Even with digital audio components, there is potential for sound tuning, especially in the analog working areas. The power supply is of central importance here. The German digital audio specialist RME knows this only too well. It is therefore not surprising that RME has recently launched two upgrade options for powering audio components that are operated on external power supplies with a DC output voltage of 12 volts. The RME DPS-2 linear power supply (1100 euros) is an uncompromising all-in-one solution: Operated directly from the mains, it completely replaces the existing 12-volt DC power supply. The much cheaper but equally exciting alternative to this is the RME LNI-2 DC active isolation filter/stabilizer (550 euros): Connected downstream of an existing power supply, it dramatically improves its electrical properties. Potential beneficiaries of the two new power supply units from RME are, first of all, the company’s own components – for example, all members of the hi-fi oriented ADI family tested by LowBeats, i.e. RME ADI-2/4 Pro; RME ADI-2 Pro FS R; RME ADI-2 DAC and RME ADI-2 Pro. Also worth considering are the compact USB audio interfaces widely used in the pro consumer sector, such as the RME Fireface UCX II or the RME Babyface Pro/Pro FS. Of course, audio components from other manufacturers can also benefit from the two RME power supply solutions presented here, as long as they work with 12 VDC operating voltage.
RME DPS-2 and RME LNI-2 DC: clean power with expertise
Compared to conventional 12-volt DC power supplies, the two RME power supply solutions are well thought-out and extremely sophisticated. They reflect the wealth of experience that RME has gathered over almost three decades in the pro audio and hi-fi sector. Here, as there, power supplies act as a link between two electrical “domains”: On the primary side, the lighting network with all its imponderables – on the secondary side, on the other hand, the audio system, which has a very different character depending on the choice of its components. With good framework conditions (i.e. a stable, clean lighting network) and favorable operating conditions (i.e. undemanding audio components), decent electrical results can be achieved even with simple off-the-shelf power supply units. However, standard power supply units literally hit the skids when weak points or electrical problems arise on the primary and/or secondary side – on the primary side, for example, the pizza oven in the restaurant two floors below or on the secondary side the music streamer docked to the home network via LAN cable. In precisely such environments – which in practice are the rule rather than the exception – the design effort of the RME power supply units pays off: While these present insurmountable hurdles for light mains-related impurities (keyword “galvanic isolation”), they suck up interference products caused by the audio system itself like a black hole (keyword “ideal voltage source with infinitely low internal resistance”). Inquisitive minds can find out about the circuitry involved in the DPS-2 and LNI-2 DC in the technical section of the accompanying, absolutely exemplary operating instructions – including numerous diagrams documenting the objectively verifiable performance of both components.
RME DPS-2 – the 2-in-1 power supply
From a global perspective, the RME DPS-2 is a transformer-based, linear power supply with electronic voltage stabilization. Its output DC voltage is 12 volts at a rated current of 2.5 amps, which corresponds to a continuous output power of 30 watts. This sounds rather unspectacular, but the transformer already reveals significant differences compared to standard power supply units. The DPS-2 uses a 60 VA toroidal transformer with an earthed protective winding – the most effective method of ensuring galvanic isolation of the primary and secondary circuits even at high frequencies (keyword: reduced winding capacitance): This means that even high-frequency interference components from the lighting network – caused by dimmers or LED lights, for example – are kept out. Thanks to the Mu metal strip shielded transformer, housed in an ultra-stable, additionally shielded sheet steel housing, the DPS-2 does not generate any stray electromagnetic fields of its own.
The rectifier circuit and a generously dimensioned filter chain are connected downstream of the mains transformer. In addition to six electrolytic capacitors with a total capacity of an impressive 30,000 microfarads, there are also coils (chokes) in the serial current paths, which again significantly reduces the residual ripple of the DC voltage. The mains switch is located on the rear of the device. In the off position, it disconnects the DPS-2 from the lighting mains with two poles and thus completely. On the primary side, the DPS-2 can be operated on 230V or 115V networks, with switching via internal jumpers. As a power supply unit in accordance with protection class I with an IEC C14 socket, the sheet steel housing is directly and permanently connected to the protective earth conductor (PE), which also applies to the screw-type earthing terminal. A ground lift switch can be used to select whether the internal circuit ground is connected to the PE conductor directly or via a 10-kiloohm resistor (soft earthing). Even in this operating mode, this ensures the reliable removal of interference-prone leakage currents (leakage or sheath currents) in the electrical earth connections of the entire signal chain. Their potential can often be felt as finger tingling when wiring the system.
Choice of DC voltage: stable or ultra-precise
A real world first for the RME DPS-2 are its two 12-volt DC voltage outputs. Both have thermal overheating protection as well as current limiting in the event of a short circuit. In terms of output voltage stability, however, they pursue different strategies (see slideshow below). The “Linear” output, for example, has a conditionally load-dependent, quasi-analog characteristic curve, meaning that its voltage drops by up to around 4 percent at output currents above 2.5 amperes. Thanks to the “floating” control circuit with low power loss, the linear output can supply currents of up to 4 amps for short periods without overheating the DPS-2 in the long term. The linear output is therefore particularly suitable for components with high peak current requirements that already have internal voltage stabilization. A prime example of this is the recently tested RME ADI-2/4 Pro SE with its powerful headphone amplifier.
