top of page

DYNX REV B

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

MAPS

Build Maps →

Open Interactive Build Map

Click to view visual component locations directly on the board.

PDFS

PDF Manuals →

PDF Build Manuals

Click to access our download archive for all our projects.

1. Introduction

Welcome to the build manual for the DYNX Rev B Dynamics Module.

​

The DYNX Rev B is a high-performance Compressor/Limiter and Gate/Expander module engineered for the popular 500 / 51X series rack format (+16V / -16V rails). Inspired by the iconic dynamics processing section of classic British large-format analog consoles (Orange 4000 series architecture), it combines aggressive tone-shaping, fast gating, and musical expansion with modern high-grade audio buffering.

​

In this revision, a dedicated Master Output Trim control has been added to provide complete level management and makeup gain flexibility when driving the circuit hard.

​

Key Features of the DYNX Rev B:

​

  • Dual Dynamics Engines: Independent Compressor/Limiter and Gate/Expander sections operating in series.

  • Classic VCA Architecture: Based on the legendary British 4000-series console dynamics topology using high-performance THAT 2181B VCAs and AD536 / MX636 true-RMS detectors.

  • Compressor Section: Variable Ratio (1:1 to ∞:1 Limiter), Threshold (+4 to -26 dBu), Release (0.1 to 4 s), and selectable Fast Attack (3 ms vs. standard 30 ms for 20 dB GR).

  • Gate / Expander Section: Switchable 20:1 Gate or 2:1 Expander mode, variable Threshold (+10 to -30 dBu), Range/Depth (0 to 40 dB), Release (0.1 to 4 s), and selectable Fast Attack (100 µs vs. standard 1.5 ms per 40 dB).

  • Master Output Trim: Clean output level adjustment providing ±20 dB Gain (functions as makeup gain).

  • Stereo Link Capability: Allows linking two units in a lunchbox for true dynamic control voltage interaction.

  • Precision LED Metering: Dual vertical LED ladders displaying active Gain Reduction for both Gate/Expander (Green) and Compressor (Red/Yellow).

  • High-Grade Interfacing: THAT 1246 balanced line receiver input stage and THAT 1646 balanced driver output stage.

  • True-Bypass Relay Switching: Silent hardware circuit engagement when disengaged.

 

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

Finished Module: DYNX Rev B 500-series compressor gate 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 main board and subboards according to the Bill of Materials. Verify values with a multimeter or color codes before placement.

  • Solder all diodes. Pay special attention to the 6V8 Zener Diode and the 1N34A Germanium Diode.

  • CRITICAL REVISION NOTE: On the subboard, resistor RT2 must be 13.7 kOhm (13k7).

  • 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, VCA Socket & Small Capacitors

  • Install all IC sockets and the specialized VCA socket (ensure notch/pin orientation matches the PCB silkscreen).

  • Install the Bridge Rectifier.

  • Solder low-profile ceramic capacitors (100nF, 22pF, etc.).

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 inter-board connectors as shown in reference photos.

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

PCB assembly showing WIMA capacitors, connectors and bridge rectifier

2.4 Relays, Voltage Regulators, Trimmers & Electrolytics

  • Solder the signal relays, voltage regulator, and PCB trimpots.

  • Install the 1x3 pin header on the subboard designated for the LED Mini-Board.

  • Install all electrolytic capacitors:

    • Attention: C6, CT4, CT3, CP7, C1, CP8, C9, C5, P1, and CP2 are polarized. Verify correct alignment (+ / -) before soldering.

    • Capacitors CO4, CO5, CT1, and CT5 are bipolar / non-polarized, so orientation does not matter.

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 the boards to dry completely.

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

3.Potentiometers, Switches and LED Assembly

3.1 Potentiometer Taper & Selection Guide

  • Check potentiometer types carefully before mounting to the board:

  • 2x 50K Linear (B50K): Used for Comp Ratio and related linear controls.

  • 1x 50K Linear Center Detent (B50K): Used for Output Trim (0 dB center detent position).

  • 4x 500K Logarithmic (A500K): Used for Threshold and Release controls.

  • 1x 10K Linear (B10K): Used for Gate Range.

3.2 Lower Board Potentiometer Fitting

  • Trim all pre-soldered leads on the bottom of the board as short and flush as possible to prevent mechanical interference with adjacent 500-series modules.

