ART EQ300 Series Graphic Equalizers

Overview

The ART EQ300 Series of graphic equalizers are designed and engineered to extremely high standards for audio performance and functionality. These innovative, high-quality equalizers are perfect for virtually any audio application where precision frequency tailoring, reliable performance, rugged design, and extremely silent processing is important.

Active Filter Sections

The EQ300 Series features active filter sections with a constant-Q design. This design ensures narrow bandwidth for each filter, minimizing interaction between filters while allowing precise processing of audio frequencies.

Precision Slide Potentiometers

The series utilizes 20mm precision slide potentiometers with center detents. These faders are positioned on ISO center frequencies: 25Hz-16kHz for the EQ341, and 20Hz-20kHz for the EQ351 and EQ355.

Independent Variable Hi and Low Pass Filtering

The EQ351 and EQ355 models incorporate independent variable Hi Pass (low cut) and Low Pass (high cut) filters. This allows users to custom tailor the audio signal by precisely controlling both high and low frequency roll-offs, offering greater control than fixed shelving switches found on competing products.

Additional Controls and Indicators

The EQ300 Series includes a variable output level control, a clip level indicator, a ground lift switch, and selectable line voltage. Additional features include selectable scale switching for ±6dB or ±12dB slider resolution, active balanced and unbalanced input/output connectors, and RFI filtering.

Passive Bypass Switch

A passive bypass switch allows for direct comparison between the equalized and non-equalized signal for each channel.

Multiple Connectivity

Each unit offers three sets of input and output connectors wired in parallel: XLR, 1/4" phone jacks, and RCA phono jacks. Only one input type should be used per channel, but any combination of output connectors can be used.

Durability by Design

Designed for durability and ruggedness, the EQ300 Series is ideal for demanding applications. They are designed for standard 19" equipment rack mounting. The vertical height is 1.75 inches for the EQ341 and EQ351, and 3.5 inches for the EQ355. The depth is 7 inches, excluding the power cord. Their rugged construction and solid audio performance make them suitable for fixed installations and touring live sound systems.

Precision and Quality

The ART EQ300 Series delivers precise, flexible, and great-sounding equalization, featuring quality components and reliable design for top-level audio performance.

General Information

The ART equalizer is a professional quality unit suitable for any audio application requiring frequency tailoring. Key features include constant-Q circuitry with accurate center frequencies, selectable ±6dB or ±12dB range, active balanced and unbalanced I/O connectors, RFI filters, independent variable Hi Pass (low cut) and Low Pass (high cut) filters (on EQ351 and EQ355), variable input level control, passive bypass switch, clip level indicator, ground lift switch, and selectable line voltage. Rugged construction and solid audio performance make these equalizers well-suited for fixed installations and touring live sound systems.

Installation

These equalizers are designed for mounting in a standard 19" equipment rack or compatible portable cases. The vertical height is 1.75 inches for the EQ341 and EQ351, and 3.5 inches for the EQ355. The depth is 7 inches, excluding the power cord.

Power Connectors

The equalizers feature internal power supplies and operate with 120 or 240 VAC, 50-60Hz mains supply, selectable via a rear panel switch. It is recommended to confirm the voltage and select the appropriate setting before connecting to power sources.

Input/Output Connections

The EQ300 series offers three sets of input and output connectors wired in parallel: 1/4" phone, XLR, and RCA. Only one input type should be used per channel, but any combination of output connectors may be used.

1/4" Phone Jack Connections: Can be used balanced or unbalanced. For balanced connections, the tip is High (+), the ring is Low (-), and the sleeve is Ground. For unbalanced connections, use a mono 1/4" cable which grounds the ring to the sleeve.

XLR Connections: Are balanced, with Pin 2 as High (+), Pin 3 as Low (-), and Pin 1 as Ground.

RCA Jack Connections: Are unbalanced, with the pin being High (+) and the outside being Low (-).

Signal Levels

Normal signal levels range from -10dBm to +4dBm, with maximum levels around +18dBm (balanced) or +22dBm (unbalanced). Microphones and instrument pickups typically require a preamp to reach line level. Connect the equalizer's outputs to line-level inputs for best results, avoiding sensitive microphone or instrument inputs.

