551E and 552E Data Sheet
User’s Guide
/552E
551E
551E and 552E
Parametric Equalizers
551E
/552E
Table of Contents
Chapter 1
Introduction
1
Chapter 2
Operator Safety Summary
2
Chapter 3
Fast Set-Up
3
Chapter 4
Front Panel Controls
4
Chapter 5
Rear Panel Connections
7
Chapter 6
Operating Tips
9
Chapter 7
Applications
11
Chapter 8
Troubleshooting
13
Chapter 9
Specifications for the 551E
14
Chapter 10 Specifications for the 552E
15
Chapter 11 Warranty
16
Chapter 12 Service
17
Appendix A Adapter Wiring Examples
18
Appendix B Declaration of Conformity
19
Rev A.02, 1 January, 1998
Symetrix part number 53551E0A02
Subject to change at our whim and fancy without notice.
©1998, Symetrix, Inc. All right reserved.
Symetrix is a registered trademark of Symetrix, Inc.
Mention of third-party products is for informational
purposes only and constitutes neither an endorsement nor
a recommendation. Symetrix assumes no responsibility
with regard to the performance or use of these products.
Under copyright laws, no part of this manual may be
reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying,
scanning, recording or by any information storage and
retrieval system, without permission, in writing, from
Symetrix, Inc.
i
Symetrix Inc.
6408 216th St. SW
Mountlake Terrace, WA 98043 USA
Tel (425) 778-7728
Fax (425) 778-7727
Email symetrix@symetrixaudio.com
Website www.symetrixaudio.com
Chapter 1
Introduction
Thank you for choosing the 551E Five Band
Parametric Equalizer or the 552E Dual Five Band
Parametric Equalizer. [With the exception of
Chapters 9 and 10, all text in this User's Guide is
applicable to both the 551E and 552E. For brevity
we will use the name “551E/552E” to refer to both
units.] Both models deliver superior fidelity,
flexibility, power, and precision through an
unbeatable combination of wide dynamic range,
ultra-low distortion, minimal phase shift and
ringing, easy to use controls and rock-solid
construction. The 551E/552E is a leap forward in
affordable equalizer technology.
station’s signature sound are the kinds of tasks
that are well within the 551E/552E’s capability.
As for sonic quality... Our proprietary topology
delivers extremely low-noise audio performance
- the kind you would normally expect only from
a much more expensive unit. We have also
included a servo balanced output that completely removes all DC offset, and directcoupled input and output stages that maximize
the 551E/552E’s low-frequency response while
minimizing noise and distortion.
Inside and out, the 551E/552E is designed to
stand up to the worst abuse your roadies can
dish out. The tour-worthy all steel chassis
houses a double-sided fiberglass circuit board a significant advantage over the more common
phenolic PCBs. Gold-plated XLR connectors, a
bypass relay, and high precision components
ensure accuracy and reliability. Last, but not
least, the 551E/552E has an internal power
supply with a detachable cord.
The five, fully parametric EQ bands are identical
in function. Each delivers up to 12 dB of boost
and 20 dB of cut, has an adjustable bandwidth
control (from .05 octaves to 2 octaves), and a
frequency control range from 10 Hz to 20 kHz.
Use each band anywhere in the audio spectrum,
not just the pre-selected ranges you find on most
equalizers. This can be very useful in sound
system work, among other things. For instance,
you can use three bands to correct low frequency
problems and still have two bands left for
midrange and high frequency work.
Feel free to contact us if you have questions,
comments or suggestions at:
You will find the 551E/552E is just as useful for
recording and broadcast applications. The
wide control range allows you to perform
creative as well as corrective equalization.
Sweetening vocal tracks, getting that huge drum
sound, disk mastering, or perfecting your radio
LOW CUT
U
22
FREQUENCY
(Hz)
18K
115
8
+15
6
3K
260
350
850
100
2K
Fax
(425) 778-7727
Email
symetrix@symetrixaudio.com
Website
www.symetrixaudio.com
Office hours - 8:00am - 4:30pm Pacific Time
CUT/BOOST
(dB)
1.0
0
FREQUENCY
(Hz)
350
850
100
2K
FREQUENCY
(Hz)
BANDWIDTH CUT/BOOST
(dB)
(OCT)
0
1.0
350
850
100
2K
BAND 5
BAND 4
BAND 3
BAND 2
BANDWIDTH
(OCT)
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
FREQUENCY
(Hz)
350
850
100
2K
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
BANDWIDTH
(OCT)
FREQUENCY
(Hz)
350
850
100
2K
CUT/BOOST
(dB)
0
1.0
42K
5K
-15
POWER
HIGH CUT
50
(425) 778-7728
/552E
INPUT
LEVEL (dB)
ACTIVE
BYPASS
FIVE BAND
PARAMETRIC
EQUALIZER
BAND 1
CUT BANDS
SYSTEM
551E
Phone
1.5K
140
X1
X10
X0.1
65K
.05
2.0
-20
+12
X1
X10
X0.1
1.5K
140
.05
2.0
-20
+12
1.5K
140
X1
X10
X0.1
.05
2.0
+12
-20
X1
X10
X0.1
1.5K
140
.05
2.0
-20
+12
X1
X10
X0.1
1.5K
140
.05
2.0
-20
+12
CLIP
TYPICAL BALANCED CONNECTIONS
TIP = HIGH(+) = PIN 2
RING = LOW(-) = PIN 3
SLEEVE = GND = PIN 1
THIS UNIT CONTAINS
NO USER SERVICEABLE
PARTS. REFER SERVICING
TO QUALIFIED SERVICE
PERSONNEL.
