Musical Fidelity NU-VISTA PAM Mono Power Amplifier

Overview

Based on our excellent Nu-Vista 800 circuit we decided to go all out “fully balanced” on the Nu-Vista range. The Nu-Vista PAM features the tried and tested Nu-Vista stage featuring 6S51N nuvistors in a discrete class A amplifier buffer.

This is followed by a balanced configuration circuit and balanced input high power, low distortion “bridged” output amplifier stage. The power stages have 2x 5 pairs of high power thermally compensated output devices for reliable and stable operation. Based on the Titan 1000W stage, it has separate capacitors for bulk supply, and one each for output device, reducing output impedance and improving dynamics. Chokes are added for further improved supply ripple and pulse current spike reduction. Bias is set for over 5W of initial class A operation thereafter the stage slides into class B operation at a point where the now much lower discontinuity is easier dealt with than “standard” crossover distortion.

The Nu-Vista PAM comes with its own dedicated external power supply. To achieve better noise performance, we removed the AC mains power supply from the main unit and built it into another matching box. In this box we took advantage the extra space to set up inbuilt mains and output filtering. This quietens up the supplies and results in almost no mains-borne artefacts getting into the sensitive audio circuitry. The Power supply has ON/Standby LEDs and is controlled from the main unit front panel. If total mains isolation is required, the power supply also has rear mounted mechanical rocker switch for full power off.