Preamplifier Soulution 727 Preamplifier

Soulution 727 reference preamplifier with paralleled instrumentation amplifiers and distributed power supply

The Soulution 727 is a reference analogue preamplifier designed with the emphasis on minimal noise, common-mode rejection and low phase errors. The input section uses paralleled instrumentation amplifiers with a bandwidth of 20 MHz, noise density below -160 dBV/√Hz and common-mode rejection above 105 dB. As a result, the unit can correctly handle even very low-level signals without the input stage itself injecting noise into the signal path.

Volume control is handled by a relay-switched network of high-precision metal-foil resistors with 80 steps of 1 dB, with each channel having its own resistor network, and the system also allows balance adjustment. During the level change itself a secondary control path based on integrated circuits is activated, eliminating clicks and voltage spikes; once the value has settled, the signal returns to the sonically superior resistive branch. The optional phono preamplifier with an instrumentation amplifier offers adjustable gain from +40 to +80 dB at 1 kHz and loading options from 20 Ω to 1 kΩ, 47 kΩ and 0 to 70 pF, allowing precise matching with both MC and MM cartridges. Fast gain stages (-3 dB at 2 MHz) contribute to accurate RIAA curve tracking in both the frequency and phase domains.

The output section operates in class A and is optimised for speed, accuracy and high peak currents. The low output impedance (0.8 Ω balanced, 0.4 Ω unbalanced) allows trouble-free driving of even long interconnect cables. A bandwidth of 20 MHz (-3 dB) and phase shift below 0.2° at 20 kHz translate into stable localisation of instruments, legibility of fine detail and a spatially three-dimensional presentation without temporal smearing. A signal-to-noise ratio above 120 dB, THD+N below -120 dB and channel separation above 130 dB meet the demands of the reference category.

The power supply is implemented as dual mono with distributed local regulators. A switch-mode power supply (SMPS) converts the mains voltage into an intermediate DC voltage, from which highly efficient DC-DC converters and exceptionally quiet fast linear regulators generate the operating voltages. Linear regulators placed directly at each current consumer (op-amp, transistor) shorten both the signal and supply paths and reduce noise on the analogue branches, eliminating the need for the bulky filter capacitors typical of classic transformer-based supplies. The unit offers three balanced XLR inputs, two RCA inputs and an optional phono input, with 2× XLR and 1× RCA outputs; weight reaches 28 kg.

Key features

• Input stage: Paralleled instrumentation amplifiers, CMRR above 105 dB
• Volume: Relay-switched metal-foil network, 80 steps of 1 dB
• Output: Class A, output impedance 0.8 Ω XLR
• Power supply: Dual mono SMPS with local linear regulators
• Phono (optional): Gain +40 to +80 dB, adjustable loading