Chassis Grounding

The equalizers are equipped with a rear panel grounding screw and a Ground Lift switch. The Ground Lift switch should normally be set to the GND position. If excessive hum or buzzing occurs, a ground differential between equipment may be the cause. The Ground Lift switch can help minimize system hum by trying different grounding combinations.

? NOTE: ALWAYS TURN YOUR AMPLIFIERS DOWN BEFORE CHANGING GROUNDS.

Ensure all chassis are connected to earth ground, either via AC power cords or rear panel grounding screws. If the equalizer is rack-mounted, the ground to the grounding screw may be lifted to prevent multiple ground paths that could cause a ground loop.

Initial Setup

Before equalizing, familiarize yourself with the unit. The BYPASS switch, when activated, illuminates its LED and routes the signal directly through the unit at unity gain, bypassing all equalization settings. This is useful for comparing equalized and unequalized audio or for bypassing the EQ in case of failure.

The RANGE selection switch offers ±6dB (green LED) or ±12dB (yellow LED) gain range for the sliders. The LEVEL control adjusts the output signal from off to +6dB. A red CLIP LED illuminates when signals are within 6dB of clipping. Occasional flickering is normal, but steady illumination indicates the need to reduce the output level.

Setup Tips:

1. Set channel output LEVELs to the center detent (0dB).
2. Engage the BYPASS switch (red LED illuminates).
3. Set all frequency slide controls to the center detent (0dB).
4. If applicable, set the HI PASS filter to 10Hz and the LOW PASS filter to 40kHz.
5. Select the ±6dB RANGE (green LED illuminates).
6. Apply a signal; if the CLIP LED is on, reduce the input signal.
7. Disengage the BYPASS switch (red LED turns off).
8. If the CLIP LED is on, reduce the Output LEVEL control.
9. Begin equalizing your system.
10. If more equalization control is needed, switch the range to ±12dB.

Operation

Front Panel Controls

The front panels of the EQ341, EQ351, and EQ355 feature various controls for audio equalization:

Power Switch

Press the upper or lower portion of the POWER switch to turn the unit on or off. ⚠️ CAUTION: Always turn on your equalizer BEFORE your power amplifiers, and turn off your equalizer AFTER your power amplifiers.

Filter Level Controls

These sliders control the signal level for each of the 31 (or 15) bandpass filters. A center detent aids in setting a flat response.

Filter Range Switch & Indicators

This switch adjusts the gain range of all filter sliders simultaneously between ±6dB and ±12dB. The green LED indicates ±6dB mode, and the yellow LED indicates ±12dB mode.

Bypass Switch & Clip Indicator LED

The red BYPASS LED indicates when the unit or channel is in bypass mode, routing the signal directly from input to output without EQ processing. This allows for easy comparison of equalized vs. unequalized audio or bypassing the EQ in case of failure.

The red CLIP LED illuminates when any section of the equalizer is near clipping. Occasional flickering is normal, but steady illumination requires reducing the output level of the preceding equipment or the equalizer's LEVEL control to prevent distortion.

Hi Pass Filter (Low-Cut Frequency Control) (EQ351 and EQ355 only)

This control adjusts the roll-off frequency of the Hi-Pass Filter (HPF) from 10Hz to 250Hz. Its steep slope is effective for cutting hum, low-frequency noise, and resonances, and for reducing rumble.

Low Pass Filter (High-Cut Frequency Control) (EQ351 and EQ355 only)

This control adjusts the roll-off frequency of the Low-Pass Filter (LPF) from 3kHz to 40kHz. Its steep slope is useful for reducing high-frequency noise and achieving a more natural sound by rolling off excessive high frequencies.

Level Control

This knob controls the output signal level. Adjust it down if the CLIP LED is steadily illuminated. It can be set for unity gain, ensuring the perceived volume remains consistent when toggling the BYPASS switch. Signal levels should be normalized, meaning the bypassed level should be the same as, or slightly lower than, the active level.