However, if you want even more stable output voltage, choose the µFilter output. This works like professional laboratory power supplies or measuring devices using four-wire sense technology¹. Using the enclosed special four-wire cable, the electrical reference point for the DPS-2’s internal, ultra-precise voltage control circuit is shifted directly to the DC input socket of the connected component in order to compensate for any losses in the connecting cable. The result: regardless of the operating current required by the connected component – 12 volts are always present at its DC input socket to an accuracy of 0.2 percent: And that with hardly any measurable interference components in the microvolt range – hence the name µFilter.

As the block diagram above shows, the linear and µFilter circuit branches are fed together from the DC bus. However, they can only be used exclusively: when connected to one of the two outputs, the other is automatically switched off. Two LEDs on the front panel indicate which of the two outputs is currently being used. A recessed pushbutton switch allows you to choose whether the LED indicator lights up permanently or goes out 30 seconds after the RME DPS-2 is switched on.
RME LNI-2 DC – the power optimizer
The RME LNI-2 DC was developed to significantly improve the electrical characteristics of existing power supplies. Powered from DC sources with output voltages from 9 to 18 volts, it does not require its own mains transformer. Thanks to its wide supply voltage range, the RME LNI-2 DC is also perfectly suited for mains-independent, potential-free operation on 12-volt batteries. It not only ensures a constant output voltage of 12 volts, but also eliminates any physically induced battery noise. Although the RME LNI-2 DC does not require a mains transformer, it still provides complete galvanic isolation between the input and output circuits. This is made possible by a powerful, integrated DC-DC converter module with an extremely low winding capacitance of just 35 picofarads between the primary and secondary coils.
When developing the LNI-2 DC, RME drew on existing resources. As the following block diagram shows, the LNI-2 DC uses exactly the same 4-wire sense circuitry for its 12-volt output as the µFilter electronics in the RME DPS-2. This means that the RME LNI-2 DC also provides a stable 12 volts with barely measurable interference spectrum at its DC output, down to 0.2 percent. Due to its different input circuit, the nominal current available at the output of the LNI-2 DC is slightly lower than that of the DPS-2 at 2 amps. This makes it ideal for audio components with a power consumption of up to 24 watts – for example the RME ADI-2 Pro FS R. With a maximum “appetite” of 30 watts, however, the RME ADI-2/4 Pro SE cannot be used as a playing partner.

Just like the RME DPS-2, the RME LNI-2 DC comes with two special four-core connection cables to feed the audio components. The cables connect to the RME power blocks via lockable, four-pole Kycoon fittings, while the consumers dock via common coaxial hollow plugs in the widely used 2.1 x 5.5 millimeter format. One of the cables is fitted with a lockable barrel connector suitable for correspondingly equipped RME components. Due to the relatively stiff four-wire cable, however, the connection on the consumer side requires a little patience.
RME DPS-2 and LNI-2 DC in practical test
Depending on the local environment, the lighting network conditions are hardly comparable; in addition, there are a wide variety of audio components, each with their own typical power supply requirements: This raises the legitimate question of the extent to which exemplary listening tests of external power supplies can achieve comprehensible results at all. In my opinion, a realistic practical test that focuses on a typical, technically demanding application is much more meaningful. And what task would be better suited to this than transferring a hot-cut, top-sounding 45rpm vinyl EP perfectly to digital? (…which is also a very obvious application for RME ADI-2/4-Pro owners due to its phono input). Years ago I already created sophisticated analog-to-digital transfers for several title CDs of the magazine stereoplay. So I know only too well that these can only be achieved in high quality in a healthy, electrical environment with careful, minimalist cable routing. A makeshift desktop setup, on the other hand, would be tantamount to a worst-case scenario – but that’s exactly what the two RME power supplies had to prove themselves in the practical test.
The test setup: Interference desired
The complete test setup was placed on a large desk top – deliberately disorganized. The vinyl player was a Thorens TD 524, equipped with a Lyra Delos MC cartridge. The central component of the system was the RME ADI-2/4 Pro SE, initially DC-fed via µFilter output from the RME DPS-2. The ADI-2/4 Pro was responsible for phono RIAA equalization, subsequent A/D conversion and monitoring via two active monitors (without PE connection) or headphones. Data was transferred via USB to the desktop computer (Mac mini, without PE connection), which was responsible for the actual recording in 32bit-float/96kHz format. The phono input of the ADI-2/4 Pro is primarily designed for MM cartridges, which also required a separate MC pre-pre before the phono input. For this purpose I successfully “alienated” my USB audio interface RME Fireface UCX II, also DC-fed via µFilter output from the RME LNI-2 DC. This in turn was deliberately powered by a rather average 12-volt switching power supply intended for mobile hard disks.

