Audio Audio/Peripherals Reviews

Nubert nuPro X-3000 RC Review – the perfect balance between a neutral studio monitor and a cheeky compact living room speaker. With extensive teardown

First of all I unscrew the whole unit from the body and am glad that the usual cross slots are not used. The compact unit can be removed relatively easily and the cables can also be safely disconnected. Only the BT antenna with the adhesive surfaces, somewhat arbitrarily buried in the endless clouds of the white insulation wool, seems a little helplessly placed, but it works. The body makes a rock-solid processed figure, also inside. We can also see the rear of the very long-throw midrange/bass driver including the magnet and the opening in the middle. Cooling the winding should not be a problem either.

By the way, the tweeter sits exactly under the bass reflex tube made of impregnated hardboard, whose length of approx. 17 cm gross (including the glued-on plastic covers) suggests a rather low tuning. The internal insulation is quite compact, so that one can also assume a proper damping.

The removable unit carries the audio board including the power amplifiers cooled via the mounting plate in the lower board layer. The power supply board is screwed over the top with spacers. By the way, the arrangement of the main transformer is quite cleverly chosen in order not to radiate unnecessarily into the sensitive areas of the audio board.

 

The power supply

Power supplies are often underestimated or are simply disregarded, but they are extremely important, especially for ensuring a constant rated power, undistorted, short-term pulse peaks and a clever isolation distance. The single layer board is manufactured by SHENZHEN SHENZE ELECTRONIC CO. LTD and is identical to the board of the nuPro A300. The parts are then loaded at the contract manufacturer. The maximum power is approx. 200 Watt, whereby approx. 180 watts should be typical. This also harmonizes with the components used, because with a specified nominal power of 150 watts per box plus the usual losses and all the other peripherals, you can quickly get into these areas.

A simple comparison measurement on the primary and secondary side showed an efficiency of up to 95% for the whole construction, whereby one must include the second, small power supply unit for the tinkering and power balancing. In normal operation it is estimated that a few more watts should be added. However, what is beneficial to efficiency is this dichotomy in any case. In this case, such an effort is always worthwhile, which also goes beyond the pure standby circuit. The soldering quality of the whole board is decent.

Most of the time you don’t want to know what is fed into a power supply unit, because the mains voltage rarely comes out of the socket alone and clean. At the latest when other consumers are connected to a distributor, it can quickly become disgusting. After the physical on/off switch, the power supply unit is equipped with a proper input filtering and smoothing against spikes and unwanted HF radiation, including a MOV as overvoltage protection. What is optically missing is a fuse on the circuit board and a real supervisor chip on the voltage rails of the secondary side including shunts if there is a short circuit. The two ordinary primary capacitors each have a capacity of 680 µF, which can even make up for short voltage drops. I’ll get to the manufacturer in a minute.

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

Both power supply units function as classic switched-mode power supplies, whereby the detour via a more complex DC-DC power supply unit for the different partial voltages of the consumers is not necessary at all, because they are two separate power supply units from the outset. The MOC3043 from On Semiconductor is the usual opto-coupler for the larger power supply, which already belongs to the better ones. With the TNY280PN you also rely on an appropriate AC/DC converter from Power Integrations. So it fits.

 

The complete capacitor assembly of the electrolytes is based on very practical 105°C models from Jianghai, both on the secondary side (in the picture below) and the primary side, as well as the voltage conversion. The almost 1500 µF on the secondary side creates a good buffer for power peaks. So it is 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 well suited to last for a few years.

And if you now tap a Chinese junk manufacturer at the manufacturer’s, you’ve got it all wrong. Jianghai is one of the oldest Chinese manufacturers and emerged from a former supplier to the People’s Army. In addition, the complete capacitor production has now been purchased from Hitachi. So in the end you get Hitachi quality at a fair price. The parts really don’t have to hide behind those from Chemicon.

 

The audio board

This multi-layer board comes as main board from SHEN ZHEN SUN & LYNN CIRCUITS CO LTD and also here the assembly and soldering quality is completely ok at the final manufacturer. The attached radio module comes as a single-layer board again from the power supply manufacturer. 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 practically the girl for everything. The system-on-chip (SoC) provides efficient and configurable audio signal path processing including equalization, dynamic range compression, mixing and filtering, and a fully configurable high-level programming interface. The integrated PWM engine supports programmable and dynamic audio output control, noise shaping, an embedded asynchronous sample rate converter and directly controls power stages with SNR values >110dB and a THD+N of

In addition, the active crossover realized with this DSP creates an almost ideal phase alignment of high and mid/low frequencies and synchronizes the critical group delay of the drivers in multi-way systems. The jump or Pulse behaviour should be fundamentally improved, which allows a very precise playing, which can also be heard. In addition, a relatively fast 32-bit arm Cortex CPU with a clock rate of up to 48 MHz is used as MCU for process handling. The firmware is stored in a separate BIOS chip.

The XU208-128-TQ64 (XMOS U30870c10) is a multi-core microcontroller from the xCORE-200 series that is a popular choice for high-quality circuits. Up to 32-channel USB and networked audio applications could be realized in this way. The integrated high-speed USB 2.0 PHY and 16 logical cores, which can deliver deterministic and responsive processing power of up to 2000 MIPS, also serve this purpose. Taking advantage of the flexible programmability of the xCORE-200 architecture, a maximum of 8 input and 8 output audio channels can be streamed simultaneously at up to 192 kHz. That’s quite enough.

   

The power amplifiers are so-called UCD (Universal Class D) switching amplifiers, which considerably improve the operation of an analog switching amplifier. This technology from the 1980s provides cleaner signal processing than conventional Class D bridge circuits and various upstream converters and drivers. The pulse-width modulated signal (PWM, 384 KHz clocking) distributed in real time to the individual branches by the DSP is sent directly in digital form to the parallel-connected PWM output bridges. Poverty of noise and jitter are then the reward for this trick. In order to get a phase stable behaviour and low TIM and THD error values, a DC voltage filtering in the low, single digit Hertz range is certainly used.

The output stage chips are thermally connected to the base plate via an intermediate piece, which also serves as a universal finned heat sink. The used pads are apparently completely sufficient, because even a full load test of several hours didn’t lead to a GAU, even if the board and the plate got quite warm by then.

Interim conclusion

The entire electrical and electronic side is well equipped. The D2Audio DSP is currently hard to beat for this price range, the MCU used is functional and the XMOS chip is almost a bit above it. All peripherals with wireless connection and connection and the IR module are ok. The direct A/D conversion of the analog inputs without further analog signal processing and the prompt transfer to the DSP ecosystem is well solved, but for most older phono equipment you still need a preamplifier. The power supply fits into the price range and does exactly what you expect it to do.

A small side note on the assessment of the soldering quality, which of course can only be a snapshot and cannot replace a real 10-year long-term test with daily vibrations. I checked the surfaces and edges under the microscope, concerning the reflow components as well as the solder joints and surfaces from the wave solder bath. In addition, the soldering of the cables and connections, as well as the search for possible manual rework and the cleaning of the circuit boards or Soldered joints. All these points make me quite optimistic that the whole thing will last a bit longer.

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About the author

Igor Wallossek

Editor-in-chief and name-giver of igor'sLAB as the content successor of Tom's Hardware Germany, whose license was returned in June 2019 in order to better meet the qualitative demands of web content and challenges of new media such as YouTube with its own channel.

Computer nerd since 1983, audio freak since 1979 and pretty much open to anything with a plug or battery for over 50 years.

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