10x TDA1543 NOS DAC

Description: In the supply section, a bridge rectifier and smoothing capacitor are utilized, followed by a common voltage regulator, the LM317, which is configured with resistors R1 and R2 to output approximately 8V. The supply line passes through an inductor to the DAC chip, theoretically reducing high-frequency interference on the power lines. The DAC outputs current, which is converted to voltage outputs using resistors R4 and R5. Occasionally, a circuit with operational amplifiers combined with a low-pass filter is employed; however, this configuration is more complex and may introduce distortion into the audio signal. The low-pass filter, intended to eliminate the sampling frequency, can inadvertently cause distortion at higher frequencies, resulting in a flatter sound profile. As the DAC does not have a symmetrical power supply, capacitors must be used in series with the outputs. High-quality capacitors with adequate capacitance are recommended, with foil capacitors of 10µF being preferred over electrolytic types. These capacitors are connected between the outputs and the output connector but are not depicted in the schematic diagram. The output should not be excessively loaded and should connect to a preamplifier or power amplifier with an input impedance of at least 10 kiloohms. For improved isolation between the S/PDIF decoder and the DAC, a separate supply from an independent winding of the power transformer is advisable. Both the voltage regulator and the DAC require cooling via a small heatsink. The transformer should be rated for a current of 0.5A. Component placement on the board should progress from smaller to larger, starting with SMD components and followed by standard parts. A small heatsink must be mounted on the DAC to prevent overheating, which can lead to damage. The heatsink is attached using two small springs connected to four pins soldered to the board. For the I2S connector, a jumper ribbon with pins or sockets can be used, depending on the desired mechanical connection between the DAC and the S/PDIF decoder. Pins are used on both sides, and two sets of 6-pin sockets are soldered together for board connection. The printed circuit board is designed with a single side and one wire, allowing for fabrication under amateur conditions. SMD components are placed on the bottom side, while components with terminals and connectors are mounted on the top side. Holes are provided for heatsink attachment and for securing the board with screws.

The circuit design incorporates several critical elements to ensure optimal performance and reliability. The LM317 voltage regulator is a versatile component that provides a stable output voltage, adjustable through the resistors R1 and R2. This configuration allows for precise voltage regulation, essential for the proper functioning of the DAC. The use of an inductor in the supply line plays a significant role in minimizing high-frequency noise, which is crucial for maintaining audio fidelity.

The DAC's current output necessitates a careful conversion to voltage, achieved through the strategically placed resistors R4 and R5. This conversion process is essential for ensuring that the output signal is compatible with subsequent audio processing stages. The implementation of a low-pass filter, while beneficial for attenuating unwanted high-frequency signals, must be approached with caution to avoid introducing distortion. The balance between filtering and signal integrity is paramount in audio applications.

The choice of capacitors in the output stage is vital; the recommendation against electrolytic capacitors stems from their potential to introduce noise and distortion. Foil capacitors, known for their superior performance in audio applications, provide a cleaner signal path. Their placement between the outputs and the connector is a design consideration that enhances overall audio quality.

To ensure compatibility with downstream audio equipment, the output loading conditions must be carefully managed. The recommendation for a minimum input impedance of 10 kiloohms helps prevent signal degradation and maintains the integrity of the audio signal. The option for a separate power supply for the DAC from the transformer enhances isolation and reduces the risk of interference, further improving audio performance.

Thermal management is addressed through the use of heatsinks on both the voltage regulator and the DAC. Overheating can significantly impact the reliability and longevity of these components, making heatsinking a critical design consideration. The method of attachment using springs allows for effective thermal dissipation while maintaining a secure connection.

The printed circuit board design reflects practical considerations for amateur fabrication, with a focus on simplicity and ease of assembly. The arrangement of components, from SMD to standard parts, facilitates efficient construction while ensuring a robust and reliable circuit. The inclusion of mounting holes for heatsinks and board attachment underscores the thoughtful engineering that has gone into this design, ensuring a high-quality audio output suitable for various applications.In supply section after bridge rectifier and smoothing capacitor is used common voltage regulator LM317, which has with R1 and R2 adjusted output voltage about 8V. Supply line goes through inductor to DAC chip for theoretically lower HF interference which goes on the power lines.

DACs have current outputs which are converted to the voltage outputs with the aid of resistors R4 and R5. Sometimes is used circuit with operational amplifiers combined with low-pass filter which is much complicated and can introduce distortion in to the sound. Low-pass filter which is used for removing sampling frequency unfortunately introduce distortion on high frequencies.

Sound is then more flat. Because DAC doesn`t have symmetrical power supply, that we must use capacitors in series with the outputs. It`s desirable to use high quality capacitors with sufficient capacity. It`s not recommended to use electrolytic capacitor. I used foil capacitors with 10uF value which are connected between outputs and output connector. They are placed out of board and they are not drawed in a schematics diagram. Output must not be too much loaded and should be connected to input of preamplifier or power amplifier with input impedance at least 10 kiloohms.

It`s possible to have separated supply for DAC from independent winding of power transformer for better isolation between S/PDIF decoder and dac with changing voltage. Voltage regulator and DACs must be cooled with a small heatsink! Transformer must be dimensed for current 0. 5A. We are placing components on board from smaller to bigger. We begin with SMD components and next with normal parts. We must mount small heat-sink on the DACs otherwise they overheats and can burns (my own experience).

I attached heatsink with two small springs hooked to four pins soldered to the board. For I2S connector we can use jumper ribbon with pins or sockets. It depends on that how we want to mechanically connect DAC with S/PDIF decoder together. I used on both sides pins and for board conection I soldered two sets of 6pin sockets together. Printed circuit board is designed with only one side and one wire. It allows to create him in amateur conditions. SMD components are placed from a bottom side and components with terminals and connectors are mounted from top side. There are holes for heat-sink fixing and for mounting board with screws.