With these two top-quality components, French manufacturer Atoll is offering us the basic links in a top-level audiophile chain. This pairing features a preamplifier, the Atoll PR400 Signature, combined with a power block, the Atoll AM400 Signature.
The Atoll PR400 Signature preamplifier has been entirely designed with the purity of the signal in mind. Firstly, to ensure that the behaviour of the amplification stages is not affected by any electrical pollution of their operating voltages, the PR400 Signature power supply features filter capacitors with a combined capacity of 112,000 microfarads!
Internal shielding further protects the signal against electromagnetic radiation from external sources. They also eliminate the risk of undesirable interactions between the two channels. What’s more, the PR400 Signature uses high-quality audiophile components selected with the greatest care in the signal path. This is particularly true of the link capacitors. Here, Atoll has opted for shielded MPK capacitors.
Symmetrical architecture
For even greater finesse and subtlety, the stages of this preamplifier have a symmetrical architecture. Each channel is completely independent of the other. In short, a dual-mono design. This layout guarantees exceptional musicality combined with great respect for timbre and a particularly vast, rich and airy stereophonic space. A final crucial point, to ensure that this preamplifier preserves the slightest subtlety in the sound message, Atoll has given it a hyper-extended bandwidth, from 0.5 HFz to 780 kHz. This more than satisfies the requirements for reproducing the most accomplished Hi-Res Audio content, from the deepest bass to the most extreme treble harmonics.
A wealth of connectivity
It’s worth remembering that, again with a view to preserving the purity of the signal, this preamplifier is exclusively analogue. No digital stage is therefore likely to interfere and degrade its quality. The Atoll PR400 Signature is equipped with a particularly rich range of connectors to enable it to exploit signals from the most prestigious sources as well as the most modest. To interconnect with the most common sources, it has five line-level inputs on RCA sockets. These are conventional unbalanced inputs.
For high-quality, even professional sources, two balanced inputs on XLR sockets are also available. As always, these are preferable when using long cables or in a particularly electromagnetically polluted environment. It should be remembered that a symmetrical link protects against the parasitic interference that can be picked up by inter-link cords by routing the signal in differential mode.
Finally, we find the same type of configuration for the outputs of the PR400 Signature. It has two RCA outputs and two XLR outputs. This duplication will be appreciated by users wishing to control their speakers in bi-amplification mode.
Impressive power
The AM400 Signature power block also boasts some impressive features. Its quadruple push-pull Mos-Fet transistors enable it to deliver 2 x 160 W at 8 ohms. It even reaches 2 x 300 W at 4 ohms. What’s more, a small selector on the rear panel allows the Atoll AM400 Signature to be operated in bridged mode. This transforms it into a monophonic power unit capable of delivering 600 W into 8 ohms.
This means that two AM400 Signature power units can be combined with the PR400 Signature preamplifier to create a very high-power installation. However, in addition to the high power output of the AM400 Signature, it is also capable of handling particularly high output currents. This ability to handle very high currents is a major asset in an audiophile environment.
It allows the AM400 Signature to drive even the most rebellious loudspeakers with a grip of steel, providing them with the ideal source for expressing their personality to the full.
A generous power supply
The fact remains that, in order to manage such high power levels, the amplifier must have a power supply that matches the ambitions of its output stages. Atoll has therefore generously calibrated the power supply for its power block. It is based around a 1015 VA toroidal transformer combined with a set of chemical capacitors with a combined capacity of 111,300 microfarads.
As a result, the Atoll AM400 Signature not only has a power supply capable of meeting its energy demand requirements, both in steady state and during the most intense bursts of dynamics. To convey this impressive power from the AM400 Signature’s motherboard to its output terminals, Atoll has used special cables with very large cross-sections.
They are based on a deoxygenated pure copper core. To preserve its very low impedance at the highest frequencies and combat the consequences of the film effect, a silver plating is applied to the copper. Finally, a Teflon sheath provides insulation. Produced specifically for Atoll, these cables guarantee transmission without any loss of signal. All these details are preserved, resulting in rich, detailed sound reproduction. To avoid interactions between the two channels, the AM400 Signature has a dual-mono architecture.
Quality connectivity
Finally, the AM400 Signature is equipped with appropriate connectivity. Two XLR sockets are provided on the rear panel, so that it can be connected to the PM400 Signature pre-amplifier in balanced mode to optimise the overall signal-to-noise ratio of the installation. However, so that it is also possible to drive its power block from a more modest preamplifier, Atoll has provided unbalanced inputs on RCA sockets. An output, also on RCA sockets, makes it possible to ‘chain’ several power units or to link them to another amplifier.
The set up
While both units have a relatively compact footprint, worthy of a 19’ rack format, their weight is imposing. 15 kg for the preamp and almost 20 for the amp. So our Centaure Ls are perfectly suited to the task. Don’t neglect the stand: it plays an important role for these beautiful electronics. As far as connections are concerned, we opted from the outset for symmetrical connections. Both to each other and to connect the sources. Each time, we noticed a real gain in listening.
