Preamplifier Soulution 525 Preamplifier

Dual-mono preamplifier with hybrid volume control and wide-bandwidth output stage

The soulution 525 is an analogue preamplifier that links source components to the power amplifier, providing impedance matching, level matching and volume control without interfering with the content of the signal. Conceptually it is derived from the flagship soulution 725 Preamplifier, from which it inherits a volume control that combines continuous adjustment with the precision of a fixed resistor network. Vishay Dale resistors and top-quality relays are used, resulting in 95 steps of 1 dB with no audible switching artefacts, across a range of +15 dB to –79 dB.

Input selection is handled by relays of the same quality, switching not only the signal but also the ground connection. Only the selected input is therefore connected, while the others remain isolated. All signals are buffered immediately after the input, so the unit presents only a minimal load to the sources. Two balanced XLR inputs with an impedance of 820 kΩ and two unbalanced RCA inputs with 47 kΩ are available; the outputs comprise 1× XLR and 1× RCA with an output impedance of 10 Ω.

The aim of keeping the number of components in the signal path to a minimum led to a single-ended circuit concept in a consistent dual-mono layout. The analogue circuits and the respective power supplies of the left and right channels are physically separated and additionally decoupled by filter networks, which translates into channel separation of 130 dB at 1 kHz. The output stage with a bandwidth of 0 – 2 MHz (–3 dB) is dimensioned to drive even very long signal cables with ease, maintaining level and phase accuracy regardless of the load.

Power is supplied by a switch-mode power supply with highly precise, exceptionally low-noise linear regulation circuits, backed by a reservoir of more than 400,000 μF. This combination delivers virtually unlimited pulse power at an imperceptible noise level, reflected in a signal-to-noise ratio of 120 dB and THD+N below 0.00009 % across 20 Hz – 20 kHz. Technically, this results in reproduction free of colouration, with precise stereo localisation and sharply defined sound sources within the soundstage.

Key features

• Volume control: 95 steps of 1 dB, Vishay Dale resistors
• Dual-mono design: Separate circuits and power supplies for both channels
• Input switching: Relays switching signal and ground, unused inputs isolated
• Bandwidth: 0 – 2 MHz (–3 dB), THD+N below 0.00009 %
• Power supply: Low-noise regulation and a reservoir above 400,000 μF