The Modulus-86 is a 65 W, Class-AB, LM3886-based power amplifier with error correction provided by an OPA627 precision opamp. It delivers clear, precise, and non-fatiguing sound; and distortion well below 1 ppm at full power. This 10th Anniversary Edition features improved performance, in part due to the further optimized PCB layout.

A limited stock of high-spec OPA627B opamps is available in DIY-friendly packages: 25 kits with the TO-99 (metal can) and 65 kits with DIP-08. The Kit will be discontinued when this stock runs out.

The 10th Anniversary Edition retains the same PCB size and mounting hole locations as Modulus-86 Rev. 3.0, allowing for a direct replacement.

Technical Documentation

Data Sheet Design Documentation

• Description
• Key Specifications
• Circuit Topology
• Downloads

• Key Features

  • Genuine parts sourced from authorized distributors or directly from the manufacturer. All boards and parts needed for a stereo pair of Modulus-86 are included.
  • World class performance ensured by an error correction circuit with local, low-noise power supply regulators.
  • Power supply agnostic by design. High performance is attained with unregulated power supplies and with switch mode supplies.
    
  • Differential (balanced) input which eliminates hum and ground loop issues. Can be used with single-ended (unbalanced) sources as well.
    
  • On-board EMI/RFI input filter and ESD protection.
  • Four-layer PCB optimized for high signal integrity. All ground management is handled on the PCB.
  • The circuit board is made in Canada and has been fully electrically tested by the manufacturer.
  • All through-hole construction.

  Build difficulty (1-5): 3 (moderate).

  To successfully build this Kit you will need decent soldering skills and the basic hand tools used in soldering. You will need to be able to correctly identify the different parts from the markings on the parts. These markings are in the form of colour codes on resistors and 3-digit codes on ceramic capacitors. The assembly guide contains all the information needed to identify the parts. Note that the markings on the parts are pretty small, so having a magnifying glass or loupe handy can be helpful. Similarly, access to an ohmmeter is helpful for telling the resistors apart.

  The OPA627 is no longer manufactured in the two DIY-friendly package options available with these Kits. Furthermore, the TO-99 (metal can) version is soldered directly into the PCB whereas the DIP-8 version is socketed. As result, I recommend that those who attempt to build the 10th Anniversary Edition of the Modulus-86 have at least a moderate level of experience. This is especially true for builders of the TO-99 version.

  The build video below shows you how to build the Modulus-86 10th Anniversary Edition amp modules. Please watch the video to gauge the skills needed.
  

• The graph below shows the THD+N vs output power for the Modulus-86 10th Anniversary Edition.

  

  The table below lists the key specifications for the Modulus-86 10th Anniversary Edition. For the full specifications, please see the data sheet on the Downloads tab.

  Parameter	Value	Notes
  Output Power	65 W	4 Ω, < 0.01 % THD+N
  Output Power	40 W	8 Ω, < 0.01 % THD+N
  THD	-127 dBc (0.00004 %)	40 W, 8 Ω, 1 kHz
  Multi-Tone IMD Residual	≤ -135 dB Ref.: 40 W	AP 32-tone, 40 W, 8 Ω
  Total Integrated Noise and Residual Mains Hum	14.1 µV RMS	20 Hz - 20 kHz, A-weighted
  Gain	20 dB	Can be increased by adding a resistor
  DC offset	≤ ±25 µV ≤ ±140 µV	Typical Guaranteed by design
  Finished Assembly Dimensions and Weight	91.2 × 69.7 × 27.5 mm 90 g	(W × D × H)
  Recommended power supply	Power-86 with 2x22 VAC, 160-300 VA power transformer
  All parameters are measured at a supply voltage of ±30 V DC.

• The block diagram of the Modulus-86 10th Anniversary Edition is shown below.

  

  The Modulus-86 10th Anniversary Edition uses an OPA627 to form a balanced composite amplifier with the LM3886. An LM4562 is used for the differential input. The LM4562 can be replaced by any unity gain stable opamp, including many discrete opamps, should you desire to experiment with other opamps.

  The differential input can be used both with differential signal sources (XLR) and with single-ended ones (RCA).

  The Modulus-86 is power supply agnostic by design. This is unique to the Neurochrome Modulus amplifiers. Due to the error correcting composite amplifier topology, the Modulus-86 performs as well on a traditional unregulated linear power supply or a switch mode power supply (SMPS) as it does on a well-regulated laboratory power supply.

  The PCB layout is crucial at the performance levels attained by the Modulus-86. The four-layer PCB employs differential signal routing and carefully designed copper pours and planes to ensure optimal circuit board performance. 

• Design Documentation

  Modulus-86 10th Anniversary Edition Design Documentation: MOD86_10AE_R1p0_DesignDocumentation.pdf

  Data Sheet

  Modulus-86 10th Anniversary Edition Datasheet: MOD86_10AE_DataSheet.pdf