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Simple Low Ripple PSU for DAC

Power supplies are needed for every type of electronic equipment and are one of the most important component in a audio electronic equipment such as a DAC.

This project illustrate how can you build a simple low cost unregulated power supply that you can use for a DAC that have an unregulated power supply input from 15V to 18V and a current  < 1500mA.

The circuit

The circuit is very simple and have low ripple and low noise. The power trasformer must be at least 45VA with a secondary voltage of 15V.

The circuit is powered by turning ON main power switch S1 and is overcurrent protected by fuse F1 250V - 200mA slow-blow type. The first capacitor C1 is a X2 type 250V and helps to reduce high frequency noise component wich comes from the 230V power mains. The transformer TR1 is a 45VA with primary at 230V and secondary at 15V AC. The capacitor C2 reduce high frequency noise. The diode bridge rectifier B1 is a 6A current rated KBL608.

Attention: this is an unregulated power supply, the output voltage vary from 20V to 15V according to load current output; verify if your DAC can accept unregulated power supply.

Low pass filter network

The decoupling network is a second order RC low pass filter. This network decreases noise transmission of the high-frequency content of any current that does pass through the resistor. The series elements are 2 small value resistors and DC voltage drop is acceptable because the current is low.

With resistors value R1 = R2 = 0.47 Ohm and capacitors value C3 + C4 = C5 + C6 = 4800uF, the 2nd order RC Low-pass filter have:

2nd order RC Low-pass filter

 Center frequency

fc

 77.5 Hz

 Q factor

Q

 0.33

 

 

Technical specifications

The table below see you the measured value in real working condition of the power supply I have designed versus the original one from AUNE AUDIO equipped with AUNE USB DAC MKII SE. 

Characteristics

ADPSLAB Simple Low Ripple PSU for DAC

Original AUNE power supply Model: MINI -- 1501

 AC Main Input

 230V - 50Hz

 230V - 50Hz

 Trasformer

 45VA 230Vpri - 15Vsec

 

 DC Votage Output (unloaded)

 20.2V (measured value)  22.8V (measured value)

 DC Voltage Output (with 500mA load)

 17.6V (measured value)  17.6V (measured value)

 DC Current Output (max)

 1.5A  1A

 

The table below see you the measured value in real working condition of my AUNE USB DAC MKII SE.

AUNE USB DAC MKII SE Power Requirements

 DC Current Absorbed (min)

USB playback working condition with Headphone Load and Volume to minimum  130mA at 19.2V (measured value)

 DC Current Absorbed (max)

USB playback working condition with Headphone Load and Volume to maximum  300mA at 18.5V (measured value)

 

Final Test

I have measured the Ripple/Frequency values of the original Original AUNE power supply Model: MINI -- 1501 and my ADPSLAB Simple Low Ripple PSU for DAC with a constant current load of 500mA. The figure below show the tests result. The tests values comes from the FFT results of oscilloscope measurements. 

 

Bibliography

Some information, material and related graphics available on this page are provided by web sites below. This are only for informational use. 

OKAWA Electric Design - 2nd order CR Low-pass Filter Design Tool - http://sim.okawa-denshi.jp/en/CRCRtool.php

Power Supply Noise Reduction - Ken Kundert - http://www.designers-guide.org/Design/bypassing.pdf

Linear Power Supply Design - Rod Elliott - http://sound.westhost.com/power-supplies.htm

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