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STAR Pure DSD DAC

Oct 2019

INTRODUCTION

The high resolution PCM at 96-192KHz 24bit offer the possibility to have a good quality digital signal exceeding the big limits of the CD.
The DSD is very different from PCM, using a sampling frequency 64 times higher than that of a standard Compact Disc, offers a frequency response of up to 100 kHz and a dynamic range of up to 120 dB across the entire audible range.
The DSD on paper should be better than hi-resolution pcm like the 192KHz 24bit because the two conversions (from and to the analog) are more simple (see this article from Korg website) but the AES Convention Paper 6086  and AES Convention Paper 5395, seems to contradict this.
The DSD signal can be directly used to reconstruct the original analog signal with a simple RC filter but with this method we get many digital noise also using a good digital and analog filters so forget this method.
I have lost many time and money to test these solution, using different USB to DSD interfaces, I2S isolators and D-type flip-flop.
The little Lampizator and RT audiodesign companies has succeeded to reduce the noise and produce a DSD DAC with this method but with some limits. 
This project here exposed has another approach, it is based on the DSC1 that is an Open Hardware, "discrete" delta-sigma D/A-converter developped by Signalyst, the DSC1 is able to convert the DSD signal to analog without noise and without a DAC chip.
The DSC converters does not work with a PCM signal so it is necesary convert the PCM to DSD on the fly during playing so it is necessary to use computers with adequate performance.
In this project we have used the CT7302PL single chip dual channel audio digital to digital bridge with a sample rate converter to convert PCM signals to DSD.


HARDWARE

The core of this design is the CT7302PL with the following specifications: 


After the CT7302PL chip there is the DSC in the differential version designed by Pavel Pogodin with the output transformers to filter and to convert the output in un-balanced and balanced signal.
 
The 74AHCT595 are high-speed Si-gate CMOS devices used for the serial-to-parallel data conversion.
This module use a mute circuit to eliminate any click in the transition from one track to another using the TS5A3167 (SPDT) single-pole double-throw analogswitch .

This module need a AC power supply in the range 6.5V - 7V and it can power the Amanero USB module with a dedicated 3.3V.
On Amanero module to exclude the USB power supply and use an external 3.3V is necessary cut a wire or remove on-board regulator.

The USB interface used is the Amanero with the normal firmware to support Native DSD.

 

The Controller module included in the kit use the 16F877 chip, a 20MHz Enhanced 8K Flash Microcontrollers.
It drive a 4 x20 characters LCD and it is connected with the I2C bus to the CT7302PL.
A separeted power transformer is used to manage the standby function.

 

OUTPUT TRANSFORMERS

The output transformers are necessary to mix the differential signals coming from the 74AHCT595 in phase and out phase.
These are also used to give un-balanced and balanced output signal, the module integrate a  relay to switch the ground connection.
The models has been selected by
Pavel Pogodin after many test and also I have compared these with other models with much higher cost always preferring these.
These have a turn ratio of 2:1+1, made with a permalloy core with a thickness of 0.16mm and an inductance about 340H.
The declared frequency response is 10Hz - 195 KHz at -0.2dB for the yellow and 20Hz - 80 KHz at -0.2dB for the black type

Yellow type has more "air" and black are probably more balanced but it all depends very much on the record or even his mood.

     

REMOTE

In same case it is necessary increase the output level so use in the setting menu the V+ and -V buttons to set +6dB. +12dB or +18dB, I suggest a max of +6dB because otherwise the distortion can increase.
There is also a function to set an amplification of +6dB for DSD tracks because some player give a lower level for these.
All the settings can be saved in the EEPROM so these will be set at the next power on (press mute button on Setting menu).

 

 

AMANERO FIRMWARE

To get the max stability is necessary set the Amanero module with the last firmware 2006be10 with DSD Native support.

1) Download the update_tools  oem tool 117  and Unzip in a folder, for example on Desktop.

2) ERASE THE FLASH




3) When you replug the erased device, Windows can ask about a driver. 

4) Be sure to be connected to internet.

5) Run ConfigOEM117.exe and select the CPLD firmware CPLD_for_1081_DSD_SWAPPED and CPU firmware 2006be10 after press Flash CPU.

6) Replug the USB cable and if it's all ok the audio driver needs to detect the device.

On Windows system install the last driver ASIO 1062 and verify it in the device manager.

Set on ASIO panel the latency at 15msec stanting the Amanero ASIO program.

To reduce problem during playing in the control panel open Sound and select as default audio device another interface.

You will select the ASIO Amanero inside the player.

 

SOFTWARE

This hardware is compatible with any PCM and DSD signal so to play music you can use any audio player.

Here follows some player in order of sound performances.

 

MEASUREMENTS 

Output at 0dB near to 1.5Vrms.

 

REVIEWS

STAR DSC took first place in the contest organized by the forum Vnav.

 

Here is the result of a test in October 2019 with a friend of mine with a lot of experience in recording and playing audio.

Yesterday evening the first serious listening test about the new dsc module with CT7302 vs NAA (Network Audio Adapter) DSC module.

The quality of the last DSC with CT7302 is very high, the same details and the same sound stage of the NAA DSC module.

The NAA DSC module with the HQplayer filters is a little bit more softer but it is not easy define if it is more or less near to the real sound.

Using the CT7302 with jRiver the sound is very natural and analog.

 

PHOTOS