PCM1794A audio DAC

Posted on Feb 6, 2014

For power supply is needed transformer with two individual secondary 12V windings. If you want to supply from transformer S/PDIF decoder and transformer doesn`t have third separated winding, we must connect supply input of decoder parallel to winding for positive branch otherwise there will be short circuit. Voltage is rectified by B1 and B2 bridg

PCM1794A audio DAC
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es and goes through filter and decoupling capacitors to low-drop regulators IC3 and IC4 which feeds analog and digital part of DAC. IC5 and IC6 regulates voltage +12V and -12V for operational amplifier. All supply inputs of DAC are properly decoupled with capacitors. DAC PCM1794A works with data from standard I2S bus. In addition to it use signal SCK - System clock, which needs for proper function and oversampling. Input data format, output type and characterics of digital filter is selected with jumpers. Circuit includes internal reset with external pull-up resistor R5. Output is current differential. For conversion to voltage output I use resistors R17 to R20. They should be high quality carbon resistors. Behind these resistors we can theoretically take out symmetrical output to high impedance input of preamplifier. C27 and C28 are used for limit of high frequencies out of audible sound. For getting of single-ended output with average value at zero I used low-noise operating amplifier TL072. Gain is about two. I inspired by original circuit because I am not specialist for operating amplifiers. In original circuit are used operating amplifiers for conversion of current to voltage output too. I used only resistors which are better and simpler. In quiet outputs have zero voltage, that theoretically we don`t need coupling capacitors. On one output was voltage about 12mV and on another 2. 6mV. It can be better by selecting...

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