Symetrix 551E User manual

551E and 552E
Parametric Equalizers
User’s Guide
551E 552E
/

i
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.
Symetrix Inc.
14926 35th Ave. West
Lynnwood, WA 98037 USA
Tel [phone]
Fax [phone]
Email [e-mail]
Website www.symetrixaudio.com
551E 552E
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1
551E 552E
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IntroductionChapter 1
551E Front and Rear panels
BAND 5
BANDWIDTH CUT/BOOSTCUT/BOOST
BAND 4
FREQUENCY BANDWIDTHCUT/BOOSTFREQUENCY BANDWIDTH
BAND 3
FREQUENCY
0
850350 1.0
1.5K
2K100 .05 2.0 -20 +12
0
350 850 1.0
140
X1
X10
1.5K140
0
1.0
850350
X1
X10
1.5K
X1 140
X10 X0.1X0.1X0.1 2K100 .05 2.0 -20 +12 2K100 .05 2.0 -20 +12
(OCT)(OCT)(Hz) (dB) (dB)(OCT)(Hz) (Hz) (dB)
BAND 2
BANDWIDTH
FREQUENCY
BAND 1
BANDWIDTHFREQUENCYHIGH CUT CUT/BOOSTLOW CUTINPUT
SYSTEM CUT BANDS
850 0
1.0
350
0
1.5K140
X1
X10
350 850 1.0
18K
1.5K
42K X1 5K
115 X10 140
X0.1X0.1
65K3K 100 2K .05 +122.0 -20 2K100 .05 2.0 -20
5022
U
ACTIVE
E
8
BYPASS
551
EQUALIZER
PARAMETRIC
FIVE BAND
POWER CLIP -15 260+15 6
LEVEL (dB) (OCT)(Hz) (dB) (OCT) (Hz) (dB)
+12
CUT/BOOST
E
LYNNWOOD, WA, USA
MANUFACTURED IN
FIVE BAND PARAMETRIC EQUALIZER
INPUTOUTPUT
BALANCED/
UNBALANCED
BALANCEDBALANCED
12 3
INPUT
BALANCED/
UNBALANCED
551
TIP = HIGH(+) = PIN 2
21 3
OUTPUT
RING = LOW(-) = PIN 3
SLEEVE = GND = PIN 1
RING
TIP
SLEEVE
PERSONNEL.
TO QUALIFIED SERVICE
PARTS. REFER SERVICING
NO USER SERVICEABLE
THIS UNIT CONTAINS
15 WATTS
MAXIMUM
AC INPUT
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
TYPICAL BALANCED CONNECTIONS
Thank you for choosing the 551E Five Band
ParametricEqualizerorthe552EDualFiveBand
ParametricEqualizer. [Withtheexceptionof
Chapters 9 and 10, all text in this User's Guide is
applicabletoboththe551Eand552E. Forbrevity
wewillusethename“551E/552E” torefertoboth
units.] Both models deliver superior fidelity,
flexibility, power, and precision through an
unbeatable combination of wide dynamic range,
ultra-lowdistortion,minimalphaseshiftand
ringing, easy to use controls and rock-solid
construction.The 551E/552Eisa leapforwardin
affordable equalizer technology.
Thefive,fullyparametricEQ 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
frequencycontrolrangefrom10Hzto20kHz.
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.
Youwillfind the 551E/552Eisjustasuseful 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
station’s signature sound are the kinds of tasks
thatarewellwithinthe551E/552E’scapability.
As for sonic quality... Our proprietary topology
deliversextremelylow-noiseaudioperformance
- the kind you would normally expect only from
a much more expensive unit. We have also
included a servo balanced output that com-
pletely removes all DC offset, and direct-
coupled input and output stages that maximize
the551E/552E’slow-frequencyresponsewhile
minimizingnoiseanddistortion.
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.
Feel free to contact us if you have questions,
comments or suggestions at:
Phone [phone]
Fax [phone]
Email [email protected]
Website www.symetrixaudio.com
Officehours-8:00am-4:30pm PacificTime
(dB)
BAND 5
(OCT)(Hz) BANDWIDTH CUT/BOOST
0
1.0
350 850
1.5K
(dB)
CUT/BOOST
BAND 4
(OCT)(Hz)
FREQUENCY BANDWIDTH
0
140
X1
X10
1.0
350 850
1.5K140
(dB)(OCT) CUT/BOOSTFREQUENCY (Hz) BANDWIDTH
BAND 3
0
1.0
X1
X10
350 850
1.5K
X1
X10 140
FREQUENCY
+122.0
100 2K .05
BAND 5
-20
(dB)
0
(OCT)(Hz)
1.0
350 850
CUT/BOOSTBANDWIDTH
+12
1.5K
100 2K .05 2.0 -20
X0.1
-20 +12.05
100 2K
BAND 4
2.0
(dB)
0
(OCT)(Hz)
1.0
350 850
BANDWIDTHFREQUENCY CUT/BOOST
X0.1
+12.05 2.0 -20
2K100
X0.1
BAND 3
(dB)(OCT)
0
1.0
(Hz)
850350
FREQUENCY BANDWIDTH CUT/BOOST
140
X1
X10
X0.1
-20 +12
1.5K
140
2K100 .05 2.0
X1
X10
.05 2.0 +12-20 X0.1
1.5K
X1
X10 140
100
X0.1 2K
FREQUENCY
BAND 2
(dB)
(OCT)
BANDWIDTH
(dB) (Hz)
FREQUENCY
0
1.0
850
1.5K
350
0
140
X1
X10
BAND 1
BANDWIDTH
(OCT)
FREQUENCY
(Hz)
HIGH CUT
1.0
350 850
1.5K
18K
X1
X10
115 5K 42K 140
CUT/BOOSTLOW CUTINPUT
LEVEL (dB)
CHANNEL 1
22 50
U
8
ACTIVE
BYPASS
CUT BANDS
-20.05
2K 2.0
BAND 2
100
-20 +12 X0.1
(dB)
(OCT)
0
1.0
850
(dB)
350
0
(Hz)
FREQUENCY BANDWIDTH
2.0.05
2K100
BAND 1
X0.1
3K 65K
(OCT)(Hz)
1.0
850350
42K
18K
5K
HIGH CUT FREQUENCY BANDWIDTH CUT/BOOST
1.5K
-20
2K .05 2.0
140
X10
X1
-20 +12 X0.1 100
1.5K
100 2K 2.0.05
X1
X10
115
3K 65K X0.1
140
2606+15-15
CLIP
CHANNEL 2
LEVEL (dB)
5022
U
ACTIVE
BYPASS
LOW CUTINPUT
PARAMETRIC
EQUALIZER
DUAL
FIVE BAND
8
-15 +15 6 260
POWER CLIP
CUT BANDS
552 E
+12
CUT/BOOST
+12
CUT/BOOST
1
3
221 3
OUTPUT INPUT
CH1 INPUT
BALANCED
CH1 OUTPUT
UNBALANCED
UNBALANCED
BALANCED
BALANCED/ BALANCED/
SLEEVE = GND = PIN 1
RING = LOW(-) = PIN 3
TIP = HIGH(+) = PIN 2
SLEEVE
RING
BALANCED TIP
BALANCED/
UNBALANCED
BALANCED/
UNBALANCED
BALANCED
CH2 OUTPUT CH2 INPUT TYPICAL BALANCED CONNECTIONS
ELECTRIC SHOCK DO NOT EXPOSE
TO REDUCE THE RISK OF FIRE OR
CAUTION
WARNING:
NE PAS OUVRIR
RISQUE DE CHOC ELECTRIQUE
No user serviceable parts inside. Refer servicing to qualified service personnel.
S’adresser a un reparateur compétent.
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
AVIS:
THIS EQUIPMENT TO RAIN OR MOISTURE
552E
AC INPUT
20 WATTS
MAXIMUM
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
LYNNWOOD, WA, USA
MANUFACTURED IN
PARAMETRIC EQUALIZER
DUAL FIVE BAND
DO NOT OPEN
RISK OF ELECTRIC SHOCK
552E Front and Rear panels

