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).
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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:
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You can see it better with the lid open:
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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:
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This is superb performance already with distortion products at -125 dB. Channel matching is excellent. Here is medium gain petformance:
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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:
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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:
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Looking at top 20 we see:
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Amazing performance! Measuring SNR at low and medium gain we get:
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OK, from here on I am going to stick with low gain mode. Here is our multitone:
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Stellar as expected. Crosstalk manages to actually land in #1 position of any amplifier tested:
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Frequency response is dead flat with no load dependency:
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Let's sweep and see how we do with 4 ohm load:
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Excellent performance. Here is how much power we get if we allow more distortion:
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Switching to 8 ohm we see that the performance actually exceeds than of Purifi (although I think that was tested at higher gain):
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Testing at other frequencies we still have great performance:
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Finally, the amplifier is stable at power up so no need to wait for it to warm up:
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Conclusions
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:
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