Applied Research and Technology (ART) HQ15, HQ31 Owner's Manual

HQ-31

SINGLE CHANNEL 31 BAND 1/3 OCTAVE GRAPHIC EQUALIZER

HQ-15

DUAL CHANNEL 15 BAND 2/3 OCTAVE GRAPHIC EQUALIZER

USER’S GUIDE

GENERAL INFORMATION

SINGLE CHANNEL 31 BAND 1/3 OCTAVE GRAPHIC EQUALIZER WITH FDC

Features constant Q circuitry with a 3% center frequency accuracy. Special features include: FDC
(Feedback Detection Circuit), analog VU metering, selectable range 6dB or 12dB, active balanced
and unbalanced input/output connectors, RFI filters, variable Hi pass (low cut) and Low pass (high
cut) filters, variable input level control, passive bypass switch, clip level indicator, ground lift switch,
and selectable line voltage switch. The unit also features automatic bypass if power to the unit is lost.

TWO CHANNEL 15 BAND 2/3 OCTAVE GRAPHIC EQUALIZER
Features constant Q circuitry with a 3% center frequency accuracy. Special features include: FDC
(Feedback Detection Circuit), analog VU metering, selectable range 6dB or 12dB, active balanced
and unbalanced input/output connectors, RFI filers, variable input level control, passive bypass
switch, clip level indicators, ground lift switch, and selectable line voltage switch. The unit also
features automatic bypass if power to the unit is lost.

FDC - ART’s FEEDBACK DETECTION CIRCUIT

FDC (Feedback Detection Circuitry – designed and developed by ART Engineering) instantly
illuminates the corresponding EQ band with the greatest signal. That is, if feedback occurs, FDC
identifies the band with the feedback frequency for quick correction.

During operation, various LED’s will illuminate as it passes signal. The loudest band will correspond
with the brightest LED. When you hear feedback, FDC (and it’s brightest LED) shows you where to
attenuate.

FDC confirms what you hear (feedback), and shows you exactly where it is. You’ll also know you
have properly attenuated the signal as the LED reduces its illumination. FDC - it is both precise and
simple.

FDC APPLICATIONS

FDC allows you to observe those frequency bands with the greatest energy when program material is
being played. In a live sound system where the HQ EQ is in the path between a microphone and
loudspeakers, dominant room modes may be seen as bands with a lot of energy when the sound

system gain is increased. These bands with excess energy will brightly illuminate the corresponding
led above the offending frequency’s fader. These frequencies will generally be the first where
feedback is likely to occur.

FDC can also be employed as a simple spectrum analyzer along with its primary use with the
equalizer. This will allow you to identify “hot” spots – area of potential feedback – and attenuate
accordingly before feedback occurs.

Of course, during a musical performance, FDC will help you quickly locate and eliminate feedback if it
occurs.

Be careful when running a soun d system close to its feedback limit. Feedback can damage
equipment as well as hearing.

FDC SYSTEM PRECISION
The HQ EQ circuitry is extremely precise. The equalizer features Constant-Q Filtering, which helps

the HQ’s FDC work with great efficiency. When feedback occurs at a certain band, the ensuing
attenuation will not affect surrounding bands. This precision is, of course, critical for professional
applications.

INSTALLATION
These equalizers are designed for mounting in a standard 19” equipment rack or one of the many
rack type portable cases available on the market. The vertical measurements are 3.2 inches. Both
models are 8.5 inches in depth.

POWER CONNECTORS

This series of graphic equalizers have internal power supplies and are designed for operation from
120-240 volt, 50-60Hz mains supply. Power consumption is 20 watts. In new installations and
portable sound systems, or any situation in which the mains power is in question, it is wise to confirm
the voltage and select the appropriate line voltage switch BEFORE connecting the equalizer to power
sources.

INPUT/OUTPUT CONNECTIONS

This series of graphic equalizers have 3 sets input output connectors wired in parallel: XLR, 1/4"
phone, and RCA phono connectors.

Only one of the 3 inputs should be used per channel. Any combination of output connectors may be
used.

XLR connections are balanced with pin 2 is High (+), pin 3 is Low (-), and pin 1 is ground.

1/4" Phone connections may be used balanced or unbalanced. When balanced, the tip is High (+),
the ring is low ( -) and the sleeve is ground. To use unbalanced use a mono phone cable, this will
automatically ground the ring to the sleeve.

RCA connections are always unbalanced.

SIGNAL LEVELS
Signal levels from -10 dBu to +4 dBu are considered normal and 20dB of headroom exists above
these levels. Do not connect microphones directly to the equalizer. Microphones require a preamp.

CHASSIS GROUNDING
The equalizers are equipped with a rear panel Ground lift switch. After setting up your system, if the
system exhibits excessive hum or buzzing, the problem may be a ground incompatibility between
your equalizer and other equipment in the same system. There are several combinations that can be
attempted. NOTE: ALWAYS TURN YOUR AMPLIFIERS DOWN BEFORE CHANGING
GROUNDS. Try different combinations of lifting grounds on units that are supplied with ground lift
switches or make sure all chassis are connected to earth ground, either through the A.C. Power cord
ground or by the front panel rack mount screws.

If the HQ equalizer is mounted in a grounded rack of equipment, the ground to the case of the HQ
may be lifted to prevent multiple ground paths, which may cause a ground loop to occur.

OPERATING INSTRUCTIONS

Before starting to equalize your sound system there is some information you should know and
procedures you should follow. Your equalizer is equipped with a bypass switch. The bypass switch,
when activated, lights the LED and cancels all equalization settings while allowing signal to flow
through the unit at unity gain.

Also included is a range selection switch with LED indicators, 6dB =green, 12dB= yellow. In addition

to the range selection switch there is an output level control potentiometer. The level control operates
between off and +6dB. Note: If there is too much gain your equalizer has a red LED Clip indicator.
The Clip LED illuminates when signals reach 5dB prior to clipping. If this situation occurs and the
overload LED flashes occasionally, this is okay, but if the overload LED is steadily on you must
readjust the level control.

Here are some tips to help you with the initial set up:

1. Set channel levels to the center detent 0dB on the front panel.

2. Bypass the bypass equalizer (Note: The red LED is on).

3. Set the frequency slide controls to the center detent or 0dB.

4. Select the 6dB range switch (Note: The green LED is on).

5. Apply signal to the system.

6. Release the bypass switch (Note: The red LED is off).

7. If the Clip LED is on you must turn down the input level control.

8.You may now start equalizing your system.

9. If you do not have enough gain for your needs, switch the range switch to the 12dB setting.

10. If the Clip LED lights continuously, turn down the level control until the LED is off most of the time.

FRONT PANEL CONTROLS

1. POWER SWITCH

To turn the equalizer ON or OFF, press the upper or lower portion of this button. CAUTION: Always