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DAC24192 - 24-bit 192KHz D/A Converter
DAC24192 is a digital to analog converter I have developed. It is probably not the most user friendly on the market, but it has its special reasons, as it was only built for development purposes. It is built over a Cirrus Logic CS4351 DAC and CS8416 S/P-DIF receiver.
The PCB simply needs a power supply and a standard optical or coaxial S/P-DIF signal to work. There is a little microprocessor on the PCB that communicates with these IC's. The two analog outputs are balanced and there is a digitally controlled analog volume control IC between the DAC and the outputs. This is a high-end device from Texas Instruments, PGA2320. The reason why I did that was to avoid using the volume control inside the DAC IC itself as it will cause poor sound quality at low volume.
While the PCB is made for development purposes there is a 10-pin header with all the I2S signals available for future experiments with DSP and much more. For standalone operation it can be bypassed with jumpers. I have created a windows program so I can try all the functions of the different circuits on the board. There is a lot of stuff to deal with. I have used this PCB everyday since I made it. All the music in my office go through this DAC.
Here are the data sheets on the ICs I have used on the PCB
The PCB is a 4-layer type with a ground plane in layer 2 so all components are effectively shielded from noise.
The schematic
A simplyfied schematic of the PCB.
software
Here is a remote program I made for testing and configuring the DA converter. The connection to it is made through an RS232 port via the small 3-pin connector at the bottom of the PCB. Here is the part about the CS8416 S/P-DIF interface circuit. The PCB is connected to a standard CD player's Toslink output. The various parameters can be read from the S/P-DIF signal.
You can see that the CD that is running is an original CD, it is pre-emphasized, the signal is a PCM signal, etc. You can also see minutes, seconds, current audio frame and many other data. At the left bottom I have made it possible to see if there is any communication errors on the S/P-DIF signal. If any errors are detected, one or more of the dark gray boxes will light up red. The software is divided into two parts. The first one (shown here) controls and monitors the CS8416 S/P-DIF interface circuit and the PGA2320 volume circuit.
The second part controls and monitors the functions of the CS4351 D/A converter. There are some other things too, such as digital volume control directly inside the DAC that can be set in 0.5 dB steps from -127.5dB to 0dB (full power), and the audio data format which can have six different standards, de-emphasis control, speed mode and also the smart ATAPI circuit which enables mixing, switching, phase reversal, digital mono, etc. on the two channels. The ATAPI circuit can be used with great advantage when controlling two or more power amplifiers.
Test setup
Here is the test setup. With a pair of headphones coupled directly to the balanced output, you can really hear how good the converter is. The volume can be controlled by the software. The sound is great. It is able to play insanely loud, as the outputs can sving up to 30 Vpp. At the same time it sounds completely clear and distortion free, so it can be difficult to keep the sound level down - you want to turn up the volume all the time. I have two sources connected to the converter in this test, the coaxial output of my PC and the optical of my CD player. I can choose the input on the software.
