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Low powered Linux Clients

Posted by John Swenson (A) on November 25, 2008 at 23:34:11

With the recent thread on Linux breaking the ice, I thought I'd share some thoughts on an interesting use for linux, the low powered network client.

There has a been a lot of talk about optimizing a PC for audio use by improving power supplies, lowering power usage and streamlining processes. There is a way to do this to a very high level, the low powered linux client.

This consists of a low powered, fanless motherboard, no moving parts so only flash disk allowed, linear power supplies (no switchers at all) and running a stripped down linux with just the bare essentials. Music storage is on another machine with connection over a standard network. These systems can run headless (no keyboard or monitor) and can sit right in a rack with other stereo equipment. The results can be spectacular.

There are two types of systems I'd like to spotlight, the mini-ITX systems and the fit-PC. I'll go over the min-ITX first.

Mini-ITX systems have been around for quite a while now, there are lots to choose from, but I'm going to outline a fairly specific version for best performance. That doesn't mean its the only way to go, but straying from this may degrade performance significantly.

My recomendation is to use one of the original fanless EPIA motherboards, they are plenty powerful for the task without a lot of extra stuff that just increases electrical noise. Stay away from the ones that take a single DC voltage, these have switching DC-DC regulators on board. Most of these contain a PCI connector so you can use them with your favorite soundcard (assuming you can get a linux driver for it1) You can use an off the shelf mini-ITX case, just don't use the PS!!!

The secret is to use a fully linear power supply to generate all the voltages that the ATX PS input requires. Unfortunately there is no such commercially available supply. So its DIY time. Because these boards are quite low power and we won't be using mechanical hard drives or optical drives the demand on the PS is quite low, so doing a linear supply is not too bad. Its still going to be big and heavy with some significant heatsinks, but this is about getting the best sound possible, right? There are some commercially available linear supplies that are almost there, but not quite, they take a little custimization to work. But they are not cheap. If you do it completely yourself be prepared for $100 to $150, $250 to $350 to buy a commercial supply and modify it.

You can get away with 250 meg of ram, more won't hurt but you probably will not wind up using most of it. For the non-volatile storage there are quite a few options. You can use a modern SSD but you don't have to. One of the ways to run such a system is to create a ramdisk out of memory and load all the programs into the ramdisk at boot, then run off the ramdisk. Using this scenario almost any form of non-volatile storage will do, SSD, compact flash card with adapter, USB memory stick, paper tape, punch cards (sorry about that) etc. If you want to run a full blown linux distribution and do web browsing, word processing and other normal desktop stuff (but why, this is supposed to be an audio specific device) the larger size of a modern SSD would be useful.

If you will be using a PCI card most cases will use right angle adapters to put the card flat rather than vertical. If you don't want to use the adapter make sure the case you choose can fit the your card in vertically.

Another option is the fit-PC. (http://www.fit-pc.com)This is a rugged, very small, very low power device. It doesn't have a PCI slot so it won't work if you want to use a PCI card but it works great with a USB DAC. These come with switching supplies but you can use a linear supply or batteries with them. The total power draw is only 5-6 watts. They have incredibly low EMI and very low noise on the USB ports. And pretty inexpensive. A diskless version costs $225, you can then add your own SSD or other storage device. Again you can use the run off ramdisk technique if you so desire. They will run windows, but thats not what this is all about.

Now on to software. There are many different linux distributions you can use with these devices. Ubuntu is very popular and will work fine. One I recommend is DSL (Damn Small Linux) it is specifically designed to work with the run off a ramdisk method. You can even buy a USB memory stick with DSL preloaded, plug it into a machine and off you go. Or you can put it on a SSD, or campact flash. What you need off of a linux distribution to run audio is very small, most of then come with a lot of common desktop tools which will not be used for an audio only machine.

Now on to how you are going to use this! The idea behind this is that you do NOT have the big hard drive(s) attached to the machine, those go on another machine (or NAS) on the network. The software that does the playing can be either on the linux box or it can be on a remote computer. If you are using a slim devices network you can run squeezeslave on the local box, the server can then run on another machine. You can even control it from another machine (at the listening location) or the fancy slim remote. There are also lots of linux applications for playing music files which you can run direct on the box which you can use with music files remote. The external music files can sit on a windows PC if you want, linux can see standard windows shared file systems.

There is also a new technology just coming out which lets you create a virtual soundcard on a PC or mac which will send the audio stream over a network to alinux box. Since this is getting kind of long I'll put that in a separate post.

There is obviously a lot more to this than I can put in this post but I hope this gets some interest for this type of system. I've been running a mini-ITX system running linux with squeezeslave for a couple years and it beats the pants off any other source I've heard for running a USB DAC (including a Mac-mini. (the fit-PC is even better for this).

John S.

• fit-PC   (Open in New Window)

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