Soekris dam1021 Frequently Asked Questions & Resources

It’s been almost 3 and a half years since the introduction of the dam1021 to the DIY audio community.

In these 3 years there have been sold close to 2500 units (according to a serial no. that I noticed on a picture of a rev.5 unit) that have made a large number of audiophiles very happy.

The dam’s main thread at diyaudio.com is about 740 pages long, and while the first post has been edited to keep the specs and the firmware info up to date, there are still certain questions that keep popping up over and over again.

In this post I’ll try to address as many of them as I can.

F.A.Q.

Q: Where can I get firmware, manuals, etc?
A: http://www.soekris.dk/download.html

Q: What are its power requirements?
A: According to the manufacturer, power should be supplied by a transformer with two secondaries at 7 to 8 volts AC. The transformer should have a rating of at least 5VA. Alternatively, you may power it by a bipolar DC power supply outputting between +/-7.5 and +/-15 Volts. Power consumption is ~160mA for the positive rail and ~60mA for the negative.

Q: Does it support DSD?
A: Yes, DSD64, DSD128 and DSD256 (only native) has been supported since firmware rev. 1.06 (released May 2016) through the I2S input. DSD does get converted to PCM in order to be converted to audio by the R2R ladder (obviously.. we’re talking about an R-2R DAC).

Q: How do I control input selection?
A: Input selection is done either by connecting switches to J3 (see manual for more details) or by commands sent through the dam’s serial ports. There also exists an “auto input selection” feature.

Q: How do I control volume?
A: Either by connecting a pot to the relevant pins on J3 (see manual) or by commands sent through the serial ports.

Q: What if I want to add IR remote control?
A: You’ll have to use a microcontroller like an Arduino. I’ve done two such projects, ArDAM1021 and ArDAM1021 Lite.

Q: How do I upload new firmware?
A: Through the serial port(s). See: http://www.dimdim.gr/2015/02/soekris-r-2r-firmware-upgrade/

Q: What is the latency from digital input to analog output?
A: About 1mS. link

Q: How come the new firmware (rev. 1.19) does not play as loud as the older firmwares?
A: According to the manufacturer “The new 1.20 firmware and 4K filters have zero at -2 dB, the dam1021 then add 1 dB gain, resulting in zero at -1 dB with 1 dB margin, ie when volume level is set to 0 then it’s 1.26V rs output at resistor network, about 1.9V at buffered single ended and 3.8V buffered balanced.” link

Q: Is there a way to run truly “NOS”?
A: Yes: http://www.diyaudio.com/forums/digital-line-level/269776-filter-brewing-soekris-r2r-post5452884.html  ???  Beware that the specific filter is not compatible with the current DAM firmware (rev 1.19), since it now supports 4K taps (it used to support 2K taps).

Q: Can I use a pair of them as a 2-way digital crossover?
A: Yes, in theory you can, but it’s not fully supported by the manufacturer. Read below to understand why that is so.

Q: Can I sync several DAMs, for example to implement a digital crossover?
A: According to the manufacturer “multiple dam1021 running on same clock will sync to within a few uS” link

Q: How do I actually implement the HP and LP filters?
A: You need to design your own custom filter files and load them. “the dam1021/dam1121 have the hardware with support for up to 15 IIR biquad filters per board” link Not for the faint of heart.

Q: I have “ Rev x”, do I need to do power mods?
A: If you have a Rev. 1 board you do need to perform the mods. Later revisions are OK. Rev. 5 has 20 x 100uF Samsung caps so definitely no need for power mods. link

Q: What can I do to make the DAM sound better?
A: a) Don’t use the buffered outputs. Their SQ is inferior to the unbuffered outputs.
b) Use a proper power supply. The better the PS, the better the sound. In my experience, the best one so far is the Salas UltraBiB.
c) Use a custom filter pack. Beware that custom filter packs may not support DSD or take advantage of the increased available number of taps made possible by the latest (rev 1.19) firmware.
d) Be sure to insulate the screw mounting holes from the (grounded) chassis by using non-conductive screws or some other method.

Q: I’m feeding my dam1021 audio from my RPi’s I2S output. Why does some music play fine while some does not?
A: Most audio RPi distributions output whatever they find in the music file without altering it, like for example a 44.1K/16bit FLAC file will produce a 16bit I2S signal. But the dam1021 only supports 32bit I2S signals. The solution is to force the RPi to only output 32bit I2S. Different audio distributions have different ways of accomplishing that.