  • Insert all potentiometers into the PCB simultaneously. Verify correct placement of 500K Log, 50K Lin, 10K Lin, and 50K Center Detent pots.

  • Solder only one middle pin per potentiometer first.

  • Verify alignment against the silkscreen outlines. Press pots flush against the PCB.

  • Attach the mounting bracket, secure with nuts, re-heat the single solder points if adjustment is needed, then solder all remaining pins.

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

3.3 Upper Subboard Assembly

  • Trim underside leads short.

  • Insert all pots and switches onto the upper subboard. Secure each part with a single solder joint.

  • Verify visual alignment, attach the blank mounting bracket, solder all remaining pins, and trim all leads short.

3.4 Front Panel Fitment & LED Alignment

  • Attach the front panel temporarily to the subboard assembly using spacers and nuts/clamps.

  • Insert pushbuttons, alignment switches, and center them precisely within the front panel cutouts. Solder switch pins completely and trim leads short.

  • LED Preparation: Keep LED legs at two distinct lengths to easily distinguish Anode (longer leg, +) from Cathode (shorter leg, -).

  • Mini-Board & Gate Metering LEDs: Mount the small LED Mini-Board directly to the 1x3 pin header. Insert Green LEDs for Gate indication into the front panel. Secure flush using masking tape on the panel face, solder one leg first, adjust alignment, then solder the second leg.

  • Compressor & Switch Status LEDs: Flip the assembly and install the Red/Yellow LEDs for Compression indication and switch status. Secure with tape, solder, and trim leads short.

  • Disassemble the front panel and bracket once alignment is verified.

4. Final Assembly and Voltage Check

4.1 Pre-Flight Power On and Voltage Check 

IMPORTANT WARNING: Some early production kit batches contained a leftover NE5534 IC. Do NOT install an NE5534 in this circuit under any circumstances!

  1. Ensure NO ICs or VCAs are inserted into any sockets.

  2. Connect the mainboard and subboard using the ribbon cables. Power the unit via your 500-series rack test rig.

  3. Verify relay switching operation (listen for clicks) and switch LED functions.

  4. Set multimeter to DC Volts and measure the main rail test points at the bottom of the PCB relative to ground (~ ±15.3 V DC due to diode drops).

  5. Verify power supply voltages at every IC socket pin prior to populating:

​

TL074 - Pin 4 (+15.3V) - Pin 11 (-15.3V)

TL072 - Pin 8 (+15.3V) - Pin 4 (-15.3V)

NE5532 - Pin 8 (+15.3V) - Pin 4 (-15.3V)

AD536 / MX636 - Pin 14 (+15.3V) - Pin 3 (-15.3V)

THAT 2181B - Pin 7 (+15.3V) - Pin 5 (-15.3V)

THAT 1246 - Pin 7 (+15.3V) - Pin 4 (-15.3V)

THAT 1646 - Pin 6 (+15.3V) - Pin 5 (-15.3V)

4.2 IC Installation and Hardware Assembly

  • Once all supply voltages are verified, populate all IC sockets (TL074, TL072, NE5532, AD536AJQ / MX636AJN, THAT 2181B, THAT 1246, THAT 1646). Pay strict attention to Pin 1 notch orientation.

  • Mount mainboard to bracket using pot nuts. Connect all ribbon cables.

  • Mate the upper subboard at an angle while connecting ribbon cables simultaneously. Fasten M7/M9 potentiometer nuts.

  • Install the 24 mm inter-board spacers between main and subboards and secure with M3 screws.

  • Attach the front panel using spacers, M3 hardware, and pot nuts.

  • Fit color-coded knob caps:

    • Grey for Compressor and Output Trim controls

    • Green for Expander and Gate controls

5. Calibration Guide

Note: The AD536 and MX636 RMS detector ICs follow the exact same calibration procedure.

​

Calibration requires passing pure sine wave signals through the unit while measuring AC/DC voltages at designated test points or analyzing THD via DAW measurement software (e.g., REW - Room EQ Wizard).

