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Audiophonics HPA-S400ET Review (Stereo Amplifier)

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 0 0.0%
  • 2. Not terrible (postman panther)

    Votes: 3 0.7%
  • 3. Fine (happy panther)

    Votes: 33 7.6%
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    Votes: 401 91.8%

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Staff Member
CFO (Chief Fun Officer)
Feb 13, 2016
Seattle Area
This is a review and detailed measurements of the Audiophonics HPA-S400ET. It was sent to me by the company after member request and costs 1 490,00 € (US $1,638).
AUDIOPHONICS HPA-S400ET Review Balanced Purifi Stereo Amplifier.jpg

I must say this is one of the best packaging of class D amplifiers (Purifi in this case) that I have seen! It is slick and has style. While the heatsink on one side is cosmetic, the other is connected to the power supply power transistors although in use nothing rose above room temperature. Back panel shows extremely high quality speaker connections:
AUDIOPHONICS HPA-S400ET Review Back Panel XLR Balanced Purifi Stereo Amplifier.jpg

You can see it better with the lid open:
AUDIOPHONICS HPA-S400ET Teardown Balanced Purifi Stereo Amplifier.jpg

I must say, this is so clean you can eat of of it! :) I simply cannot find any fault with the assembly and design. Bottom to modules are Purifi 1ET400A modules fed by their own custom buffer/pre-amp gain stage. Jumpers let you select from different settings (see measurement section).

Audiophonics HPA-S400ET Measurements
Given the three different gain stages, it was a challenge to decide what to test so that this job doesn't become nearly infinite in scope. I will first show you the dashboard for all three gains starting from high gain:
AUDIOPHONICS HPA-S400ET Measurements High Gain Balanced Purifi Stereo Amplifier.png

This is superb performance already with distortion products at -125 dB. Channel matching is excellent. Here is medium gain petformance:

AUDIOPHONICS HPA-S400ET Measurements Medium Gain Balanced Purifi Stereo Amplifier.png

This is a nice setting as max power is achieved at 4 volts meaning you can use all of our modern/desktop amps to drive the unit and gain a bit of performance.

If you have a pro interface that goes up to 10 volts out, you can utilize the low gain mode:
AUDIOPHONICS HPA-S400ET Measurements Low Gain Balanced Purifi Stereo Amplifier.png

This gain is actually close to how I measured our two top performers (Benchmark AHB2 and Topping PA5) so let's see how the Audiophonics ranks:

Best Stereo Amplifier Review.png

Looking at top 20 we see:
Top Stereo Amplifier Review.png

Amazing performance! Measuring SNR at low and medium gain we get:

AUDIOPHONICS HPA-S400ET Measurements Low Gain SNR Balanced Purifi Stereo Amplifier.png

AUDIOPHONICS HPA-S400ET Measurements Medium Gain SNR Balanced Purifi Stereo Amplifier.png

OK, from here on I am going to stick with low gain mode. Here is our multitone:
AUDIOPHONICS HPA-S400ET Measurements Low Gain Multitone Balanced Purifi Stereo Amplifier.png

Stellar as expected. Crosstalk manages to actually land in #1 position of any amplifier tested:

AUDIOPHONICS HPA-S400ET Measurements Low Gain Crosstalk Balanced Purifi Stereo Amplifier.png

Frequency response is dead flat with no load dependency:
AUDIOPHONICS HPA-S400ET Measurements Low Gain Frequency Response Balanced Purifi Stereo Amplif...png

Let's sweep and see how we do with 4 ohm load:
AUDIOPHONICS HPA-S400ET Measurements Low Gain Power into 4 ohm Balanced Purifi Stereo Amplifier.png

Excellent performance. Here is how much power we get if we allow more distortion:
AUDIOPHONICS HPA-S400ET Measurements Low Gain Max and Peak Power into 4 ohm Balanced Purifi St...png

Switching to 8 ohm we see that the performance actually exceeds than of Purifi (although I think that was tested at higher gain):

AUDIOPHONICS HPA-S400ET Measurements Low Gain Power into 8 ohm Balanced Purifi Stereo Amplifier.png

Testing at other frequencies we still have great performance:

AUDIOPHONICS HPA-S400ET Measurements Low Gain Frequency vs Power vs Distortion ohm Balanced Pu...png

Finally, the amplifier is stable at power up so no need to wait for it to warm up:
AUDIOPHONICS HPA-S400ET Measurements Warm up Balanced Purifi Stereo Amplifier.png

The Audiophonics HPA-S400ET comes in a beautiful package with super performance to match its good looks. Yes, it builds on Purifi's excellent platform but they managed to add value without messing with its performance. The gain settings are well thought through. The whole thing is so well executed and must be a delight to our European members who can buy it locally. Having been built in France, it is also a feather in the cap of our French members. :)

I am happy to give my strongest recommendation to Audiophonics HPA-S400ET. You have a lot of power with superb fidelity and transparency.

Edit: video review just posted:

As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
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Senior Member
Forum Donor
May 31, 2020
Great, a review of something that measures well! At least this one won't attract the trolls... :p

As always, dedicated work @amirm, cheers.

The "but how does it sound" and "it's cold, lifeless and certainly not musical" trolls will never be far away....


Active Member
Oct 5, 2019
Glad to see Audiophonics come out so well. Had nothing but the best experiences, incl. customer support, in my dealings with them. Even in English!:D


Major Contributor
Forum Donor
Sep 20, 2018
Thanks, @amirm. Excellent price/performance ratio, for sure!:)

But we unsurprisingly get what is expected performance from a close-to-reference design : 1ET400A + SMPS1200 + transparent buffer board (which is good). Minor differences are due to either production variation or Gain settings. Personally, I would spend a bit more for BoXem Arthur 4215 (for form factor, auto off/on and overall build quality) but none would "sound" any better than the other.;)

For those who don't know, there's also a cheaper version, with the exact same components in a smaller case:
audiophonics-lpa-s400et-class-d-stereo-amplifier-purifi-2x400w-4-ohm (2)~2.jpg

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Forum Donor
Dec 6, 2019
Rome, Italy
Fantastic results, I was waiting them.
We have our king of Europe here, well done Audiophonics.
Any explanation on why the low gain mode (should just bypass the input board) is performing slightly better than the Purifi Eval1 itself?
Très bien!


Addicted to Fun and Learning
Forum Donor
Apr 12, 2019
Coventry, UK
I almost went for Audiophonics Hypex 122 unit but decided on Topping PA5. This shows that I would have been happy with either choice :)


Active Member
Forum Donor
Mar 11, 2020
Essex, UK
Congrats to Audiophonics for a stellar piece of kit. Looks like I have found my power amp.
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