Post by Javier on Aug 7, 2013 19:51:48 GMT
As many have noticed, DSD has been going through a second youth for the last two years. It has changed from being almost dead due to the market failure of Sony’s SACD disks to almost every manufacturer, big and small, having some DSD capable product.
The biggest contribution to this renewed interest was probably the release in 2011 of the SACD Ripper software tools that allowed the extraction of the content of SACD disks in its native DSD format, either as a perfect disk image (ISO file) containing all tracks or as individual tracks, be them stereo or multichannel (DFF or DSF). Since them small audiophile labels have made available many DSD downloads in standard DSD64 and even in DSD128 format. It is easy to find many free samples through Google.
The are plenty commercial DSD products available ranging from 800$ to well over 20,000$ and also a few DIY DACs but the market is not as mature as that for regular PCM products and the low cost segment has no offerings at the moment. Not everyone can or wants to spend well over 500€ in a product they are not 100% sure about, for example, they may not have enough DSD material to justify the extra expense or they may think the music they like/want will become available in DSD or they could even doubt DSD will be any better than regular PCM. A couple of friends and I discussed this and felt there was indeed a gap no one had addressed yet , we thought that something with good performance and quality available at an affordable price which allowed people to test DSD could be of interest (certainly it was for us) for those who wanted to give this format a go.
Most chip manufacturers like ESS, Texas Instruments, AKM, etc. have entry level parts with high integration, good performance and low cost like the ES9023 or the PCM5102. These include on chip the critical current to voltage conversion (aka I/V) allowing for very simple designs and a significantly reduced board and parts budget compared to the more expensive chips thta need and external I/V stage. On the other hand, currently there is only one such part capable of DSD, Texas Instruments’ Burr Brown DSD1793. Its specifications are on par or slightly better than those of the above mentioned PCM chips but has a significant handicap compared to them in that it needs an external controller to manage it in “software mode”.
Unlike most recent mid to high end offerings from ESS (ES900x and ES901x series) which can detect incoming format and change from PCM to DSD mode and back, the rest of the currently available DSD chips need to be “told” what type of signal is coming in and change their internal registers in order to enable DSD decoding. For this task some sort of micro controller capable of communicating with the chip in either I2C or SPI languages is needed. Fortunately we all had experience with product that solved this problem and provided the perfect platform on which to build our project.
There are many USB adapters that can output both I2S (PCM), a few also are capable of DSD but there is only one which can do that and also is capable of a whole range of additional functions, the Amanero Combo384 (www.amanero.com). This adapter decodes up to 32/384 PCM and DSD up to an amazing DSD512 (DSD256 and DSD512 are only supported under Windows using ASIO). Other functionality includes voltage triggers to control external switches, event based I2C capability and an incredible array of configurable options like outputting Left Justified or Right Justified for older R2R chips, 32fs Bit Clock, enable/disable DoP, Master and Slave modes, independent PCM/DSD channel swap, etc. As an added bonus, since its release its designer has been continuously kept improving this board and adding new functionality for free making it terrific value and, in our humble opinion, the best USB audio adapter available which made it a no brainer to select it for our DAC.
Once the source was agreed upon the next step was deciding on the DAC’s chip. We thought theone that suited best our needs was the DSD1793, a 24/192 PCM and up to DSD256 chip that has integrated I/V though it still requires external Low Pass filtering/buffering to get rid of digital by products and achieve 2.1Vrms. Its main specs are a dynamic range of 113dB and a THD+N of -100dB (0.001%).
In our design we decided to offer optional galvanic isolation for all signals incoming from the USB using three different ICs: one for audio signals, another for voltage triggers and a third bi directional one for I2C communications. Using these ICs will greatly reduce PC noise reaching the critical analogue section but in case someone doesn’t want to put them in, for whatever the reason, bypassing pads are provided.
Unlike the PCM5102 which can generate clock signals from its internal PLL or the ES9023 which runs from a single clock in asynchronous mode, the DSD1793 needs two external oscillators, one for each fundamental frequency family (i.e. 44.1KHz and 48KHz). Pads for 7x5mm and 2.5x2mm (NDK NZ2520SD low phase noise series) XOs are provided on the board. The DAC will work with 22.xxx/24.xxx oscillators but for best performance it is recommended to use 45.xxx/49.xxx.
The opamps in the LPF/buffer stage are dual 1 channel and both DIP-8 (top layer) and SOIC8 (bottom layer) encapsulations can be used enabling a wider choice.
The board has 4 onboard low noise serial voltage regulators (2 x 3.3V, 5V and -5V) but in case should anyone prefer to use higher performance serial or shunt regulators the PCB has headers for using external PSs. If onboard ones are used the DAC can be powered using either a single transformer with 3 secondaries or two transformers with two secondaries each. Secondaries can be anything from 3.3 to 20V.
On the software side, using the Combo384 as a micro controller provides automatic PCM to DSD mode change and also the choice of two filters for PCM and 4 FIRs for DSD, Delta-sigma oversampling rate selection or digital volume control when future Combo384 drivers permit it.
Here is a pic of the PCB:
Now that the design is finished we hope to order the first proto board in September and if all goes well soon after we could offer boards and BOM to anyone interested.
For cost and performance reasons this project is all SMD with the only exception of the optional DIP8 opamps, so some experience and the correct gear will be needed to build this project though we may offer finished modules for those who can’t build it themselves.
