Universal Audio 537 User manual

BEFORE PROCEEDING WITH COMPLETE UNPACKING AND SETUP,
READ THE SECTION ON UNPACKING AND INSPECTION
model 537
GRAPHIC EQUALIZER
fU
UREI Incorporated
8400 BALBOA BOULEVARD
NORTHRIDGE, CA. 91325-4100 U.S.A.
PHONE: (818) 895-UREI (895-8734)
FAX: [phone]
©Copyright 1978,1988 UREI Incorporated

TABLE OF CONTENTS
PAGE
SECTION I. INTRODUCTION
1.1 DESCRIPTION 1
1.2 SPECIFICATIONS 2
1.3 CONTROLS 3
1.4 PHYSICAL 3
1.5CONNECTIONS 3
SECTION II. INSPECTION AND INSTALLATION
2.1 UNPACKING AND INSPECTION 4
2.2 ENVIRONMENTAL CONSIDERATIONS 4
2.3POWERING 4
2.4 LINE VOLTAGE SWITCH 5
2.5 EXTERNAL CONNECTIONS 5
2.6 IMPEDANCE AND TERMINATION 7
2.7 SIGNAL LEVEL AND OVERLOAD DETECTOR 8
2.8 ACCESSORIES 8
SECTION III. OPERATING INSTRUCTIONS
3.1 GENERAL 9
3.2 SYSTEM CHECK 9
3.3EXPERIMENTATION 9
3.4DOCUMENTATION 9
3.5 APPLICATION 9
3.6 GAIN STRUCTURE AND SIGNAL-TO-NOISE 12
3.7 INPUT LEVEL 13
3.8 OVERLOAD INDICATOR 14
SECTION IV. THEORY OF OPERATION
4.1 INPUT AMPLIFIER 13
4.2 ONE-THIRD OCTAVE FILTERS 13
4.3 EQ IN-OUT SWITCH 16
4.4 OUTPUT AMPLIFIER 16
4.5 OVERLOAD DETECTOR 17
4.6 POWER SUPPLY 17
SECTION V. MAINTENANCE
5.1 GENERAL 18
5.2 REPAIRS AND WARRANTY 18
5.3 SERVICE ADJUSTMENTS 18
5.4 ON OP AMPS 20
SECTION VI. ILLUSTRATIONS
FIGURE 5. SCHEMATIC DIAGRAM OF UREI MODEL 537 21

SECTION I
INTRODUCTION
FIGURE 1. MODEL 537 FRONT PANEL.
1.1 DESCRIPTION
The Model 537 is an active filter set for general purpose
frequency response adjustment of audio signals. It offers alarge
control range with optimum signal-to-noise ratio at any filter
setting, and is therefore an ideal tool for creative equalization
in professional sound recording, sound reinforcement, broadcast,
motion picture and TV recoroing, and live performance.
The 537 provides 12 dB of boost or cut at each of its 27
frequencies, which are centered at ISO 1/3-octave increments
from 40 Hz to 16 kHz. The filter characteristic has been optimized
for excellent combining action with minimum phase shift. The
position of the 27 control arms provides agraphic representation
of the response curve selected. An adjustable front panel control
provides up to 20 dB gain. An overload detection circuit monitors
the signal throughout the unit. If the signal level approaches
overload, afront panel LED flashes to warn the user. Abypass
switch permits switching the equalization out for A-B tests. The
optional security cover (SC-1) may be installed to protect all
operating controls against inadvertent disturbance or tampering at
fixed installations.
Due to the front panel's uncluttered and logical arrangement,
operation is simple and self-explanatory. However, athorough
understanding of the Model 537 Graphic Equalizer and its application
can only benefit the user, so we recommend carefully reading this
manual
.
NOTE: Throughout this manual, where the expression "dB" is
used to denote asignal level, it is referenced to
0dB =0.775 volts rms.
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1.2 SPECIFICATIONS
ELECTRICAL:
INPUT; Balanced bridging, differential amplifier.
INPUT IMPEDANCE: 40 kohms ,used as balanced input.
20 kohms, used as unbalanced
(single-ended) input.
MAXIMUM INPUT LEVEL; +20 dB (7.75 volts).
EQUIVALENT INPUT NOISE: Less than -90 dB. Typically -94 dB;
15.7 kHz bandwidth with all controls set
flat, output terminated with 600 ohm
load
.
GAIN: from unity to +20 dB, ±1 dB.
FREQUENCY RESPONSE: ±1 dB, 20-20,000 Hz (with no EQ)
.
OUTPUT: Floating, transformer isolated.
OUTPUT LOAD: 150 ohms or greater.
POWER OUTPUT: +24 dBm into 600 ohm load (12.28 volts),
+26 dBm into 150 ohm load (7.75 volts).
