THIS DEVICE
Audial USB
board
is a USB audio decoding stage,
which also generates clock signal for D/A conversion.
At one side it connects to PC via USB port and, by
operating as asynchronous (master) USB Audio Class
2.0 device, it is able to accept audio sampling rates up
to 192 kHz. Up to 384 kHz operation is available as
optional feature.
The board decodes USB signal to raw PCM that can be
sent to D/A chips. Also, it provides galvanic decoupling
between USB and PCM side, thus also separating PC
from audio clocks and other audio circuits.
Two low jitter clocks are included, one that works with
44.1/88.2/176.4 kHz, and the other that works with
48/96/192 kHz sampling frequencies. This way the unit
achieves clean clocking scheme, and all the audio
clock signals in the system are generated only by
frequency dividing, and not by using PLL synthesizers.
MARK 2
The Mk2
board
version is shipped as a ready made
module
, or as
completed uni
t
.
Modules are intended for use inside or close to the
D/A converters, and output signal is available on the
set of nine U.FL PCB connectors. These U.FL outputs
are 3.3 V level, with 50 Ohm build-out resistors, and
they can drive several gates, but are not meant to drive
terminated lines. Modules do not include BNC output
connectors, nor do they include associated line
drivers.
Module requires transformer with two secondary
windings: one 7-8 VAC (AC1) for USB front end, and
one 8-10 VAC (AC2) for clocking and output side. AC1
can be up to 10 VAC too, but transistor Q1 (BD139,
TO-
1
2
6 package
) should have some heatsink in that
case.
Transformer should be capable to supply 500mA, for
both AC1 and AC2. The current actually needed by
AC1 is 100 mA typically (120 mA max). The current
needed by AC2 is normally 20-30 mA, but if BNC
outputs are added to drive terminated lines, it will
increase to about 100 mA. Overall, a small 10 VA
transformer is enough to feed this module, and 20 VA
is plenty, under any circumstances.
Completed unit includes line output drivers, and PCM
signal, including the master clock, is available on the
set of BNC connectors, located along the right side of
the unit. BNC outputs are typically 5 V level, 75 Ohm
series terminated, and with 75 Ohm load they will
provide 2.5 V at receiving end, but on request they can
be set for 3.3 V output too.
3
Audial USB board
Mk2