2
551E 552E
/
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.
CAUTION
WARNING:
ATTENTION:
RISQUE DE CHOC ELECTRIQUE
NE PAS OUVRIR
S’adresser a un reparateur compétent.
THIS EQUIPMENT TO RAIN OR MOISTURE
ELECTRIC SHOCK DO NOT EXPOSE
TO REDUCE THE RISK OF FIRE OR
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.
DO NOT OPEN
RISK OF ELECTRIC SHOCK
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 mainte-
nance (servicing) instructions in the literature
accompanyingthe551E/552E(i.e.thisguide).
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 Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 551E/552E.
Equipment Markings
Operator Safety Summary Chapter 2
Caution Identifies information that, if not
heeded, may cause damage to the
551E/552E or other equipment in
your system.
Warning Identifiesinformationthat,if
ignored,maybehazardousto
yourhealthorthatofothers.
CAPITALS Controls, switches or other
markingsonthe551E/552E's
chassis.
Boldface Strong emphasis.
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.
Dangerfrom loss ofground- 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.
Properpowercord-Useonlythe powercord
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 condi-
tions: explosive atmospheres, in wet locations,
in inclement weather, improper or unknown AC
mains voltage, or if improperly fused.
Stayoutofthebox-Toavoidpersonal 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.

3
551E 552E
/
Plugthe551E/552E into anACoutlet
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.
Push the Active/Bypass button IN.
Set the Input Gain control to 12:00 (unity
gain).
Turn the Low Cut control fully counter-
clockwise and the High Cut control fully
clockwise.
Set all five Cut/Boost controls to 12:00
(zero detent).
You are ready to start.
Now read the manual.





















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:
Chapter 3




4
551E 552E
/
Front Panel Controls Chapter 4
Input Level
Use this control to adjust the input sensitivity
by±15dB. Since the551E/552E’sinputhas 18
dB of headroom above +4dBm, the unity gain
position(12:00)shouldworkfornormal
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.
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.
Thiswill optimize the signal-to-noise ratio.
Figure 1 - Partial view of front panel controls.
Diagram 2 - Low cut filter with
12 dB per octave.
AUDIO PRECISION 551E vs 23 MAY 96 10:49:15
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
Bypass Button
Push this button into the ACTIVE position to
engagethe551E/552E’scircuitry.TheBY-
PASS (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: The relay mechanism is also engaged
when the AC power is disconnected,
enabling the unit to pass signal even
when the power is off.
HIGH CUT
42K
115 5K
18K
3K 65K
SYSTEM
LOW CUTINPUT
LEVEL (dB)
8
U5022
E
ACTIVE
BYPASS
2606+15-15
POWER CLIP
551
EQUALIZER
PARAMETRIC
FIVE BAND
CUT BANDS
[Withthe exceptionof Chapters 9 and 10,all textin thisUser's Guideis applicableto boththe
551E and the 552E. For brevity we will use the name “551E/552E” to refer to both units.]
Low Cut Filter
Diagram2illustrates a12dB
per octave low frequency
roll-off filter. Use this to
protect subwoofers in
sound systems, clean-up
muddy recordings, or
increase speech intelligibil-
ity in announce systems.
The frequency range is 6Hz
(essentially this is bypass)
to260Hz.
SystemControls
CutBandControls

5
551E 552E
/
Cut/Boost Knob
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. SeeDiagram5.
Note: We’ve provided a wide
range on this knob to
help you take care of the
occasional drasticprob-
lem, but you’ll get better
results from this (or any)
EQ if you use this control
inmoderation.
Diagram 3 - High cut filter
with 12 dB
per octave.
Figure 4 - Front panel view of one EQ band.
AUDIO PRECISION 551E vs 23 MAY 96 10:54:00
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
BAND 1
(Hz) (OCT)
BANDWIDTHFREQUENCY CUT/BOOST
(dB)
+12
850
1.5K
-202.0.05
2K
140
X1
X0.1
X10 100
350 1.0 0
Bandwidth
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 1.0-
2.0 range for “tone control” type sweetening.
Diagram 5 -Typical Cut/Boost curve.
AUDIO PRECISION 551E vs 23 MAY 96 10:01:21
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
High Cut Filter
Diagram3illustratesa12dB
per octave high frequency
roll-offfilter.Therangeof
this control is 3kHz to
65kHz.
EQControls