DISTORTION: Less than 0.5% THD, 30 Hz to 15 kHz at
maximum rated output.
POWER REQUIREMENTS: 100-125 VAC or 200-250 VAC, 50/60 Hz,
switch selectable, less than 10 W.
ENVIRONMENT: Operating 0°C to +50°C (+32°F to +122°F);
storage -20°C to +60°C (-4°F to +140°F)
.
FILTER TYPE: 27 individual L-C type active filters.
FILTER BANDWIDTH: 1/3-octave at -3dB points with 8dB
boost or cut.
CENTER FREQUENCIES: Standard ISO (Hz) 40 50 63 80 125 160 200
250 315 400 500 630 800 IK 1.25K 1.6K 2K
2.5K 3.15K 4K 5K 6.3K 8K lOK 12. 5K 16K.
FREQUENCY ACCURACY: ±3% of center frequency.
RANGE OF BOOST AND CUT: 0to ±12 dB, single filter section.
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CALIBRATION OF
BOOST AND CUT: Within 1dB of indicated setting,
0to ±5 dB,
Within 1.5 dB of indicated setting,
±5 to ±12 dB, single filter section.
1.3 CONTROLS
:
EQUALIZATION: 27 vertical slide controls, continuously
variable 0to ±12 dB.
GAIN: Screwdriver adjustable from unity to
+20 dB.
EQ IN/OUT: Front panel toggle switch.
POWER: Front panel toggle switch.
INDICATORS: LED, Power ON;
LED, Overload Condition, levels monitored
at 4circuit points;
MAINS VOLTAGE: Rear panel slide switch, 115/230 volts.
CONNECTIONS
:
Input and output, through rear chassis
barrier strip;
Power through 3-wire power cable.
1.4 PHYSICAL:
DIMENSIONS: 4tt3 X89 mm rack panel; Depth behind panel
203 mm. (19" x3-1/2" x8")
FINISH: Panel is 3.18 mm (1/8") brushed clear
anodized aluminum in two shades.
Chassis is cadmium plated steel.
WEIGHT: 5.00 kg (11 pounds).
SHIPPING WEIGHT: 7.23 kg (16 pounds).
ACCESSORIES: Model SC-1 Security Cover, smoke gray
transparent plastic; covers all operating
controls.
1.5 CONNECTIONS:
All connections for
barrier strip at the rear
structions. Section 2.5.,
input and output are made through a
of the chassis. (See Installation In-
Figures 2and 3.)
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SECTION II
INSPECTION AND INSTALLATION
2.1
UNPACKING AND INSPECTION
Your Model 537 was carefully packed at the factory, and the
container was designed to protect the unit from rough handling.
Nevertheless, we recommend careful examination of the shipping
carton and its contents for any sign of physical damage which
could have occurred in transit.
If damage is evident, do not destroy any of the packing mater-
ial or the carton, and immediately notify the carrier of apossible
claim for damage. Shipping claims must be made by the consignee.
The shipment should include:
Model 537 Graphic Equalizer
UREI Instruction Manual (this book)
Two-part Warranty Card bearing the
same serial number as the Model 537.
Rack mounting hardware.
2.2
ENVIRONMENTAL CONSIDERATIONS
The system will operate satisfactorily over arange of ambient
temperatures from 0°C to +50°C (+32°F to 122°F), and up to 80%
relative humidity.
If the system is installed in an equipment rack with high heat
producing equipment (such as power amplifiers), adequate ventilation
should be provided in order to assure longest component life.
Also, while circuitry susceptible to hum pick-up is sufficiently
shielded from moderate electromagnetic fields, installation should
be planned to avoid mounting the system immediately adjacent to
large power transformers, motors, etc.
2.3
POWERING
The 537 may be operated from either 100-125 VAC or 200-250
VAC mains (50 or 60 Hz, single phase.) As indicated in section
2.4, the nominal line voltage may be selected with arear panel
switch. BE SURE TO VERIFY BOTH THE ACTUAL LINE VOLTAGE, AND THE
SETTING OF THE VOLTAGE SELECTOR SWITCH BEFORE CONNECTING THE
537 TO THE MAINS.
To comply with most Electrical Codes, the 537 is supplied
with athree-wire AC cord, the grounding pin of which is connected
to the chassis. In some installations this may create ground-loop
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problems. If ground problems are experienced, check for the
possibility of ground loops by using a3-prong to 2-prong AC
adapter. This ungrounds the Model 537, and will sometimes cure the
problem, but is not asubstitute for proper grounding. Be aware
that unless the Model 537 mainframe is properly grounded, asafety
hazard can exist. UREI accepts no responsibility for legal actions
or for direct, incidental or consequential damages that may result
from violation of any electrical codes.
