After my old big speakers slowly died and just took up too much space, I looked for smaller active
speakers. In a for me rare occasion, I did online shopping and ordered different pairs of speakers
home. In this environment, I tried to do a blind test to find which speakers fit my home, budget,
taste of music and technical requirements best. So I ended up with a pair of Nubert nuPro
X-4000.
I like their clean look. With clean I mean that there is no promiment logo, although an eagle-eyed
person will spot the logo at the bottom of the tweeter. Even the display can turn off after a short
while. Really nice! It’s a speaker that stays visually in the background, not a status symbol.
Instead, it delivers on its sound: As subjective as this is, I like it, with the big depth the
speakers create and their precide mid and high reproduction. It’s not too analytic, has sound for
the price and enough inputs for my needs.
As a set of speakers at home, not studio monitors, I like the possibility to gang together a pair of
speakers wirelessly or by wire. The wireless more incurs a latency of “< 20 ms” according to the
data sheet. I could measure how much it actually is, but since I like my audio chain to have as
little latency as possible, I chose to use a cable.
But what’s inside, you ask? Let’s have a look and lift the lid – err, active amplifier module – on it!
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The speaker’s backside (not depicted here) consists of the amplifier module and bass reflex opening.
The amplifier module itself has a rubbery layer so that it creates an airtight connection to the
speaker case. After removing the eight screws that hold the module, you can lift it out, carefully
disconnect the cables to the two speakers, front panel/display assembly and bluetooth antenna.
The amplifier module turns out to be a sandwich of multiple PCBs. All cables are wrapped in foam.
Whether this prevents chafing or unwanted noises by things beating together, I don’t know.
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Detail: abgerundete Leiterbahnen
The power supply (ID: Nupro A300-VM1.0-PSU) is well-built. All parts whose leads could bend or break
because of vibration are gunked to the PCB. Even the windings of the AC noise filter inductor are
gunked to its ferrite core. Such attention to detail is highly appreciated! Apart from the usual
issue that the big capacitors are right next to hot power semiconductors, the power supply is
decently designed and made. Also, take a look at the curved edges of the traces on the PCB.
Beautiful!
Audioplatine
Audio-Platine ohne Funkmodul
versteckter Klasse-D-Verstärker
Let’s take a look at stack of PCBs below the power supply. The biggest board connects to the inputs,
bears the amplifier itself and does all audio processing. It also carries another PCB for wireless
communication. Yet another, small PCB connects to the XLR jack.
The big PCB contains the following semiconductors:
TI DRV603: click-free audio output driver (for the subwoofer output?)
XMOS XU208-256: micro controller with USB; xCORE 200 series (labelled: U30870C10, GT173501)
The amplifier itself is a Class-D amplifier. The D2-92634-LR is probably used as a modulator that
creates the PWM signals that drive the output stage on the backside (probably some power MOSFET
bridges). That stage is coupled to the backplate that doubles as a heat sink by a piece of metal.
In addition, there’s a pair of really beautiful inductors that smooth out the PWM signal close to
the output stage.
Let’s look at the one weird part of the speaker: The wireless module stack. It’s not a single PCB,
but a carrier PCB with two additional modules, one for Bluetooth, one for the wireless audio link.
When you try to unplug the Bluetooth antenna, you’ll notice that it’s held in place by yet another
small PCB, the one with Chinese characters on top. I’ve never seen such a connector get loose, but
well. Better safe than sorry, I assume. The bluetooth module itself is some off-the-shelf module,
although Nubert decided to use an external antenna instead of the integrated one. I didn’t check
whether the Bluetooth module outputs audio as analog or digital signal. Most of these modules only
output an analog signal. Not that this matters much, since the supported Bluetooth codecs (SBC, AAC,
aptX) don’t come close to “CD quality”. SBC has really low latency, but sounds similarly bad as GSM. I
wouldn’t even use this for voice. AAC is more modern than MP3. aptX is easily discernable from CD
quality, still. In addition, the speaker will beep when you select Bluetooth as input
and a devie then connects to it. Like a cheap 5 € AliExpress Bluetooth module. Finally, in a set of
stereo speakers, both speakers are visible via Bluetooth, even though the slave speaker is fully
remote-controlled by the master speaker. That’s just confusing.
The last PCB we’ll take a look at is the module for wirelessly ganging together a set of speakers:
It’s a DWAM83 module by Microchip. The module seems to be an all-in-one solution that effectivly
gives the system integrator a reliable channel to transport uncompressed audio. The datasheet
doesn’t say whether it’s 16 or 24 bit audio and what the sample rate is, though. Also, latency is
spoecified as “< 20 ms”. When I tested it, it worked fine. Yet, I don’t like the unspecified
latency.
We’ve talken a look at most parts of the active speaker. I didn’t take apart the display and
transducers. I have to say, I pretty much like the build quality of the speakers. Only the wireless
communication module is a bit odd.
