Shelford 5051 Inductor EQ / Compressor

Introduction

Thank you for purchasing the Shelford 5051 Inductor EQ / Compressor. Rupert Neve Designs hopes you enjoy using this tool. Please review the safety concerns and power requirements before use.

Safety

General safety advice:

• Do not operate the 5051 module in or around water.
• Clean only with a dry cloth.
• Do not block any ventilation openings.
• Do not install near heat sources.
• Do not defeat the safety purpose of polarized or grounding-type plugs.
• Protect the power cord from being walked on or pinched.
• Only use attachments/accessories specified by the manufacturer.
• Unplug during lightning storms or when unused for long periods.
• Refer all servicing to qualified service personnel.
• Do not expose to rain or moisture.
• Connect to a mains socket outlet with a protective earthing connection.

Important Note on Liquid Spills: If liquid is spilled, switch off immediately. Sugars and acids can cause detrimental effects, and the mixture can harden, get hot, and cause permanent damage. Contact support for resolution.

Front Panel

The front panel features controls for EQ and Compression:

• Line Select: Selects between Line 1 and Line 2 inputs.
• High Frequency Shelf / Peak: Selectable at 8 kHz and 16 kHz. Offers continuous gain from -15 to +15 dB with selectable shelf or peak curves.
• Mid Parametric EQ: Selectable center frequencies at 200, 350, 700, 1.5 kHz, 3 kHz, and 6 kHz. Provides continuous gain from -15 to +15 dB and a selectable Hi Q setting.
• Low Frequency EQ: Selectable frequencies at 35, 60, 100, and 220 Hz. Offers continuous gain from -15 to +15 dB with selectable peak or shelf curves.
• EQ IN: Engages all EQ bands except the high-pass filter.
• EQ Pre / Post: Switches the order of the EQ and compressor sections. When 'Pre', EQ is before the compressor; when 'Post', EQ is after.
• HPF: Engages an 18 dB/octave high-pass filter. Cycles through bypassed, 60 Hz (indicated by a blue LED), and 120 Hz (indicated by a red LED).
• Make-Up Gain: Applies post-compressor gain adjustment.
• SC HPF: Applies a 250 Hz, 12 dB/octave high-pass filter to the VCA side chain signal.
• Attack Time: Sets the compressor's attack time, ranging from 5 ms to 75 ms.
• Release Time: Sets the compressor's release time, ranging from 100 ms to 2.5 seconds.
• FF / FB: Selects between Feed-Forward (input signal triggers compression) and Feed-Back (signal after gain change triggers compression) modes.
• Threshold: Sets the level at which the compressor begins to react, adjustable from -30 dBu to +20 dBu.
• Ratio: Adjusts the amount of gain reduction above the threshold, from 1.1:1 to 40:1.
• Comp IN: Engages the compressor, indicated by a green button.
• Level & Gain Reduction Meters: 8-segment LED meters for monitoring gain reduction and output level.
• Link: Allows multiple 5051 modules to be linked together for stereo operation or shared control.

Back Panel

The back panel provides connectivity options:

• S/C Insert (Send/Return): 1/4" unbalanced phone jacks for sending and receiving side chain signals. The return can be used as a "key" input. This is a half-normal connection.
• Link In/Out: 1/4" phone jacks used to connect the compressor VCAs for linking multiple units.
• Line Inputs (LINE 1, LINE 2): Transformer-balanced XLR inputs for line-level signals.
• Output: Transformer-balanced XLR output.
• Power In: A proprietary 4-pin polarized input for +24V and -24V DC power supply.

Block Diagram

The block diagram illustrates the signal flow through the 5051. The audio signal passes through an input transformer, input select, EQ stages (Mid Band, Shelves, HPF), an EQ Pre/Post switch, and then to the compressor section (VCA, FF/FB mode, Threshold, Attack, Ratio, Release, Gain). The signal then goes through an output transformer. Side chain (S/C) connections and Link functionality are also depicted.

Technical Discussion

Power Requirements: The Shelford 5051 requires a specialized stand-alone power supply module, providing +24V and -24V DC power. Supplies are available in 5-way and 25-way configurations.

The Need for Dynamic Control: This section discusses how the dynamic range of sound often exceeds the capabilities of recording equipment. It highlights the necessity of managing dynamic range for different listening environments and the role of compressors in achieving clarity, intelligibility, and proper level control, especially in challenging audio situations.

A Note on Distortion: This section delves into the complexities of human hearing perception, including timing resolution and the subtle effects of distortion. It emphasizes the importance of linear transfer characteristics in audio components to maintain signal integrity and avoid unwanted artifacts.

