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The Volume2 serves as a system-independent analogue volume regulator in all areas of audio processing and playback. It focuses exclusively on high-quality active control and was designed for those who do not need additional monitoring functions but want a cost-effective solution. The Volume2 is based on active switching to avoid response nonlinearities from impedance changes as incurred by passive designs when changing levels. It represents a form of no-compromise solution for digital audio workstations, D/A converters and professional sound cards. A vast majority of professional monitoring devices provide nothing by way of analogue level control and this introduces the necessity of varying signal levels at the converter outputs in the digital domain. The result is a lowered bit rate, which can lead to a commensurate loss of sound quality. At its price, the SPL represents an interesting opportunity to improve sonics.

Beyond audio monitoring, another application is in a straightahead audiophile stereo system where the Volume2 sits between source and power amp or active speakers. In such cases, the source must offer analogue outputs. The SPL then provides for minimal financial and electronic contortions and the most direct signal path with high-quality balanced stages and extremely good common-mode rejection to minimize interference.

The Volume 2 uses an elegant but spartan compact housing (215 x 80mm or 8.5 x 3.5") that makes for a flexible desktop utility in a professional environment and a space-saving solution in a hifi system.

The Volume2 is built with well-designed but simple analogue circuitry. Senior developer and founder Wolfgang Neumann is very pragmatic when designing audio gear using the proper parts where important and being less impressed with costly boutique issue. For instance, the massive 45mm diameter aluminium knob fronting the Alps RK18 pot makes for consistent, precise and refined handling. While not considered a hot-rodded part, the RK18 is a good potentiometer that handles high continuous voltage and controls the signal directly without a VCA or DAC interface. It has appeared in several high-end references such as the Denon PMA-S10II, Musical Fidelity A5 and KW500.

The power supply was carefully engineered to provide clean and consistent current as an important prerequisite for good performance. Built around a 3.5VA toroidal transformer, the power supply generates a minimal electromagnetic field without hum or mechanical noise. The output is RC filtered to reduce noise and hum inherent in commercial AC power networks. All audio-related parts are fed by two separate voltage regulators to minimize interference. The rear panel sports single XLR i/o ports. If you need more connections, look at the 2Control model instead.

The balanced stages are based upon custom ceramic components like laser-trimmed sulfate resistors for best tolerances. They are called upon to provide high CMR, neutral sound and great robustness. The only concession to creature features is the frontal mute switch to cut the output without changing volume. Looking inside, the overall impression is one of an empty box. This reflects SPL’s focus on PCB layouts favoring space. Wolfgang Neumann loves designs that allow plenty of space between circuit-board tracks to reduce cross talk and inductive coupling. The accurate schematic designed by SPL leads to a very organized and optimized PCB.

That's old school. SPL goes light on SMD components and prefers big discrete parts which take up more space but then seem to breathe a bit better. The op-amps are no voodoo either. The Texas Instrument low-noise TL07 series JFET input is honest stuff but not the highest performance option available today. It’s simply known for being neutral and often championed by important high-end companies like Accuphase.

The Volume 2's frequency response offers excellent channel matching with wide bandwidth, being one 1dB down above 100kHz.

The Volume2 is a highly linear design (output spectra are shown at close to normal 2V output level). Only 50Hz harmonics protrude from the –120dB noise-floor. This level of performance is comparable to the most expensive preamps in the high-end sphere.