AC INPUT
15 WATTS
MAXIMUM
1
OUTPUT
INPUT
INPUT
BALANCED/
UNBALANCED
1
3
551E FIVE BAND PARAMETRIC EQUALIZER
BALANCED/
UNBALANCED
MANUFACTURED IN
LYNNWOOD, WA, USA
SLEEVE
RING
TIP
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
OUTPUT
2
2
3
BALANCED
BALANCED
551E Front and Rear panels
CUT BANDS
CHANNEL 1
INPUT
LEVEL (dB)
LOW CUT
U
ACTIVE
BYPASS
22
DUAL
FIVE BAND
PARAMETRIC
EQUALIZER
350
5K
-15
FREQUENCY
(Hz)
18K
+15
6
3K
260
BAND 2
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
850
FREQUENCY
(Hz)
350
BAND 3
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
850
FREQUENCY
(Hz)
350
BAND 4
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
850
FREQUENCY
(Hz)
350
BAND 5
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
850
BANDWIDTH
(OCT)
FREQUENCY
(Hz)
350
CUT/BOOST
(dB)
0
1.0
850
42K
115
8
552 E
BAND 1
HIGH CUT
50
140
X1
X10
X0.1
65K
1.5K
100
.05
2K
2.0
-20
+12
X1
X10
X0.1
140
1.5K
100
.05
2K
2.0
+12
-20
X1
X10
X0.1
140
1.5K
100
.05
2K
2.0
-20
+12
X1
X10
X0.1
140
1.5K
100
.05
2K
2.0
-20
+12
X1
X10
X0.1
140
1.5K
100
.05
2K
2.0
-20
+12
CUT BANDS
CHANNEL 2
INPUT
LEVEL (dB)
LOW CUT
U
ACTIVE
BYPASS
22
50
6
260
+15
FREQUENCY
(Hz)
18K
5K
350
850
100
2K
BAND 3
BAND 2
BANDWIDTH
(OCT)
FREQUENCY
(Hz)
CUT/BOOST
(dB)
0
1.0
350
850
100
2K
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
FREQUENCY
(Hz)
0
1.0
350
850
100
2K
BAND 4
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
FREQUENCY
(Hz)
0
1.0
350
850
100
2K
BAND 5
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
FREQUENCY
(Hz)
0
1.0
350
850
100
2K
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
0
1.0
42K
115
8
-15
POWER
BAND 1
HIGH CUT
551E
CLIP
3K
65K
140
X1
X10
X0.1
1.5K
.05
2.0
-20
+12
X1
X10
X0.1
140
1.5K
.05
2.0
-20
+12
X1
X10
X0.1
1.5K
140
.05
2.0
-20
+12
X1
X10
X0.1
1.5K
140
.05
2.0
-20
+12
X1
X10
X0.1
140
1.5K
.05
2.0
-20
+12
CLIP
CH1 OUTPUT
FIVE BAND
PARAMETRIC EQUALIZER
552 E DUAL
CAUTION
BALANCED/
UNBALANCED
CH1 INPUT
BALANCED/
UNBALANCED
RISK OF ELECTRIC SHOCK
DO NOT OPEN
MANUFACTURED IN
LYNNWOOD, WA, USA
BALANCED
BALANCED
TO REDUCE THE RISK OF FIRE OR
SHOCK DO NOT EXPOSE
WARNING: ELECTRIC
THIS EQUIPMENT TO RAIN OR MOISTURE
AC INPUT
20 WATTS
MAXIMUM
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
DE CHOC ELECTRIQUE
AVIS: RISQUE
NE PAS OUVRIR
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
No user serviceable parts inside. Refer servicing to qualified service personnel.
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
S’adresser a un reparateur compétent.
CH2 OUTPUT
BALANCED/
UNBALANCED
CH2 INPUT
BALANCED
TYPICAL BALANCED CONNECTIONS
TIP = HIGH(+) = PIN 2
RING = LOW(-) = PIN 3
SLEEVE = GND = PIN 1
BALANCED/
UNBALANCED
BALANCED
SLEEVE
RING
TIP
1
2
2
1
3
3
OUTPUT
INPUT
552E Front and Rear panels
1
Operator Safety Summary
The information in this summary is intended
for persons who operate the equipment as well
as repair personnel. Specific warnings and
cautions are found throughout this manual
wherever they may apply; they do not appear
in this summary.
The notational conventions used in this manual
and on the equipment itself are described in the
following paragraphs.
Chapter 2
Caution
Identifies information that, if not
heeded, may cause damage to the
551E/552E or other equipment in
your system.
Warning
Identifies information that, if
ignored, may be hazardous to
your health or that of others.
CAPITALS
Controls, switches or other
markings on the 551E/552E's
chassis.
Boldface
Strong emphasis.
Equipment Markings
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
TO REDUCE THE RISK OF FIRE OR
SHOCK DO NOT EXPOSE
WARNING: ELECTRIC
THIS EQUIPMENT TO RAIN OR MOISTURE
DE CHOC ELECTRIQUE
ATTENTION: RISQUE
NE PAS OUVRIR
No user serviceable parts inside. Refer servicing to qualified service personnel.
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
S’adresser a un reparateur compétent.
551E
/552E
The lightning flash with arrowhead symbol
within an equilateral triangle is intended to alert
the user of the presence of uninsulated
"dangerous voltage" within the product's
enclosure that may be of sufficient magnitude
to constitute a risk of electric shock to persons.
