Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm

Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Class D stereo power amplifier based on two PURIFI 1ET400A modules and a HYPEX SMPS1200A400 power supply.

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Shipping date: 19-10-2021.

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This device is supplied as standard in 230V. If you need 110V input voltage, please specify it clearly in the comment field when ordering.


Power Amplifier PURIFI 2x400W 4 Ohm

We are proud to present AUDIOPHONICS HPA-S400ET, a class D stereo power amplifier based on two PURIFI 1ET400A modules. This ready-to-use version is designed for audiophiles needing a foolproof amplification solution, with a considerable power reserve as well as impeccable linearity. The PURIFI modules are indeed among the most rigorous Class D amplification solutions on the market, with simply exceptional measured performance.

This device offers high level sound reproduction which will be suitable to drive demanding speakers, to sonorize large listening rooms or for studio applications requiring a considerable headroom without compromising on the precision and richness of the audio message.

All of the components are integrated in a sober and robust 100% Aluminum housing with openings and heatsinks to help heat dissipation. Its design also allows it to block signal interference.

Dual PURIFI 1ET400A module

  • Both channel of the amplification circuit uses its own PURIFI 1ET400A module. These high performance Class D amplifier circuits each offer a very comfortable power of 200W (@ 8Ω) while making the most of Class D amplifiers high efficiency rating.
  • The 1ET400A modules has a >75dB high gain loop over the entire frequency band, providing high performance across the whole spectrum and surpassing any amplifier regardless of its class.
  • Thanks to hyper-low intermodulation distorsion (IMD) the HPA-S400ET achieves incredible precision on its stereophonic image over the whole spectrum, unmatched by audio amplifiers of any technology or operating class.
  • THD remains extremely low at any frequency and any power level right until clipping. This translates into a total lack of sonic signature, and an ability to reproduce any type of music without preference for genre or production style.
  • The output noise is negligible, which allows deep silences and prevents losing details when listening at low volume.
  • The circuit benefits from a high level of rejection (PSRR) which minimizes the impact of power supply on audio performance.
  • Load-invariant frequency response and negligible output impedance enables the HPA-S400ET to drive the most demanding speakers with ease.
  • Very low idle losses and reduced electromagnetic interference (EMI). The High loop gain allows relaxed timing of the power MOSFETs without degrading audio performance.
  • The HPA-S400ET uses these amplifier modules with an interface card specially developed for optimal integration.

Power Module Hypex SMPS1200A400

The SMPS1200 switching power supply is a model with very high maximum output power of 1200 Watts. It has been specifically designed and developed by Hypex to provide 2 x 64V voltage required for operation of the most demanding amplifier modules.

This low noise high quality Power supply, meets every energy needs of the amplification modules.

Audiophonics Interface Card

Both modules are driven in opposite phase, to cancel out the «Power-Supply Pumping» effect. This allows greater stability in the power supply by alternately distributing current draws on each rail, thus increasing its overall capacities.

We opted for a two stage voltage regulation in order to optimize the power supply to the OPAs and the auxiliary voltage supplied to the modules. 

A Texas Instrument LM4562 OPA per channel is used, these are very low distortion AOPs offering the greatest transparency with a very low THD. They are mounted on socket allowing their replacement if necessary

To suit all uses we opted for 3 gain settings, adjustable by jumper on the interface card:

  • Gain of + 7.2dB, for a total of 20dB (default) - Maximum power reached with a signal of ~ 4.2V RMS
  • Gain of + 12.5dB, for a total of 25.3dB - Maximum power reached with a signal of ~ 2.2V RMS
  • Bypass: in this case the signal passes directly from the inputs to the modules, allowing the lowest possible gain of 12.8dB. This mode can be interesting when using a powerful preamplifier, capable of driving a load of 2 to 4kOhm and reaching a voltage of ~ 10V RMS


Designed for easy integration, the HPA-S400ET has a balanced stereo (XLR) and unbalanced (RCA) input. Bipolar selectors make it easy to change the input source and even allow independent channel control.

On output side, BP-207 Carbon / Gold 24K Ø5.5mm speaker terminals ensure excellent connection with the speakers.

A trigger module allows the amplifier to be switched on automatically from a distance. This is compatible with voltages from 5 to 12V.