Q: What does the dam1021’s output buffer schematic look like?
A: The circuit has changed since the first revision. The current (rev.4&5) circuit looks like this: http://www.diyaudio.com/forums/vendor-s-bazaar/259488-reference-dac-module-discrete-2r-sign-magnitude-24-bit-384-khz-post5347636.html



Resources

Official thread on diyaudio.com: http://www.diyaudio.com/forums/vendor-s-bazaar/259488-reference-dac-module-discrete-2r-sign-magnitude-24-bit-384-khz.html
Filter brewing thread: http://www.diyaudio.com/forums/digital-line-level/269776-filter-brewing-soekris-r2r-147.html
Soekris’ DAC implementations : http://www.diyaudio.com/forums/digital-line-level/267948-soekris-dac-implementations.html
Wiki: http://www.diyaudio.com/wiki/Soekris_R2R_DAC?
HiFiDuino : https://hifiduino.wordpress.com/
Randytsuch : http://randytsuch-audio.blogspot.com/2015/11/soekris-r2r-dam-dac.html
moredamfilters.info: https://web.archive.org/web/20161025204639/http://www.moredamfilters.info/

..and of course my posts about the dam1021:

Main Soekris DAC page: http://www.dimdim.gr/diyaudio/soekris-dam1021-sign-magnitude-r-2r-dac/
dam2012 s/pdif inputs board page: http://www.dimdim.gr/diyaudio/soekris-dam1021-spdif-usb-board/
ArDAM1021 page: http://www.dimdim.gr/arduino/ardam1021-project/
ArDAM1021 Lite page: http://www.dimdim.gr/arduino/ardam1021-lite-project/
dam1021 Vref mod : http://www.dimdim.gr/2015/09/soekris-dam1021-vref-mod/
dam1021 firmware update info : http://www.dimdim.gr/2015/02/soekris-r-2r-firmware-upgrade/

Let me know if I missed anything (I’m sure I did..).

I’ll try to keep this FAQ updated.

Soekris R-2R: Sound impressions with Salas BiB PS & alpha20 line stage

A couple of days ago I took my DAM and headed out to a good friend of mine to do some listening tests.

My DAM at the moment is powered by a Salas BiB at 12VDC. It has a DIYINHK XMOS based USB to I2S interface powered by a Salas Reflektor-D at 3.3VDC. The same power supply powers the isolated side of the DAM.

IMG_9263_resize(note that this picture is a bit old. I have since swapped the transformer for the one shown in the next picture plus I have used an IEC with a built-in filter)

The first objective was to assess the importance of a good DC power supply instead of a plain transformer. In order to do that I took with me an extra 50VA toroidal with 2 x 7V windings.

My friend’s system consists of Magnepan speakers, a DIY fet-based preamp and DIY power amp (solid state, 60KG monster). It is widely regarded as a very revealing and non-forgiving system. Any change in any of its components (or a component withing the components) is clearly heard.

The DAM was connected to the preamp through its unbuffered outputs.

We gave the system some time to warm up (it was probably a couple of hours) and then sat down to listen. We started with the DAM as it was, with the Salas BiB. We then unplugged the Salas and hooked up the plain transformer.

The change was immediately obvious. The sound thinned, it became more harsh in the high end. It also lost resolution and detail. Going back to the BiB made all the good qualities come back.

Thus, I can definitely recommend a proper DC power supply for the DAM. I cannot say whether it was the Salas that did the work or that any DC power supply would do the same, but the improvement was definitely there. Note that I have the BoM for the Salas BiB I built in the Soekris’ page.

The second objective was to assess the difference that could be made by using a “proper” output stage after the unbuffered outputs.

So I built a pair of AMB alpha20 line amplifiers. I set their gain to 2 and powered them temporarily by the same Salas BiB that powers the Soekris.

2015-03-27 01.36.57_resize

Note that my DAM outputs roughly 1V RMS at its output @ 0db since I’m using a filter that includes attenuation at FIR2 (I can’t really remember which one it is though..). This meant that the alpha20 brought its output to a nice 2V RMS.

Going back and forth between using the alpha20 and just the unbuffered outputs, the conclusion was that the alpha20 removed a small amount of the “magic” of the DAM while not really helping in anything besides output volume. I was hoping that it would help improve the dynamics of the DAM – its Achilles’ heel IMHO. In my friend’s system the DAM sounds “flat” compared to his other sources (a heavily modified Sony 50ES cdp, a Buffalo 3 DAC, and an Aune S16). However, this “flatness” is not particularly obvious in other more forgiving systems.