The exclamation point within an equilateral
triangle is intended to alert the user of the
presence of important operating and maintenance (servicing) instructions in the literature
accompanying the 551E/552E (i.e. this guide).
Caution
To prevent electric shock, do not
use the polarized plug supplied
with the 551E/552E with any
extension cord, receptacle, or
other outlet unless the blades can
be fully inserted.
Terms
Several notational conventions are used in this
manual. Some paragraphs may use Note,
Caution, or Warning as a heading or certain
typefaces and capitalization are used to
identify certain words. These are:
Note
2
Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 551E/552E.
Power source - This product is intended to
operate from a power source that does not
apply more than 255Vrms between the power
supply conductors or between either power
supply conductor and ground. A protective
ground connection, by way of the grounding
conductor in the power cord, is essential for
safe operation.
Danger from loss of ground - If the protective
ground connection is lost, all accessible
conductive parts, including knobs and
controls that may appear to be insulated, can
render an electric shock.
Proper power cord - Use only the power cord
specified for the product. Use only a power
cord that is in good condition.
Operating location - Do not operate this
equipment under any of the following conditions: explosive atmospheres, in wet locations,
in inclement weather, improper or unknown AC
mains voltage, or if improperly fused.
Stay out of the box - To avoid personal injury
or injury to others, do not remove the product
covers or panels. Do not operate the product
without the covers and panels properly
installed.
Chapter 3
Fast Set-Up
This is the section for those of you who are really in a hurry and cannot take a moment to wade
through another owner’s manual. Just follow these steps:
Œ

Plug the 551E/552E into an AC outlet
using the IEC-type detachable power
cord.
Connect audio inputs and outputs. If
you do not know how to do this, forget
Fast Set-Up and read Chapter 5.
Ž Push the Active/Bypass button IN.
the Input Gain control to 12:00 (unity
 Set
gain).
’
“
Set all five Cut/Boost controls to 12:00
(zero detent).
You are ready to start.
Now read the manual.
/552E
‘
Turn the Low Cut control fully counterclockwise and the High Cut control fully
clockwise.
551E

3
Front Panel Controls
Chapter 4
CUT BANDS
SYSTEM
INPUT
LEVEL (dB)
551E
U
ACTIVE
BYPASS
FIVE BAND
PARAMETRIC
EQUALIZER
LOW CUT
22
18K
50
5K
8
-15
POWER
HIGH CUT
+15
42K
115
6
260
3K
65K
CLIP
Figure 1 - Partial view of front panel controls.
[With the exception of Chapters 9 and 10, all text in this User's Guide is applicable to both the
551E and the 552E. For brevity we will use the name “551E/552E” to refer to both units.]
551E
/552E
System Controls
Input Level
Bypass Button
Use this control to adjust the input sensitivity
by ±15 dB. Since the 551E/552E’s input has 18
dB of headroom above +4dBm, the unity gain
position (12:00) should work for normal
operating conditions. However, if you apply
extreme amounts of EQ boost or find that the
input signal level is too high (the clip LED will
illuminate), you may need to increase your
input headroom. Do this by turning the knob
counterclockwise to attenuate the input signal.
Push this button into the ACTIVE position to
engage the 551E/552E’s circuitry. The BYPASS (out) position shunts the input signal
directly from the input jacks to the output
jacks via a relay. There are no passive or
active components in the signal path in this
mode.
Note:
If you find that the input signal is very low (the
output of a -10 device is a good example), turn
the input level control clockwise to boost the
level of the signal going through the 551E/552E.
This will optimize the signal-to-noise ratio.
The relay mechanism is also engaged
when the AC power is disconnected,
enabling the unit to pass signal even
when the power is off.
Cut Band Controls
Low Cut Filter
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
23 MAY 96 10:49:15
20.000
Diagram 2 illustrates a 12 dB
per octave low frequency
roll-off filter. Use this to
protect subwoofers in
sound systems, clean-up
muddy recordings, or
increase speech intelligibility in announce systems.
The frequency range is 6Hz
(essentially this is bypass)
to 260 Hz.
15.000
10.000
5.0000
0.0
-5.000
-10.00
-15.00
Diagram 2 - Low cut filter with
12 dB per octave.
4
-20.00
20
100
1k
10k
20k
High Cut Filter
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
23 MAY 96 10:54:00
20.000
Diagram 3 illustrates a 12dB
per octave high frequency
roll-off filter. The range of
this control is 3kHz to
65kHz.
15.000
10.000
5.0000
0.0
-5.000
-10.00
-15.00
Diagram 3 - High cut filter
with 12 dB
per octave.
-20.00
20
100
1k
10k
20k
EQ Controls
Bandwidth
BAND 1
350
X1
X10
X0.1
BANDWIDTH
(OCT)
CUT/BOOST
(dB)
1.0
0
850
140
1.5K
100
2K
.05
2.0
-20
This knob determines how wide an area the
band will affect, hence the term bandwidth.
The knob is calibrated in terms of octaves. The
range is .05 (1/20th) to 2 octaves. Use the .05
setting for notch filter applications and the 1.02.0 range for “tone control” type sweetening.
+12
/552E
FREQUENCY
(Hz)
Figure 4 - Front panel view of one EQ band.
Cut/Boost Knob
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
23 MAY 96 10:01:21
20.000
Note:
We’ve provided a wide
range on this knob to
help you take care of the
occasional drastic problem, but you’ll get better
results from this (or any)
EQ if you use this control
in moderation.
15.000
10.000
5.0000
551E
This control delivers up to 12 dB
of boost or 20 dB of cut at the
frequency selected by the
frequency control and range
switch. See Diagram 5.