Design Notes: The Shelford 5051 is an addition to the 5088 family, featuring a new inductor EQ circuit and compressor elements derived from the Portico II: Master Buss Processor. It utilizes traditional transformer-coupled inputs and outputs and Class-A gain blocks. The EQ design is inspired by vintage Rupert Neve designs, offering flexibility with shelf/peak curves and frequency choices. The compressor incorporates Class-A gain blocks and offers both modern feed-forward and traditional feed-back compression topologies.

5051 Features

• LINE 1 / LINE 2: Allows two sources to be pre-patched into the 5051, such as an outboard microphone pre-amp or a DAW output.
• EQ IN: Engages all bands of the equalizer, excluding the high-pass filter.
• HF (High Frequency): Adjusts up to 15 dB of boost or cut at selected high frequencies. The 8K/16K switch selects between 8 kHz and 16 kHz corner frequencies. The HI PEAK button switches between shelf mode (approx. 6 dB/octave slope) and peak mode (bell-shaped curve).
• MID FREQ: A 6-position rotary switch selects the center frequency for the mid-band EQ stage, utilizing inductor and capacitor circuits inspired by 70's console designs. Frequencies include 200 Hz, 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, and 6 kHz.
• MID HI Q: Adjusts the resonance (Q) of the mid-band EQ. When pressed, the Q narrows to approximately 3.5, compared to a typical Q of 2 when out.
• MID LEVEL: Adjusts up to 15 dB of boost or cut at the selected mid frequencies.
• EQ PRE / POST: Switches the order of the equalizer and compressor. 'Pre' places EQ before the compressor; 'Post' places EQ after.
• HPF: Engages an 18 dB/octave Butterworth high-pass filter. Pressing the button cycles through 'OFF', 60 Hz (blue LED), and 120 Hz (red LED).
• LOW FREQ: A 4-position rotary switch selects corner or center frequencies for the low-band EQ: 35 Hz, 60 Hz, 100 Hz, or 220 Hz.
• LO PEAK: Selects between shelf mode (boost/cut below corner frequency) and peak mode (bell-shaped curve) for the low-frequency band.
• LF (Low Frequency): Adjusts up to 15 dB of boost or cut at the selected low frequencies.
• GAIN: Adjusts the final output level of the compressor, serving as make-up gain to restore signal levels.
• S/C HPF: Engages a 250 Hz, 12 dB/octave high-pass filter for the compressor side chain to prevent low-frequency material from excessively controlling the compressor.
• ATTACK: Sets the compressor's attack time from 5 ms to 75 ms, controlling how quickly gain reduction is applied.
• RELEASE: Sets the compressor's release time from 100 ms to 2.5 seconds, determining how fast gain returns to normal after the signal drops below the threshold.
• LINK: Allows multiple 5051 modules to be linked for stereo operation, where the unit with the highest control voltage dictates the compression for all linked units.
• FF / FB: Selects between feed-forward and feed-back compression modes, offering different sonic characteristics.
• RATIO: Adjusts the ratio of compression above the threshold, from 1.1:1 to 40:1.
• COMP IN: Engages the compressor.
• THRESHOLD: Sets the level at which compression begins.
• GR METER: Gain Reduction meter displays dB of gain reduction.
• LEVEL METER: Displays the final peak output level.
• S/C INSERT SND/RET: 1/4" jacks for side chain input/output, enabling external processing or keying.

Specifications

EQ Frequency Response Graphs: The document includes graphs illustrating the frequency response for Low Frequency EQ, Mid Band EQ, and High Frequency EQ. These graphs show the effect of various boost, cut, shelf, and peak settings across different frequency ranges, with accompanying tables detailing the specific settings (sweep, trace, color, comment) for each curve.

Product Warranty

Rupert Neve Designs warrants this product to be free from defects in materials and workmanship for a period of three (3) years from the date of purchase. The company agrees to remedy any defect identified within this period by repairing or replacing the product, at their option.

Limitations and Exclusions

This warranty does not apply to products that have been improperly installed, subjected to usage for which they were not designed, misused, abused, damaged during shipping, or altered. The warranty extends only to the original end-user purchaser. A purchase receipt or satisfactory proof of purchase date is required for warranty service. This express, limited warranty is in lieu of all other warranties, express or implied. Rupert Neve Designs shall not be liable for any special, incidental, or consequential damages resulting from the use of this product.

Warranty Service

If you suspect a defect, please call 512-847-3013 or contact support staff at service@rupertneve.com for troubleshooting. If the device is malfunctioning, a Return Material Authorization will be issued along with shipping instructions.

Contact Information:
Rupert Neve Designs
PO Box 1969
Wimberley TX 78676
www.rupertneve.com
Tel: +1 512-847-3013
Fax: +1 512-847-8869