All questions and suggestions are welcomed
(*) The Combo384 can be purchased straight from Amanero at 79€ for a single board which comes down to 39€/ea if more than 60 are purchased, for example through one of the ongoing Group Buys at DIYAudio.
The biggest contribution to this renewed interest was probably the release in 2011 of the SACD Ripper software tools that allowed the extraction of the content of SACD disks in its native DSD format, either as a perfect disk image (ISO file) containing all tracks or as individual tracks, be them stereo or multichannel (DFF or DSF). Since them small audiophile labels have made available many DSD downloads in standard DSD64 and even in DSD128 format. It is easy to find many free samples through Google.
The are plenty commercial DSD products available ranging from 800$ to well over 20,000$ and also a few DIY DACs but the market is not as mature as that for regular PCM products and the low cost segment has no offerings at the moment. Not everyone can or wants to spend well over 500€ in a product they are not 100% sure about, for example, they may not have enough DSD material to justify the extra expense or they may think the music they like/want will become available in DSD or they could even doubt DSD will be any better than regular PCM. A couple of friends and I discussed this and felt there was indeed a gap no one had addressed yet , we thought that something with good performance and quality available at an affordable price which allowed people to test DSD could be of interest (certainly it was for us) for those who wanted to give this format a go.
Most chip manufacturers like ESS, Texas Instruments, AKM, etc. have entry level parts with high integration, good performance and low cost like the ES9023 or the PCM5102. These include on chip the critical current to voltage conversion (aka I/V) allowing for very simple designs and a significantly reduced board and parts budget compared to the more expensive chips thta need and external I/V stage. On the other hand, currently there is only one such part capable of DSD, Texas Instruments’ Burr Brown DSD1793. Its specifications are on par or slightly better than those of the above mentioned PCM chips but has a significant handicap compared to them in that it needs an external controller to manage it in “software mode”.
Unlike most recent mid to high end offerings from ESS (ES900x and ES901x series) which can detect incoming format and change from PCM to DSD mode and back, the rest of the currently available DSD chips need to be “told” what type of signal is coming in and change their internal registers in order to enable DSD decoding. For this task some sort of micro controller capable of communicating with the chip in either I2C or SPI languages is needed. Fortunately we all had experience with product that solved this problem and provided the perfect platform on which to build our project.
There are many USB adapters that can output both I2S (PCM), a few also are capable of DSD but there is only one which can do that and also is capable of a whole range of additional functions, the Amanero Combo384 (www.amanero.com). This adapter decodes up to 32/384 PCM and DSD up to an amazing DSD512 (DSD256 and DSD512 are only supported under Windows using ASIO). Other functionality includes voltage triggers to control external switches, event based I2C capability and an incredible array of configurable options like outputting Left Justified or Right Justified for older R2R chips, 32fs Bit Clock, enable/disable DoP, Master and Slave modes, independent PCM/DSD channel swap, etc. As an added bonus, since its release its designer has been continuously kept improving this board and adding new functionality for free making it terrific value and, in our humble opinion, the best USB audio adapter available which made it a no brainer to select it for our DAC.
Once the source was agreed upon the next step was deciding on the DAC’s chip. We thought theone that suited best our needs was the DSD1793, a 24/192 PCM and up to DSD256 chip that has integrated I/V though it still requires external Low Pass filtering/buffering to get rid of digital by products and achieve 2.1Vrms. Its main specs are a dynamic range of 113dB and a THD+N of -100dB (0.001%).
In our design we decided to offer optional galvanic isolation for all signals incoming from the USB using three different ICs: one for audio signals, another for voltage triggers and a third bi directional one for I2C communications. Using these ICs will greatly reduce PC noise reaching the critical analogue section but in case someone doesn’t want to put them in, for whatever the reason, bypassing pads are provided.
Unlike the PCM5102 which can generate clock signals from its internal PLL or the ES9023 which runs from a single clock in asynchronous mode, the DSD1793 needs two external oscillators, one for each fundamental frequency family (i.e. 44.1KHz and 48KHz). Pads for 7x5mm and 2.5x2mm (NDK NZ2520SD low phase noise series) XOs are provided on the board. The DAC will work with 22.xxx/24.xxx oscillators but for best performance it is recommended to use 45.xxx/49.xxx.
The opamps in the LPF/buffer stage are dual 1 channel and both DIP-8 (top layer) and SOIC8 (bottom layer) encapsulations can be used enabling a wider choice.
The board has 4 onboard low noise serial voltage regulators (2 x 3.3V, 5V and -5V) but in case should anyone prefer to use higher performance serial or shunt regulators the PCB has headers for using external PSs. If onboard ones are used the DAC can be powered using either a single transformer with 3 secondaries or two transformers with two secondaries each. Secondaries can be anything from 3.3 to 20V.
On the software side, using the Combo384 as a micro controller provides automatic PCM to DSD mode change and also the choice of two filters for PCM and 4 FIRs for DSD, Delta-sigma oversampling rate selection or digital volume control when future Combo384 drivers permit it.
Here is a pic of the PCB:
Now that the design is finished we hope to order the first proto board in September and if all goes well soon after we could offer boards and BOM to anyone interested.
For cost and performance reasons this project is all SMD with the only exception of the optional DIP8 opamps, so some experience and the correct gear will be needed to build this project though we may offer finished modules for those who can’t build it themselves.
All questions and suggestions are welcomed
(*) The Combo384 can be purchased straight from Amanero at 79€ for a single board which comes down to 39€/ea if more than 60 are purchased, for example through one of the ongoing Group Buys at DIYAudio.
.