0.0
-5.000
-10.00
-15.00
-20.00
20
100
1k
10k
20k
Diagram 5 - Typical Cut/Boost curve.
5
Frequency Knob
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
23 MAY 96 10:02:53
20.000
Use this knob, in conjunction with
the Frequency Switch, to adjust
the center frequency of the area
affected by the filter band. See
Diagram 6.
Frequency Switch
Think of this as a Frequency knob
multiplier. When you put the
toggle in the X1 position the
range of the Frequency control
corresponds to the numbers
printed around the knob - 100 Hz
to 2kHz. Use this position when
you want to work in the midrange.
The X10 position shifts the
Frequency knob’s range upward
by a factor of 10. The range
becomes 1kHz to 20 kHz; suitable
for high-frequency adjustments.
The X0.1 position moves the
range downwards (10 Hz to 200
Hz), for fine resolution in the lowfrequency area. See Diagram 7.
15.000
Frequency
knob range
10.000
5.0000
0.0
-5.000
-10.00
-15.00
-20.00
20
100
1k
10k
20k
Diagram 6 - Frequency graph.
AUDIO PRECISION 551E
AMPL(dBu)
vs
FREQ(Hz)
23 MAY 96 10:09:46
20.000
1kHz
X0.1
15.000
1kHz
X1
1kHz
X 10
1k
10k
10.000
5.0000
551E
/552E
0.0
Before you ask, we want you to
know that we know it seems to
makes no sense that X1 is the top
switch position, X10 is middle,
and X0.1 is bottom. Our resident
circuit guru informs us that there
is no way to wire this toggle
switch so that it works in the
logical order. If you need proof
just look at someone else’s
parametric EQ toggle switch.
6
-5.000
-10.00
-15.00
-20.00
20
100
20k
Diagram 7 - Range switch action.
Chapter 5
Rear Panel Connections
OUTPUT
TYPICAL BALANCED CONNECTIONS
TIP = HIGH(+) = PIN 2
RING = LOW(-) = PIN 3
SLEEVE = GND = PIN 1
SLEEVE
RING
TIP
2
1
2
1
3
3
OUTPUT
INPUT
INPUT
BALANCED/
UNBALANCED
BALANCED/
UNBALANCED
BALANCED
BALANCED
Figure 8 - View of rear panel connectors.
Input Jacks
Output Jacks
The 551E/552E is equipped with an XLR and a
¼" jack. Both will work either balanced or
unbalanced and will generally accommodate
just about any standard +4dBu nominal line
level audio source. If you plan on plugging a
mic directly into the 551E/552E’s XLR input...
don’t bother. It will not hurt anything, but it
just will not work. The input jacks are configured as follows:
There are two output jacks wired parallel to
each other - a balanced XLR, and a balanced
¼" TRS. These can drive balanced or unbalanced inputs but you should check Appendix
A for wiring examples. The outputs are
configured as follows:
XLR
pin 1=ground
pin 2=+/high
pin 3=-/low
¼" Balanced
tip = +/high
ring=-/low
sleeve=ground
XLR
pin 1 = ground
pin 2 = +/high
pin 3 = -/low
¼" Balanced
tip = +/high
ring = -/low
sleeve = ground
551E
/552E
See Appendix A for adapter wiring examples.
7
8
/552E
551E
Chapter 6
Operating Tips
Setting the Frequency Controls - Part 1
How do I find the right frequency to cut or boost if I don’t have a spectrum analyzer? There
are a couple of tune-by-ear methods that, although crude, are quite effective. For lack of a
better name we’ll call the first method “boost-and-sweep”.
Pretend for a second that you are recording an acoustic guitarist in your studio. Everything is
fine until you notice that there is a weird low-mid resonance in the guitar body that makes the
open A string sound louder than everything else. All you really want to do is reduce the
volume of the open A without affecting any other note. No problem. Just insert the 551E/552E
in the input channel send/return loop and follow this procedure.
First, select an EQ band and set its BANDWIDTH very narrow (.50 or lower). Then take the
BOOST/CUT knob and crank it to +12 dB. This will sound terrible (and is risky to do in a live
sound situation), but hang in there. Now turn the FREQUENCY control (and toggle the
RANGE switch) until the offending note gets really loud. Although this will sound incredibly
bad, it lets you know that you have adjusted the FREQUENCY control correctly. Now adjust
the CUT/BOOST (try a starting cut of around 3-6dB) and BANDWIDTH (try widening it a
little) until the open A string sounds like it should.
Setting the Frequency Controls - Part 2
Try a “cut-and-sweep” approach if you are using the 551E/552E in a concert sound application.
Use basically the same procedure as in Tip #1, but use an extreme amount of cut, not boost, to
find the trouble spot. This is a more subtle approach to corrective equalization that you can use
during soundchecks (even during shows) without getting nasty looks from the audience.
Bandwidth Control
551E
Though a narrow bandwidth setting can be very useful for the “surgical” removal of a problem
area, it can cause excessive ringing (and generally sound worse) if used for boosts. Wide band
boosts (over 1.0 octaves) sound more natural, more like a tone control.
/552E
Most professional engineers follow this rule of thumb: Use narrow bandwidths for cutting, and
wide bandwidths for boosting.
9
Overlapping Bands
Although each EQ band can cover the entire audio spectrum, the 551E/552E will give you the best
(read: most accurate) results if you use adjacent bands for overlapping cuts and boosts. See
Diagram 9.
