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W92X REV A

Interactive Assembly, Calibration Guide & Bill of Materials for the 500 / 51X Series Equalizer Kit

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1. Introduction

Welcome to the build manual for the W92X / SLQ51X Equalizer Kit (W92X Rev A).

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The W92X Rev A is a high-performance 4-band parametric equalizer module engineered for the popular 500 / 51X series rack format. Inspired by classic German analog console EQ designs (W492 circuit architecture), it combines broad tone-shaping flexibility with high-grade components to deliver precise sound control for both tracking and mixing.

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Key Features of the W92X Rev A:

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  • 4 Bands of Equalization (LF, LMF, HMF, HF) with sweepable frequencies, ±15 dB Gain range, and dedicated individual band bypass switches.

  • Fixed Shelving response on HF/LF bands and musical Bell response on HMF/LMF mid-bands.

  • Integrated Low Cut filter section with internal 80 Hz / 160 Hz jumper selection.

  • Master Output Trim control providing ±20 dB of clean output gain adjustment.

  • High-grade THAT 1246 balanced line receivers and THAT 1646 line drivers for maximum headroom and low noise floor.

  • True-bypass relay switching for silent circuit engagement.

  • Rev A Design: Streamlined multi-board layout for an intuitive and accurate assembly process.

 

This manual will guide you step-by-step through component selection, board assembly, initial voltage checks, and precision alignment. Please take your time, read all instructions carefully before soldering, and double-check component polarities at each stage.

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Finished Module: W92X Rev A 500-series equalizer module featuring black aluminum front panel

2. Step-by-Step Assembly Guide

2.1 Resistors and Diodes

  • Place and solder all low profile resistors on the PCB according to the Bill of Materials.

  • Install all diodes.

  • Important: Double check the orientation and polarity cathode stripe matching PCB silkscreen of all diodes before soldering.

Main PCB with color-coded resistors and diodes positioned and soldered

2.2 IC Sockets and Ceramic Capacitors

  • Install all IC sockets (ensure notch orientation matches the PCB silkscreen).

  • Solder the low-profile ceramic capacitors:

PCB assembly showing IC sockets and low profile ceramic capacitors

2.3 Film Capacitors and Inter-Board Connectors

  • Place and solder all WIMA film capacitors.

  • Install the PCB board connectors as shown in the reference photos:

    • On the small subboard, ensure the short pins are seated flush against the PCB before soldering.

    • Crucial: Press the headers firmly onto the board during soldering to guarantee they sit perfectly straight and level. This is vital for flawless mechanical alignment during final assembly.

PCB assembly showing WIMA capacitors, connectors and bridge rectifier

2.4 Relays, Voltage Regulators and Electrolytics

  • Solder the signal relays and voltage regulator.

  • Install the electrolytic capacitors:

    • Attention: There are polarized and non-polarized Electrolytics in this kit. Verify correct alignment plus or minus before soldering.

PCB assembly showing electrolytic capacitors, relais

2.5 Board Cleaning and Trimpots

  • Clean the PCB thoroughly using Isopropyl Alcohol or flux remover to clear away all solder residue.

  • Allow to dry, then install and solder all trimpots (0DbTrim1, LCTRIM1, HF_MAX, HMF_MAX, LMF_MAX, LF_MAX).

  • Warning: Do NOT clean the PCB with liquids AFTER installing trimpots, potentiometers, or switches. Solvents can penetrate component casings, wash away internal conductive grease, and ruin electrical contact permanently.

2.6 Potentiometers Switches and Subboard Assembly

Potentiometer Taper Guide

Before soldering, check the code printed on the potentiometer body (Letter = Taper / Number = Value):

  • A – Logarithmic / Audio (e.g., A10K): Non-linear curve matching human hearing. Used for Q-factor and frequency controls where fine control at lower settings is needed.

  • B – Linear with Center Detent (e.g., B50K): Even resistance change across full turn, featuring a tactile notch at 12 o'clock. Used for Gain boost/cut controls to feel the 0 dB center position.

  • C – Reverse Logarithmic / Anti-Log (e.g., C50K): Inverse curve designed for frequency sweeps, giving a smooth and natural sweep feel across high-frequency ranges.

 

Lower Subboard:

  • Trim all pins of previously soldered pin rows on the bottom of the lower subboard as short and flush as possible to prevent shorts in your rack.

  • Insert all potentiometers into the subboard simultaneously. Verify Gain pots with center detents (B10K) and the Output Trim pot (B50K) are in their designated spots.

  • Solder only one middle pin per potentiometer first.

  • Press each potentiometer flat against the board and verify its body is perfectly aligned with the printed silkscreen outlines.

  • Attach the mounting bracket to the pots, tighten the nuts, and solder all remaining pins.

  • Trim all potentiometer pins short, then temporarily remove the mounting bracket.

 

Upper Subboard:

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  • Trim all pre-soldered leads on the underside as short as possible.

  • Insert all potentiometers and switches. Secure each part with a single solder joint first.

  • Check visual alignment against the silkscreen, install the blank bracket, and solder all remaining pins. Trim all leads short.

2.7 Front Panel Fitment and LED Alignment

  • Attach the front panel to the subboard assembly using the provided spacers and hardware or clamps to align pushbuttons and switches within their panel cutouts.

  • Solder all switch pins completely, then trim their leads short.

  • Prepare LEDs: Trim LED leads at slightly different lengths so you can easily distinguish the anode (longer leg) from the cathode (shorter leg).

  • Solder LEDs: Insert LEDs into position so they sit flush with the front panel surface. Solder one leg first to adjust depth and height, verify fitment, then solder the second leg.

