Integrated Amplifier Soulution 331 Integrated Amplifier

Integrated amplifier with separate preamplifier and power amplifier circuits and an optional phono and D/A module

The Soulution 331 is an integrated amplifier that avoids the usual approach in which volume control, input selection and amplification are merged into a single multi-purpose circuit. Instead, it combines a separate preamplifier and a separate power amplifier in one chassis, complemented by a phono stage and a D/A converter as optional modules. The power section delivers 100 W into 8 Ω, 200 W into 4 Ω and, for short periods, 400 W into 2 Ω with a maximum current of 30 A.

Power is supplied by four switch-mode power supply modules with a continuous output of 1,200 VA for the power stage and a peak capability of up to 4,200 VA for more than 5 seconds. The modules use filtering on both the input and the output side along with fast Soulution voltage regulators, which keep the supply voltage more stable than conventional designs with a classic transformer. The amplification section is derived from Series 5 technology, with current amplification taking place in three stages, each operating within a narrow, almost perfectly linear range.

Volume is handled by an 80-step attenuator (1 dB) with relay-switched high-precision metal-foil resistors. During the actual level change a secondary path with an integrated circuit is activated to eliminate clicks and voltage spikes; once the setting is made, the signal returns to the sonically superior resistor path. The preamplifier's bandwidth exceeds 2 MHz (-3 dB), which drastically reduces phase shift in the audible band — at 20 kHz it is less than -3°. Combined with THD below 0.0005 %, noise below -140 dBV/√Hz and a damping factor above 5,000, this contributes to precise imaging of instruments, readability of detail and control of the bass range.

The optional phono stage with two-stage active-passive RIAA equalisation uses close-tolerance passive components for accurate time constants and provides 60 dB of gain in three wide-bandwidth, low-noise stages. The termination impedance, adjustable from 20 to 1260 Ω, can be set by remote control or from the front panel to suit the MC cartridge in use. The optional D/A converter with four digital inputs (SPDIF, AES/EBU, Network, USB) converts the incoming signal to DXD format via a DSP processor, applying zeroPhase processing and LEEDH volume control; conversion is handled by a PCM1792 in mono configuration per channel with the internal digital filter bypassed and a passive reconstruction filter built from precision custom components.

Key features

• Separate circuits: Independent preamplifier and power amplifier in one chassis
• Power supply: Four switch-mode modules, 1,200 VA continuous, 4,200 VA peak
• Volume control: 80 steps of 1 dB with metal-foil resistors
• Bandwidth: 0 – 800 kHz, phase shift at 20 kHz below -3°
• Optional modules: RIAA phono stage and DAC with PCM1792 per channel