6
551E 552E
/
Diagram 6 - Frequency graph.
Diagram 7 - Range switch action.
AUDIO PRECISION 551E vs 23 MAY 96 10:02:53
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
Frequency
knob range
AUDIO PRECISION 551E vs 23 MAY 96 10:09:46
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
1kHz
X0.1 1kHz X 1 1kHz X 10
FrequencyKnob
Use this knob, in conjunction with
the Frequency Switch, to adjust
the center frequency of the area
affected by the filter band. See
Diagram6.
FrequencySwitch
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
becomes1kHzto 20 kHz;suitable
for high-frequency adjustments.
The X0.1 position moves the
rangedownwards (10 Hz to 200
Hz), for fine resolution in the low-
frequency area. See Diagram 7.
Before you ask, we want you to
know that we know it seems to
makes no sense that X1 is the top
switchposition,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
parametricEQtoggleswitch.

7
551E 552E
/
Rear Panel ConnectionsChapter 5
Input Jacks
The551E/552EisequippedwithanXLRanda
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
micdirectlyintothe551E/552E’sXLRinput...
don’t bother. It will not hurt anything, but it
just will not work. The input jacks are config-
ured as follows:
XLR
pin 1=ground
pin2=+/high
pin3=-/low
¼"Balanced
tip = +/high
ring=-/low
sleeve=ground
See Appendix A for adapter wiring examples.
Figure 8 - View of rear panel connectors.
INPUT
BALANCED/
UNBALANCED
BALANCED/
OUTPUT
BALANCED
3
INPUT
221
3
RING
TIP
SLEEVE
1
OUTPUT
TYPICAL BALANCED CONNECTIONS
UNBALANCED
BALANCED
RING = LOW(-) = PIN 3
SLEEVE = GND = PIN 1
TIP = HIGH(+) = PIN 2
Output Jacks
There are two output jacks wired parallel to
each other - a balanced XLR, and a balanced
¼" TRS. These can drive balanced or unbal-
anced inputs but you should check Appendix
A for wiring examples. The outputs are
configured as follows:
XLR
pin 1 = ground
pin 2 = +/high
pin3 = -/low
¼"Balanced
tip = +/high
ring=-/low
sleeve = ground

8
551E 552E
/

9
551E 552E
/
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.
Operating TipsChapter 6
Most professional engineers follow this rule of thumb: Use narrow bandwidths for cutting, and
wide bandwidths for boosting.
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.
Setting the Frequency Controls - Part 1
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.
Setting the Frequency Controls - Part 2
BandwidthControl

10
551E 552E
/
Diagram 9 - Overlapping EQ curves on adjacent bands.
AUDIO PRECISION 551E vs 23 MAY 96 16:51:46
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 20k
FREQ(Hz)
Band 1 Band 2
Band 1+2
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
Diagram9.
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/parallelconfigu-
ration to ensure the
most accurate band
interactionwhile
maintaining the best
noise and distortion
performance.
Tomaximizethe
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, overlap-
ping 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 applica-
tions.SeeDiagram10.
OverlappingBands
AUDIO PRECISION 551E vs 28 MAY 96 12:42:32
-20.00
-15.00
-10.00
-5.000
0.0
5.0000
10.000
15.000
20.000
AMPL(dBu)
20 100 1k 10k 30k
FREQ(Hz)
Band 1
Band 3
Band 1+3
Diagram 10 - Overlapping EQ curves on nonadjacent bands.

11
551E 552E
/
ApplicationsChapter 7
StudioApplications
SoundSystems
Monitor Mixes
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.
MultitrackRecording
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 makethe551E/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.
ControlRoomTuning
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.

