Усилители мощности моно — Chord ULTIMA

Chord Electronics names the ULTIMA its flagship mono amplifier, rated at 780 W RMS into 8 ohm and 2,500 W into 2 ohm. Chord presents it as the first completely new design since the company was founded, built on circuit topology from founder John Franks some 34 years in the making, and describes it as its most accomplished amplifier in that period. The design draws on three decades of amplifier manufacturing with proprietary technology at the Kent company. Every unit is built by hand in Britain, and the warranty runs for 5 years.

Key specs that matter

Peak output current exceeds 500 A. THD is 0.005%, noise sits better than -90 dB below signal and gain is 30 dB. Frequency response is -1 dB from 0.2 Hz to 46 kHz and -3 dB from 0.1 Hz to 200 kHz. Input impedance is 100 kOhm whether the signal arrives balanced or single-ended, while output impedance is 0.04 ohm. Power draw reaches 3,500 W at full output and 10 W in standby. On its Integra legs the amplifier is 30.5 cm tall, 48 cm wide and 75 cm deep, while optional side blocks change this to 28.5 x 42 x 75 cm. Weight is 66.7 kg, and Chord builds the case in either black or silver.

Engineering and use context

Error correction uses a dual feed-forward topology, a progression of a technical paper by Dr Malcolm J Hawksford, emeritus professor at Essex University, later refined by Bob Cordell of Bell Labs. Chord adds Franks' own concepts in ultra-high-frequency switch-mode power supplies to that circuit. The output stage carries 64 proprietary MOSFET power devices biased in Class AB with a sliding bias arrangement, and the drive circuitry operates at a slew rate of 300 V per microsecond. Signal handling is balanced throughout, and cooling is by convection with no fans inside the solid aluminium case. Inputs come as pairs of XLR and gold-plated RCA sockets in inverted and non-inverted form, so one amplifier accepts either polarity on either connection type. A 12 V trigger input handles automatic switch-on, and bi-wiring is possible through a double set of gold-plated high-current loudspeaker posts. Dimmable feature lighting is fitted, with a top light ring supplied in the box.

Pairing

Being a mono design, each ULTIMA feeds a single loudspeaker, so stereo requires a pair. Its low-impedance rating together with the high peak current shows that very low impedance loudspeakers are within its operating range.

Alternatives

Also in the ULTIMA mono range, the Chord ULTIMA 2 is rated at 750 W RMS into 8 ohm in a lower 18 cm chassis.