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Description. Chord definitely design as though for a science fiction movie. Their amps emit an otherworldly glow in a darkened room. Build quality and finish are in line with the high sticker. The two monos look solid as rocks and likely to outlast a user's lifetime. The finish is nevertheless more industrial than high-end audio jewelry. As such it's perhaps closer to Krell than Luxman or Zanden for example. The top of each amp is made of a sophisticated machined piece of aluminium which frames the internal circuitry. The profusion of blue LEDs can seem excessive but it certainly does confer a strong hi-tech identity to this Chord gear.
The front panel is clean and minimalist: a logo decal and a power switch which glows red for off, green during warm-up and blue during operation. The rear panel has the power IEC, in-phase and out-of-phase RCA and XLR inputs and two massive sets of speaker binding posts. These 66cm deep amps on their twelve metal columns ending in small rubber feet take up a lot of space. Any dedicated rack might lead toward further expenses as choices for that size would seem limited and quite expensive. I personally had no other option than park them on the floor of my dedicated listening room.
The Chord amps have a very sophisticated power supply. This 5th-gen iteration uses spread-spectrum tech, phased clocking, high-frequency auxiliary and a few other advanced solutions from the aerospace sector. Each amp includes three 4kW power supplies in parallel but working individually. Surprisingly the SPM-6000 never got even slightly warm. Don't expect to use these as space heaters during the winter.
Chord believe that despite their excellent transconductance behavior bipolar transistors are not the most efficient choice because of distortion created by on/off switching. Neither do Chord embrace traditional class A bias which never shuts off its output devices to overcome issues of nonlinear operation. Class A for these power ratings is far too inefficient and thermally impractical. Chord's transistors of choice are developed exclusively for them by a UK semiconductor fabrication house formerly involved in the aerospace sector. Chord's parts are based on metal on silicon
But the Chord cornerstone must be their high-frequency switching power supply which can reload far more often than conventional variants. These self-contained self-monitoring supplies can be run individually or in parallel for great flexibility in amplifier design. Wall power is filtered, rectified to DC and stored in a bank of high-voltage capacitors. It then converts to an HF waveform with high-voltage Mosfets running at 80kHz. At this point the high-frequency waveform encounters a custom-made ceramic-core transformer wound with multi-strand Litz. Considering HF mode, Chord don't need big trafos to rectify this waveform. At the transformer's output a bank of high-speed rectifiers, a small coil and small capacitors convert the waveform back to DC whence it hands off to Chord's dynamic coupling of the power supply rails prior to being absorbed by a final bank of storage capacitors.
This technique is said to provide better thermal matching of the output devices and to eliminate the need for temperature-balancing resistors in the output stage to substantially improve efficiency and overall stability. A specific output protection system relies on magnetic flux generated between the power supply rails. The amplifier monitors differences in flux density between the rails over a given period as determined by mathematical algorithms which switch the amplifier into standby when required. Output bias is sliding class AB. It operates in class A during low-level signal and transitions into class B during demanding conditions.
