Arduino controlled Dual Mono AK4490 DAC (Part 3)

Posted on March 4, 2018 by Dimdim

Following up on Part 2, it’s time to talk about the output stage.

This output stage is the brainchild of my friend Kostas, all I did was lay out the PCB.

It is a fully discreet single-ended class-A output stage, outputting ~2.4V RMS.

This is its schematic:

This is the PCB:

And this is the BoM: AK4490 dual mono DAC - Discrete Analog stage BOM (152520 downloads )

The BoM includes part numbers for most parts from Mouser. The only parts that are not in production and must be found elsewhere are the UPA68H. Ebay is a good bet. Chances of getting fake parts are pretty small, but just in case do this to double check the ones that you bought: http://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5330311.html (Thank you Salas for the info and the idea to use them in the first place!)

The only parts that need matching are T8A with T9A and T8B with T9B. There’s no need to go crazy with the matching – within 5% should be enough.

Power should be ideally +/-16VDC. A bit less is OK (I did my initial testing with +/-12VDC) but more will most likely damage the board. The board is running in class-A so current draw is constant. A power supply with 100mA current capacity should be enough.

Bias current is adjusted by the multi-turn trimmers R26A and R26B. They should be adjusted to their mid value before soldering to the board (~1K). To adjust bias just measure current consumption at one of the rails while turning the pot. Adjust for ~25mA total current draw per rail and per channel. Current draw on the negative rail should be about 1mA higher than on the positive rail. Bias should be re-adjusted if the power supply voltage needs to change.

After bias adjustment and with no input signal you should check for DC at the outputs. If everything went well you should be seeing anywhere between 0 to a few mV of DC voltage.

A few design notes:

This design is inverting. I’ve set up my AK4490 code to also invert the 4490’s outputs so as to end up with a non-inverting overall output. But it doesn’t seem to be making much of an audible difference, since I can’t hear a difference as I’m switching between inverting and non-inverting output.
There is provision for a relay that switches between the default filter for PCM (-3db @ ~90KHz) to a more proper filter for DSD (-3db @ ~50KHz). This feature has not been tested yet..

Regarding the resistors, we’ve chosen to go with mini MELF resistors (type 0204) because of their high quality and in general excellent reputation for audio. We are aware that some of the necessary values ATM are kind of hard to source so we’ve included notes in the BoM with the really critical parts and valid value ranges for the less critical other values. Note that “+/-5% from initial value” does not mean that the parts tolerance can be 5% – it means that instead of for example a 10K resistor you can use a 10K + 5% = 10.5K part. It still has to be matched to its counterpart, of course.

I am including these substitutions, as reference:

Instead of the proposed 604R : —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/MMA02040C6190FB300/?qs=sGAEpiMZZMsU0eETUM64Jwu1lXnAfA1Az%2fUBmHPWxBQ%3d
Instead of the proposed 62R —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/MMA02040C5909FB000/?qs=sGAEpiMZZMsU0eETUM64JzhzDaxYafIopmV6xoU7Pd%2faEeFyYr39dw%3d%3d
Instead of the proposed 49,9R —-> https://gr.mouser.com/ProductDetail/Vishay/CMA02040X3909GB300/?qs=%2fha2pyFaduinSoUQ%252bxM%252bcspKJgxV2WgydeZC1mFkJQ0%3d
Instead of the proposed 499R —-> https://gr.mouser.com/ProductDetail/Vishay-BC-Components/CMA02040X4700GB300/?qs=sGAEpiMZZMsU0eETUM64J9XrXp4g00LTnadULizxluo%3d
Instead of the proposed 33R —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/CMA02040X3309GB300/?qs=sGAEpiMZZMsU0eETUM64J5DAE%2fHuiq02KfqnEeQjWns%3d
Instead of the proposed 10R —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/CMA02040X1009GB300/?qs=sGAEpiMZZMsU0eETUM64J5wRh77yguxgpX8F3yMYvKE%3d

The value of two of the required 1K resistors (the R20A & R20B) is critical, so you should use these —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/CMA02040X1001GB300/?qs=sGAEpiMZZMsU0eETUM64J5DAE%2fHuiq026nqxTapoB%252bc%3d
for the other 6 non-critical 1K resistors you can use these —-> https://gr.mouser.com/ProductDetail/Vishay-Beyschlag/CMA02040X1201GB300/?qs=sGAEpiMZZMsU0eETUM64J5DAE%2fHuiq02Tdrq8lX57XI%3d

The value of the 120R resistors is critical, so are the tolerance of the 49.9R (substitution for 39R) resistors. Their values should be matched.

This concludes Part 3. The next post will detail how everything works together.

