chassis power receptacle (25) and connect male plug to a
three-wire grounding ac power receptacle providing 108
to 132 V, 50/60 Hz (SE30 only). Model SE30-2E: Obtain
a suitable three-pin male plug and attach it to the line
cord. Plug should be installed by qualified service per­sonnel. (Brown lead goes to “hot” or “live” terminal, blue
lead to neutral terminal, and green/yellow lead to ground

or earth terminal.) Select the proper operating voltage

(108-132 V or 216-264 V) using the voltage selector switch
(27). Insert female end of line cord into chassis power re-

ceptacle (25) and connect male plug to a three-wire

grounding ac power receptacle providing the proper ope-

rating voltage (108-132 V or 216-264 V, 50/60 Hz).

Battery Operation: Unit will automatically operate on bat-

teries installed in Battery Compartment (24) if unit is not
supplied with ac power. Condition of the 9-volt batteries
should be checked periodically with the Batt. Check Switch
(9) and batteries should be replaced as the meter indica­tion approaches 0 VU with the unit in operation. Standby
battery condition may be checked even during ac line
operation, but an indication of +½ VU should be con­sidered as the replacement point, since the battery voltage
will drop somewhat under load. The auxiliary light D cell
may be checked by operating the Aux. Light switch (10).
If the light becomes extremely dim, promptly replace or
remove the D cell to avoid damage due to leakage.

The unit will remain operative, except for the light, regard-

less of the condition of this cell.
Automatic Switchover: If batteries are installed in Battery
Compartment (24). operating power will be supplied by
these batteries in the event that the ac line voltage drops
too low or is removed. The switchover is automatic and

noiseless.
External DC Operation: An external source of dc may be
connected to the 30 Volts DC jacks (26) to operate the

unit if ac power is not used. The SE30 will draw approxi­mately 12 ma. at 30 volts and must be operated at 30 volts

± 20%.

INPUT CONNECTIONS:
Microphones: Inputs (13) with switches (14) set to MIC.

are designed to accept signals from low impedance (25 to
600 ohms) dynamic, ribbon, or condenser microphones,
or microphone level signals such as the low impedance
microphone level output of a mixer. Inputs are balanced
(transformer coupled, mumetal shielded) and connections

are pins 2 and 3 “hot,” pin 1 ground. For unbalanced
sources, connect either pin 2 or pin 3 to ground at the

input cable connector.

High Level Signals: With switches (14) set to LINE the

(See Figure 2)

inputs (13) will accept balanced 600-ohm line signals.
Inputs are bridging (with 66 K ohm impedance) so that

higher impedance sources such as Aux. signals (up to
33 K ohms) may also be used. For such unbalanced in­puts, the signal may be applied to pin 3, with pins 1 and
2 ground. Input 1 can accept two high-level signals simul­taneously through the three-pin Input connector (13a), and
through the Aux. Line Input jack (15), which are electrically
isolated but identical in gain and impedance.

OUTPUT CONNECTIONS:
Microphone: The microphone level output is available at

the Output connector (16) when the switch (17) set to MIC.
It is used for feeding a low-impedance microphone line
or the low impedance microphone input of an associated
piece of equipment. This is a balanced output with pin 1
ground and pins 2 and 3 “hot” and in phase with the cor­responding input pins. This output is isolated and may be
used simultaneously with all other outputs appearing on
other connectors.
Line: The line output is available at the Output connector
(16) when the switch (17) is set to LINE, and at all times

at the Line Output terminals (20). These two connectors
are then wired in parallel and are provided for intercon­nection convenience for either standard three-pin audio
connectors or for wires such as a telephone twisted pair.

This is a balanced output, transformer coupled with pin 1

ground and pins 2 and 3 “hot” and in phase with the cor­responding input pins. The Line Output terminals (20) are

similarly numbered for phase indication. This output may

be used to drive impedances above 150 ohms but the VU
meter is properly calibrated for use with a 600-ohm termi-

nated line. The line output transformer will operate prop­erly with up to 100 ma. flowing through the line, permitting
the use of ordinary “dialed-up” telephone lines with dc
across them. Operation at +4 dBm output is recommended
for this use to avoid any significant increase in distortion
due to overdriving the phone line. This output is isolated
and may be used simultaneously with all other outputs ex­cept that the Output connector (16) and Line Output termi­nals (20) are wired in parallel when the switch (17) is set to
LINE.

