UD-301

The USB input facility allows DSD native playback which converts 5.6MHz DSD files directly into analog signals without needing first to convert it to PCM. It supports both the ASIO2.1 and DoP (DSD over PCM) conversion methods. Using the AI-301DA in conjunction with the TEAC HR Audio Player* high-resolution playback computer software application, anyone can easily explore the world of high-rez digital audio, including 5.6MHz DSD or 32bit/192 kHz PCM files, without having to grapple with complex settings etc.

When receiving digital audio signals from a computer via USB cable, the unit can operate in asynchronous mode, controlling the timing of the input signal using the UD-301's internal clock (which is identical to the one used in the UD-501). With asynchronous transmission over USB, signal compromising jitter is effectively eliminated, allowing digital audio signals to be transmitted in a pure, unadulterated state.

When handling digital signals of 96kHz and less, users have the option to upconvert to double or quadruple the original signal sampling frequency. Even when playing back a 44.1kHz sound source (equivalent to CD sound quality) a smoother analog audio signal can be obtained in order to convert to a higher resolution digital signal. Naturally, this up-conversion facility can be switched in or out, according to the user's preference.

In order to process the audio signal from a high-resolution sound source in a purer state, we adopt a dual monaural circuit design whereby each of the left and right channels comprises its own single monaural circuit. This avoids mutual interference between the left and right channels and enables pure stereo playback.

The two internal BurrBrown 1795 digital-to-analog converter units each work on a single channel (left or right) for true dual monaural operation. They are capable of 32-bit processing and so have the capacity to process 5.6MHz DSD data in large quantities, making them indispensible for faithful and accurate playback of high-resolution sound sources.

We use these in the analog circuit, they are a vital element in determining the final sound quality. They transform the electrical current output of the D/A converter into a voltage signal. We opted for a dual monaural configuration for the operational amplifiers, employing two MUSES8920 operational amplifier units, one on each of the left and right channels. These devices are made by New Japan Radio and are designed especially for hi-fi audio.

The 100mW + 100mW output (at 32 ohms load) headphone amplifier uses CCLC (Coupling Capacitor Less Circuit) technology. In conventional headphone output circuits, a capacitor is used for output-stage coupling, and so the sound is unavoidably colored. When the capacitor is combined with a high-pass filter this often results in phase lags, or low frequency level degradation. With CCLC the negative impact of capacitors on sound quality is eliminated, providing full low-frequency sound and a responsive headphone listening environment with great spatiality.

In addition to the dual monaural headphone circuits, there are options to switch off the XLR and RCA outputs on the rear panel. By cutting the power supply and isolating those circuits that are unrelated to the headphone output, the performance of the UD-301's headphone output can be maximized. This feature also makes the headphone amp very easy to use as the volume control for the headphones is completely separate from the output mode (Fixed, Adjustable or Off) on the rear panel.

A high-efficiency toroidal core power transformer with low magnetic flux leakage is used to guarantee the stable operation of the twin left and right D/A converters that are so essential to the UD-301's high-speed signal processing. This transformer provides a stable power supply even in situations where a sudden surge of power is required, such as when starting up at very high volume.

Following on from our development of the 501 series concept (small high-performance audio components that can be fitted on a desktop) we decided, at the outset, that the 301 series would be an even more compact design. Now, the casework has been shrunken to just 215mm wide, allowing greater freedom in positioning the amplifier. External highlights include aluminum panels and a motor-driven volume knob with the tactile feel you'd expect from controls found in high end full-size hi-fi components. At the same time, the solid enclosure underpinned by the metal chassis, is impressively inert, minimizing the effects of vibration on the unit's sound quality.

The UD-301 is equipped with an XLR balanced output that can be connected not only to other domestic hi-fi components but also to professional audio equipment. As a highly versatile, high-performance D-A converter, the UD-301 offers a high degree of interoperability with devices ranging from those used by discerning consumers all the way up to those used in the professional domain.

The XLR balanced output and RCA unbalanced outputs on the rear panel can both be set at Fixed, Adjustable or Off. Using the Adjustable setting, the UD-301 can be connected to a power amplifier to create a system with a separate pre amp and power amp or, alternatively, can be directly connected to an active speaker.