Arduino controlled Dual Mono AK4490 DAC (Part 2)

Posted on December 24, 2017 by Dimdim

Following up on Part 1, it’s time to talk about the “brains of the operation”. Bare with me, this is going to be a rather long read.Hardware selection

The DAC needed to be controlled by a microcontroller so I looked into my options. I wanted something that would:

Be easy to program, so the Arduino IDE was a must.
Be able to drive a TFT.
Have enough storage capacity to store enough code & fonts for the TFT.
Be readily available.
Be relatively low cost, since it would have no influence on the dac’s SQ.
Be easy to build / integrate into a new design, even by a novice.

After some consideration, I decided to use an STM32F103 ready-made module. It would plug in to a “mainboard” of my design, along with the chosen TFT. It would be fast enough, have enough flash & ram, be easy to integrate and develop for and it would cost next to nothing.

Next up was the TFT. I’d seen on Ebay an interesting one that was relatively big, high resolution and inexpensive. It was this one:

It can be found on Ebay by searching for “3.5 tft uno 320 x 480”. Expect to pay 6-8€ inc. shipping.

After some searching I found a suitable library that (after some slight tinkering) would allow my tiny STM32 to drive it properly. (Note: do not download the library from this link. I will provide a customized version of the library together with my code).

I found a ready-made library for configuring the Si570 and modified it to run on my STM32, using one of its hardware I2C ports. I will also include this library in my code. To complete the recipe I also found working rotary encoder and IR receiver libraries.

The code

Next up was the prototyping work. I adapted my TFT HiFiDuino Pro code to run on the STM32 & TFT combo, with support for AK4490 dual mono operation. The end result had this feature list:

Support for either Dual Mono or single chip setups.
Support for the Amanero Combo384 USB to I2S module (must be set up as slave with MCLK/2 and F0,1,2,3 enabled).
Control with one rotary encoder with push-to-select functionality.
IR Remote support.
Support for software volume control, from -99dB to 0dB
Display incoming signal sampling rate and type, determined by “reading” the relevant I/O pins of the USB to I2S board.
Display and control of the AK4490’s digital filter.
Selection of the proper MCLK frequency according to incoming SR and type and programming of the Si570 accordingly.
Control of “DSD Direct” function of the AK4490s.
Control of the DSD Filter’s Frequency (50KHz or 150KHz).
Control of the Sound Mode of the AK4490.
Choice of either inverted or normal analog output for the AK4490s.
Choice of two sets of MCLK frequencies, either 22/24MHz or 45/49MHz.
Remote power on/off functionality (or always on – configurable in the code).

Software Requirements:

TFT Library (included in ZIP, derived from this one: http://stm32duino.com/viewtopic.php?f=9&t=1751). I have also available a modified library that will work with 3.5″ TFTs using the ILI9486 controller, such as the ones offered on Ebay lately. Download here: Adafruit ILI9486 8bit STM library (161468 downloads )
Rotary Encoder library: https://github.com/mathertel/RotaryEncoder
Adafruit MCP23008 library (included in ZIP, derived from this one: https://github.com/adafruit/Adafruit-MCP23008-library)
Adafruit GFX library: https://github.com/adafruit/Adafruit-GFX-Library
Si570 library (modified to utilize the STM32’s hardware I2C pins, included in ZIP, derived from this one: https://github.com/afarhan/radiono/tree/master/radiono)
IR remote library, compatible with the SMT32 (modified version of this library, sourced from here, also included in the ZIP)

In the download I am including the modified versions of the libraries (as mentioned above) as well as the necessary font files. Be sure to extract the contents of “Libraries (place in Libraries folder)” to your Arduino IDE’s “libraries” folder.

Download it here: aKduino v2 (83375 downloads )

Here is the revision history:

v1.72 24/12/2017:

Minor changes to make compatible with current stm32duino core (changed HardWire.h to Wire.h and other minor stuff).
First public release as part of completed dual mono DAC project.

v1.66 10/10/2017:

Minor volume bugfix.
SuperSlow filter still problematic.
Enabled DAC synchronization feature (experimental..).

v1.64 30/09/2017:

Bugfixes.

v1.60 20/09/2017:

Added support of rotary encoder and IR remote control.
3.5″ TFT support.

v1.50 07/01/2017:

Added support of rotary encoder for volume control.
Bugfixes related to DSD.

v1.41 06/01/2017:

Added support for dual mono mode.

v1.36 03/01/2017:

Added very basic TFT support.

v1.35 20/12/2016:

Code cleanup for first public release.

v1.33 19/12/2016:

Added full control of sound parameters through serial port.

v1.27 18/12/2016:

First functional version.
Automatic switching between PCM and DSD by monitoring DSDPIN.

The “motherboard”

After I was certain that everything related to the software was working the way it should, I designed a “motherboard” that would take care of the following:

Accept the STM32F106 board.
Accept the 3.5″ TFT.
Accommodate an 24LC256 EEPROM chip, used to store the DAC’s configurable settings.
Accommodate two sets of I2C signal isolators and I/O expanders.
Include headers for the encoder, IR receiver, power relay, non-isolated and isolated I2C communication, unused uC pins, etc.