Aux. Output: An unbalanced output 20 dB below line level

is available at the Aux. Output jack (18) for a Separate,
isolated lower level feed. The impedance is 4.3 K ohms,

suitable for driving high impedance (10 K ohms or greater)

loads, such as reel to reel or cassette tape recorders or
power amplifiers. Tip of jack is in phase with tip of Aux.
Line Input jack (15).

Headphones: The headphone output appears on the rear
panel and is designated “Headphones.” A three-conductor
phone jack is used to provide a choice of level for different
sensitivity or impedance headphones. Normally, a two-con­ductor phone plug should be used. If inserted only par­tially (to the first detent), the available voltage is approxi­mately .18 volts into 1,000 ohms with +4 dBm out of the
Line Output. With the same output conditions (+4 dBm),
the second position will provide approximately .38 volts.
These voltages are selected for normal operation with
600-ohm to 2,000-ohm headphones. Other headphone im­pedances may be used, but with a variation in the head­phone monitor level. The headphone jack is isolated from
the line output and with the headphone output shorted the
maximum change in line level output is .5 dB. If stereo
phones are used, the three-conductor plug may be inserted
completely (to second position) and output will appear in
both phones.

7

GENERAL OPERATION (Cont’d)

The “Tip” connection of the headphone plug will be in

phase with Pin 3 of all Input (13) and Output (16) connec­tors, and with the tip of the Mix Bus jack (12).

TYPICAL SET-UP AND OPERATION

A typical set-up and operation procedure is described

for remote amplifier applications, with a single input source

(microphone).

1. Connect microphone to Input 1 connector (13a) and
set Input switches (14) to MIC. Set Output Switch (17)
to LINE and connect phone line either to Output jack
(16) or Line Output terminals (20). Insert ac line cord
into ac receptacle (25) and plug cord into ac source,
unless battery operation is desired. Monitor head­phones may be connected to Headphone jack (19).

2.

Set Compressor (22) and Gated Memory (21) switches
to ON, Meter switch (8) to DB COMP, Lo-Cut switches
(2) and VU Range switch (4) as appropriate.

3. Rotate Input Control (1) and Output Control (3) full
counterclockwise to 0, and set Response Rate Control
(6) to 3, assuming a typical speech input.

4. Turn Power switch (11) ON and wait approximately 1
minute for the circuitry to stabilize. DB Comp. meter (7)
should read full scale left (line below zero on lower
scale) and Gated Memory indicator (5) should be red.

5.

Set Input 1 switch (2a) to TONE OSC. and rotate Input
1 Control (la) clockwise for a DB Compression meter
(7) reading of 10 (lower scale). Gated Memory indi­cator (5) will change to white.

6. Set Meter switch (8) to VU and rotate Output Control
(3) for a VU meter (7) reading of 0 VU (upper scale).
Tone will be heard in headphones. The signal thus ap-

plied to the line may be used for calibration of the

equipment receiving the signal.

7. Reduce setting of the Output control (3) for a meter

reading of -2 VU, and return Input 1 switch (2a) to

IN. Note setting of Output Control (3) for future use.
(This reduction in sine-wave output is made to account
for the moderate short-term output dynamic range en­countered for speech with the suggested Response
Rate control setting. A faster setting would eliminate
the need for this, but the compression would then be­come more audible.)

8. Set Meter switch (8) to DB COMP.

9. Now, with the expected average sound level entering
the microphone, set the Input 1 control (la) for an
average DB Compression meter (7) reading of ap-

proximately 10 (lower scale). This is the recommended
operating level for the SE30, since the unit will now
be able to maintain a substantially constant output
level for input reductions of 10 dB and increases of
as much as 30 dB.

10. Observe the operation of the Gated Memory indicator
(5). It should be white during speech input and change
to red during pauses between sentences and words,

indicating that the DB compression level is being
“remembered” during program lapses.

If the indicator remains white or “jitters” with no
spoken input to the microphone, it is an indication
that the acoustic background noise level at the micro-

phone is near or above the Gated Memory threshold.

