Allo impressed me with their DigiOne SPDIF
board and USBridge USB board for the Raspberry Pi.
Their Piano series of DAC boards were less
to my liking, they are clearly aimed at different market.
I heard more positive words on the
Boss and just when I was ready to look,
I was notified an updated version wouldcome available at short notice: the Allo Boss version 1.2.
Allo has two lines of audio products, one
for the Raspberry Pi and one for their own
Small Board Computer, the Sparky. Their USBridge,
for instance, is designed for the Sparky as
where the DigiOne is designed for the Raspberry
Pi. See the two reviews I did, the links are
in the show notes. The Boss is also designed
for the Raspberry Pi. It is in essence a digital
audio converter with only a I²S input. I²S
is a digital audio bus that was designed for
use inside a device - like a cd-player. The
somewhat strange name is an abbreviation from
Inter IC Sound, IIS. Techies of course changed
that to I²S. It uses separate busses for
clock and serial data. The Boss board uses
the so called I²S Master Mode where the clock
oscillators on the Boss are in control - hence
the name Boss, I suppose. This way the - for
audio - poor clocking signal of the Raspberry
Pi is omitted. There is nothing wrong with
the Raspberry Pi, but it’s not designed
to do high quality audio rendering. The I²S
Master Mode solves one problem, another is
a polluted power supply when the DAC board
is fed from the voltage bus on the Raspberry
Pi. Of course this can be filtered, the Boss
even splits up the power in three separately
filtered and regulated voltages: one for the
digital audio part, one for the analogue audio
part and one for the clock oscillator. But
the best solution is not to use the power
from the Raspberry Pi. That is why I soldered
print headers on the HiFiBerry boards - see
the link in the show notes. And that’s why
the Boss has a separate power input on the
board in the shape of a USB C connector. You
can still feed the Boss/Raspberry Pi combination
over the microUSB power input on the Raspberry
Pi - which is the least optimal, feed the
combination over the USB C connector on the
Boss - which is the better option, or remove
a jumper and feed the Raspberry Pi and Boss
separately - which is the best option.
People in forums often focus on the DAC chip
used. But it’s not this chip that makes
a DAC unique, it is the quality of the power
supply, the jitter on the digital bus and
the precision of the clock oscillator that
drives the DAC chip. Then there is the quality
of the analogue part that converts the current
coming from the DAC chip to a voltage to drive
an amplifier. The power supply - of course
- is external so you can choose your own and
- as reported - you can use separate power
supplies for the Raspberry Pi and the Boss.
Note that you need a power supply with miniUSB
A connector for the Raspberry Pi and one with
USB C connector for the Boss. Next to that
USB C connector you find the jumper to disconnect
the power supply connection between the Raspberry
Pi and the Boss, essential if you do use two
power supplies. And while we’re here, the
Texas instruments PCM5122 DAC chip - sub-branded
Burr Brown - is situated HERE. The double
NDK oscillators are in a shielded housing
with next to it two clock distributors. So
there are separate clocks for 44.1 kHz based
and 48 kHz based clock frequencies. For those
that want to connect the Allo Volt Class D
amp-board an audio connection is provided
in this header while 5 volts and a mute signal
is sent using the extended GPIO header. Those
small surface mounted components make it very
hard to identify the voltage regulators. But
according to the info by Allo Linear LT3042
regulators are used. In the analogue stages
I found film capacitors, which are easier
to identify, just like the supercapacitor
on the rear of the board that provides extra
current when needed. All these measures plus
the print layout influence the audio quality.
I have said it before, I measure all equipment
but I am very reluctant so show the measurements,
not to scare people off with incomprehensible
graphs. But this one is not that hard to understand
and quite illustrative. It is a spectrum of
the noise. It shows that the sampling frequency
at 44.0818 kHz leaks through, together with
some interference or clock at about 31 kHz.
Nothing to worry about for it is still at
a low level. It clearly sticks out since the
overall noise level is very low - which by
the way is what you want. Now, this graph
shows us another thing since it combines two
measurements: the green lines being measured
with the sBooster power supply and the blue
lines being measured with a switching mode
power supply as is often sold with the Raspberry
Pi for less than ten euros. Now, it’s only
a few dB’s but it is also far less stable.
So it’s probably causing other irregularities
too. But enough tech.
Since I have discovered that Volumio, piCorePlayer
and Ropieee all sound the same, I only used
Ropieee for the listening test. It is a very
fine, self installing Roon Ready endpoint
software for the Raspberry Pi and it supports
many audio boards, including the Allo Boss.
See the link in the show notes for my review.
I skipped powering through the Raspberry Pi
and only concentrated on powering the Raspberry
Pi through the Boss with either the El Cheapo
wall wart or the sBooster. I have explained
before that a DAC is in essence the same as
a digitally controlled beer tap. If you feed
the tap with quality beer at the correct pressure
and temperature and if the digital control
signal is flawless, you get a perfect beer
time after time. But feed it with low quality
beer and you get a poor beer time after time.
Now substitute the beer with electric power
and the tap with the DAC. The digital control
signal is the audio signal that defines how
wide the ‘tap’ will be opened and thus
how much current is passing through the DAC.
A so called current to voltage circuit converts
that to the output voltage. As with the beer,
if you feed the DAC with polluted power, the
output of the DAC will produce portions of
that polluted power, resulting in a more or
less distorted signal. I can tell you that
using the El Cheapo power supply is an insult
to the designers of the Boss. At least buy
an iFi iPower or Audiophonics power supply
and if you can spare the money, go for the
sBooster. See the link in the show notes for
the review of these three. You can use the
El Cheapo power supply to power the Raspberry
Pi and then use one of the aforementioned
quality ones to power the Boss. That gives
the best result although you always should
be careful with cheap switching mode power
supplies for they also pollute the mains and
could influence for instance your amp this
way. That’s why I always use a mains filter
to use these power supplies.
Up till now I found the Raspberry Pi with
DAC board to fit only my setup 3, my sub 1000
euro reference. The Boss places itself in
the lower end of my setup 2, which is clearly
more critical and costs around 4000 euros.
Now, don’t get me wrong, it’s no USBridge
with Chord Mojo. But the limitations - every
DAC has a level of limitations - don’t get
in the way of enjoying the music. The stereo
image isn’t as wide and deep, it’s not
that open and analytic but for instance sibilance
is surprisingly well controlled. And, again,
it is clearly better than other DAC boards
for the Pi. I would easily listen to it in
my setup 2 for hours without fatigue.
At 68 euros the Boss version 1.2 clearly isn’t
the cheapest DAC board around. It simply can’t
be, given the components used. And then don’t
forget to order spacers, a USB C adaptor for
the power and a housing. A complete kit, including
a microSD card with an operating system and
software of your choice installed will set
you back around 125 euros. For that money
you can have a streamer, renderer or Roon
Endpoint, depending on the choice of software.
I challenge you to find an equally good sounding
streamer. renderer or Roon Endpoint for that
money. A Sonos or Bluesound will cost clearly
more and certainly the Sonos Connect will
sound less. Of course, the software by Sonos
and Bluesound is clearly superior to the software
available for the Pi. But regardless whether
you use Volumio, piCorePlayer, RoPieee or
any other piece of software, it usually will
be free. Isn’t this a lovely time where
you can buy a complete Boss 1.2 player kit
plus a hard disk, install Volumio or equal
and you have a complete streamer for less
than 200 euros. Did I mention developments
in digital audio are rapid? Therefore subscribe
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If you have a question, post it below this
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thank you for watching and see you in the
next show or on theHBproject.com.
And whatever you do, enjoy the music.