So, my assessment of the DAM so far is as such: It has great detail, exceptional mid-range, proper bass, it is a little soft on the highs, but its main problem is the dynamics. It can sound a bit “flat”, with this “quality” either accentuated or minimized, depending on the rest on the system.

If there was a way to improve its dynamics, to make it more “aggressive”, it would be a stellar performer (with a proper DC power supply of course). As is, it is just great VFM.

Soekris R-2R: Firmware upgrade

The DAM1021 originally came with FPGA firmware 0.8. Since then Soren has released a new version of the firmware, Rev 0.9.

J10-serial
In order to upload it to the DAC one must connect the DAC to a computer using either a “classic” serial port, like the one found at the back of older computers, or a USB to Serial adapter. Then a cable must be made connecting three pins of the DB9 connector to the connector J10 on the DAC board.

These pictures illustrate the connections that are needed:

RS-232_to_Soekris

RS-232_to_Soekris_2

You use your new cable to connect the DAM to your computer’s serial port (or USB-to-serial adapter). You do not power on the DAM DAC just yet.

Once you are done with making the physical connection, you need to get your hands on some software that supports the XModem 1K data transfer protocol. This is a pretty old protocol, so your choices in software are pretty limited. One such choice is the “classic” HyperTerminal, but since it is no longer available with Windows I chose the more modern ExtraPUTTY. It is a fork of the classic PuTTY telnet/ssl client software that also supports “vintage” transfer protocols such as XModem.

Once you have it installed it is pretty easy to establish a serial connection at 115200, 8, n, 1, as specified by Soekris. You click on the “serial” tickbox and enter your computer’s serial port (in my case it’s COM5) along with the specified speed (115200bps):

ExtraPutty-configuration

You click on “open” and you get a black terminal screen. You now need to power on the DAC. Once you do that, you should get something like this:

ExtraPutty-after-power

This means that everything is fine. You might see an “I0” instead of an “I3”. That is OK.

Now you need to get to the uManager prompt. You type “+++” and wait for a second. You will not see the “+” characters as you type them. That is OK. You will get this:

ExtraPutty-uManager

Now type “download”, followed by Enter. You will see something like this:

ExtraPutty-uManager-send

This means that you have 30 seconds to begin sending your file. To do that you click on File Transfer -> Xmodem 1K -> Send. Select your firmware file and off you go!

firmware upload (crop)

When the transfer completes you will see something like this:

ExtraPutty-uManager-done

You type “exit” (and Enter) to exit the uManager prompt and you are ready to power cycle the DAC. Once you have done that, you repeat the above steps to get to the uManager prompt and you verify that you have successfully updated the firmware. You should now be at FPGA firmware 0.9!

firmware upload 0.9 installed (crop)

If are having problems connecting, such as getting garbage like this in your serial console:

screenshot terminal jibberish 2

chances are that your USB to serial adapter is not a “true” RS-232 interface, but outputs TTL levels instead. You can confirm that by measuring the voltages between GND and the RX & TX pins. You should be getting zero volts in one case and about -9V in the other. If you are getting 3.3 or 5 volts, your interface will not work with the DAM. You should try to find a proper RS-232 interface.

The Soekris R-2R DAC

The UPS guy just dropped off my brand new Soekris R-2R DAC:

2015-01-30 13.55.04_resize

Also known by the very bland designation “DAM1021”.

It is a sign-magnitude R-2R DAC (a.k.a. “ladder” DAC), meaning that it is quite different in operation than the regular run-of-the-mill DACs.
It is more like a PCM1704-based DAC but with 192KHz+ support plus a bunch of high tech goodies, such as a built-in FIFO buffer.

It is available in three versions, with resistors of different tolerances (0,01% (high grade), 0,02% (mid), 0,05% (basic)). I got my hands on the 0,02% version.

It has three inputs:
1) I2S (electrically isolated)
2) Coax s/pdif
3) TTL for a Toslink receiver

Board-diagram

It is powered directly by a 2 x 7-8V transformer, but may be powered by a bipolar DC power supply.

It outputs a single ended signal at 1.4V RMS and also has a buffer for balanced output at 4V RMS.

It has a serial port for firmware upgrades as well as control.

I have already began work on a Soekris R-2R version of my TFT HiFiDuino Arduino code, tailored to controlling this particular DAC via its serial port.

The board will of course get its own page pretty soon.. Edit: the board now has a page.

To do: hook the board up and actually listen to it play. Stay tuned.