Bass-to-Go at its best: Nubert nuSub XW-800 Slim Review – Movies, Studio and Gaming with more Depth | Teardown

Body and chassis

Nubert relies mainly on 19 mm MDF for the body, although the base plate with the recessed subwoofer and the mounting plate including the control panel has been reinforced to 25 mm. The recessed chassis sits perfectly on its outer rubber ring on the smooth surface and is neatly screwed from the outside with six solid wood screws (Torx). The cables to the audio board are sufficiently long and I mention it yes, that foreign objects penetrated through the bass reflex tube should be better removed. If such a mishap should really happen: Please unscrew ONLY the chassis and NOT the plate with all the electronics!

The 4-ohm chassis with its 22.4-cm diameter was supposed to come from Peerless, although the Danish company is now just a pure brand after being bought out by Tymphany and became “made in China” like almost all American offshoots. At least with Peerless, this does not detract from the quality for now. In addition, it is always quite practical to produce the chassis, for example, right where you are sitting on large neodymium deposits. Rare earths, at least there, are not so rare and, above all, cheaper. The rest is an appealing series consistency that Nubert would hardly manage so perfectly with a complete in-house production. This way, however, one can calmly build on what already exists and optimize it even further.

The massive, upright basket already shows that this is a Cassis with a very large stroke. The membrane made of a polypropylene composite material creates quite a large deflection, which then also explains the minimum requiered distance to the floor.

The power supply board

The audio and power supply boards are attached to the rear panel with the inputs and controls in a stacked fashion with spacers, and the switching power supply is effectively the top layer. In order to keep the values for standby operation, the standby branch is designed separately and the subwoofer switches off after a maximum of 20 minutes without a signal. Depending on the source selection (wireless or RCA), the wireless module is also still active, whose power consumption is still up to 1.5 watts even in standby. If you want to save money and can’t shimmy all the way to the plug, you can switch the part via app. On vacation, as always, unplug or flip the switch.

Most of the time, you don’t even want to know what is fed into a power supply, because the mains voltage rarely comes out of the socket cleanly and on its own. At the latest when other consumers are connected to a distributor, things can quickly get nasty. After the physical on/off switch, the power supply is equipped with proper input filtering and smoothing against spikes as well as unwanted RF radiation, including an MOV as overvoltage protection. What is visually missing is a fuse on the board and a real supervisor chip on the voltage rails of the secondary side including shunts, if there is a short circuit after all. The two decent primary electrolytic capacitors each have a capacitance of a whopping 680 µF, which can even make up for short voltage drops. I’ll come to the manufacturer in a moment.

Despite the high capacity, the inrush current per box is still within a tolerable range. However, I would strongly advise against hanging the subwoofer and both speakers behind a shared wireless socket (you don’t do that anyway). If you have very sensitive 16 A fuses in the control box, you may find yourself in the dark sooner than you would like. But that is the problem with all switching power supplies.

The complete capacitor assembly of the electrolytics relies on very practical 105 °C models from Jianghai, both on the secondary side (shown in the picture below) and the primary side, as well as the voltage conversion. With almost 1500 µF on the secondary side you create a decent buffer for power peaks. So it’s not a “hard” power supply that sticks to the limit like a cutter, but rather “soft”. These designated Low Impedance and High Ripple Current capacitors are best suited to last a few years. Jianghai is one of the oldest Chinese manufacturers and has bought the complete capacitor production from Hitachi. So, in the end, you have Hitachi quality at a fair price. So the parts don’t have to hide behind those from Chemicon.

The radio modules

The Wi-Fi radio module for signal transmission, which is screwed upright on the side of the stack, relies on a custom SoC from Renesas for the 5 GHz or 5.8 GHz band. The whole thing is plenty proprietary, which makes sense so nothing sparks. Transmitter and receiver are automatically matched and harmonize only in the Nubert cosmos. The 2.4 GHz band is reserved for the Bluetooth module, so competing bands have been intentionally left out.

The 2.4 GHz Bluetooth module sits piggyback on the audio board and uses a CSR 1011. This is a decent low-latency chip without any major special features.

The audio board

By the way, the whole circuit boards are manufactured by Huizhou Glorysky Electronics Co Ltd. in Sun City Industrial Park, but the development of the circuit comes from Nubert itself. Huizhou is located in Guangdong province, the park is really huge and also quite modern. Ok, I digress… Let’s better get to the audio board, which isn’t that mysterious either if you’ve already disassembled other Nubert systems.

Almost centrally located is the heart of the entire concept: the D2-92634 D2Audio from Renesas. This D2-3(S) Audio SoC acts as a Digital Sound Processor (DSP) and is basically the girl for everything. The system-on-chip (SoC) built here provides efficient and configurable audio signal path processing including equalization, dynamic range compression, mixing and filtering, as well as a fully configurable high-level programming interface. The integrated PWM engine supports programmable and dynamic control of audio output, noise shaping, an embedded asynchronous sample rate converter. It also directly drives the PWM power stage with SNR values >110 dB and a THD+N of <0.01%.

In addition, the active crossover for frequency limiting realized with this DSP creates an almost ideal match with quite a steep slope. The bounce and impulse behavior can be described as good. In addition, a relatively fast 32-bit Arm Cortex CPU is used as the MCU for process handling. The firmware is stored in a separate BIOS chip.

The power amplifier is a so-called UCD switching amplifier (Universal Class D), which significantly improves the operation of an analog switching amplifier. By means of this technology from the 1980s one creates a cleaner signal processing than with conventional Class D bridge circuits and various upstream converters and drivers. The pulse-width modulated signal (PWM, 384 KHz clocking) divided by the DSP in real time to the individual branches is sent without detours in digital form to the PWM output bridge with a TAS 5162. Low noise and low jitter are then the reward of this trick. In order to obtain a phase-stable behavior and low TIM and THD error values, a DC voltage filtering in the low, single-digit Hertz range is used.

The TAS 5162 sits here at the back under an aluminum heat sink, the two screws are used for mounting. There is also a heat conduction pad between the cooler and the mounting plate. On the top of the PCB, the relevant area has been gold-plated and looks like a breadboard.