Monday, August 15, 2011

USB Audio Interface

This circuit is the quality of a preamplifier with a built-in USB DAC Leachamp my power amplifier. The system is PCM2902 Datasheet. Circuit includes DAC and ADC, SPDIF input and output of HID and 3 + button to the MUTE, VOL-and VOL.

For playback of high quality requires an external low-drop voltage regulator for the DAC. LP2951CM DAC is used, which were easily available in local stores. Output voltage is fixed at about 3.7 V, with two resistors. The circuit was designed for the placement of the well and the separation of digital and analog ground. This land is connected to a certain point of the USB connector.
PCM2902 data sheet recommends connecting the low pass filter the DAC output to filter out frequencies above the audio band produced by the conversion of oversampling. Digital integrated circuits, which includes frequencies above 100 kHz LPF. Notes application filter sites recommended by the manufacturer of the first order LPF (simple RC), or 2 Amps order preamp works, it works well. I am a simple RC LPF with the recommended values ​​for R and C. 4N7 1k It 'best to use the scroll-ceramic capacitor in place. I did not hear the sound difference between the filter or not, but in relation to other components of the audio chain is best to use. The best cut-off frequency, which can change the value of the capacitor 3N3

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