The dbx 30 Series Graphic Equalizers are high-performance, multifunctional audio signal processing units designed for professional use, offering precise frequency control across the audible spectrum. These equalizers are suitable for a wide range of applications, from studio work to live sound reinforcement.
Function Description:
The primary function of the 30 Series Graphic Equalizers is to allow users to boost or cut specific frequency bands within an audio signal. This enables fine-tuning of the sound to compensate for acoustic environment characteristics, eliminate feedback, enhance clarity, or achieve a desired tonal balance. The units feature multiple frequency bands per channel, with either 1/3 octave or 2/3 octave ISO standard center frequencies, depending on the model.
Key features include:
- Equalization: 31 ISO standard center 1/3 octave constant Q frequency bands per channel (models 3031, 3031C, 3231L) or 15 ISO standard center 2/3 octave constant Q frequency bands per channel (model 3215).
- Filters: Variable high-pass and switchable low-pass 12dB/octave filters for precise control over the frequency extremes. The low-cut filter is variable from 25 Hz to 200 Hz, and the high-cut filter is fixed at 15 kHz.
- Input/Output: Electronically balanced inputs with superior common mode rejection and servo-balanced outputs. Connections are provided via XLR, barrier strip, and TRS connectors, supporting both balanced and unbalanced configurations.
- Gain Control: Input gain control capable of -12dB to +15dB.
- Bypass: Relay bypass on power-down ensures signal continuity even if power is lost. An active EQ IN/OUT switch allows for comparison between the equalized and unprocessed signals.
- Grounding: Chassis ground lift capability and an input ground lift switch help prevent ground loops and electronic hum in sound systems.
Important Technical Specifications:
- Connectors: Electronically Balanced XLR (pin 2 hot), barrier strip, 1/4" Jack (tip hot).
- Impedance: 75kΩ balanced, 50kΩ unbalanced.
- Max Level: +22 dBu (ref: 0.775Vrms).
- CMRR: >85dB at 1kHz.
Output:
- Connectors: Servo Balanced XLR (pin 2 hot), barrier strip, 1/4" Jack (tip hot).
- Impedance: 100Ω balanced, 50Ω unbalanced.
- Max Level: +22 dBu (ref: 0.775Vrms).
- Noise: < -90dBu @ ±6dB boost/cut range (faders flat, test bandwidth 22 Hz to 22kHz).
- Frequency Response: 20Hz to 20kHz, ±1dB (all faders flat).
- THD+Noise: < .004% (at 1kHz, +4 dBu input, test bandwidth 22 Hz to 22kHz).
- Dynamic Range: 112dB.
- Control Range:
- 3031, 3231L, 3215: ±6 dB or ±12dB cut/boost.
- 3031C: -10 dB or -20dB cut.
- Frequency Bands:
- 3031, 3031C, 3231L: 31 ISO Standard, 1/3 octave bands from 20Hz to 20kHz (20, 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, and 20k).
- 3215: 15 ISO Standard, 2/3 octave bands from 25Hz to 16kHz (25, 40, 63, 100, 160, 250, 400, 630, 1k, 1.6k, 2.5k, 4k, 6.3k, 10k, and 16k).
- Headroom Meter: 3 to 42 dB, 8 LED segments.
Power:
- Requirements: 100, 120, 230, 240 VAC 50/60 Hz, 30 watts.
Physical:
- Dimensions: 7.9" x 3.5" x 19" (20.06 cm x 8.88 cm x 48.25 cm) for 3031, 3031C, 3215.
- Dimensions: 7.9" x 5.25" x 19" (20.06 cm x 13.33 cm x 48.25 cm) for 3231L.
- Weight: 8.5lbs (3.85 kg) for 3031, 3031C.
- Weight: 12 lbs (5.44 kg) for 3231L.
- Weight: 9lbs (4.08 kg) for 3215.
Usage Features:
- Front Panel Controls:
- Power Switch/LED: Turns the unit ON/OFF and indicates power status.
- EQ IN/OUT Switch: Engages or bypasses the equalizer's input gain and individual slider controls from the signal path, while still allowing HI CUT and LOW CUT filters to operate.
- BOOST/CUT RANGE SELECTION SWITCH: Selects between two boost/cut ranges (e.g., ±6dB or ±12dB; -10dB or -20dB for 3031C).
- HEADROOM BAR GRAPH: Eight LEDs indicate peak levels within the equalizer, with the top LED indicating 3dB below clipping.
- INPUT GAIN CONTROL: Adjusts the signal level to the equalizer.
- FREQUENCY BAND SLIDER CONTROLS: Individual slider potentiometers for boosting or cutting specific frequencies. Center detent position indicates a flat response.
- LO CUT FREQUENCY CONTROL and LO CUT IN/OUT SWITCH: Varies the cutoff frequency of the 12dB/octave low-cut filter (25 Hz to 200 Hz) and engages/bypasses it.
- HI CUT IN/OUT SWITCH: Engages or bypasses the 12dB/octave high-cut filter (15 kHz).
- Installation: Designed for rack mounting. It is recommended to mount the unit away from excessive heat sources, with ambient temperatures not exceeding 113° F (45°C). While shielded against RF and EMI, extremely high fields should be avoided.
- Cabling: Supports both balanced and unbalanced connections using XLR, TRS 1/4" jacks, and barrier strips. Proper cabling is crucial to avoid issues like phase cancellation or ground loops. The manual provides detailed wiring diagrams for various connection types.
- Application Notes: Useful for tuning acoustical environments, eliminating feedback (especially with the LOW CUT filter for stage rumble), and modifying/enhancing audio signals in studio settings. When used with a spectrum analyzer, the EQs can flatten frequency response and increase clarity.
Maintenance Features:
- Reliability: The dbx EQs are solid-state products with high-performance components, factory-tested and burned-in for reliability. No adjustments are typically required throughout the unit's life.
- Fuse Protection: Equipped with a fuse to protect against electrical faults. The manual provides a list of appropriate fuse types for different AC voltage configurations (e.g., T 250mA 250V for 100VAC, 200mA 250V Slow Blow for 120VAC). Users are advised to determine and remove the cause of a fuse failure before replacement.
- Grounding Options: The INPUT GROUND LIFT SWITCH and CHASSIS GROUND LIFT STRAP (removable jumper on the barrier strip) provide flexibility in managing ground connections to prevent "hum" or "ground loops" in a sound system.
- Service: In case of repair, it is recommended to return the EQ to the factory after obtaining a Return Authorization number from dbx customer service. Technical support is available for troubleshooting, requiring a description of the problem and the unit's serial number.
- Optional Accessories: An optional Input and/or Output Transformer kit is available for special applications, which can be installed by a dealer or contractor.
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