Audio Optimum NOS-DAC 2

As a combination of a non-oversampling DAC and preamplifier with a balanced cable driver and remote-controlled volume control, the Audio Optimum NOS-DAC 2 is the ideal complement to our active speakers, ensuring they are driven at an equally high level. Additionally, a high-quality headphone output is available.

The NOS-DAC 2 is miniaturized for the shortest signal paths, reaching the limits of what is technically feasible. The power supply is implemented with integrated switching voltage converters, which are equipped with higher-order filter chains on both the primary and secondary sides for ripple suppression. The output voltages (±15V for preamp, ±5V for DAC, +5V for control) are as smooth and stable after the secondary filters as would be difficult to achieve with voltage regulators prone to oscillation. The connection to the 230V power grid is made via an EMC-optimized 12V linear power supply.

The non-oversampling DAC corresponds to the Audio Optimum NOS-DAC, but additionally features three switchable SPDIF inputs, which can be either coaxial (75Ω RCA) or balanced (110Ω XLR). Additionally, the analog reconstruction filter can be manually switched for different sampling frequencies, allowing for a linear frequency response up to 20kHz without distortion caused by oversampling with a digital filter, for both 44.1kHz (Audio CD), 48kHz (digital broadcasting), and ≥88.2kHz (Audio DVD).

For connecting an analog source, there is a balanced analog input with XLR connectors, which can optionally be equipped with RCA connectors for quasi-balanced signal transmission. With two balanced input stages that only amplify the voltage differences between the two inner conductors and the two shielding rings, the usual ground loop between stereo channels is eliminated, meaning that quasi-balanced signal transmission with shorter RCA cables provides nearly the same transmission quality as true balanced transmission.

The preamplifier is fully DC-coupled, features active offset compensation, and is built with integrated dual operational amplifiers, which, after extensive listening tests, were found to offer the best sound quality. No amount of complexity in circuits using discrete transistors or vacuum tubes can match or surpass the sound quality of these operational amplifiers, and would only lead to increased susceptibility to interference due to longer signal paths. Contrary to popular belief that a balanced output stage should be extremely low-impedance (which is only necessary for very long cables), additional impedance converters are omitted. What is not in the signal path cannot distort the sound. The complementary output signals A+ and A- are each directly connected to the outputs of an integrated dual op-amp through 47Ω resistors. As long as the cable length to the active speakers remains under 10m (even up to 20m with low-capacitance cables is no problem), this is the sonically optimal solution.

The classic ALPS motorized potentiometer is used as the volume control, which, unlike electronic volume controls, has no impact on the sound and offers more than sufficient accuracy (channel balance) in practice. The remote control has a unique feature: it does not use digital codes (which cause annoying delays), but instead operates with pulse-width modulation, allowing the motorized potentiometer to be adjusted without delay and in finely controlled steps.

The headphone output is driven by a DC-coupled, fast transimpedance amplifier with active offset compensation. The voltage swing is sufficient to fully drive headphones with impedances ranging from 30Ω to 600Ω. Assuming a clean SPDIF source, the transimpedance amplifier, in conjunction with the NOS-DAC, can drive the best headphones in the world with greater precision than has been possible with any other headphone amplifier to date.

For both driving active speakers and operating headphones, the Audio Optimum NOS-DAC 2 offers a level of sound quality that is unlikely to be surpassed, regardless of price.

Scope of Delivery:

1 x NOS-DAC 2
1 x 12V1A Linear Power Supply
1 x Remote Control
Enclosure: Acrylic