2.4 LINE VOLTAGE SWITCH
Unless atag on the line cord specifies otherwise, the
Model 537 was shipped ready for operation with nominal 115 VAC
power mains. In order to change this for nominal 230 V(50 or
60 Hz), slide the VOLTAGE SELECTOR switch on the rear panel to
the 230 position. The voltage is visible in awindow next to the
switch slot. Be sure to change the fuse to the correct value:
1/8-amp slo-blo when changing to 230 Voperation or 1/4-amp slo-
blo for 115 Voperation. Asmall screwdriver may be used to move
the recessed switch.
2.5EXTERNAL CONNECTIONS
Permanent input and output signal wires should be shielded
cable, and connected in accordance with standard wiring practice,
as indicated on the rear panel barrier strip.
If the Model 537 output is connected to ahigh impedance
circuit, we recommend shunting the ''±" and "COM" output terminals
with a620 ohm, 1/2 watt resistor. This assures optimum loading
of the output stage. (See section 2.6 regarding input termination).
(See Figures 2&3, next page)

OUTPUT GRD INPUT
FIGURE 2. CONNECTING THE MODEL 537 WITH BALANCED
INPUT AND BALANCED OUTPUT CIRCUITS.*
FIGURE 3. CONNECTING THE MODEL 537 WITH UNBALANCED
INPUT AND UNBALANCED OUTPUT CIRCUITS.*
*With abalanced input and unbalanced output, or vice-versa,
use the appropriate connections suggested by each of the above
diagrams. No special switching or transformers are needed.
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2.6 IMPEDANCE AND TERMINATION
Audio engineering had its roots in the telephone industry, and
"600 ohm circuits" (together with their predecessors, "500 ohm
circuits") are carry-overs from telephone transmission practices.
Long audio transmission lines, like their video counterparts, must
be properly sourced from and terminated in equipment which matches
their characteristic impedance, if optimum frequency response and
noise rejection are to be achieved.
However, transmission line theory and techniques are not
only unnecessary but impractical within modern recording studios,
broadcast studios and other local audio systems where transmission
circuits are seldom more than several hundred feet in length. The
advent of negative feedback circuitry and solid-state electronics
has spawned modern audio amplifiers and other signal processing
devices having source impedances of only afew ohms. They are
essentially indifferent to load impedances and by varying their
output current inversely to changes in load impedance, maintain
the same output voltage into any load impedance above arated
minimum, with no change in frequency response. Most new designs
(all at UREI) have high input impedance to allow use with various
source impedances.
Most modern audio systems, therefore, utilize amplifiers and
other active devices which have very low output impedances and high
(lOK to 50K) input impedances. These products may thus be cascaded
(operated in tandem), or many inputs may be connected to asingle
output of apreceeding device, without regard to impedance "matching"
Switching, patching, etc. is simplified because "double loads" and
"unterminated" bugaboos are essentially eliminated. "Floating"
(ungrounded) transformer outputs minimize ground loop problems, and
differential transformerless input circuitry (or input transformers)
minimize common mode noise or interference which may be induced
into the interconnecting wires or cables, or produced by different
ground potentials.
Where audio must be transmitted through cables or wire pairs
of more than several hundred feet in length, however, transmission
line termination practices should still be observed.
The Model 537 has an input impedances of 40,000 ohms when used
in abalanced, differential input configuration, and 20,000 ohms
when used unbalanced (one side grounded). This makes the equalizer
suitable for use with any normal source impedance, low or high.
Only when it is used from asource which requires alow impedance
termination (such as a600-ohm transmission line or older vacuum-
tube equipment) is asource termination resistor required at the
537 input.
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2.7 SIGNAL LEVEL AND OVERLOAD DETECTOR
The Model 537 's differential input amplifiers are capable of
being driven by signals up to alevel of +20 dB (Ref. 0.775 Vrms),
above which clipping and distortion occurs. The overload LED turns
on when peak signals exceed the clipping level, and it will remain
on long enough to be seen even if the excess signal is only abrief
transient. To avoid audible distortion, when the LED indicator
flashes more than occasionally, either lower the output level of
the source feeding the equalizer, or use an external attenuation
pad
.
Because of the possible combination of control settings, the
overload is monitored at several points in the circuit;
1. Input amplifier (maximum signal level +20 dB,
ref .0.775V rms )
.
2. Filter amplifiers, which could be driven into clipping as
aresult of boost equalization.
3. Output amplifier, which is capable of delivering +24 dBm
into a600-ohm load (12.3 Vrms), or +26 dBm into a150-ohm
load (7.75 Vrms )
.
2.8 ACCESSORIES
Asecurity cover may be installed over the 537 front panel.
This protects all controls from unwanted adjustments. Only the power
switch remains accessible. The smoke gray plexiglas cover is trans-
parent enough to allow viewing of the control settings.
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