To maximize the
performance of this type
of layout, make sure
you use adjacent EQ
bands (i.e. Bands 1 and
2, 2 and 3, 3 and 4, etc.)
when you are applying
overlapping boosts or
cuts. Diagram 9 shows
how adjacent, overlapping bands produce a
curve that is the result of
correctly adding the
curves of the individual
bands. Nonadjacent
bands (1 and 3 for
instance) produce a
combined curve that is
not correctly summed,
even though it might be
useful in some applications. See Diagram 10.
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
23 MAY 96 16:51:46
20.000
Band 1+2
15.000
10.000
Band 2
Band 1
5.0000
0.0
-5.000
-10.00
-15.00
-20.00
100
20
1k
10k
20k
Diagram 9 - Overlapping EQ curves on adjacent bands.
AUDIO PRECISION 551E
AMPL(dBu)
vs FREQ(Hz)
28 MAY 96 12:42:32
20.000
15.000
Band 1+3
10.000
Band 3
Band 1
5.0000
0.0
-5.000
-10.00
-15.00
-20.00
551E
/552E
Although the five EQ
bands have identical
ranges and functions,
they are not identical in
one respect - the way in
which they combine.
We have implemented a
series/parallel configuration to ensure the
most accurate band
interaction while
maintaining the best
noise and distortion
performance.
20
100
1k
10k
30k
Diagram 10 - Overlapping EQ curves on nonadjacent bands.
10
Chapter 7
Applications
Studio Applications
Multitrack Recording
During tracking, the 551E (or one channel of the 552E) could either be placed in the insert point of a
console channel or, if you are using a direct-to-tape approach, following the mic preamp. Use the 551E/
552E for creative sweetening of the sound source, or to minimize unwanted noises that exist within the
signal you wish to record. Full frequency microphones are great, but can be overly sensitive to rumble
or air noise - you may want to eliminate this before it goes to tape. This is especially necessary if you are
forced to mix two signals onto the same track. It is much harder to fix problems once the signals are
combined.
Mixdown
Patch the 551E (or one channel of the 552E) into the signal path of an individual track - usually on the
insert point of the console channel. In this application, use the unit to boost frequencies needed to
make that instrument/voice/whatever stand out in the mix, or perhaps cut irritating or nonmusical
frequencies. The five, fully overlapping bands make the 551E/552E very versatile in this application.
Mixdown/Mastering
Another place you might need the power of a five band parametric equalizer is on the entire mix. Of
course, you need a 552E for stereo applications. Think of the difference a boost at 40 Hz will do for the
dance mix, while a boost at 4kHz could rescue a vocal part at the last moment.
Control Room Tuning
An entirely different studio application for parametric equalizers is in control room monitor tuning. Most
engineers want to be able to control the tuning of the speakers to fix problems caused by the room.
Graphic equalizers may be able to give you a quick picture of their settings, but they lack the precision
necessary to really dial in the sound. A parametric equalizer, especially one with five full range bands, is
perfect for tuning a room.
Though graphic equalizers are the most popular tools for equalizing onstage monitors, the task of
feedback suppression is an area where parametrics excel. The continuously variable FREQUENCY
KNOB on the 551E/552E allows you to zero in precisely on the feedback area. Narrowing the
bandwidth allows you to make very drastic cuts while minimizing the effect on the rest of the audio
spectrum. Graphic EQs, while easy to use, cannot approach this kind of precision.
Mains
There is no better tool than a parametric EQ for balancing the frequency response of your sound
system. Use a couple of bands in notch filter mode to compensate for standing waves or feedback
problems. You will still have a few bands left over for sweetening the PA sound.
Aux Send To Subwoofer
If you are using an Aux send on your console to drive your subwoofers, you will still need an EQ
somewhere before the crossover. Your best choice for this job is a parametric (a graphic EQ does not
have enough precision in the low end) especially if you set the subwoofer crossover point at 100 Hz or
lower. With five completely tunable filters at your disposal, you can ensure that your system delivers
maximumimpact.
Channel Insert
Have you ever wished for a couple of extra EQ bands to really perfect your kick drum sound? The 551E/
552E is perfect for the job. Five bands give you the power to make any kick drum sound huge by dialing
out unpleasant rings, accentuating the attack of the high end, and adding extra low end. You can use
the 551E (or one channel of the 552E) at the channel insert of any mixer channel that requires special
attention, from drums to vocals.
11
551E
Monitor Mixes
/552E
Sound Systems
Broadcast Systems
While analog equalizers do not enjoy the status of the latest multiband digital audio processors,
there is not a program director in the world who does not want a good equalizer somewhere in the
audio processing chain. The equalizing finesse possible with the Symetrix 551E/552E can provide
the final touch in producing a signature sound which trounces the competition.
On previous pages you learned how a parametric equalizer, especially the 551E/552E, runs circles
around a graphic EQ because of the precise adjustments possible. The important question
remaining is, “Where should I install the 551E/552E?”
Install the 551E/552E before the final limiter (see Diagram 11). If wired in the audio chain after the
final limiter, the frequencies you boost will cause over-modulation of the transmitter. If the 551E/
552E connects directly to the output of the console, sloppy board operation and unusually loud
peaks may combine to overload the equalizer’s input, in spite of its +22 dBu headroom. Ideally an
AGC, like the Symetrix 422 AGC-Leveler, should be installed between the console output and the
551E/552E’s input.
This combination provides protection for the 551E/552E’s input stage and delivers a leveled signal
to the final limiter. The station benefits from a consistent, finely equalized signature sound which
does not change with the program material, or each on-air shift change.
/552E
Diagram 11 - Recommended audio processing chain for broadcast systems. (Alternately, you could
substitute one 552E for the two 551E’s in this setup.)
