1ET400A is a single-channel, ultra-high performance, analog-input Class D Amplifier module capable of over 400W of power at an audio quality level that sets the standard for power amplifiers of any operating class. Its compact size and high reliability makes it fit a broad range of applications, while its audio quality makes it the undisputable choice even in applications where all the premium is on sound quality. PURIFI’s continuing research into nonlinear control theory has produced the first mathematically exact largesignal model of self-oscillating amplifier controllers. This breakthrough allows complete optimization of the feedback circuit and improves performance by at least an order of magnitude over existing implementations. The amplifier module further incorporates a comprehensive protection system that makes it tremendously robust and easy to integrate.

Output Power: 450W(2Ω), 450W(4Ω), 227(8WΩ)

Output Current: ~25A

THD+N: <0.00017% (~116dB) @ 100W, 4Ω, 20-20kHz

Dynamic Range: ~131dB(A)

Output Noise: 11.5μV(A)

Gain: 12.8dB

Output Impedance: <65μΩ @ 1kHz

Efficiency: >94%

Idle losses (outpt stage): ~1.7W

The graph shows the distortion level (THD + N%) in relation to the output power. For a more tecnical info you can see the tests made on audiosciencereview: https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-purifi-1et400a-amplifier.7984/


These circuits and methods provide many practical and audible benefits:

  • High loop gain (>75dB) in the entire audio band

    • This figure corresponds to an unprecedented 110MHz Gain-Bandwidth Product and produces consistent ultra-high performance across the audio spectrum unmatched by audio amplifiers of any technology or operating class.

  • Negligible Intermodulation Distortion (IMD)

    • A very good measure for how well an amplifier handles complex signals. Sonically low IMD means a highly resolved and stable stereo image across the whole spectrum, even during very complex and busy passages.

  • THD remains extremely low at any frequency and any power level right until clipping

    • Translates into a total lack of sonic signature, and an ability to reproduce any type of music without preference for genres or production style.

  • Negligible output noise

    • No audible noise. Deep black silences and a generous and detailed sound even at very low playback volumes.

  • High power supply rejection ratio (PSRR)

    • The module places no particular demands on the power supply quality. A simple off-the-shelf unregulated SMPS will not degrade audio performance.

  • Load-invariant frequency response and negligible output impedance

    • The amplifier handles difficult loudspeakers with ease, including those that challenge most other amplifiers.

  • Controlled, second-order low-pass response

    • Very flat audio-band response with a sensible, 60kHz bandwidth.

    • Reduced sensitivity to out-of-band noise from DACs, reducing the requirements on the DAC reconstruction filter. This leaves a shorter signal path between DAC and loudspeaker.

    • Problem-free operation with outboard DACs over which you may have no control.

  • Very low idle losses and reduced electromagnetic interference (EMI)

    • The enormous loop gain allows relaxed timing of the power MOSFETs without degrading audio performance.

    • Idle losses are minimized.

    • Very little to no effort needed to pass regulatory tests.

  • Exceptionally clean clipping and clipping-recovery in both voltage and current domains

    • Clips cleanly and recovers immediately without “overhang”. Current limiting is equally instantaneous and glitch free. This guarantees the smallest amount of audible artefacts when pushed into clipping or overload protection.

NCX2 + 1ET400A



The NCX2 is our new high-performance i / o board. Gain: 26dB. Input impedance: 47Kohm.

The NCX2, in default, always uses the OPA1612 in the buffer stage, perhaps among the best IC's on the market for transparency and clarity of sound (without adding color), whose power is entrusted to the small and fast TI TPS7 voltage regulators ( LDO).

Basically, therefore, the same circuit as the previous NCX.


The new feautures, which makes NCX2 unique, is that it is nevertheless designed to add a discrete op-amp  on DIP8 and the Hypex HxR audiophile voltage regulators.

This "addition", however, does not replace the default setting of the circuit and its basic components (OPA1612 + TI TPS7) since, by moving the appropriate jumpers on the board, the user can always choose and select in any moment the combination (operational-voltage regulator) he prefers:

  • OPA1612 with TPS7 voltage regulators,

  • OPA1612 with HxR voltage regulators,

  • discrete components operational with TPS7 voltage regulators,

  • operational components with discrete components with HxR voltage regulators.


POWER SUPPLY. To supply each 1ET400A amplifier module, we use the Hypex SMPS1200A400 switching PSU. 

HYPEX SMPS1200A400 High Line Input Voltage: 190-250Vac, Low Line Input Voltage: 95-130Vac, Output Voltage: 2x64Vdc, Max. Output power at 230Vac: 2x600W into 4 Ohm load, 2x340W into 8 Ohm load, Switching Frequency: 100kHz   

  • Hi-end mono, stereo and multichannel amps 

  • Hi-end home theatre solutions

  • ​Monitor loudspeakers for recording and mastering studios