The solution to this is to reduce the setting of the

Input 1 Control (1a) until the Gated Memory Indicator
(5) is consistently red without speaking into the micro­phone. The DB Compression level will then be deter­mined by the loudness of the speaker and his proximity

to the microphone. This adjustment is very important
to insure proper operation in situations having very
high background noise levels, such as sporting events
or parades.

OPERATING CONSIDERATIONS

LARGE CHANGES IN INPUT LEVEL

If the overall sound and noise levels entering the micro­phone do not significantly change from those encountered
during set-up, as indicated by a DB Compression meter
(7) reading of 0 to 20 dB, and if proper operation of the
Gated Memory indicator (15) continues, it will not be neces­sary to adjust any controls further.

If, however, large changes in the signal going into the
microphone and/or in background noise do occur, some

Input 1 control (1A) readjustment may be advisable, as
indicated by the DB Compression meter and Gated Mem­ory indicator. For example, a significant increase in back­ground noise and signal may occur during an exciting por­tion of a sporting event, such that the Gated Memory no
longer “holds” during pauses and the DB Compression
reads higher than previously indicated. A gradual reduc­tion of the Input 1 control (1a) setting will not be noticeable
to the listener, due to the automatic effect of the compres­sor, but proper action will be restored.

During a later, more subdued portion of the program, it
may become apparent that the DB Compression meter (7)
is reading near zero, and the Gated Memory indicator does
not always change to white during speaking. A gradual
increase of the Input 1 control (la) setting will then allow
operation at the proper level. Thus, during operation, after
setting the proper output level with the master gain control,
it is generally necessary only to monitor compression level
on the DB Compression meter (7) and to observe proper
action of the Gated Memory indicator (5).

Control setting changes need only be made for long­term, large changes in signal or noise levels. It is not nec­essary to “ride gain” to maintain a constant line output
level as measured by the VU meter, since that is the com­pressor’s function.

RESPONSE RATE ADJUSTMENT

The proper setting of the Response Rate control (6)
is determined by subjective factors, according to the type
of program material. Generally, a slower setting will result

in less audible compression, but a wider short-term out-

put dynamic range, that is, a less consistent output level.
Faster settings will result in a more nearly constant output
level but will make the effect of compression more audible.
The Response Rate control (6) setting may be changed
during operation for more satisfactory results if desired. A
guideline for an initial setting according to program mate­rial is: Speech-3; Popular Music-5; Symphonic Music-

7. The output leveling effect may be observed for various
settings by observing the VU meter (Meter switch (8) set to
VU), while the subjective effect is best ascertained by

listening on monitor headphones.

MULTIPLE INPUTS

Up to three microphones or input sources may be used

simultaneously with the SE30. In this case, the overall

“mixed” signal and background noise levels determine

DB Compression and Gated Memory action. For the best

results when several inputs are to be used one at a time,

only the used Input controls should be turned up. For a

8

OPERATING CONSIDERATIONS (Cont’d)

conference or conversation situation, with several micro­phones “live” but only one speaker talking at a time, each
Input control should be set so that each speaker results in
approximately the same amount of compression, observing
that the overall level is correct for proper Gated Memory
action.

SIMULTANEOUS MIXED INPUTS

With simultaneous (mixed) inputs, the compressor will
automatically maintain a constant overall output level, so
that the balance among the sources may be adjusted easily
by monitoring with headphones. Simply observe that the
DB Compression meter (7) is reading in the normal oper­ating range and that Gated Memory action is proper.

AUTOMATIC “DUCKING”

The balance between two sources may be adjusted to
produce automatic “ducking,” for example, for an an­nouncer’s voice over musical programming. In this case,
set the Input control for the music source for a low amount
of compression, such as 5 dB. Then set the announcer’s
microphone Input control for 15 dB compression when he
is speaking. When the announcer talks during music, the
SE30’s gain will be reduced by 10 dB, “ducking” the music
level below the voice level by that amount. When he stops
speaking, the music will return to full output.

ADDITIONAL INPUTS

To accommodate more inputs than three, a Mix Bus
jack (12) is provided which may be connected to a similar
jack on another SE30 or M67 Mixer. When a Mixer
with a mix bus is used in conjunction with the SE30, a
compressed output may be obtained from the SE30, and
an uncompressed output of the same mixed material will

be available from the Mixer.

