this project / page is under construction
Table of Content
Introduction
2016/11/08
Since many years I have the idea to build my own DAC. In the meantime I generated at least 4 designs, all of them around Burr Brown / Texas Instruments converters, but finally I never realised them. Mid of 2015 I gave this project a new try.
In opposite to my previous designs I decided this time to take a chip from ESS Technology – the ES9018 SABRE32 Reference Audio DAC. The problem was that there are no generally accessible publications of the data sheets and that I had to sign a non-disclosure agreement to get these documents.
At least this procedure seems to be too complex for me and I decided to look for a finished design with these chips. I found a very nice implementation from Twisted Pear Audio whose Buffalo-IIISE DAC I used in my implementation in a dual mono version – therefore I had to buy two boards.
The complete DAC is based on 2 chassis with the following circuit parts :
- DAC Signal Module
- RStAudio S/PDIF input module
- Amanero Technologies USB OEM Combo384 module
- Twisted Pear Audio Hermes-Amanero USB isolator module
- Twisted Pear Audio Cronus re-clocking module with 45,1584MHz / 49,152MHz Rhea pair
- 2× Twisted Pear Audio Buffalo-IIISE DAC
- 2× RStAudio I/V converter
- 2× RStAudio discrete symmetrical voltage regulator for the I/V stages
- 2× RStAudio discrete voltage regulator for the DAC modules
- 2× RStAudio integrated voltage regulator for the digitale front ends
- DAC Power Supply Module
- 230V/AC supply
- 2× unregulated symmetrical voltage supply for the analoge circuit parts
- 2× unregulated voltage supply for the DAC’s
- 2× unregulated voltage supply for the digitale front ends
- Remote on/off
In the following table the data formats and the sampling frequencues the DAC is able to transfer are listed.
| Sample Rates | Format (Output / Input) | |
|---|---|---|
| S/PDIF Input | up to 192kHz | I2S 24Bit |
| Amanero USB | up to 384kHz | I2S 32Bit up to DSD512 |
| Buffalo-IIISE | up to 384kHz | I2S 32Bit, S/PDIF, DSD |
Description of the Hardware
2016/11/18
In this chapter I decribe each hardware module. For the parts I bought I have no schematics available, for some of the other I don’t want to publish the schematics. However I hope that the informations on this page for DIYers with Twisted Pear Audio DAC’s are of interest.
S/PDIF Receiver
Core of the S/PDIF receiver is the CS8416 Digital Audio Receiver from Cirrus Logic. I use the chip in it’s hardware mode and therefore I can only use a maximum of 4 input channels. These inputs are coupled with digital isolated transformers. One input is wired for the professional AES/EBU and the 3 others for the consumer S/PDIF format. The third S/PDIF input can be used alternatively with a TOSLINK receiver module.
Amanero USB Interface
In search of an USB interface for the DAC I found very quickly the boards from Amanero Technologies. In the meantime you can order them also directly from Twisted Pear Audio. It was very important for me that this interface works asynchronous and is also able to transfer all actual used HiRes formats. With 384kHz I2S and DSD512 this board is enough equippeded. I bought it directly from the manufacturer and therefore I had to reprogram the firmware for the use togehter with the Cronus module (see below). The operation of the USB interface with a Windows 7 PC on one hand and with the Twisted Pear Audio module as a receiver on the other hand is working without any problems.
Amanero Technologies USB Interface (Picture Source)
In cooperation with the Cronus / Hermes boards the firmware have to reprogrammed because the USB interface has to work in slave mode. There are 2 chips on the boards with a firmware and both needs another software for this mode. The CPLD gets the Slave_For_1080 and the CPU the firmware_1096c3w2 firmware. At the homepage of the manufacturer you can download everything incl. the driver for Windows. You also find a description how to reprogram the chips. If you follow this description carefully than the programming is not an issue.
Configurations Bits for the Amanero Board
Everything is very nice described in this thread on diyaudio.com. I took the screen shot above from this discussion. You have to set the configuration bits after the reprogramming in the same way as shown.
If you order the board directly from Twisted Pear Audio they are prepared for the cooperation with Cronus and Hermes and therefore you don’t have to regrogram the firmware.
Hermes-Amanero
With this module the Amanero Technologies USB interface is isolated to the Twisted Pear Audio Cronus module. The interface is running in slave mode and gets his clock from the Cronus oscillators. To use the words of the developer Russ White:
This is not really simply reclocking – it is in fact simply a perfectly time aligned USB source.
