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: 19-01-2021.

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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.


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
Accepts Banana PlugsYes
Light symbolYes
ClassClass D / T
Fuse holderYes
Input voltage (V)230V AC
amplifier chipPurifi 1ET400A
Maw power (W)400.0
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Average votes
4.2 / 5
5 reviews
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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
Note :
Date :
HPA-S400ET - Got it to swing
First weeks not too happy with the amp. I knew the LM4562 was not my taste and planned to swap it anyway. Changed it to OPA627 I had lying around and it improved, but not as much as expected. Next adjustment was swapping to Sparkos SS3602. This was good step forward in frequency response and soundstage nice and fluid only after changing internal cables and binding post. Signal cable changed to single core silver plated and screened occ cable (not sure about brand, got it ‘donated’). The binding posts were changed to eti bp-20c. The internal speaker cable was changed to elacaudio hp-25occ (non-twisted). I first tried untwisting the original cable to check whether or not audible noise would occur, this was not the case. Now the sound is very fluid with broad and high soundstage.
I believe in original state the amp is OK-ish and for me an item to sell again (for me max 2 stars then). It is a keeper after the changes. Rather minus 1 star because of the many changes required.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
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Date :
Excellent amp, great value
Great-sounding amp: neutral, clean, effortless. Component-style chassis fits perfectly with other equipment, with ample heatsinks. Speaker connectors are good quality and easy to use. Front-panel power button is smooth. Plenty of power, great modules.

For someone moving from traditional Class A/Class AB to Class D, this amp provides 25dB of gain, very close to the traditional 26-29dB that most Class AB amps provide. This enables this amp to fit nicely into an existing system with nothing more than a minor volume adjustment to your preamp or source component.

Customer service was excellent - personal emails, updates on when it was being assembled and when it was shipped, with full international tracking.

Only things to be aware of are the the RCA/XLR toggle switches on the back are not labeled (down is RCA, up is XLR); and the front power LED is a little bright and not dimmable.

It's currently impossible to beat the price and value here: full-size metal case with two Purifi modules for under 1500€/$1400US. Well done, Audiophonics!
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
Note :
Date :
Excellent produit
J'ai acheté ce produit pour upgrader mon système. J'avais auparavant un ampli surpuissant de la marque à la couronne et j'ai constaté une net amélioration en terme de musicalité, les voix et les medium ressortent davantage. Certains sons dans les aigus qui étaient un peu fatiguant sont plus doux tout en gardant beaucoup de détails.
La scène est plus ouverte également. J'alternais avant beaucoup entre mon ampli A/B (plus vivant dans les médiums et aigus) et mon ex ampli de classe D (pour les bass) selon mes humeurs et le style de musique.
Aujourd'hui plus du tout.

J'aurais volontier mis 5 étoiles pour cet incroyable rapport son/prix. Mais l'ampli que j'ai reçu n'avait qu'un canal fonctionnel. J'aurais pu échanger l'ampli mais étant un peu bricoleur, j'ai ouvert la bête et noter quelques branchements qui n'allaient pas en comparant avec le canal fonctionnel.

Je suis déçu par ce "made in france".
Message from Audiophonics service
Nous sommes sincèrement navré de cette situation.

N'hésitez jamais à contacter notre SAV pour tout problème, ils feront le nécessaire au plus vite.
This review has been posted for Audiophonics HPA-S400ET Amplifier Class D Stereo Purifi 2x400W 4 Ohm
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Date :
I do not have any measurement equipment but I'm very satisfied using this amplifier based on what others write about purifi modules I'd bet it's top notch. Price is competitive but it comes with a small drawback which is the case. I think the surface gets scratches very easily. Hence one star removed. Binding Posts are good. I also like that you can switch RCA to XLR Left or Right independantly.

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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