Atoll electronique AM400 Evolution
Atoll AM400 Evolution stereo power amplifier, 170 W into 8 Ω, designed and manufactured in France, bridgeable to mono.
Description
The AM400 Evolution is a stereo power amplifier from Atoll Electronique, designed and manufactured in France in Brecey. It is placed downstream of a preamplifier to provide the power stage of a hi-fi system, with the option of being used in classic stereo configuration or in bridged mono mode to power a single speaker with greater power.
Its electronic stages have been reworked to make it insensitive to capacitive loads, allowing it to drive demanding speakers without instability. It delivers 170 W per channel into 8 Ω and 320 W into 4 Ω, or 600 W in bridged mono mode into 8 Ω. The 1050 VA power supply and total capacitance of 111,300 μF demonstrate a substantial energy reserve, useful for reproducing dynamic peaks without compression. The signal-to-noise ratio of 105 dB and a distortion at 1 kHz of only 0.005% reflect very low background noise and colouration. The bandwidth extends from 5 Hz to 200 kHz, with a rise time of 1.5 μs, ensuring good responsiveness on transients. The high-quality, shielded MKP coupling capacitors also contribute to sound fidelity.
The amplifier has a stereo RCA input and a stereo XLR input, for integration with sources or preamplifiers fitted with balanced or unbalanced outputs. Its consumption ranges from 14 W to 800 W in operation, and it draws nothing once the switch is turned off.
This model is aimed at enthusiasts wishing to separate preamplification and power amplification, particularly for driving current-demanding speakers or building a bi-amplified configuration in bridged mono mode. Its dimensions of 440×370×130 mm for 19 kg correspond to a dense power amplifier, intended for a stable cabinet or stand.
Technical specifications
| Power Wrms/channel/8Ω | 170 W |
| Power Wrms/channel/4Ω | 320 W |
| Power in bridged mono mode/8Ω | 600 W |
| Power supply | 1050 VA |
| Total capacitance | 111,300 μF |
| Number of stereo inputs | 1 RCA + 1 XLR |
| Consumption with switch off | 0 W |
| Consumption in operation | 14 W - 800 W |
| Input impedance | 220 kΩ |
| Sensitivity | 1.7 V |
| Signal to noise ratio | 105 dB |
| Distortion at 1 kHz | 0.005 % |
| Bandwidth | 5 Hz - 200 kHz |
| Rise time | 1.5 μs |
| Dimensions (H × W × D) | 440×370×130 mm |
| Weight | 19 Kg |
What to check before buying used
With this type of power amplifier, attention should be paid to the volume or gain potentiometer, which is prone to crackling if the tracks become oxidised, and to the condition of the power supply capacitors, whose ageing can reduce the dynamic reserve. Checking that the bridged mono mode functions correctly and that the protection relays operate properly at power-up rules out any malfunction of the output stages. The chassis ventilation is also worth checking, as the power delivered generates noticeable heat during prolonged use.
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