I have nothing to add to this statement.
Twisted Pear Audio Hermes-Amanero Board (Picture Source)
Cronus and Rhea
The Cronus board is an electronic module which delivers clock signals with a very low jitter. They are used as a master clock for a digital source – the USB interface in my implementation. Therefore the Cronus has two crystal oscillators with an extreme low phase noise in use – the Rhea modules. I have ordered the oscillators with 45.1584MHz and 49.152MHz. They are the basis for the 44.1kHz and 48kHz clock family of the digital signal processing.
Twisted Pear Audio Cronus Board (Picture Source)
It is important to set the jumper on the Cronus board with the above mentioned Rhea clocks to 1:2 for the Amanero USB interface.
Because of the construction of the Hermes board you can stacked all 3 boards. This gives you the shortest connections, a very high operation reliability and a small footprint (see below).
Amanero Technologies and Twisted Pear Audio Stacked Boards (Picture Source)
Buffalo-IIISE DAC
As I wrote above the basis of the two boards are the ESS Technology ES9018 SABRE32 Reference Audio DAC. The chip has 8 D/A converters integrated. On the Buffalo-IIISE board 2×4 of them are connected in parallel. You get a stereo DAC with a better noise performance compared to one single DAC on the chip. With the dual mono version I have in use you take 2 boards and connect the two channels on one board in parallel – at least you have all 8 converters of one chip connected together, with the result of an additional improvement of the noise performance.
You have to take care with the cabling towards the I/V converter. The two analoge outputs of the Buffalo-IIISE have not the same pin configuration. You find a very nice descriptions of it in the instruction manual
leonvb-buffalo_iii_dac_integration_guide_v2.1.3.pdf
for the boards (on page 44). You can download this manual on the homepage of the manufacturer.
I/V Converter
The DAC’s delivers symmetrical output currents. The function of the I/V stage is to convert these currents in voltages and take care of the speciality of symmetrical signals. In the circuit I describe here I took integrated circuits as active elements. Best suitable for these job is the symmetrical OPA1632 from Texas Instruments, which audiophile performance is exceptional.
The complete circuit of one channel consists of two OPA1632. The first chip is wired as a current to voltage converter, followed by a passive symmetrical low pass filter. All digital signals have to passed an oversampling stage in it’s DAC and therefore the output sampling rate is high. As a consequence the anti-aliasing filters can be very simple – I have first order filters in use. The second OPA1632 is working as a voltage amplifier and as an output driver.
These stage is a first implementation to get a good sounding solution very quickly. It is very similar to the design of the Twisted Pear Audio IVY III Balanced Linestage. As a final solution I want to use a discrete I/V stage and these converter here I will use as a reference for my own development.
In the above mentioned description you can find a dimensioning instruction for the I/V stage. For 8 DAC’s in parallel – as in the mono configuration – a feedback resistor of 360Ω is recommended for the current to voltage converter. With such a value the voltage level behind the first OPA1632 is considerably too high and must be lowered from the second stage. This was definitely not my prefered solution. I have lowered both feedback resistors to 150Ω and the amplification factor of the second stage matched to the output level of my SACD player.
Prototype of the DAC
Voltage Supplies
The complete power supply beginning from the DAC’s is designed in a dual mono configuration. Naturally this is not possible with the digital front end.
For the voltage regulators of the I/V converters and the DAC boards I have my proven discrete regulators in use which I also installed in my VV5 preamp – the modified Pass regulators. The circuits for the I/V stages delivers symmetrical voltages and for the DAC boards only one voltage each. For the supplies of the pure digital circuits I use the integrated voltage regulator LT3080 from Linear Technology, a really remarkable and multifunctional chip.
In front of the regulators the unregulated DC supplies are working in the Power Supply Module. It starts with a 230V/AC DC filter ahead of the transformers. Between the secondary windings and the bridge rectifiers I placed snubber networks. The bridge rectifiers I build with discrete ultra fast soft recovery diodes, following by CLC filters with relatively big electrolytic capacitors. At the output of all unregulated power supplies I have cap multipliers in use – as I said, proven technology which I use also in my preamplifier.
The complete voltage supplies for the I/V stages is designed in a way that I can have output voltages up to ±32V/DC for the analoge circuits. To hold the power losses of the regulators within an acceptable range the each secondary winding of the transformers for these stages have two outputs.
Prototyp of the DAC Power Supply