422 STEREO AGC/LEVELER
551E
551E PARAMETRIC EQ
551E PARAMETRIC EQ
FINAL LIMITER
12
Chapter 8
There is no output signal.
Check input and output cables and
connections.
Determine that there really is a signal
coming from the source, and that it is
getting to the 551E/552E.
Distortion in the output signal.
Put 551E/552E into BYPASS. If problem
remains, check your signal source.
Check the level of the input signal. Is it
overdriving the 551E/552E’s input? If so,
reduce the incoming signal level. Is the
551E/552E’s clip indicator lit?
Is the incoming signal already distorted?
Listen “up stream” from the 551E/552E to
determine that you are feeding it a clean
signal.
Troubleshooting
Controls don’t seem to have any effect.
Is AC power connected to the unit? Since
the 551E/552E uses an automatic bypass
relay, it will still pass audio even when
power is turned off, though the controls
will have no effect.
Is the Active/Bypass button in the correct
position?
The 551E/552E does not power up or does not
respond properly.
Consult a qualified service technician or
the Symetrix factory.
The 551E/552E is not plugged in, but works
great anyway.
Call us. Call us now.
Are you using an EQ band or bands to
apply a lot of boost? If so, you may be
running out of headroom. Fix this by
lowering the input level control, or
reducing the amount of boost.
Buzz in the output.
Check input and output connector wiring.
/552E
Check for ground loops between interconnected system equipment.
Are all system components on the same
AC ground?
Noise (hiss).
Put 551E/552E into BYPASS. If problem
remains, check your signal source. Is the
input signal already noisy? Listen “up
stream” from the 551E/552E to determine
that you are feeding it a clean signal.
551E
Check input signal levels and input level
control settings. The input signal may be
too low in level. If so, boost the incoming
signal (if possible).
Make sure that you are feeding the 551E/
552E/ a line-level signal, not a mic-level
signal.
13
Specifications for the 551E
Chapter 9
Architects and Engineers Specifications
The parametric equalizer (EQ) shall be a single
channel unit that shall provide five independent filter bands. There shall also be separate
high-pass and low-pass filters. The unit shall
occupy one rack space (1U).
Each filter band shall have the following
controls and control ranges: a cut/boost
control with a -20 dB to +12 dB range, a
frequency sweep control with a 100 Hz - 2kHz
range, a frequency range multiplier switch with
X10, X1, and X0.1 settings, and a bandwidth
control with a .05 octave - 2.0 octave range.
There shall also be a 12 dB/Oct high-pass filter
with a user-adjustable cutoff frequency range
of 6Hz to 260 Hz, and a 12 dB/Oct low-pass
filter with a cutoff frequency range from 3kHz to
65 kHz. A front panel input level control shall
provide ±15 dB of gain adjustment.
551E
/552E
When the unit is inoperative (either by loss of
power or via the BYPASS switch), the inputs
and outputs will be wired together by a relay.
The frequency response with all filter bands
flat, EQ in, high-pass and low-pass set to the
outside extremes of their ranges, shall be 20Hz
to 62 kHz (-0.5dB, -3dB). The total harmonic
distortion plus noise shall be less than 0.002%
(EQ in, all bands flat). The dynamic range shall
be greater than 114 dB. The EQ shall accept a
maximum input signal of +21 dBu and have a
maximum output level of +21 dBu. There shall
be a front panel clip indicator that will illuminate at 1dB below clipping. It shall monitor the
input, output and each EQ band.
The inputs shall be direct-coupled, active
balanced designs terminated with 3-pin XLR
(AES/IEC standard wiring), and ¼" TRS female
connectors. The input circuitry shall incorporate RFI filters. There shall be a servobalanced, direct-coupled output that shall
terminate in 3-pin XLR (AES/IEC standard
wiring) and ¼" TRS connectors.
The EQ shall be capable of operating by
means of its built-in power supply connected
to 117V nominal AC, 105-130V, 50-60 Hz (230V
nominal AC, 207-253V, 50 Hz where applicable). Power consumption shall be 15 watts
maximum. There shall be a rear panel receptacle for an IEC-type detachable power cord.
The EQ shall be UL and CE approved.
The unit shall be a Symetrix, Inc. model 551E
Five Band Parametric Equalizer.
Technical Specifications
Maximum Input Level
Maximum Output Level
THD+Noise (1kHz at +4dBu)
Signal to Noise Ratio
Dynamic Range
Frequency Response
Input Impedance
Output Impedance
EQ band Control Specs:
Frequency Control Range
Cut/Boost Range
Bandwidth
14
+21 dBu balanced
+21 dBu balanced
+17 dBu unbalanced
<0.002%
(<10 Hz to 30 kHz measurement bw)
-eq in, all bands flat
>96 dB (unweighted, ref to +4dBu)
-eq in, all bands flat
>114 dB
-0.5 dB, -3dB (20 Hz - 62 kHz)
20k ohms balanced, 10k ohms unbal.
300 ohms balanced, 150 ohms unbal.
10 Hz - 20 kHz (inc. Frequency Switch)
-20 dB, +12dB
.05 oct - 2.0 oct
Chassis Size
1.72"H x 19" W x 8.25" D
4.37cm H x 48.26cm W x 20.955cm D
Shipping Weight
8 lbs, 3.64 kg
AC Requirements
via internal supply
117V AC, nominal, 95-130V AC, 50-60 Hz
230V AC, nominal, 165-255V AA , 50 Hz
Power Consumption
15 watts, maximum
In the interest of continuous product improvement, Symetrix, Inc.
reserves the right to alter, change, or modify these specifications
without prior notice.
