Shure SR107 Audio Equalizer: Operation and Service Manual
Description
The Shure SR107 Audio Equalizer is a compact, versatile unit designed to adjust tonal balance on an octave-by-octave basis across the audio frequency range. It is utilized in sound systems for feedback control in live performances, playback equalization (correcting for equipment response and room acoustics), and improving the sound quality of live performances. It addresses issues like transducer incompatibility, low-frequency rumble, tape hiss, and disc surface noise. The SR107 is a balanced input and output line-level device, typically installed between the audio console/mixer and the power amplifier.
The unit features ten octave band, minimum phase, combining type filters covering frequencies from 31 Hz to 16 kHz, each adjustable for approximately 15 dB of boost or attenuation. The equalized output is adjustable over a 15 dB range, with an overall gain of up to 20 dB available. A peak-responding overload indicator (LED) is present on the front panel. Connectivity includes professional three-pin and phone jack inputs and outputs, plus a phone jack auxiliary output.
Designed for simplicity, the SR107 uses high-quality components operated within their ratings for reliability. The SR107 operates on 108-132 Vac, 50/60 Hz, while the SR107-2E operates on 105-125 or 210-250 Vac, 50/60 Hz (switch-selectable). The SR107 is listed by Underwriters' Laboratories, Inc., and certified by the Canadian Standards Association. Units are supplied with rack-mounting screws and can be used with optional Shure carrying cases.
Specifications
| Specification | Value |
|---|---|
| Equipment Type | All transistor inductorless active equalizer |
| Voltage Gain (GAIN Control at UNITY) | 0 dB LINE INPUT to LINE OUTPUT; -27 dB LINE INPUT to AUX OUTPUT; -50 dB LINE INPUT to MIC OUTPUT |
| Voltage Gain (GAIN Control at +20 dB) | +20 dB LINE INPUT to LINE OUTPUT; -7 dB LINE INPUT to AUX OUTPUT; -30 dB LINE INPUT to MIC OUTPUT |
| LEVEL Control | Provides additional gain adjustment of +15 dB over values given above, EQUALIZER IN mode only. |
| Frequency Response | ±2 dB from 30 Hz to 20 kHz, EQUALIZER IN or BYPASS |
| Signal to Noise Ratio (20 Hz-20 kHz) | Typically 99 dB at maximum output with Filter Controls and LEVEL Control at zero and GAIN Control at UNITY in EQUALIZER IN mode. |
| Output Noise, Maximum (300 Hz-20 kHz at LINE OUTPUT) | -84 dBV (63 µV); -69 dBV (0.50 mV), LEVEL Control at +15, Filter Controls at -15; -91 dBV (28 µV), EQUALIZER Switch in BYPASS |
| Output Hum and Noise, Maximum (20 Hz-20 kHz at LINE OUTPUT) | -83 dBV (71 µV); -67 dBV (0.56 mV), LEVEL Control at +15, Filter Controls at -15; -88 dBV (40 µV), EQUALIZER Switch in BYPASS |
| Input Common Mode Rejection | 90 dB minimum at 100 Hz |
| Clipping Level (30 Hz-20 kHz) | Input: +18 dBm minimum (+15.8 dBV, 6.2V) GAIN Control at UNITY; -2 dBm minimum (-4.2 dBV, 0.62V) GAIN Control at +20 dB |
| Overload Indicator | Illuminates 3 dB ±1.5 dB before output clipping occurs |
| Input Impedance | 70 kilohms actual, balanced bridging (for use with line level source, 10 kilohms or less.) |
| Output Impedance | MIC OUTPUT: 1 ohm actual, balanced (for use with 25 to 600-ohm inputs); LINE OUTPUT: 115 ohms actual, balanced (for use with 600-ohm lines); AUX OUTPUT: 630 ohms actual, unbalanced (for use with auxiliary circuits of 600 ohms or more impedance) |
| Distortion (Intermodulation) | 0.25% max. at 12.2 dBm (3.2V) (LINE OUTPUT) with a 60 Hz and 7.0 kHz input at a 4:1 ratio |
| Distortion (Harmonic) | 1% max. total harmonic distortion at 12.2 dBm (3.2V) (LINE OUTPUT), 30 Hz-20 kHz with Filter Controls at +15, GAIN Control +20 dB and LEVEL Control at +15 |
| Phase | Pin 3 and tip contacts of LINE INPUT Connectors are in phase with pin 3 of MIC/LINE OUTPUT and tip contacts of LINE and AUX OUTPUT Connectors |
