Streambox with Focusrite Soundcard

Overview


This is a new recipe for a high quality streambox built around a Focusrite USB audio interface, with software by Locus Sonus and others. It brings together various resources, as described with acknowledgements below.

The streambox is available ready-built and can be customized to different situations. 

The notes below should also allow you to build your own box from scratch. 

Questions, support and help with sourcing materials: 
— grant@soundtent.org

Introduction


The Scarlett 2i2 2nd Gen USB soundcard from Focusrite has widely recognised high quality preamps. The 2nd Gen seems to maintain quality and clarity at high gain (whereas the 1st Gen deteriorates markedly in the last part of the dial).

A new disk image from SC or a small tweak to the code, allow this card to be used with the web interface by Stef Cousot at Locus Sonus.

A clever and simple modification is required to use the Primo EM-172 and its successor with 48V Phantom power. This produces an exceptional microphone and works very well with the Focusrite (and potentially other USB soundcards, including those from Behringer..) The ‘Simple P48’ modification has been developed by Ricardo Lee and others at the micbuilders yahoo group and interpreted and shared by Tom Benedict. The original circuit is by David McGriffy.

For very quiet situations, 4 capsules can be used, resulting in a modified SASS with very good stereo image and acoustic ‘transparency’. This approach is from Vicki Powys. In practical terms, this means almost no hiss,  even when the user turn the volume up well above the levels at the source. This model can be heard at
http://locusonus.org/soundmap/ >> london-camberwell

By using 48V phantom power and delivering the optimal voltage to the capsules, the streambox seems to resist clipping, resulting in more flexible dynamics.

It appears to have good resistance to Electromagnetic Interference (EMI), probably making it easier to work with in field broadcast situations (ie close to routers, dongles and / or WiFi modules).

Listen to the streambox installed at Loughborough Junction, S London:

How to



Values of the resistor and the capacitor
R=100kOhm [1]
C=4.7 µF

Disk Image


Available from SC, includes the modified code. Contact Grant for a copy. 

This can then be flashed to an 8GB Class 10 SD card using eg Apple-Pi Baker:

Modifying the code


Start by flashing the basic Locus Sonus disk image to an SD card and load into a Pi no later than 3 B (3 B+ is not fully supported without going through all the updates, which is tedious but should work)

Download the disk image from: