Preamplifiers — Octave Audio Phono Module

The Phono Module is a modular hybrid phono preamplifier from Octave Audio that combines solid-state input circuits with a valve equalisation stage. It builds on over thirty years of Octave valve preamplifier design and is aimed at serious vinyl listeners who need flexibility, including owners of more than one turntable.

Key specs that matter

RIAA equalisation is accurate to within plus or minus 0.2dB from 10Hz to 50kHz. Channel separation is better than -60dB at 1kHz on the phono inputs and -80dB on the line inputs. The subsonic filter starts at 15Hz (-3dB) with a slope of -12dB per octave. Up to three input modules can be installed and used simultaneously. The single-ended MM module offers 1k or 47k ohm input impedance. The unbalanced MC module has impedance switchable from 50 ohms to 1k ohm and two gain steps, and the balanced MC module adds XLR inputs with the same impedance and gain settings.

Engineering and use context

Instead of a step-up transformer, the MC input uses an electronic gain stage. Octave avoids transformers here because they pick up magnetic stray fields and limit load impedance and gain. The RIAA stage is taken directly from the HP 500 SE preamplifier and uses three valves to provide the gain that accurate equalisation needs. According to Octave, pairing a solid-state MC input with a valve RIAA stage gives the Phono Module cleaner spectral performance and a better signal-to-noise ratio than a conventional all-valve design. Power comes from a separate, magnetically shielded outboard supply with high-precision, low-noise voltage regulation, which holds the output steady even when the mains voltage swings widely. The plain casework hides a heavily built interior.

Pairing

With all three modules fitted, an MM cartridge, an unbalanced MC cartridge and a balanced MC cartridge can stay connected at once. That covers several turntables or tonearms without swapping cables, and the unit can grow with a system over the years.

Alternatives

The Octave Phono EQ.2 is a simpler single-chassis phono stage with adjustable gain steps and selectable impedance, suited to a system with one turntable.