Frequency response

THD vs Freq

TypePower Amplifier
Output power (max)8Ω @1%THD : 227W
4Ω @1%THD : 425W
2Ω @1%THD : 450W
THD+NPO=1W, f=1kHz 0.0007 %
PO=10W, f=1kHz 0.00026 %
PO=100W, f=1kHz 0.00015 %
PO=1W, f=20-20kHz 0.0007 %
PO=10W, f=20-20kHz 0.00029 %
PO=100W, f=20-20kHz 0.00017 %
IMD (CCIF)PO=1W, f=18kHz+19kHz 0.00025 %
PO=10W, f=18kHz+19kHz 0.00022 %
PO=100W, f=18kHz+19kHz 0.00027 %
IMD (DIM)PO=1W, DIM30 0.002 %
PO=10W, DIM30 0.002 %
PO=100W, DIM30 0.002 %
Idle noiseA-weighted 11.5 µV
Dynamic rangeA-weighted 4Ω 131 dB
SNRA-weighted 4Ω 131 dB
Frequency responseRL= 8Ω, f= 20-20kHz ±0.01 dB
RL= 4Ω, f= 20-20kHz ±0.01 dB
RL= 2Ω, f= 20-20kHz ±0.01 dB
Output impedance1kHz, Iout=1A 0.07 mΩ
20-20kHz, Iout=1A <0.65 mΩ
Input impedanceRCA: 47kΩ / XLR: 94kΩ
Bypass: 2.2 / 4.4 
Power supply230V (110V on request)
Dimensions413 x 322 x 60mm
Weight5.63 kg
Data sheet
OutputSpeaker terminal
ChannelDual Mono
Light symbolYes
ClassClass D / T
Fuse holderYes
Amplifier chipPurifi 1ET400A
Power (W)400.0
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Average votes
4.3 / 5
9 reviews
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Note :
Date :
très Satisfait
Je suis un objectiviste donc pas très fan du "son " prétendu des amplificateurs. Mais ayant des enceintes difficiles à driver j'ai décidé de me lancer dans l'achat d'un fameux Purifi 1ET400A. Le prix est très compétitif. J'ai rencontré un problème : une boucle de masse (j'entendais le son des HDD dans les enceintes)... après plusieurs tests cela venait de mon installation car la même multiprise partageait l'ampli et mon PC. Je conseille donc d'utiliser ce modèle sans autres électroniques type PC, box, chargeur de téléphone sur la même prise. Merci à l'équipe d'audiophonics pour les réponses à mes questions.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Note :
Date :
a potential game changer
I've been a fan of Bruno Putyz and his designs for many years and consider him a pioneer of Class D. Hypex, N-core have been adopted by so many high end manufacturers NAD, Bel Canto etc etc. I was very excited when Purifi announced eigentakt. Even more so when audiophonics packaged it so attractively and affordably for the enthusiast with the well proven Hypex SMPS power supply. An immediate buy. I love building but dont have the machinery or time for nice casework.
Comments. Excellent build quality in and out. If you want pretty spend another 5k.
initially disappointed with sound compared to Nord n core monblocks with hardy discrete amps.
Immediately looked at lm4652 (see other reviews) and replaced with sparkos discrete dual opamps. A revelation. up there with the very best. This is super audiophile at bargain basement prices.
Tres bien. Merci beaucoup.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Note :
Date :
Très bon ampli
Le HPA-S400ET est une belle bête. Sobre, bien réalisé, il n'a pas à rougir face à une concurrence bien plus chère en terme de fabrication / finition. Les borniers sont impressionnants. A l'écoute, je ne sais pas encore si c'est mieux - je manque de recul - mais c'est en tout cas assez différent de mon Audio Analogue. Les graves vont plus bas et sont plus tendus, mieux définis. A l'inverse, le haut du spectre est moins dynamique mais a priori tout aussi précis. Parfait pour être associé avec mes enceintes Dynarex qui ont des aigus très agressifs. Avec des Klipsch Cornwall iii qui ont un naturel assez "sombre", l'association n'est pas idéale. En revanche je trouve que la scène stéréo manque un peu de largeur, peut être n'ai je pas encore trouvé le bon placement des enceintes, mais face à l'Audio Analogue, la différence est assez fragrante. Je suis un peu plus réservé sur l'alimentation. En effet à chaque fois que j'éteins l'ampli - volume à zéro - j'ai un "clac" dans les enceintes assez désagréable. Cet ampli me fait l'effet d'une loupe : il amplifie le moindre bruit, signal ... qui provient de la source voire du pré-ampli. Dans l'ensemble je prends plaisir à écouter mes disques et rien que pour cela, le HPA-S400ET est bien recommandable vu son prix.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Note :
Date :
Rather good, but needs modification
The positive binding post of R Ch is unfavorably connected to GND due to the phase inversion at R Ch for reducing bus pumping. This is because negative output of 1ET400A is connected to GND internally.
Sound quality is not good enough for me, though is better than that of Hypex NC400 with SMPS600N400. I replaced the interface card with Purifi FE02 front-end board, in which OPA1612AID OPamps and low noise discrete regulators are incorporated. They seem to have higher performance than LM4562NA OPamps and conventional 3-terminal 7815 and 7915 regulators used in the interface card. I also changed cables connecting output Faston-tabs and binding posts to Cardas CROSSLINK 1S speaker cables that have star-quad configuration. The sound quality has come to be worth 5 stars.
I hear that FE02 is not permitted to be incorporated in commercial products by Purifi. Sound quality would be better if discrete 3-terminal regulators were used instead of the IC regulators in the interface card, because some sound degradation probably originates from noise and inadequate transient response of the regulators. The reason for reduction of 2 stars here is that modification is necessary for excellent sound.
Apart from the product, I felt kindness and faithfulness in customer service personnel.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Note :
Date :
Amplificateur Stéréo Class D Purifi
C'est juste incroyable comment ça peut donner un son aussi puissant et aussi musical.

Il alimente mes Jenzen Illuminator DIY, en complément (provisoire) d'un DAC préamplificateur OPPO SONICA, le tout connecté en XLR SUPRA.

Beaucoup de détails, ampli neutre.
De la puissance et une attaque super franche sur le registre grave.
Le tout est super équilibré, tout est bien à sa place. Du détails, mais jamais analytique.
Dernière étape pour mon setup, je dois choisir un préamplificateur à tubes symétrique.
Qualité de fabrication et sérieux d'Audiophonics. Au top les gars franchement! MERCI


This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Class D stereo power amplifier based on two PURIFI 1ET400A modules and a HYPEX SMPS1200A400 power supply.

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