This is what I ended up with:

Basic Hardware Requirements:

STM32F106 module (a.k.a. “blue pill”, search Ebay for “stm32f106c8t6 board”)
3.5″ TFT with resolution of 320 x 480 (Search Ebay for “3.5 tft uno 320 x 480”)
24LC256 EEPROM chip
I2C Isolator ICs, I/O expanders, passive components, etc (see BoM)
Rotary Encoder
IR Receiver
Compatible IR remote control (Apple Remote or other – in any case you must edit the code and input the proper IR codes for your remote, see below)

[table “” not found /]

How do I make it work?

Power

You have to supply the board with 5VDC at ~300mA through header DC_5V.
[table “” not found /]

Basic connectivity

Serial port:
[table “” not found /]

Rotary encoder:
[table “” not found /]

IR control:
[table “” not found /]

If you will be controlling a power on/off relay, you can use the POWER_RELAY header:
[table “” not found /]

Expansion header:
[table “” not found /]

I2C header (non-isolated):
[table “” not found /]

Isolated I2C ports

The board has provisions for two separately isolated I2C ports, complete with I/O expanders on their isolated sides. The idea is to connect the DAC board to one of the isolated ports (I2C_ISOL1 & MCP_ISOL1) and your USB-to-I2S board to the other isolated port (usually MCP_ISOL2)
[table “” not found /]

[table “” not found /]
[table “” not found /]
[table “” not found /]

That’s it for Part 2. Stay tuned for Part 3: The output stage.

Arduino controlled Dual Mono AK4490 DAC (Part 1)

Posted on November 10, 2017 by Dimdim

For the better part of a year I’ve been busy developing what one would call a “respectable” DAC from scratch. It has been a team effort, with different people becoming more involved with specific aspects of the project, but pretty much everyone involved ended up learning a lot about DACs. Right now, the project is for the most part finished, in that it is fully functional with a USB input and a pair of single ended outputs (or balanced, if you use a passive transformer-based stage). It is controlled by an Arduino-compatible micro-controller, running my aKduino v2 code (more on that in a future post).

I will do a series of posts detailing the design and build process, with each post covering a specific PCB. When the series is complete, the contents of all of the posts will be concatenated into a project page.

So, without further ado, this is the schematic of the main DAC board:

(Right click, Save Image As.. to download it in full resolution)

This is the 4-layer PCB:

This is the parts placement diagram:

And this is the BoM (v1.9) in xls format: Dual AK4490 DAC (main board BoM) (13795 downloads )

Design considerations

The design goal was to do a dual mono design so as to maximize SNR and channel separation. A 4-layer PCB design was chosen so as to have a very solid, low impedance ground plane as well as proper power and signal planes. The I2S, audio signals and power after the local LDO regulators are routed on the top layer, the 2 middle layers are ground and power planes, and the bottom layer serves to route I2C signals and some power lines.

Power

All of the local power supplies are implemented using the currently top-of-the-line LT3042 LDOs. The VDDL & VDDR (analog power supplies) are set to 7.2V so as to maximize SNR and dynamic range. There is provision for providing separate pre-reg power supplies for the L and R channels (headers AVDDL and AVDDR) but I don’t consider that to be critical to SQ since there are local LDOs and the power draw is very very small. In my implementation I’m using a common pre-reg for both the AVDDL & AVDDR. The AVDDs and DVDDs are also supplied by LT3042 LDOs set to output 3.3V. The Si570 has its own dedicated 3.3V supply implemented with an LT3042 and features extra filtering.

Overall, the power requirements of the board are:
1) AVDDL: 8-10V DC at 40mA max
2) AVDDR: 8-10V DC at 40mA max
3) DVDD: 4-6V DC at 200mA max

Clocking & input signals

It was decided that the MCLK would be provided by a programmable low jitter oscillator, namely the Si570. This way we could select different MCLK frequencies at will, supporting different sampling rate families and different USB to I2S boards.

Speaking of USB to I2S boards, the DAC board has a very specific requirement: The USB board must be able to receive MCLK externally. In other words, the DAC board and USB board must be clocked from the same oscillator. This is due to the AK4490’s design. Unlike the ESS designs which by default run asynchronously, it needs to be on the same clock domain as its I2S sources.

So, the DAC board needs to output MCLK back to the USB board. There exist a number of USB boards that support that. The most popular ones are the Amanero Combo384 and JLsounds’ I2SoverUSB.