12
551E 552E
/
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
remainingis,“Where shouldIinstallthe 551E/552E?”
Installthe551E/552Ebeforethefinallimiter (see Diagram 11). If wired in the audiochainafterthe
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’sinput.
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.
FINAL LIMITER
551E PARAMETRIC EQ 551E PARAMETRIC EQ
STEREO AGC/LEVELER
422
Diagram 11 - Recommended audio processing chain for broadcast systems. (Alternately, you could
substitute one 552E for the two 551E’s in this setup.)

13
551E 552E
/
TroubleshootingChapter 8
Thereisnooutputsignal.
Check input and output cables and
connections.
Determine that there really is a signal
coming from the source, and that it is
gettingtothe551E/552E.
Distortionintheoutputsignal.
Put551E/552EintoBYPASS.Ifproblem
remains, check your signal source.
Check the level of the input signal. Is it
overdrivingthe551E/552E’sinput?Ifso,
reduce the incoming signal level. Is the
551E/552E’sclipindicatorlit?
Is the incoming signal already distorted?
Listen“up stream”fromthe551E/552Eto
determine that you are feeding it a clean
signal.
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.
Buzzintheoutput.
Check input and output connector wiring.
Check for ground loops between intercon-
nected system equipment.
Are all system components on the same
AC ground?
Noise (hiss).
Put551E/552EintoBYPASS.Ifproblem
remains, check your signal source. Is the
input signal already noisy? Listen “up
stream”fromthe551E/552Etodetermine
that you are feeding it a clean signal.
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/aline-levelsignal,notamic-level
signal.
Controlsdon’tseemtohaveanyeffect.
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?
The551E/552Edoesnotpowerupordoesnot
respondproperly.
Consult a qualified service technician or
theSymetrixfactory.
The551E/552Eisnotpluggedin,butworks
greatanyway.
Callus.Callusnow.

14
551E 552E
/
Specifications for the 551E
Technical Specifications
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.
Theparametric equalizer (EQ) shall beasingle
channel unit that shall provide five indepen-
dent 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
frequencysweep control with a 100Hz- 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.
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
to62kHz(-0.5dB,-3dB).Thetotalharmonic
distortion plus noise shall be less than 0.002%
(EQ in, all bands flat). The dynamic range shall
Architects and Engineers Specifications
Chapter 9
Maximum Input Level +21 dBu balanced
Maximum Output Level +21 dBu balanced
+17 dBu unbalanced
THD+Noise (1kHz at +4dBu) <0.002%
(<10 Hz to 30 kHz measurement bw)
-eq in, all bands flat
Signal to Noise Ratio >96 dB (unweighted, ref to +4dBu)
-eq in, all bands flat
DynamicRange >114 dB
Frequency Response -0.5 dB, -3dB (20 Hz - 62 kHz)
Input Impedance 20k ohms balanced, 10k ohms unbal.
Output Impedance 300 ohms balanced, 150 ohms unbal.
EQ band Control Specs:
Frequency Control Range 10 Hz - 20 kHz (inc. Frequency Switch)
Cut/Boost Range -20 dB, +12dB
Bandwidth .05 oct - 2.0 oct
be greater than 114 dB. The EQ shall accept a
maximum input signal of +21 dBu and have a
maximumoutputlevelof+21dBu.Thereshall
beafrontpanelclipindicatorthatwillillumi-
nate 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/IECstandardwiring),and¼"TRSfemale
connectors. The input circuitry shall incorpo-
rate RFI filters. There shall be a servo-
balanced, direct-coupled output that shall
terminatein3-pinXLR(AES/IECstandard
wiring) and ¼" TRS connectors.
The EQ shall be capable of operating by
means of its built-in power supply connected
to117VnominalAC,105-130V,50-60Hz(230V
nominalAC,207-253V,50Hzwhereappli-
cable). Power consumption shall be 15 watts
maximum.Thereshall be arearpanelrecep-
tacle for an IEC-type detachable power cord.
The EQ shall be UL and CE approved.
Theunitshallbe aSymetrix,Inc.model551E
FiveBandParametricEqualizer.