The electrical phase must be observed with care: it also has an influence. It is standardised, i.e. to the right. Finally, the speakers! We used the Atoll AM400 Signature with four very different pairs of speakers with diametrically opposed outputs, and in practice, this amplifier seems insensitive to load.
The sound of the Atoll PR400 and AM400
You’ll agree that nothing is simpler than qualifying sonic authenticity, which defines the purity of the musical phrase expurgated from the gangue of its support, be it vinyl, silicon or polycarbonate. The task of an amplifier is therefore both dauntingly easy and difficult: to take in a message that is exhaustive but minuscule, and to amplify it tenfold without altering it.
Over the last quarter of a century, Atoll has conscientiously endeavoured to fulfil this mission with simple, wonderfully effective and increasingly ambitious products. The proposal it is submitting to us today is quite simply the highest of its career. It comes after many years of experience in which the French manufacturer has slowly built up its expertise to become one of the leading players in our industry.
This feeling of having fully reached maturity is the first thing that emerges from listening to our Atoll PR400 & AM400 Signature duo. First and foremost, this ensemble is coherent. In fact, it takes several hours of listening to recorded music in its company to begin to identify its ‘personality’.
We’ve put this term in brackets, because we’re not sure it’s appropriate in the circumstances. It’s almost a lack of personality that we should be talking about here. The Atoll ensemble fully embraces the perfectly mastered duality of being undetectable to the ear and at the same time completely present. Undetectable, because the sound signature is virtually invisible.
But fully present, because it anchors us totally in the present time of listening by making it particularly embodied. How do you achieve the feat of forging a remarkable presence without being able to detect its style? First and foremost, by masterfully controlling the bandwidth, which is exceptionally balanced in this price range.
The spectrum reproduced is broad, but that’s the least we can do. On the other hand, it unfolds with a very successful homogeneity. More than the realism of the timbres, it’s their thickness and texture that surprise. The Atoll PR400 & AM400 Signature duo reproduce the flesh of the message with infinite delicacy. The result is a complex listening experience that’s easy to appreciate. The nuances and specificities of each melodic line are easily perceived.
Another decisive criterion is the way in which the sound architecture is transcribed. Listening to the PR400 & AM400 Signature in a vast room with large speakers makes you realise the potential of this amplification in terms of spatial reproduction. A veritable soundscape materialises with each new recording. By turns grandiose or intimate, it perfectly captures the dimensions and volumes of each recording, alternately relegating you to the role of spectator or actor, keeping you at a distance or placing you close by.
After their distinction and sense of perspective, the Atoll PR400 & AM400 Signature will win you over with their demonstration of strength. And it’s a fully mastered force that’s being expressed here. The energy reservoir of these two machines seems limitless. Some of our listening sessions were conducted at very high speed and volume. There was never a hint of dynamic decay.
On the contrary, both devices responded instantly to demand, even when it was particularly high. Whether the message was complex or not, plethoric or not, high volume or not: the two Atolls were unflappable. You almost get the impression that the more you ask of them, the more at ease they seem.
Our conclusion
With its 400 Signature series, manufacturer Atoll has established itself more than ever as a major player in separate-element amplification. We had already tested the Signature version of the 400 preamp, an excellent product, but never the amp. Now we’ve done it, and done it very well! These two products display remarkable potential and maturity.
Obviously, they work harmoniously with each other. And it’s naturally in this configuration that we prefer to use them. When you add up the price of the preamp and the amp, you’re still looking at under €10,000, which means we can offer an excellent level of performance in this price range. And the obvious bonus is that it’s possible to flange the power block in mono to add a second amplification channel, and that’s an entirely different story.
We’ll conclude by saying that this extremely interesting possibility of evolution for the consumer guarantees a particularly relevant alternative to the very top-of-the-range integrated amplifiers that are currently flourishing.
When it comes to making a choice, this is something to bear in mind.
Authors: Estève Fabry and Laurent Thorin
Technical sheet: Atoll PR400 Signature
- Origin: France
- Price : €4,890
- Dimensions : 440 x 130 x 370 mm
- Weight : 15 kg
- Frequency response : 0.5 Hz to 780 kHz
- Rising time : 0.4 microseconds
- Total harmonic distortion : 0.004
- Input impedance : 357 kilo-ohms
- Input connectors : 2 x balanced on XLR, 5 x unbalanced on RCA, 1 x bypass
- Output connections : 2 x balanced on XLR, 2 x unbalanced on RCA, 1 x monitoring on RCA
Technical sheet: Atoll AM400 Signature
- Origin: France
- Price : €4,590
- Dimensions : 440 x 370 x 130 mm
- Weight : 19 kg
- Power: 2 x 160 W at 8 ohms (600 W in bridge mode), 2 x 300 W at 4 ohms
- Frequency response : 5 Hz to 200 kHz
- Rising time : 1.5 microseconds
- Signal-to-noise ratio : 100 dB
- Total harmonic distortion : 0.005
