NuForce P-20 Preamplifier

Description

The P-20 Preamplifier’s elegantly sculpted aluminum case encloses a number of significant advances over the preamp’s award-winning P-9 predecessor in several key areas, especially with respect to volume control. A preamp’s volume-control capabilities are among its most critical features. In practical terms, we saw room for improvement over the already excellent P-9’s volume control within the areas of transparency and noise.

The P-20’s numerically controlled, switched-resistor ladder network features the last word in thin-film technology. In order to improve precision and lower the noise floor to the vanishing point, we’ve implemented a single thin-film, ultra-low-noise resistor in the signal path for each of the volume control’s 0.5dB gain settings, thus permitting the listener to achieve the desired volume level in precise 0.5dB steps. As a further benefit, the listener is able to adjust any input’s level to exactly correspond with any other, thereby simplifying the matching of source-component volume levels.

The heart of the P-20 boasts an all-discrete, fastidiously precise amplifier module. Because speed is of paramount significance, we’ve reduced capacitive loading on the final voltage amp with the implementation of ultra-low-noise, monolithic dual JFETs, specially selected VMOS FETs, and extremely flat hFE bipolar transistors in a dual cascode configuration, all of which are combined within a driven-shield arrangement. The P-20 offers a 5MHz power bandwidth, an S/N ratio exceeding 100dB, and a dynamic range in excess of 120 dB. There are no capacitors or DC-servos in the inherently stable P-20’s gain circuit.

And, in keeping with these advances, we’ve paid a great deal of attention to isolation. We’ve covered the amplifier modules with thermal insulation along with heavy copper shields in order to avoid thermal drift or signal-degrading heating effects. Each amp module’s self-contained shunt regulator further assists in isolation from power supplies. A similarly isolated floating-current source supply feeds each module to insure separation from ground-system noise.

Since all control functions are powered by discrete power supplies, the P-20’s design prevents any logic circuitry clock-signal noise from ever contaminating the analog section's low-level signals. In keeping with the P-20’s state-of-the-art features, we include a delightfully convenient, custom-designed remote control. In sum, the P-20’s near-to-molecular clarity offers the last word in utterly transparent, organic sound – in effect, a stress-free listening experience as close to live as audio permits. Better still, these features can be activated by a 12V trigger signal enabling system integration without the need for manual intervention. All that's required is a processor or receiver with a common 12V trigger connection.