The information provided here is a bit sparse. I expect to have it fully fleshed out by the beginning of March, 2018.

The Modulus-686 circuit boards are currently being manufactured. I expect to have them in stock by the middle of March, 2018. The information provided below is based on the prototype build of the Modulus-686 and is subject to change. You can pre-order your Modulus-686 by clicking the Buy It Now button below.

The Modulus-686 is a balanced composite bridge/parallel amplifier. It uses six LM3886 amplifier ICs to provide nearly 400 W into 4 Ω loads at vanishingly low distortion. With a typical output current capability of 33 A, the Modulus-686 easily drives even the most challenging loads, including loads with impedance dips into the 2 Ω range. The block diagram of the Modulus-686 is shown below.

Key Features

  • Mono construction.
  • 4-layer, gold plated, ROHS compatible circuit board. Professionally assembled in Calgary, Canada.
  • Output power: 380 W (4 Ω) – 220 W (8 Ω).
  • Ultra-low 0.00026 % THD+N (140 W, 8 Ω, 1 kHz).
  • Ultra-low 0.00029 % THD+N (260 W, 4 Ω, 1 kHz).
  • Gain: +26 dB. Changeable by resistor option. Minimum gain: +20 dB.
  • On-board EMI/RFI input filter and ESD protection.
  • Power supply agnostic circuit architecture. The Modulus-686 performs identically on an unregulated supply as it does on a well-regulated supply.

The prototype build of the Modulus-686 is shown below.

Build Budget

The Modulus-686 circuit board is available as a fully assembled and tested module and as a DIY-friendly partially assembled option, which has all the surface mounted parts pre-populated. The cost of the additional parts needed to complete the SMD pre-populated board option is approximately $56.

The Modulus-686 circuit boards are professionally assembled in Calgary. My assembly vendor uses a pick-and-place machine for component placement and solders the boards using a 13-zone solder reflow oven. This procedure eliminates the issues with component cracking that you often see from the overseas assembly houses, resulting in a high-quality, high-reliability product.


The preliminary specifications for the Modulus-686 are tabulated below. These were measurements of the prototype and are subject to change.

Parameter Value Notes
Output Power 220 W 8 Ω, < 0.1 % THD+N
THD 0.00011 % 1 W, 8 Ω, 1 kHz
THD TBD % 140 W, 8 Ω, 1 kHz
THD+N 0.00026 % 140 W, 8 Ω, 1 kHz
Output Power 380 W 4 Ω, < 0.1 % THD+N
THD TBD 260 W, 4 Ω, 1 kHz
THD+N 0.00029 % 260 W, 4 Ω, 1 kHz
IMD: SMPTE 60 Hz + 7 kHz @ 4:1 -103 dB 100 W, 8 Ω
IMD: DFD 18 kHz + 19 kHz @ 1:1 -115 dB 100 W, 8 Ω
IMD: DFD 917 Hz + 5.5 kHz @ 1:1 -110 dB 1 W, 8 Ω
Multi-Tone IMD Residual < -110 dBV AP 32-tone, 100 W, 8 Ω
Gain 26 dB Resistor programmable. +20 dB min.
Input Sensitivity 2.1 V RMS 220 W, 8 Ω
Bandwidth 127 kHz 1 W, -3 dB
Slew Rate 16 V/µs 8 Ω || 1 nF load
Total Integrated Noise and Residual Mains Hum 25.4 µV RMS 20 Hz – 20 kHz, A-weighted
Total Integrated Noise and Residual Mains Hum 32.0 µV RMS 20 Hz – 20 kHz, Unweighted
Output DC Offset Voltage < 2.0 mV Typical performance
Residual Mains Hum < -120 dBV
Dynamic Range (AES17) > 120 dB 1 kHz
Common-Mode Rejection Ratio TBD dB 1 kHz
Common-Mode Rejection Ratio TBD dB 20 kHz
Damping Factor TBD
All parameters are measured at a supply voltage of ±36 V unless otherwise noted.

Performance Graphs

The THD+N vs output power for 8 Ω and 4 Ω load are shown below. Note that the 8 Ω graph compares the performance of the Modulus-686 for two different power supplies: Linear unregulated supply (Power-86 with an Antek Inc. AN-5225 2×25 VAC 500 VA transformer) and a switching supply (Mean Well SE-600-36). The slightly lower output power of the Modulus-686 with the Power-86 is due to the rail voltage droop of the linear supply.

More plots will be added when the first samples of the professionally assembled boards become available.