[DIY design] TNT LiQuid - an audiophile PC

TNT LiQuid - DIY Audio PC - Part 1

A Computer born for music!

Project: TNT LiQuid - DIY custom audio computer
Manufacturer: various producers, is a custom assembly
Cost: from 350 EUR upward, depending on configuration
Availability: NOT FOR SALE - free DIY design by TNT-Audio
Designer: Giorgio Pozzoli - TNT Italy
Designed: March, 2012

Introduction

Liquid (adj.): late 14c., from O.Fr. liquide "liquid, running," from L. liquidus "fluid, liquid, moist," figuratively "flowing, continuing," from liquere "be fluid," related to liqui "to melt, flow," from PIE *wleik- "to flow, run." Of sounds, from 1630s (the Latin word also was used of sounds).
Quid: from Latin quid ("what, something"), neuter singular of quis ("who").

The results of the Zotac NM-10 motherboard review (and other facts, including the good audio quality expressed also by my oldish laptop) have convinced me that it is the time to start experimenting with a PC specifically assembled for audio purposes.

The initial ideas

In my personal view, such a PC should look quite different from a normal personal computer. Ideally must be more similar to an audio component, with all the flexibility added by the power of recent computers.

Usual periferals, keyboard, mouse, display therefore should not be normally present, even though I would never suggest to anyone to make anything to prevent their connection, as this could make very difficult to recover from anomalous situations (for example in case of viruses, just to name one of the major risks for a computer).

The casing appearance must also match the other audio components. My DIY components have all the same look, with a black case with a natural wood front panel.

The system must be as open as possible, so that it might on time evolve up to the point of getting the single point of control (SPOC) of the whole audio system.

As all audio components, the PC must be very silent, without being extravagant.

Finally, a problem that makes me crazy any time I listen to an unknown composition on the radio or television is the fact that I am pretty sure I'll never know what I'm listening to, because I have lost the beginning. So, a small, character display giving some playing track info would be a nice improvement, also potentially useful to give alarms or other system info.

A note about cost. Cost is an issue, but the other elements above should be considered mandatory.

The technical requirements

The Audio PC must have several audio inputs and outputs in 2 channels mode: at least
- SPDIF digital audio output (RCA pin)
- optical digital audio output (standard TOSLINK)
- analog audio line output
- analog audio line input
Note that there is no digital input, but for my purposes it is not necessary.
it must be perfectly silent: motherboard and power supply must be based on passive cooling, that is obtained only through the use of large radiators, and no fan at all. Even hard drives must be either solid state or silenced.
as a consequence, the enclosure must allow a lot of air flow
it must support a Wi-Fi connection, possibly avoiding dongles (whose capabilities seem rather limited compared with cards with one or two antennas)
it must support remote access, in order to be able to completely control it without connecting any keyboard, mouse, monitor or network
an enhanced graphic card is not necessary and undesired: increases electronic noise and power consumption with no corresponding benefit
it should have enough computational and storage power for audio recording and playback without any problem or hitch
it should have a low power consumption
it must be very reliable

Functional specification

A major point in an audio (or multimedia) PC is the selection of the playback software to be installed. The idea of developing sw ad hoc seems definitely to be excluded: there are so many products available that it would really be difficult not to find what we need.

However, there are lots of different software available, and the choice is not easy at all.

Basically, I think that such a system must be as easy and open as possible to use.

One way to achieve this result is to implement the UPnP standard.

I do not enter here in details, as there will be a specific article about UPnP. Just to give a very high level overview, UPnP is a standard which allows many kind of devices to interact in a flexible manner. In the field of multimedia devices, each system can implement and expose one or more of three different elements:

media server: represents an intelligent multimedia files container
media renderer: is a media player
media controller: is the typical control center of a player

Media servers and renderers can be remotely accessed and controlled by media controllers, that can live on any kind of different hardware, provided it has an human interface. A media controller can in particular tell a media renderer on another machine to play a piece from a media server on a third machine.

The fact that our system must implement UPnP technology means (in theory...) that any component compatible with this standard should be able to work in collaboration with our system.

Unfortunately, in practice any UPnP implementation has a slightly different flavor, so that complete interoperability is not easy to find at all...

The human interface

As I wrote above, the system should not have any traditional screen interface.

One possible exception might be the usage of a small touchscreen display to control the system. However, these displays are rather expensive and consume precious real estate on our crowded audio racks, so this is not an ideal solution.

The other 'regular' solution is to connect the video output of a multimedia pc to the television set, and then use a remote to control it. This is another more than acceptable solution, generally, especially because the multimedia pc is usually video oriented. However the video connection is for sure a channel through which a lot of electronic garbage can reach our precious audio signal: the tv set is connected at least

to the power supply (and if you are an audio addict I suppose that your audio systems have definitely better isolation and cleaner rectification than your tv set...)
to a lot of other noisy electronic stuff (video player, recorder, satellite and/or digital tv receivers, and so on)
directly or indirectly, to the antenna system, which in a large building interconnect a lot of flats and can also intercept other radio signals
and finally to your audio pc... just think about the high speed video signals going through long cables wrapped around our beloved audio connections....

The best solution in terms of insulation would be to use an infrared remote control but without a video interface it can only implement cd-player style commands (play / pause /stop / volume /next / previous). For sure an IR remote is so fast and simple to use that it is definitely worth implementing it. But cannot give the full control required by such a flexible system.

So, considered that wireless UHF signals is these days inevitably pervade our homes, and that wifi seems to have no effect whatsoever on audio systems, I think that the only solution could be to use as remote control some kind of tablet connected via Wi-Fi.

Even this solution could be not enough. For example, if you must rearrange your media directories, or rip a disk or record an analog program, the best solution remains a laptop connected via remote desktop (rdp) or similar technology (OpenVNC, Teamviewer, etc.) to the audio pc, so that you can have full access to all resources.

If you therefore need a single control point, the ideal solution is a nettop, avoiding obviously the ones with a fan or anyway noisy. If you have money to spend, already have a laptop and really want something cool, add a tablet...

Conclusion

This is all, for now.

Next time we will go a little deeper in UPnP systems.