| Equalization Filters Center Frequencies | Octave spaced from 31 Hz to 16 kHz. Accurate to within ±10% of labeled value |
| Equalization Filters Characteristics | ±15.5 ±2 dB boost or attenuation at center frequency; 6.5 ±2 dB at maximum boost or attenuation at one-half octave above or below center frequency |
| Operating Voltage and Power | SR107: 120 Vac ±10%, 50/60 Hz; 6 watts maximum. SR107-2E: 105-125 or 210-250 Vac, 50/60 Hz; 6 watts maximum. |
| Accessory Power | 31 Vdc open circuit, 27 Vdc at 10 mA, maximum |
| Temperature (Operating) | -7°C to 57°C (20°F to 135°F) |
| Temperature (Storage) | -29°C to 71°C (-20°F to 160°F) |
| Dimensions | 44.4 mm height x 483 mm width x 218 mm depth (1-3/4 in. x 19 in. x 8-9/16 in.) |
| Weight | 3.5 kg (7 lb, 12 oz) |
| Finish | Matte black |
| Installation | Equipped for standard 19 in. (483 mm) audio rack mounting; may be operated in optional A30A or A105A Carrying Case. |
| Certifications | Listed by Underwriters' Laboratories, Inc.; listed by Canadian Standards Association as certified (SR107 only). |
Applications
The SR107 Audio Equalizer is designed for several key applications in audio systems:
- Feedback Control: Adjusts sound system frequency response to provide maximum gain before feedback and improve sound quality in live performance situations, applicable to both house and stage monitor systems.
- Playback Equalization: Adjusts audio playback system frequency response to compensate for electrical or acoustical deficiencies, aiming for more natural sound reproduction.
- Live Performance Equalization: Adjusts sound system frequency response to achieve a tonal balance appropriate for the performance and to reduce feedback tendencies.
Operating Instructions
General Operating Instructions: The SR107 is typically connected between an audio console/mixer and a power amplifier. It can also be used between a limiter/compressor and a power amplifier, or in systems with 'Link Out' and 'Link In' jacks. Ensure secure rack mounting or use of carrying cases before making connections.
Connection Steps: Connect audio console/mixer line output to SR107 LINE INPUT. Connect SR107 LINE OUTPUT or 3-pin OUTPUT to power amplifier input. For Link use, connect SR107 AUX OUTPUT to the console/mixer link input. Set all Filter and LEVEL Controls to zero, EQUALIZER switch to BYPASS, and GAIN to UNITY (or +20 dB for Link use). Connect power as appropriate for SR107 or SR107-2E model. Position speakers and microphones for optimal performance. Set console/mixer tone controls to flat and phase switches to in-phase.
Powering On and Level Setting: Apply power to the sound system. The POWER ON/OFF switch activates the unit, indicated by the Power-On Indicator Lamp. Adjust console/mixer output to make the SR107 OVERLOAD Indicator flicker slightly on loud peaks for optimal signal-to-noise ratio. Avoid constant flickering or solid illumination of the OVERLOAD Indicator, which indicates distortion.
Equalization Adjustment: With the EQUALIZER switch set to IN, adjust Filter Controls for desired equalization. Use the LEVEL Control to maintain consistent volume. Avoid exceeding system bandwidth limits. For best results, use minimal control adjustments. Conduct listening checks to ensure satisfactory sound quality throughout the audience area.
Feedback Control Procedures: For house systems, adjust mixer levels below feedback, then increase LEVEL until feedback occurs. Use Filter Controls to attenuate problematic frequencies, starting with mid-to-high frequencies for high-pitched feedback or low frequencies for low-pitched feedback. Repeat gain increases and feedback elimination until desired sound levels are achieved. For stage monitor systems, follow similar procedures, focusing on monitor speaker feedback.