  • Disassemble the front panel and mounting bracket once alignment is complete to prepare for joining the boards.

3. Final Assembly and Voltage Check

3.1 Board Joining

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  • Connect the mainboard and lower subboard using two M3 screws and nuts as temporary height spacers in the corners.

  • Solder one pin per header row first, press the boards tightly together, then solder all remaining header pins and trim flush.

  • Remove the temporary corner spacer screws.

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3.2 Pre Flight Power On and Voltage Check without ICs

  • Ensure NO ICs are inserted into any sockets.

  • Connect the joined boards using the ribbon cables and power the unit via your 500 series rack or lunchbox.

  • Set your multimeter to DC Volts and measure supply voltages at the socket pins relative to chassis ground:

    • NE5532 sockets: Supply rails equal ~ ±15.3 Volts DC (due to diode drop)

    • THAT 1246 socket: Supply rails equal ~ ±15.3 Volts DC

    • THAT 1646 socket: Supply rails equal ~ ±15.3 Volts DC

  • Verify that status LEDs light up and relays respond to switching commands properly.

  • Power off the rack.

3.3 IC Installation and Hardware Assembly

  • Once correct power rails of approximately ±15.3 V DC are confirmed, insert all ICs into their sockets. Pay strict attention to the Pin 1 notch orientation on every IC package.

  • Re-attach mechanical hardware: brackets, ribbon cables, subboards, 24 millimeter inter-board spacers, and the front panel using the potentiometer nuts as well as M3 front hardware.

  • Fit the color-coded knob caps to their respective controls:

    • Blue for HF Band

    • Green for HMF Band

    • Yellow for LMF Band

    • Red for LF Band

    • Grey for Master Output Trim

4. Calibration Guide

Calibration is straightforward and requires playing sine waves into the unit while measuring the output level.

 

Test Requirements:

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  • Headroom: Keep at least 20 dB of headroom on your audio interface to avoid clipping during boost adjustments.

  • Software: Any DAW with an oscillator and level meter works, but REW (Room EQ Wizard) is highly recommended.

  • Reference Level: Max level reference: +6 dBu (1.545 V RMS). Test signal level: -12 dBu (0.195 V RMS).

 

Recommended Resources:

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Initial Check:

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  1. Set all front panel gain and frequency controls to their center/detent positions.

  2. Engage the EQ in circuit.

  3. Send a White Noise signal through the unit and verify using an oscilloscope, analyzer, or monitoring system that all bands boost, cut, and sweep correctly.

  4. Switch generator output to a Sine Wave to begin precision calibration.

 

Output Trim Calibration (0DbTrim1):

  1. Set all controls to center detent position. Set all individual bands to OFF.

  2. Set front panel Output Trim knob to center detent (0 dB position).

  3. Switch main EQ section IN.

  4. Send a 1 kHz Sine Wave at +6 dBu (1.545 V RMS) into the module input.

  5. Connect multimeter probe to test point TP_IN1 and GND (reads ~1.32 V AC).

  6. Move probe to test point TP_TRIM2 and GND.

  7. Adjust the 0DbTrim1 trimpot until the voltage at TP_TRIM2 matches the input level exactly (unity gain).

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Low Cut (LC) Filter Calibration (LCTRIM1):

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  1. Set all controls to center detent and Output Trim to center detent.

  2. Engage Low Cut switch.

  3. Send a 1 kHz Sine Wave at +6 dBu into the unit.

  4. Measure AC voltage at TP_IN1 (~1.32 V AC) and at TP_LC2.

  5. Adjust the LCTRIM1 trimpot until the output level at TP_LC2 matches the input level (unity gain).

 

HF Band Calibration (HF_MAX):

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  1. Set all controls to center detent.

  2. Set sine oscillator to 3 kHz (-12 dBu).

  3. Engage EQ and switch HF Band ON (all other bands OFF).

  4. Set HF Gain fully clockwise (+15 dB Boost).

  5. Set HF Frequency fully counter-clockwise (3 kHz).

  6. Adjust the HF_MAX trimpot until the peak output reads exactly +15 dB of boost relative to bypassed level.

 

HMF Band Calibration (HMF_MAX):

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  1. Set all controls to center detent.

  2. Set sine oscillator to 1 kHz (-12 dBu).

  3. Engage EQ and switch HMF Band ON (all other bands OFF).

  4. Set HMF Gain fully clockwise (+15 dB Boost).

  5. Set HMF Frequency fully counter-clockwise (1 kHz).

  6. Fine-tune generator frequency slightly to find the exact resonance peak.

  7. Adjust the HMF_MAX trimpot until the peak output reads exactly +15 dB of boost.

 

LMF Band Calibration (LMF_MAX):

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  • Set all controls to center detent.

  • Set sine oscillator to 1 kHz (-12 dBu).

  • Engage EQ and switch LMF Band ON (all other bands OFF).

  • Set LMF Gain fully clockwise (+15 dB Boost).

  • Set LMF Frequency fully clockwise (1 kHz).

  • Fine-tune generator frequency slightly to find the exact resonance peak.

  • Adjust the LMF_MAX trimpot until the peak output reads exactly +15 dB of boost.

 

LF Band Calibration (LF_MAX):

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  1. Set all controls to center detent.

  2. Set sine oscillator to 400 Hz (-12 dBu).

  3. Engage EQ and switch LF Band ON (all other bands OFF).

  4. Set LF Gain fully clockwise (+15 dB Boost).

  5. Set LF Frequency fully clockwise (400 Hz).

  6. Adjust the LF_MAX trimpot until the peak output reads exactly +15 dB of boost.

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5. Interactive Bom

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