The D28.38 by Audio-GD combines the function of DAC, disrete preamplifier / transistor (non-feedback balanced design). It uses an ESS ES9038PRO DAC chip, which features the famous Hyperstream II technology and can support audio streams up to 384kHz / 32bit (PCM) and DSD512 (native DSD decoding). Belonging to the last generation of Audio-GD devices, the front face displays a control panel for easy and fast access to all options relative to digital stream decoding (reconstruction filters, clock strategies ... etc). ConnectivityThe D28 provides large connectivity and uses only high quality connectors. The device has a coaxial input, an optical input, an I2S (HDMI LVDS) input, a stereo RCA input, a stereo XLR input and on top of all, a USB input. The latter is based on an USB interface Amanero 384 combo (built-in option) which is known today as one of the best USB interface for Audio. On the Output size, it includes a RCA (single-ended), XLR and ACSS output (balanced). On the front panel, one can found two headphone connectors. One works through a XLR 4-poles plug while the other works for regular 6.35mm jack plug. Optimized signal pathThis High Fidelity DAC is equipped with ESS ES9038Pro Sabre 32-bit. This conversion chip is capable of handling high definition audio stream formats (PCMDSD) with and excellent signal to noise ratio. This DAC model is one of the most famous 32bit 8 channel DAC technology. It is used in many very high audio performance environnements such as audiophile systems, mixing studios, SACD players, Blu-Ray, digital audio workstation ... etc. This component embeds ESS' Hyperstream II architecture and offers considerable signal precision with its active jitter reduction function, 132 dB dynamic range (stereo) and -120dB THD + N, . This conversion stage is integrated in a ACSS circuit (signal via current), which allows to channel the signal through a single stage of conversion only, which results in an extremely short signal path between the DAC and the pramplification stage. Output stagesThe balanced output of uses 4 Diamond Rhombus preamplification group which were fully designed and tested for this specific audio device. The output stages are articulated around 4 pairs of 15W transistor. this arrangement provides excellent power reserves with all the advantages that this represents in terms of headroom and distortion. The headphone amplifier operates in pure class A (1500mW 9500mW @ 100ohm up to 25ohm) which allows the D-28 to drive most demanding headphones. Oversized powerAs usual with Audio-GD, particular care was given to the device's power-supply and all components involved in powering units. An R-core transformer provides a clean supply operated by not less than 10 PSUs. Of these, 7 units are grouped into two-stage in order to supply the digital circuit separately and prevent contamination of a signal on the other. Because ES9038PRO chip is highly sensitive to power supply noise and ripple, two groups of transistors are installed respectively on the right and left channels to prsever any crosstalk. This feature can greatly deepen the soundstage. Volume ControlQuality volume control is particularly important in a balanced system. Indeed, it must guarantee the accuracy of the control signal on the four channels to achieve a perfect balance. If these conditions are not met, the signal is exposed to significant levels of distortion. This can even sometimes limit the interest of a balanced system. To maintain this balance, Audio GD offers several very relevant strategies from an audiophile point of view:Audio-GD made the choice to use a I/V converter (Transimpedance Amplifier). The volume control is the result of a passive voltage / current conversion directly at the output of the ACSS amplifier. This keeps all the details in the signal even at very low volume. The 4 buffer diamonds without feedback output stage, allowing to obtain a very low output impedance. In-circuit shieldingThe D-28 uses a Amanero Combo 384 as USB interface. Built into almost all Audio-GD devices, this module is known as one of the best existing USB interface. It is moreover totally electrically isolated, as to avoid being subjected to potential interference that could degrade the signal. In addition, the various internal components / groups of the circuit are isolated from each other by multi-layer shielding plates in order to prevent any signal pollution for each stage of the device. The IEC connector dedicated to the power supply is itself encased in a copper film to complete the insulation of the circuit.

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