As planned, the test setup required a certain amount of cabling. In addition, there were other provoked problems such as multiple earthing due to the computer’s network connection, two audio components in the signal path that were also linked via USB and two 230-volt power supplies several meters apart. All in all, according to the rules of the German physicist Kirchhoff, the result is a power grid with many meshes and nodes and plenty of internal interference potential. External electromagnetic interference was also welcome: For example, the 750-volt DC overhead line of the busy light rail system just under eight meters away, or the Dulux fluorescent lamp hovering less than 30 centimetres above the vinyl turntable – whose mains transformer was naturally allowed to use the same distribution board as most of the other components.
Double victory for RME
Despite all the deliberate technical adversities, the vinyl-to-digital transfer (Bert Kaempfert: Hits On 45 – from the original mastertape; released on the Sommelier du son label) actually sounded breathtaking. In addition, the noise floor was so low that the pre-echoes caused by magnetic print-thru on the mastertape were clearly audible in the pauses before the next track. Unfortunately, for licensing reasons, I am not allowed to post this on the web – so I had to find another, convincing proof. This can be found, at least visually, in the following slideshow in the form of three spectrograms that document the spectral noise carpet of the signal chain in the recording branch.
The results are briefly summarized: As long as the DPS-2 and LNI-2 DC were used as power supplies, there were no interference spectra in the signal despite the worst-case electrical environment, while the signal-to-noise ratio was excellent (diagram 1). It was therefore no coincidence that the vinyl-to-digital transfer, powered by the RME power supplies, sounded excellent. On the other hand, there were clear interference peaks at 50, 150, 250 and 350Hz when the RME DPS-2 was replaced by an off-the-shelf, linear, stabilized 28-watt power supply before the RME ADI-2/4 Pro (spectrogram 3). The practical test also revealed that both the RME ADI-2/4 Pro SE and the RME Fireface UCX II, thanks to their internal voltage conditioning, were even quite insensitive to power supply problems – as evidenced by their still respectable signal-to-noise ratios even with a qualitatively mediocre power supply (see spectrogram 3). There were USB-AD-DA converters from other suppliers that were much more “permeable” to such interference.
Conclusion RME DPS-2 and RME LNI-2 DC
More than 2000 words of text for two 12 VDC power supply units – isn’t that rather excessive? Not at all, as it requires some explanation as to how a typical 50-euro power supply differs in design and quality from one costing 1100 euros – in a comprehensible, serious manner and without voodoo. The RME DPS-2 power supply and the RME LNI-2 DC power conditioner were excellent starting points for this: technically uncompromising and practically designed, both behave just as exemplary in the test laboratory as they do under real operating conditions in the hi-fi and pro audio environment. The fact that the RME DPS-2 and RME LNI-2 DC are limited to components powered by 12 volts DC does not detract from their performance. On the one hand, they cover exactly those devices that work in the small signal range – and are therefore electrically most susceptible to power supply-related interference. On the other hand, the RME DPS-2 and RME LNI-2 DC are examples of the level of quality that can be achieved even at higher output voltages. Of course, power supplies cannot “improve” the inherent (“innate”) sonic characteristics of audio devices in the usual sense. But one thing is certain: Powered by RME DPS-2 or RME LNI-2 DC and thus freed from any interference from the mains and/or the system itself, hi-fi or pro audio components reach their full sonic potential. In other words: Powered by RME – the safe bank for good sound. By the way: Kenwood developed a comparable technology, called “Sigma Drive”, back in the early 1980s for lossless speaker connection to its high-quality hi-fi amplifiers.
Rating
UsabilityWorkmanshipTotal |
The rating always refers to the respective price category. |
| High-quality linear power supply for replacing existing 12 VDC power supplies |
| Extremely accurate, stable output voltage with hardly any measurable interference components |
| Two 12 V DC voltage outputs with different characteristics |
| Robust sheet steel housing and shielded transformer for low stray field operation |
Distribution:
Hörzone GmbH
Balanstraße 34
81669 Munich
Phone: +49 89 721 10 06
www.hoerzone.de
Price (manufacturer’s recommendation):
RME DPS-2 1,100 Euro
Rating
UsabilityWorkmanshipTotal |
The rating always refers to the respective price category. |
| Dramatically improves existing 12 VDC power supplies |
| Extremely accurate, stable output voltage with hardly any measurable interference components |
| Can be powered by 12-volt battery (or packs) |
| Compact, robust housing |
Distribution:
Hörzone GmbH
Balanstraße 34
81669 Munich
Phone: +49 89 721 10 06
www.hoerzone.de
Price (manufacturer’s recommendation):
RME LNI-2 DC 550 Euro
Mentioned in the article:
Test ADDAC headphone preamp RME ADI-2 Pro
Major firmware update for RME ADI-2 Pro
Test RME ADI-2 Pro FS R Black Edition
RME ADI-2/4-pro SE – HiFi meets Pro Audio