Phono Preamplifier Soulution 757 Deemphasis Preamplifier

Reference de-emphasis preamplifier for analogue sources with equalisation curve accuracy of ±0.05 dB

The Soulution 757 is a reference de-emphasis preamplifier designed for connecting all analogue sources — from MM and MC magnetic cartridges through tape heads to DS Audio optical cartridges. The input stage is built around paralleled instrumentation amplifiers with a bandwidth of 2 MHz, noise density below -170 dBV/√Hz and common-mode rejection in excess of 100 dB, so that even the faintest cartridge signals enter the signal path without added noise. Adjustable loading impedance allows precise matching to a specific magnetic system: 10 Ω – 1000 Ω for MC, 47 kΩ with capacitance of 0 – 750 pF for MM.

When the input is configured for a tape head, a tape head calibration network is activated, compensating for roll-offs in the transfer characteristic caused by head imperfections. A separate input is dedicated to DS Audio optical cartridges and works with a wideband transimpedance amplifier optimised for converting the current output signal. Gain control uses high-speed, extremely low-noise operational amplifiers and relay-switched precision metal foil resistors in 80 steps of 1 dB, with each channel having its own unit, which also allows balance adjustment. During a gain change, a secondary IC-based path is temporarily activated to eliminate clicks and voltage spikes; once settled, the signal returns to the sonically superior main branch.

The unit offers a wide choice of equalisation curves — for vinyl RIAA, DECCA, COLUMBIA, LONDON, TELDEC and NARTB, for tape IEC2-30ips, IEC1-15ips, IEC1-7.5ips and NAB-15ips. Extremely fast gain stages guarantee reproduction of the selected equalisation with an accuracy of ±0.05 dB from 20 Hz to 200 kHz. The Class A output stage is optimised for speed, accuracy and high peak currents; an output impedance of 0.8 Ω balanced and 0.4 Ω single-ended drives even long interconnects without difficulty. A bandwidth of 20 MHz (-3 dB) and the resulting minimal phase shift in the audible band translate into stable localisation of instruments, three-dimensional spatial imaging and natural tonal colours.

Power is handled by the Distributed Local Power Supply concept in a dual-mono layout. A switched-mode supply converts the mains voltage into an intermediate DC voltage, which is then processed by highly efficient DC-DC converters and fast linear regulators with extremely low noise. Local linear regulators placed directly at every current draw — op-amp or transistor — shorten both signal and supply paths and keep noise on the analogue branches to a minimum, without the need for the large filter capacitors typical of classic transformer-based supplies. Harmonic distortion is unmeasurable and channel separation exceeds 100 dB.

Key features

• Inputs: 2× MC, MM or tape head, 1× DS Audio optical
• De-emphasis accuracy: ±0.05 dB from 20 Hz – 200 kHz
• Gain control: 80 steps of 1 dB, metal foil resistors
• Output stage: Class A, 20 MHz bandwidth
• Power supply: Dual mono with local linear regulators