Classic Audio Parts


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Quick Overview

New for 2016.

Advanced Pure-Balance 7-channel amplifier rated at 200W RMS x 7 at 8-ohms and 300W RMS x 7 at 4 ohms offers exemplary performance. Utilizing a new input topology, current feedback, dual-DC servos and ThermalTrak output devices, distortion and noise are low, low, low. Signal-to-noise ratio (THD + N) is an astounding 128 dB ("A" Wtd.)

These 4000 series amplifiers have dual toroidal transformers but have only a single power switch and a single power cord. They operate perfectly with a 15A (standard) AC Outlet.

AT4000Signature Amplifier

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  • AT4000Signature Amplifier
  • AT4007 production view
  • AT4007 Rear Panel


Advanced Limited Edition amplifier designed by Morris Kessler. The “Signature Series” designation with a facsimile of Kessler’s signature on the main panel acknowledges the special nature of these designs.

Based on the award-winning (4 Amplifier of the Year Awards from 4 different publications) AT6000 Series amplifiers, the AT4000's share the same circuitry and performance with power output reduced to 200W RMS per channel at 8 ohms and 300W RMS per channel at 4 ohms.  Otherwise performance is identical. 

Beyond Kessler’s personal identification, these amplifiers are new in more significant ways.

1. As in Kessler’s previous top-of-the-line designs, these amplifiers are fully balanced, differential amps, but unlike his earlier balanced designs which were essentially balanced bridged amplifiers, the 6000 series uses only a single input stage with dual-differential output stages. The reason: the advantages of balanced designs are retained and noise is reduced by 50%.

2. The design uses current feedback instead of the more common voltage feedback. The reason: current feedback amplifiers are faster with virtually unlmited slew rate and are better able to reproduce today’s best music and film.

3. Kessler used Thermaltrak output devices for the 6000 series. Unlike traditional designs where external diodes attached to the heat sinks track the amplifiers operating conditions and use the details to adjust bias, Thermaltrak devices have the temperature sensor in the same package as the transistors. The results: bias is optimized in real-time.

4. The 6000 series use dual DC servos to track and maintain DC offset. The result: DC in the amplifier’s output is reduced to insignificant levels.

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