15
551E 552E
/
Specifications for the 552E
Technical Specifications
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.
Theparametric equalizer (EQ) shall be a dual
channel unit that shall provide five indepen-
dent 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
frequencysweep control with a 100Hz- 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
filterwithacutofffrequencyrangefrom3kHz
to 65 kHz. A front panel input level control
shall provide ±15 dB of gain adjustment.
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
to62kHz(-0.5dB,-3dB).Thetotalharmonic
distortion plus noise shall be less than 0.002%
Architects and Engineers Specifications
Chapter 10
Maximum Input Level +21 dBu balanced
Maximum Output Level +21 dBu balanced
+17 dBu unbalanced
THD+Noise (1kHz at +4dBu) <0.002%
(<10 Hz to 30 kHz measurement bw)
-eq in, all bands flat
Signal to Noise Ratio >96 dB (unweighted, ref to +4dBu)
-eq in, all bands flat
DynamicRange >114 dB
Frequency Response -0.5 dB, -3dB (20 Hz - 62 kHz)
Input Impedance 20k ohms balanced, 10k ohms unbal.
Output Impedance 300 ohms balanced, 150 ohms unbal.
EQ band Control Specs:
Frequency Control Range 10 Hz - 20 kHz (inc. Frequency Switch)
Cut/Boost Range -20 dB, +12dB
Bandwidth .05 oct - 2.0 oct
per channel (EQ in, all bands flat). The dynamic
range shall be greater than 114 dB. The EQ
shallacceptamaximuminputsignalof +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/IECstandardwiring),and¼"TRSfemale
connectors. The input circuitry shall incorpo-
rate RFI filters. There shall be servo-balanced,
direct-coupled outputs that shall terminate in 3-
pinXLR(AES/IECstandardwiring)and¼"
TRS connectors.
The EQ shall be capable of operating by means
of its built-in power supply connected to 117V
nominalAC,105-130V,50-60Hz(230Vnominal
AC,207-253V,50Hzwhereapplicable).Power
consumptionshallbe20wattsmaximum.There
shall be a rear panel receptacle for an IEC-type
detachable power cord. The EQ shall be UL and
CE approved.
Theunitshallbe aSymetrix,Inc.model552E
DualFiveBandParametricEqualizer.

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551E 552E
/
Warranty Chapter 11
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.
Theforegoingwarrantiesareinlieuofallotherwarranties,whetheroral,written,express,
impliedorstatutory.Symetrix,Inc.expresslydisclaimsanyIMPLIEDwarranties,including
fitnessforaparticularpurposeormerchantability.Symetrix'swarrantyobligationand
buyer'sremedieshereunderareSOLELYandexclusivelyasstatedherein.
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 consum-
ers for personal, family, or household use, Symetrix expressly disclaims allimpliedwarran-
ties,includingbutnotlimitedtowarrantiesofmerchantabilityandfitnessforaparticular
purpose.
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.
Warranty Registration must be completed and mailed to Symetrix within thirty (30) days of the
date of purchase.
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
informationonbehalfofSymetrix.
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.
551E/552ELimitedWarranty

17
551E 552E
/
Service
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:
Returnauthorization
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 [phone], Monday through Friday,
8AM(800hours)though4:30PM(1630 hours), Pacific Time.
In-warrantyrepairs
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.
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.
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-warrantyrepairs
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.
Servicing the 551E/552E
Chapter 12

18
551E 552E
/
Appendix AAdapter Wiring Examples
FROM UNBALANCED OUT
FROM NON-TRANSFORMER (ELECTRONIC)
BALANCED OUTPUT
(TYPICAL OF SYMETRIX PRODUCTS)
FROM BALANCED OUT
FROM UNBALANCED OUT
FROM BALANCED OUT
FROM BALANCED OUT
FEMALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
MALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TERMINAL STRIP
(+) = HIGH
(-) = NOT USED
= GROUND
FEMALE XLR
PIN 1 = GROUND + LOW
PIN 2 = HIGH
PIN 3 = NOT USED
2
2
2
3
3
3
1
1
1
RING
RING
SLEEVE
SLEEVE
TO BALANCED IN
TO BALANCED IN
TO UNBALANCED IN
TIP
TIP
TO UNBALANCED IN FROM
TRANSFORMER COUPLED OR
FLOATING BALANCED OUTPUT
TO BALANCED IN
REV-B