Inputs may also be added by connecting the line level
or microphone level output of another mixer to one of the
SE30 inputs.

EXCESSIVE AMBIENT NOISE

Under certain conditions, such as high noise levels,
it may be impossible to adjust the Input control (1) so that
the Gated Memory can consistently discriminate between
background and program. In such a case, the Gated Mem­ory switch (21) should be set to Disable and the amount of
compression should be reduced to minimize the audible
effects of “pumping.”

In extremely severe cases, compression should not be

used at all, since the increase in background noise during

pauses will be quite unpleasant. The SE30 may then be
used as a high-quality linear mixer by setting the Comp.
switch (22) to DISABLE and setting the Meter switch (8)
to VU to monitor output level. As with any mixer it will then

be desirable to set the Input control (1) as high as pos­sible without clipping, and set the output VU level with
the Output control (7), to provide best signal-to-noise ratio.

FADING TECHNIQUE WITH COMPRESSION

Fading of inputs with a compressor must be accom­plished somewhat differently than with a linear mixer.
Since a slow reduction of input level within the compres­sion region will be compensated for by an increase in

gain, no audible fading will occur. Consequently, fading

an input down should be done rapidly, at least to the point
at which the Gated Memory changes to the “hold” state.

For overall program fades, it is desirable to use the
Output control (3), since it does not affect the amount of
compression but only the output level.

SPECIAL APPLICATION

CONSIDERATIONS

SOUND REINFORCEMENT

The SE30 may be used in sound reinforcement installa­tions, but some care must be exercised in such applica­tions. Since this compressor can only reduce its gain when
a signal exceeds its compression threshold, maximum gain
occurs with low signal levels, and the sound-reinforcement
system’s gain must be adjusted to be stable (no ringing or
howling) with no compressor gain reduction. This may be
accomplished by adjusting system gain with the SE30’s
Comp. switch (22) set to DISABLE. With proper system
adjustment, the SE30 may be used to level the sound of
a “wavering” speaker, or to prevent power amplifier over-

drive with extremely strong signals.

STEREO OPERATION

Two SE30’s may be synchronized to operate together for

stereo applications by interconnecting their Stereo Parallel

jacks (23) and performing the adjustment procedure out-

lined in the Service Section of the manual.

One unit will compress the left channel signal and the
other will compress the right channel signal, but both will
respond equally to the sum (left and right) signal to mini­mize apparent stereo image shift.

Because of the necessity of providing the two units
with a properly balanced stereo signal, it is recommended
that stereo applications be restricted to single inputs for
each channel, with mixing and balancing being accom­plished in another mixer prior to the SE30’s.

SINGLE INPUT PROGRAM COMPRESSOR

When the SE30 is used as a single line input, perma-

nently installed program compressor, it is possible to im­prove the signal-to-noise ratio by disabling two of the
inputs and thus reducing the electrical noise of the mixing
system. This modification is outlined in the Service Section.

RESPONSE RATE KNOB REMOVAL

To prevent inadvertent misadjustment of the Response

Rate control (6) the knob may be removed and the hole

filled with the plastic plug included with the SE30. This

procedure is described in the Service Section.

THEORY OF OPERATION

(See Figure 3)

Operation of the SE30 Gated Compressor/Mixer may be

explained by referring to the Functional Block Diagram,

Figure 3. The active devices in each stage, as well as other
important components, are identified by their reference
numbers, for ease of location on the Schematic Diagram
(Figure 4) and the Chassis Parts and Printed Circuit Board

Parts Placement diagrams (Figures 5 and 6). The first digit
of three-digit references indicates the printed circuit board

upon which the part is located.

INPUT-OUTPUT SIGNAL PATH

Balanced input signals entering through J1, J2, and J3
are amplified by the three transformer-coupled, variable­gain input preamplifiers. Low-level signals are applied di­rectly to the transformer primaries, and high-level (line)
signals are attenuated by balanced -48 dB resistive pads.

The Input controls are ganged, dual-section potentiometers

arranged such that a reduced control setting increases the
negative feedback around the stage, thus reducing gain
and increasing the input clipping level. Since the pream-

plifier stage gain cannot be reduced below 6 dB from its

9

FUNCTIONAL BLOCK DIAGRAM - FIGURE 3