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.

Pipo X7: An ultra low cost Windows PC as a music transport

A few days ago I received the Pipo X7 that I had pre-ordered back in January.

It took so long to source & ship because it is immensely popular – after all, for less than 100€ I got:
– An Intel Baytrail Quad Core CPU @ 2.16GHz
– 2GB of low power DDR3 RAM
– A 32GB SSD drive (Samsung MBG4GC)
– An HDMI out
– WiFi b/g/n, 10/100Mbps Ethernet & Bluetooth connectivity
– 4 x USB 2.0 ports

All of that inside a slick aluminum box, not much larger than a CD, powered by a silent 12V/2.4A power supply.


But the best part is that it runs a fully activated copy of Windows 8.1 (32bit)!

Yes, Microsoft is essentially giving away Windows 8.1 for use in small devices (like set-top boxes, such as this one) with only one catch for the OEM: He is not allowed to set Google Search as the default search engine. However, this does not mean that you can not set Google as your preferred search engine if you wish (instead of the dreadful Bing).

Now, I must admit that this was largely an impulse buy for me, since I already have a full size HTPC and a Squeezebox Touch as an audio transport, but I just couldn’t resist the temptation. So, since I had it, I decided to run a series of audio-oriented tests on it.

My player of choice is Foobar, feeding a Buffalo III DAC through an Amanero Combo384. The files were stored on a file server on my LAN and the Pipo was connected to the LAN via 100Mbps Ethernet.

The first test included outputting DSD to the Amanero. All the necessary Foobar components were loaded, including of course the Super Audio CD Decoder and the necessary configuration was performed:

Note: There are several steps involved in getting Foobar to output DSD. It is not the purpose of this post to fully outline them. A Google search would turn up a number of guides / how-tos.

First up was a “plain” DSD64 file. The Pipo had no problem playing it back, with less than 1GB of RAM use and about ~13% CPU utilization:


Let’s make it more interesting. DSD128:


Still no problem. As a matter of fact, CPU load has actually decreased! That is probably because the DSD64 file was from a SACD ISO, so some CPU time was used in handling the big file.

Moving on to a worst case scenario: A DXD file:


Still, no sweat, with the CPU barely sweating at 16% load. RAM has not climbed above 800MBs.

Since the machine appeared to have some decent horsepower, I thought I would try the well-known SoX Resampler DSP for Foobar. I set it up as best I could, since I don’t really have much experience with the actual DSP:


I chose to go the “x4” upsampling way, with the “Best” quality setting. This meant that a 44.1KHz file would be upsampled to 176.4KHz and a 96KHz file would be upsampled to 384KHz, hitting the limits of the Amanero interface. A 192KHz file would not be supported, since that would mean that it would have to be upsampled to 768KHz. The idea was to do a benchmark, so I just played two versions of the same files, one at 44.1K and one at 96K. This was the result:



So, still no serious sweat, with the CPU averaging 29% load, with one of its cores (presumably the one doing the actual upsampling) getting about 50% usage.

At that point, I called it a day.

In conclusion, it seems that the Pipo X7 is perfectly capable of supporting audio playback, even with upsampling enabled. As a matter of fact, I might keep it as a music transport.