The Fox Report
Barry Fox’s technology column
Analog2Digital
I
wanted an easy way to take
analog audio from a Hi-Fi system
and turn it into digital data, in high
quality, for easy storage.
The first challenge was how to get
line audio out of an amplifier. Using the
signal from the speakers or a headphone
socket creates signal level problems.
Older Hi-Fi systems have stereo (left/
right) fixed-level line output sockets,
with phono/RCA plugs, for connecting
a tape recorder or CD burner. However,
these sockets are now seldom provided.
Often, the only option now is to use the
line level outputs provided for connecting a separate amplifier or multi-room,
multi-zone system. If there are multiple
RCA/phono sockets, for surround sound
and a woofer, use the front stereo pair.
The system will probably need to be set
up to steer a fixed-level replica of the
main Zone 1 audio to the Zone 2 sockets.
Details will vary from amplifier to
amplifier, and there is no alternative to
reading the manual, Googling or asking an AI to figure out how to do this.
The next challenge is how to convert
the analog, stereo line-out audio accurately into the digital domain.
There are many accessory boxes and
dongles that can do the job. Cheap ones,
often designed to digitise low-quality
video and audio from a VHS VCR, may
deliver iffy audio quality. Units that
use high-quality ADCs (analog-to-digital
converters) are expensive.
When I recently looked for something
affordable to use for digitising old
audio tapes, discs or radio broadcasts,
with halfway-to-decent audio quality,
I found a big gap in the market.
Modern LP turntables now often
have a built-in ADC and USB socket
that provides a digital version of the
analog vinyl music. But this is no help
when trying to digitise other sources.
Highly respected Austrian Hi-Fi company Pro-Ject has for many years made
a small accessory box, costing around
£200. This takes in the very low-level
“phono” feed from MC (moving coil)
or MM (moving magnet) turntable cartridges and uses a pre-amp, equaliser
and high-quality ADCs to produce a
line-level signal for connection to an
amplifier without a phono input, plus
a digitised stream via USB.
I suggested to Pro-Ject that it might be
a smart move to add line level inputs;
Practical Electronics | September | 2025
that way, the expensive ADCs could be
used for two tasks, digitally converting
from phono level signals and also from
line level signals. Surely all it would
need, I suggested, would be a simple
pre-amp/EQ bypass switch.
Scott Lawson, Technical Services
Manager for Henley Audio, the British
company that handles the Pro-Ject brand,
was quick to shoot down my suggestion:
“Bypassing the ‘pre-amp’ doesn’t
make sense for a phono stage, because
all you’d be left with is a very low signal
output, which wouldn’t be much use
for recordings via the USB.... I doubt
this is of any interest to Pro-Ject, as their
market is predominantly turntables.”
Fortunately, a clever new device
from enterprising British company
A2D2 (https://a2d2.net/) goes a long
way towards doing the conversion job,
plus a lot more besides, for just £150.
The A2D2 Stream is a small box
that takes any line-level analog stereo
signal (from disc, tape, radio etc) and
converts it into a digital stream, which
can then be shared by WiFi, Bluetooth
or Ethernet cable to streaming players
and amps, smart speakers, phones,
tablets or computers.
The digital stream can be accessed
by pointing a web browser at the device address (http://a2d2.local/). The
browser then shows a list of the many
open source and proprietary playback
options that the A2D2 device supports.
These include AirPlay, ChromeCast,
HEOS (Marantz/Denon), Sonos and Alexa (with some extra tweaking needed),
standard Bluetooth or headphone pairing and direct “Listen on this Device”
(eg, decode and play with a computer
sound card) with the choice of 48kHz
or 96kHz audio quality.
The device also has analog line output sockets so it can ‘pass through’ the
signal to another analog audio device.
The software-based options are so
wide and varied that I am still experimenting. For one practical test, I took
the analog stereo Line Out from a Hi-Fi
amplifier (a fixed-level Zone 2 connection for multi-room playback) and fed
it into the A2D2 box for conversion
into a digital stream. This then went by
Ethernet cable into my home network.
To play the stream, I entered the LAN
web address (http://a2d2.local/) in my
desktop computer Chrome browser,
chose “Play on this Device” and was
offered the option to click “Play”.
I could then listen to the stream
through the computer’s speakers or,
more usefully, capture the stream, for
instance with the open-source, free
software Audacity. Just set the Audacity input to “Speakers”.
To complete the experiment, I connected the A2D2 line out (pass-through)
sockets to a stereo cable, which then
ran to the Line In socket of the desktop computer. This provided an easy
playback and capture choice between a)
digital streaming via the home network
and b) direct line level connection by
analog stereo cable.
I am reserving judgement on whether
the capture quality is better by network
or line cable. What matters is that there
is a simple, working choice available.
One practical point to note is, because
the A2D2 box has an http web address
(rather than https), your browser may
show a security warning. This can be
safely bypassed because the connection
is local, not via the Wild West Internet.
The makers say that for streaming
speakers, the A2D2 box self-adjusts
quality to match the connected device;
for example, 44.1kHz for Airplay, 48kHz
for Sonos and 96kHz for Chromecast.
Device control is mainly with the
(free) A2D2 mobile App.
I was disappointed to find no option
to feed an analog signal into the A2D2
box and get out a USB digital stream.
But this appears to be on a roadmap for
the future, along with the opportunity
for MP3 and FLAC encoding. In addition to the USB-C socket used for 5V DC
power, there is already a standard USB
output socket on the box, earmarked
for data input and/or output.
It’s not clear whether these and other
future options, such as DLNA/UPnP
support, NAS and Alexa integration,
will be added by software updates.
Hopefully so, but even if not, the A2D2
box is already a remarkably versatile
bit of kit which, for £150, comes close
to offering all things for all users.
The problem facing the A2D2 sales
team may be that technically challenged
influencers and casual gadget reviewers will not devote the time and effort
needed to get to grips with the product.
I freely admit that I still feel I have
only scratched the surface of its potential. But I have already understood more
than enough to heartily recommend
what could well become a standard
PE
tool for streaming.
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