Copyright, 1998, Symetrix, Inc. All rights reserved.
Chapter 10
Specifications for the 552E
Architects and Engineers Specifications
The EQ shall be capable of operating by means
of its built-in power supply connected to 117V
nominal AC, 105-130V, 50-60 Hz (230V nominal
AC, 207-253V, 50 Hz where applicable). Power
consumption shall be 20 watts maximum. There
shall be a rear panel receptacle for an IEC-type
detachable power cord. The EQ shall be UL and
CE approved.
The unit shall be a Symetrix, Inc. model 552E
Dual Five Band Parametric Equalizer.
Technical Specifications
Maximum Input Level
Maximum Output Level
THD+Noise (1kHz at +4dBu)
Signal to Noise Ratio
Dynamic Range
Frequency Response
Input Impedance
Output Impedance
EQ band Control Specs:
Frequency Control Range
Cut/Boost Range
Bandwidth
+21 dBu balanced
+21 dBu balanced
+17 dBu unbalanced
<0.002%
(<10 Hz to 30 kHz measurement bw)
-eq in, all bands flat
>96 dB (unweighted, ref to +4dBu)
-eq in, all bands flat
>114 dB
-0.5 dB, -3dB (20 Hz - 62 kHz)
20k ohms balanced, 10k ohms unbal.
300 ohms balanced, 150 ohms unbal.
Chassis Size
3.5"H x 19" W x 8" D
8.89cm H x 48.3cm W x 20.32cm D
Shipping Weight
11 lbs, 5kg
AC Requirements
via internal supply
117V AC, nominal, 95-130V AC, 50-60 Hz
230V AC, nominal, 165-255V AC, 50 Hz
Power Consumption
20 watts, maximum
In the interest of continuous product improvement, Symetrix, Inc.
reserves the right to alter, change, or modify these specifications
without prior notice.
Copyright, 1998, Symetrix, Inc. All rights reserved.
10 Hz - 20 kHz (inc. Frequency Switch)
-20 dB, +12dB
.05 oct - 2.0 oct
15
/552E
When the unit is inoperative (either by loss of
power or via the BYPASS switch), the inputs
and outputs will be wired together by a relay.
The frequency response with all filter bands
flat, EQ in, high-pass and low-pass set to the
outside extremes of their ranges, shall be 20Hz
to 62 kHz (-0.5dB, -3dB). The total harmonic
distortion plus noise shall be less than 0.002%
per channel (EQ in, all bands flat). The dynamic
range shall be greater than 114 dB. The EQ
shall accept a maximum input signal of +21 dBu
and have a maximum output level of +21 dBu.
There shall be front panel clip indicators for
each channel that will illuminate at 1dB below
clipping. These indicators shall monitor the
input, output and each EQ band.
The inputs shall be direct-coupled, active
balanced designs terminated with 3-pin XLR
(AES/IEC standard wiring), and ¼" TRS female
connectors. The input circuitry shall incorporate RFI filters. There shall be servo-balanced,
direct-coupled outputs that shall terminate in 3pin XLR (AES/IEC standard wiring) and ¼"
TRS connectors.
551E
The parametric equalizer (EQ) shall be a dual
channel unit that shall provide five independent filter bands per channel. There shall also
be separate high-pass and low-pass filters per
channel. The unit shall occupy two rack
spaces (2U).
Each filter band shall have the following
controls and control ranges: a cut/boost
control with a -20 dB to +12 dB range, a
frequency sweep control with a 100 Hz - 2kHz
range, a frequency range multiplier switch with
X10, X1, and X0.1 settings, and a bandwidth
control with a .05 octave - 2.0 octave range.
There shall also be a 12 dB/Oct high-pass filter
with a user-adjustable cutoff frequency range
of 6Hz to 260 Hz, and a 12 dB/Oct low-pass
filter with a cutoff frequency range from 3kHz
to 65 kHz. A front panel input level control
shall provide ±15 dB of gain adjustment.
Warranty
Chapter 11
551E/552E Limited Warranty
Symetrix, Inc. expressly warrants that the product will be free from defects in material and
workmanship for one (1) year. Symetrix's obligations under this warranty will be limited to
repairing or replacing, at Symetrix's option, the part or parts of the product which prove
defective in material or workmanship within one (1) year from date of purchase, provided that
the Buyer gives Symetrix prompt notice of any defect or failure and satisfactory proof thereof.
Products may be returned by Buyer only after a Return Authorization number (RA) has been
obtained from Symetrix. Buyer will prepay all freight charges to return the product to the
Symetrix factory. Symetrix reserves the right to inspect any products which may be the subject
of any warranty claim before repair or replacement is carried out. Symetrix may, at its option,
require proof of the original date of purchase (dated copy of original retail dealer's invoice).
Final determination of warranty coverage lies solely with Symetrix. Products repaired under
warranty will be returned freight prepaid by Symetrix via United Parcel Service (surface), to
any location within the Continental United States. At Buyer's request the shipment may be
returned via airfreight at Buyer's expense. Outside the Continental United States, products will
be returned freight collect.
The foregoing warranties are in lieu of all other warranties, whether oral, written, express,
implied or statutory. Symetrix, Inc. expressly disclaims any IMPLIED warranties, including
fitness for a particular purpose or merchantability. Symetrix's warranty obligation and
buyer's remedies hereunder are SOLELY and exclusively as stated herein.