Since I had decided to do reclocking using flip-flops as close to the AK4490s as possible, and the flip-flops are clocked by the MCLK, its frequency needs to be sufficiently high in order to reclock signals corresponding to high sample rates. This translates to 49.152 MHz for sampling rates of 384KHz. If you’re content with going only up to 192KHz, you can use a MCLK of “just” 24.576 MHz. Of course you will also need the corresponding MCLKs of 45.1584 and 22.5792 MHz for the 44.1K families of SRs.

If you decide that you don’t want to do reclocking on the DAC board, you can just not solder on the flip-flops and just connect the proper pads together with some wire so as to bypass them. That way you can run with 22.5792 & 24.576 MHz clocks with SRs up to 384KHz (and probably beyond..).

If you decide that you would also prefer to not use the Si570 and just clock the DAC board directly from your USB to I2S board (or other suitable I2S source) you can also do that. You just don’t solder-on the Si570 and make a couple of changes to the Arduino code (to be implemented..).

But I urge you to try the Si570 & reclocking way first..

Construction hints

Start by first soldering on the power supply components (LDOs, resistors, caps, etc.) and testing that everything works the way that it should.

The LT3042s are pretty tiny and its easy to make a mistake while soldering them. I’ve found that the easiest method is by using a hot air rework station. First I use a regular soldering iron to tin the thermal pad and the pads with a small amount of solder. Then I apply a good amount of high quality solder paste, put the LDO on top of the pads and heat the area of the board until the solder melts. I set my hot air station to a relatively low temp of ~280 degrees C and the process takes less than a minute (per LDO). But you could also solder them with a soldering iron. To solder the heatpad, warm up the pad from the underside of the board and add solder.

After the power section, you should solder on the AK4490s and other low profile components. I do that with a low power (18W) soldering iron with a fine tip.

Next up is the Si570 programmable oscillator. I start by putting a little solder on one of the pads:

Then I add soldering paste and I place the Si570 on top of the pads. I use the fine tipped soldering iron to melt the solder on the tinned pad, effectively soldering the Si570 on the board. I then proceed to solder the rest of the pads by applying heat with the soldering iron to the side of the pads of the Si570 and adding solder.

You should finish up by soldering the electrolytic capacitors and other higher profile parts.
Beware that the spacing around the electrolytics is very tight. You should take that into account when selecting parts. The parts in the BoM are sure to fit in the available space.

That’s it for Part 1. Stay tuned for Part 2: The Controller.

Winter 2017-2018 teaser :-)

Posted on September 1, 2017 by Dimdim

So many projects, so little time.. Here’s a teaser on what’s to come:

PGA2311-based preamp, with multiple inputs board, controlled by a custom Arduino, with an OLED screen.

Salas DCG3 preamp, powered by custom Salas Shunt Reg 1.2R.

MPD TFT display for Rasberry Pi, controlled by an STM32.

Ian’s Multichannel FIFO.

Allo.com’s DigiOne RPi HAT.

Dual Mono AK4490 DAC with on-board Si570 programmable oscillator and reclocking, Single ended Class A discreet output stage, Arduino controlled with STM32 controller and 3.5″ TFT screen.

Arduino controlled AK4118 based s/pdif receiver, with AK4137 SRC.

Controlling an AK4490 DAC with an Arduino

Posted on December 20, 2016 by Dimdim

These days I’m co-developing an AK4490 based DAC. The aim is to end up with a no-compromise dual mono design, one that would perform at the very least on par with my Buffalo III.

Of course, to do that one has to run the 4490s in software mode.

As a matter of fact, it is generally preferred to run a 4490 in software versus hardware mode, for several reasons.

To begin with, in software mode the 4490 supports DSD decoding. It goes as far as to support a “Volume Bypass” feature which bypasses most of the processing done on the DSD signal (a.k.a. “the ΔΣ modulator”), resulting in more pure sound. But of course we do lose the ability to do volume control in software.

Software mode also allows us to try out all of the supported SQ features, like the different “Sound Setting” modes.

At last but not least, we get digital hardware volume control.

This is the prototype that we designed, getting I2S input from an Amanero and being controlled by my custom STM32 controller (more on that in the near future).

I searched the Net for any ready-made code that would control the 4490, but I couldn’t find anything worthwhile, so I began virtually from scratch.

So, my Arduino code (a.k.a. “aKduino”) enables:

Controlling an AK4490 through the I2C bus.
Automatic switching between PCM and DSD. It does rely on getting a “DSD type signal” from our USB-to-I2S interface of choice. The 4490 by itself is not capable of determining whether its input is PCM or DSD.
Setting the volume (in 9 steps.. just to confirm that volume control does indeed work).
Selecting “Volume Bypass” for direct DSD processing.
Selecting the internal DSD filter’s cutoff frequency (50KHz or 150KHz).
Selecting one of the 4 available PCM filters.
Enabling or disabling the Super Slow filter.
Selecting one of the 3 available “Sound Quality” settings.
Displaying all of the registers’ settings (for troubleshooting purposes).