Rear Panel Connectors & Controls

Power Cord

Connects the equalizer to the AC power source. ⚠️ CAUTION: Equipment for USA installation includes a three-pin polarized plug. Do not remove the center grounding pin.

Fuse Holder, Line Voltage Switch & Grounding Screw

The fuse holder contains the AC primary fuse, which should be replaced with the same type if blown. Continuous fuse blowing indicates a need for qualified service. ⚠️ CAUTION: Ensure the correct fuse (0.5Amp/500mA for 95-125VAC and 220-240VAC) is installed and the holder is securely seated. The line voltage switch determines the operating voltage range.

Ground Lift Switch

This switch disconnects signal ground from mains and chassis earth ground. Set to the LIFT position if "Hum" caused by a ground loop is audible at the speakers.

Input/Output Connectors

The rear panels provide various input and output connectors:

• EQ341: Features two channels, each with balanced XLR and 1/4" TRS inputs and outputs, plus unbalanced RCA outputs.
• EQ351: Features a single channel with balanced XLR and 1/4" TRS inputs and outputs, and unbalanced RCA outputs.
• EQ355: Features two channels, each with balanced XLR and 1/4" TRS inputs and outputs, and unbalanced RCA outputs.

Detailed wiring for 1/4" TRS (balanced/unbalanced), XLR, and RCA connectors is provided in the specifications section and on page 11.

Applications

Graphic equalizers are versatile tools for modifying the frequency contour of sound systems, addressing various sound problems or creative needs.

Typical Reinforcement Application of a Two Channel Equalizer

This diagram illustrates a common setup where a mixer sends audio to a power amplifier (P Amp), which then drives a speaker. The equalizer (EQ) is placed in the signal path to shape the frequency response.

Equalization of Audio Signals from a Mixer

This diagram shows an EQ placed in an effects loop or auxiliary send/return path from a mixer, allowing for precise tonal shaping of specific audio signals before they are returned to the main mix.

Equalization of a Musical Instrument

This setup demonstrates how an EQ can be used with a musical instrument. The instrument's signal first goes through a preamplifier (PreAmp), then to the EQ, and finally to an amplifier (Amp) or speakers.

Equalization of an Effects Loop

This diagram shows an EQ integrated into an effects loop, typically used with stereo effects. The signal from a preamplifier (PreAmp) goes through the effects loop, which includes the EQ and an amplifier (Amp), allowing for tonal control of the effects.

Warranty Information

Limited Warranty

Applied Research and Technology (ART) warrants this product and its components to be free from defects in workmanship and materials for three years from the date of purchase. ART will repair or replace defective products at no charge upon prepaid delivery to their factory service department or an authorized service center, accompanied by proof of purchase.

Exclusions

This warranty does not cover misuse, abuse, unauthorized alterations, or repairs. It is void if the serial number is altered, defaced, or removed. ART reserves the right to make design changes without obligation to apply them to previously manufactured products. ART is not liable for consequential damages, including loss of use. Some states may not allow limitations on incidental or consequential damages, so these exclusions may not apply to all users.

For units purchased outside the United States, service will be provided by an authorized distributor of Applied Research and Technology.

Service

In the unlikely event your unit requires service:

1. Verify the unit is the source of the problem. Check power supply, cable connections, and cable condition. Consult your dealer for assistance with troubleshooting or testing your configuration.
2. If the ART unit is suspected to be faulty, visit www.artproaudio.com. Contact Customer Service for assistance or request a Return Authorization in the "resources" section of the website.
3. When returning the unit for service, pack it in its original carton or a suitable substitute. Consider placing the packaged unit in another box for shipping. Print the RA number clearly on the outside of the shipping box and include your return shipping address.
4. Include with your unit: the RA number, your contact information (including return shipping address – P.O. boxes are not accepted – and a daytime phone number), and a description of the problem (preferably attached to the unit). Also include a copy of your purchase receipt.

Fill in the following information for your reference:

Date of purchase: ___________________
Purchased from: ___________________
Serial number: ___________________

Specifications