This Symetrix product is designed and manufactured for use in professional and studio audio
systems and is not intended for other usage. With respect to products purchased by consumers for personal, family, or household use, Symetrix expressly disclaims all implied warranties, including but not limited to warranties of merchantability and fitness for a particular
purpose.
551E
/552E
This limited warranty, with all terms, conditions and disclaimers set forth herein, shall extend
to the original purchaser and anyone who purchases the product within the specified warranty
period.
Symetrix does not authorize any third party, including any dealer or sales representative, to
assume any liability or make any additional warranties or representation regarding this product
information on behalf of Symetrix.
This limited warranty gives the buyer certain rights. You may have additional rights provided
by applicable law.
Limitation of Liability
The total liability of Symetrix on any claim, whether in contract, tort (including negligence) or
otherwise arising out of, connected with, or resulting from the manufacture, sale, delivery,
resale, repair, replacement or use of any product will not exceed the price allocable to the
product or any part thereof which gives rise to the claim. In no event will Symetrix be liable for
any incidental or consequential damages including but not limited to damage for loss of
revenue, cost of capital, claims of customers for service interruptions or failure to supply, and
costs and expenses incurred in connection with labor, overhead, transportation, installation or
removal of products or substitute facilities or supply houses.
16
Chapter 12
Service
Servicing the 551E/552E
If you have determined that your 551E/552E requires repair services and you live outside of the
United States, please contact your local Symetrix dealer or distributor for instructions on how
to obtain service. If you reside in the U.S., then proceed as follows:
Return authorization
At the Symetrix factory, Symetrix will perform in-warranty or out-of-warranty service on any
product it has manufactured for a period of five years from date of manufacture.
Before sending anything to Symetrix, contact our Customer Service Department for a return
authorization (RA) number. The telephone number is (425) 778-7728, Monday through Friday,
8AM (800 hours) though 4:30 PM (1630 hours), Pacific Time.
In-warranty repairs
To get your 551E/552E repaired under the terms of the warranty:
1. Call us for an RA number.
2. Pack the unit in its original packaging materials.
3. Include your name, address, daytime telephone number, and a brief statement of the
problem.
4. Write the RA number on the outside of the box.
5. Ship the unit to Symetrix, freight prepaid. We do not accept freight collect shipments.
If you choose to send us your product in some sort of flimsy packaging, we'll have to charge
you for proper shipping materials. If you don't have the factory packaging materials, then do
yourself a favor by using an oversize carton, wrap the unit in a plastic bag, and surround it
with bubble-wrap. Pack the box full of Styrofoam peanuts. Be sure there is enough clearance in
the carton to protect the rack ears (you wouldn't believe how many units are returned with
bent ears). We won't return the unit in anything but Symetrix packaging for which we will have
to charge you. Of course, if the problem turns out to be operator inflicted, you'll have to pay
for both parts and labor. In any event, if there are charges for the repair costs, you will pay for
the return freight. All charges will be COD unless you have made other arrangements (prepaid,
Visa or Mastercard).
Out-of-warranty repairs
551E
If the warranty period has passed, you'll be billed for all necessary parts, labor, packaging
materials, and freight charges. Please remember, you must call for an RA number before
sending the unit to Symetrix.
/552E
Just do these five things, and repairs made in-warranty will cost you only one-way freight
charges. We'll prepay the return (surface) freight.
17
Adapter Wiring Examples
Appendix A
TO BALANCED IN
2 31
FEMALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
13 2
FROM BALANCED OUT
TO UNBALANCED IN FROM
TRANSFORMER COUPLED OR
FLOATING BALANCED OUTPUT
FROM BALANCED OUT
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
TIP
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
RING
SLEEVE
TO BALANCED IN
FROM UNBALANCED OUT
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
TIP
RING
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
SLEEVE
FROM BALANCED OUT
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TO BALANCED IN
TERMINAL STRIP
(+) = HIGH
(-) = NOT USED
= GROUND
FROM NON-TRANSFORMER (ELECTRONIC)
BALANCED OUTPUT
(TYPICAL OF SYMETRIX PRODUCTS)
FEMALE XLR
PIN 1 = GROUND + LOW
PIN 2 = HIGH
PIN 3 = NOT USED
2 31
TO UNBALANCED IN
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
REV-B
551E
/552E
FROM UNBALANCED OUT
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
18
Appendix B
Declaration of Conformity
Declaration of Conformity
We, Symetrix, Inc., 6408 216th St. SW, Mountlake Terrace, Washington, USA,
declare under our sole responsibility that the product:
551E and 552E Parametric Equalizers
to which this declaration relates, is in conformity with the following standards:
EN 60065
Safety requirements for mains operated electronic and related
apparatus for household and similar general use.
EN 50081-1
Electromagnetic compatibility - Generic emission standard
Part 1: Residential, commercial, and light industry.
EN 50082-1
Electromagnetic compatibility - Generic immunity standard
Part 1: Residential, commercial, and light industry.
The technical construction file is maintained at:
/552E
Symetrix, Inc.
6408 216th St. SW
Mountlake Terrace, WA, 98043
USA
The authorized representative located within the European Community is:
World Marketing Associates
P.O. Box 34
Newquay, Cornwall, TR7 1TU, U.K.
551E
Date of issue: 1 January 1998
Place of issue: Mountlake Terrace, Washington, USA
Authorized signature:
Dane Butcher, President, Symetrix Incorporated.
19
/552E
551E
6408 216th St. SW
Mountlake Terrace, WA 98043 USA
Tel (425) 778-7728
Fax (425) 778-7727
Email symetrix@symetrixaudio.com
Website www.symetrixaudio.com
20
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