Playback Equalization: Evaluate sound quality at the listening position and adjust Filter Controls to compensate for system deficiencies, using the LEVEL Control to maintain volume. Specific recommendations are provided for adjusting bass, rumble, brightness, vocal presence, and room resonance issues.
Live Performance Equalization: Similar to playback equalization, but with microphones and performers as the sound source. Initial equalization for feedback is recommended, followed by adjustments for sound quality during rehearsal. Caution is advised as secondary equalization can affect the feedback threshold.
Equalization Instrumentation: Acoustic measurement equipment (pink noise generator, analyzer) can assist in achieving consistent equalization by measuring system response.
Diagrams and Visuals
Figure 1: SR107 Front Panel depicts the front panel controls, including GAIN, LEVEL, ten octave band FILTER Controls, EQUALIZER IN/BYPASS switch, POWER ON/OFF switch, and the OVERLOAD LED indicator.
Figure 2: SR107 Rear Panel illustrates the rear panel connections and controls, showing LINE INPUT (3-pin and phone jack), OUTPUT (3-pin and phone jack), AUX OUTPUT (phone jack), MIC/LINE slide switch, AC (MAINS) POWER connector, and the VOLTAGE SELECTOR switch (on SR107-2E).
Figure 3: Overall Dimensions provides the physical dimensions of the unit: 44.4 mm height, 483 mm width, and 218 mm depth, with a weight of 3.5 kg (7 lb, 12 oz).
Figure 4: SR107 Block Diagram illustrates the signal flow within the unit, showing input stages, the equalizer circuitry, level control, and output stages.
Figure 5: Typical Filter Characteristics presents graphs demonstrating the boost or cut response of individual filters at different settings (e.g., 7.5 dB boost/cut, maximum boost/cut).
Figure 6: External VU Meter shows a diagram for connecting an external VU meter to the LINE OUTPUT via a series resistor.
Figure 7: SR107 Top View, Cover Removed displays the internal layout of the unit with the cover off, showing the placement of circuit boards and components.
Figure 8: Transistor Lead Codes illustrates the pin configurations (Base, Collector, Emitter) for NPN and PNP transistors used in the unit.
Figures 9 & 10: Amplifier and Equalizer Circuit Board Parts Location show the physical layout of components on the respective circuit boards.
Figure 11: SR107 Audio Equalizer Circuit Diagram provides detailed schematic diagrams for the amplifier and equalizer sections, including power supply details.
Service Instructions
General Service: The SR107 uses high-quality components for longevity. Servicing should only be performed by qualified personnel due to hazardous voltages.
Replacement Parts: A detailed parts list is available, specifying Shure part numbers and commercial alternates. When ordering, specify the Shure Replacement Kit Number, description, model number, and serial number.
Cover Removal: The top cover can be removed by unscrewing eight screws.
Fuse Replacement: The SR107 uses a 1/16A, 250V Slo-Blo fuse (F1), and the SR107-2E uses a 1/8A, 250V Slo-Blo fuse (F1). Replace with identical fuses and use insulating tubing.
Knob Replacement: Front panel control knobs are pull-off types.
Ferrite Beads: These are used on signal leads to input/output connectors (except AUX OUTPUT) and must be replaced if removed during servicing.
Printed Circuit Board Removal: Instructions are provided for accessing and removing the Amplifier (A1) and Equalizer (A2) boards, including disconnecting leads and removing screws.
Transistor, Diode, and LED Removal/Testing: Procedures for removing and testing active components using an ohmmeter are detailed, including specific instructions for replacing the OVERLOAD LED (D6).
Troubleshooting: A general troubleshooting approach is outlined, starting with checking power, fuses, and voltage outputs. Specific tests for AC and DC voltages are described, referencing points on the circuit diagram.
Guarantee
Shure products are guaranteed against electrical and mechanical defects for one year from the date of purchase, covering parts and labor. This guarantee is in lieu of all other warranties, and consequential or incidental damages are not recoverable.
Shipping Instructions
To return the unit for service or repair, repack it carefully and ship prepaid to Shure Brothers Incorporated, Attention: Service Department, 1501 West Shure Drive, Arlington Heights, Illinois 60004. For international customers, return the unit to your dealer or an Authorized Shure Service Center.