 

Test Requirements:

​

  • 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:

​

 

Control Initial Setup (Global Baseline)

​

Set all controls to the following baseline before starting calibration:

  • Comp Ratio: 1:1 (Fully Counter-Clockwise / ACW)

  • Comp Threshold: +4 dBu (Fully ACW)

  • Comp Fast Attack: IN (Engaged)

  • Comp Release: 0.1 s (Fully ACW)

  • Gate Ratio: 0 (Fully ACW)

  • Gate Threshold: -30 dBu (Fully ACW)

  • Gate Fast Attack: IN (Engaged)

  • Gate Release: 0.1 s (Fully ACW)

  • EXP Switch: OFF (Disengaged)

  • Link Switch: OFF (Disengaged)

  • Output Trim: Center Detent (0 dB)

  • Main Bypass (ON): IN (Engaged)

 

Compressor RMS Detector & Gain Calibration (VR2 & VR1)

​

  1. Set controls to Global Baseline.

  2. Input a 1 kHz Sine Wave into the module.

  3. Connect multimeter to TP4 and GND. Adjust generator level until TP4 reads exactly 1.54 V AC (+6 dBu).

  4. Measure DC voltage at TP2. Adjust trimpot VR2 (5k 0dBm, located next to test point) until TP2 reads exactly -5.00 V DC.

  5. Change front panel Compressor settings:

  6. Comp Ratio: ∞:1 (Fully Clockwise / CW)

  7. Comp Threshold: -26 dBu (Fully CW)

  8. Check TP2 again. Readjust VR2 if necessary to ensure it remains at -5.00 V DC.

  9. The compression LED meter ladder should now display gain reduction activity.

  10. Lower signal generator level until compression LEDs turn off.

  11. Slowly increase generator level until the first Gain Reduction LED lights up. Note this level in your DAW/measurement software.

  12. Increase signal generator level further. The output level should remain virtually flat (within ±1 dB) as input increases, due to the ∞:1 limiter setting.

  13. If the output rises or compresses excessively, adjust trimpot VR1 (500R SET GAIN / SET COMP):

  14. Procedure: Drop input signal below threshold, then raise until GR starts. Note peak level. Increase input further. Adjust VR1 so output level stays within 1 dB of the onset level.

  15. Once VR1 is set, re-verify TP2 with a 1.54 V AC input at TP4. Readjust VR2 to -5.00 V DC if minor drift occurred.

  16. Expected Reference Values for a Calibrated Circuit:

    Signal at TP4 = 1.55 V AC (+6 dBu)  TP2 = -5.00 V DC, TP1 = -0.536 V DC

    Signal at TP4 = 0.052 V AC (-23.4 dBu)  TP2 = -1.832 V DC, TP1 = -3.694 V DC

    (Note: Do not calibrate to a fixed voltage at TP1; prioritize correct Gain Reduction curve response.)

 

Gate Threshold Calibration (VR3)

​

  1. Return controls to Global Baseline, then adjust Gate controls:

  2. Gate Ratio / Range: Fully Clockwise (CW - 40 dB depth)

  3. Gate Threshold: Fully Clockwise (CW - +10 dBu)

  4. Send a 1 kHz Sine Wave into the unit.

  5. Measure AC voltage at TP4. Adjust signal generator until TP4 reads 1.54 V AC.

  6. Adjust trimpot VR3 (100k SET GATE) until the signal just passes cleanly through the gate.

 

Output Trim Calibration (10K 0dB Trim)

​

  1. Set controls to Global Baseline.

  2. Send a 1 kHz Sine Wave into the unit.

  3. Measure AC voltage at TP4. Adjust signal generator until TP4 reads 1.54 V AC.

  4. Measure AC voltage at TP5.

  5. Adjust trimpot 10K 0dB Trim (located on the subboard) until TP5 reads exactly 1.54 V AC (matching input level / unity gain).

 

VCA Symmetry / Harmonic Distortion Calibration (VR4)

​

To perform symmetry calibration, use a THD analyzer or REW’s Real-Time Analyzer (RTA) with "Show Distortion" enabled.

  • Set front panel controls:

  • Comp Ratio: ∞:1 (Fully CW)

  • Comp Threshold: -26 dBu (Fully CW)

  • All other controls at Global Baseline.

  • Send a 1 kHz Sine Wave into the unit.

  • Measure AC voltage at TP4 and set generator level to 1.54 V AC.

  • Monitor the 2nd Harmonic Distortion (h2) peak on your RTA display.

  • Adjust trimpot VR4 (50k SYM) back and forth to find the minimum distortion null point.

  • Once the 2nd harmonic is minimized, your DYNX Rev B module is fully calibrated and ready for studio use!

 

​

6. Interactive Bom

bottom of page