Lehmann Audio Black Cube SE II black, MM/MC phono preamp
A phono cartridge delivers a few millivolts, sometimes less than half a millivolt, and even the slightest hum is immediately audible. Lehmann Audio, a German manufacturer based near Cologne, built its reputation on the Black Cube, a compact phono preamp that tackles this problem methodically. The SE II version pairs the audio unit with a more substantial separate power supply, supports almost every cartridge on the market and adds an adjustable bass filter with a degree of precision rarely found in this form factor.
Two enclosures to keep noise at bay
The Black Cube SE II consists of an audio section and an independent PWX power supply. The first enclosure, made of non-magnetic aluminum with a black front panel, takes up barely more space than a hand (114 × 124 mm) and can sit right next to the turntable: the cable from the tonearm stays short and picks up less interference along the way. Inside, Lehmann adds filter modules to counter hum, high frequencies and stray voltages, on a double-sided circuit board whose layout limits interference between tracks.
The PWX power supply houses a custom-made 30 VA toroidal transformer, protected by an electrostatic shield and connected to ground. Placing it in a separate enclosure keeps its magnetic field away from the input stages, the most sensitive parts of the system. The two units are connected by a shielded cable fitted with Neutrik XLR connectors with gold-plated contacts, long enough to place the power supply at the back of the cabinet while the audio section stays near the turntable. The whole setup consumes less than 3 W.
Gain and loading suited to each cartridge
Moving magnet cartridges (MM) generally produce 3 to 5 mV, while moving coil cartridges (MC) often produce ten times less. The preamp therefore needs to provide more or less amplification depending on the model fitted to the tonearm. The Black Cube SE II offers four gain levels, 36, 46, 56 and 66 dB: the first two suit MM cartridges, the next two suit MC cartridges, and the highest setting is sufficient for even the lowest-output moving coils.
The input impedance, meaning the electrical load seen by the cartridge, can be set to 47 kΩ (the standard value for MM cartridges), 470 Ω or 100 Ω. With an MC cartridge, this parameter affects the tonal balance, particularly in the treble. When the cartridge manufacturer recommends another value, a slot beneath the chassis accepts a plug-in resistor that sets the exact impedance required. Input capacitance remains fixed at 100 pF. All these adjustments are made using miniature switches beneath the enclosure: it is best to choose the settings before final installation rather than turning the unit over once it is wired up.
Passive RIAA equalization between two linear stages
A vinyl record is cut with reduced bass and boosted treble, allowing more music to fit into the groove and reducing hiss. The preamp must apply the inverse curve, standardized under the name RIAA, to restore an accurate balance. Lehmann assigns this equalization to a passive network made solely of resistors and capacitors, placed between two constant-gain amplification stages. This arrangement avoids incorporating equalization into an amplifier’s negative feedback loop, and the brand sees it as the key to precise equalization, good transient reproduction and very little deviation between the left and right channels.
The signal-to-noise ratio reaches 71 dB with 46 dB of gain and 63 dB at the maximum setting: the more amplification is applied, the more the background noise rises along with the signal. The right setting is therefore the lowest one that provides a listening level comparable to the system’s other sources. At the output, an impedance below 100 Ω allows the preamp to drive any line input without concerns about the length of the connecting cable to the amplifier.
Sixteen filter settings for warped records
A slightly warped record makes the tonearm rise and fall with every revolution. The cartridge translates this movement into infrasound, frequencies too low to be heard but strong enough to make bass driver cones pump and needlessly consume amplifier power. Most preamps cut these frequencies at a single threshold, or not at all.
The Black Cube SE II incorporates a fully passive filter with a gentle slope, which gradually attenuates the bottom of the spectrum rather than cutting it off sharply, and offers sixteen cutoff frequency settings. It can be left very low with a well-isolated turntable and flat records, raised for an old or worn collection, or used to tame speakers whose bass overwhelms a small room. This fine control over the bottom of the spectrum is the SE series’ main advantage over preamps with fixed filters.
