H2 Audio 2128 Helios 500 Series Microphone Preamp

The classic Helios 2128 microphone preamp circuit takes on a compact, modular form in the H2 Audio 2128 Helios 500 Series microphone preamp. Derived from the mic preamp section of H2 Audio's flagship 0011, the 2128 provides 25–75dB of stepped gain in precise 5dB increments, with a custom input transformer and transformer-balanced output stage forming the foundation of its analog signal path. A -20dB pad accommodates higher-level sources, while 48V phantom power, phase inversion and a selectable high-pass filter provide essential control during tracking. An output amplifier with transformer output and dedicated level control adds further gain-staging flexibility. Together, these features give engineers a versatile analog front end for capturing vocals, drums, guitars, bass and other studio sources within a standard single-slot 500 Series format.

Classic 2128 Preamp Architecture in 500 Series Format

The 2128 adapts the microphone preamp circuit from H2 Audio's recreation of the Helios 0011 channel module for modern 500 Series systems. Its stepped gain control spans 25–75dB in 5dB increments, giving engineers repeatable settings across a wide range of microphones and recording levels. A custom input transformer works alongside an output amplifier and transformer-balanced output to preserve the transformered signal path central to the design. The dedicated output level control provides up to +10dB of additional adjustment, allowing the input and output stages to be balanced independently when setting recording levels or exploring different gain structures.

Essential Controls Adapt the Preamp to the Source

A focused set of onboard controls makes the 2128 practical across varied recording sessions. The -20dB pad accommodates higher-level sources, while 48V phantom power supports compatible condenser microphones and phase inversion helps address polarity relationships in multi-mic setups. The selectable high-pass filter provides 0Hz, 40Hz and 80Hz settings, allowing unwanted low-frequency content to be controlled at the preamp before it reaches later stages of the signal chain. Gold-plated audio toggle switches, ELMA gold-plated rotary switches and sealed conductive-plastic pots complement the circuit in a single-slot module designed for integration into compatible 500 Series racks.

Helios-Inspired Analog Gain for Modern Recording Rigs

With stepped input gain, independent output control and practical tools for managing level, polarity and low-frequency content, the 2128 provides a focused analog front end for both project and professional studios. Its single-slot format makes it easy to integrate alongside other 500 Series processors, while the transformer-based input and output stages carry the architecture of H2 Audio's 0011 preamp into a more flexible modular system. Hand-assembled in Detroit, the H2 Audio 2128 Helios 500 Series microphone preamp combines classic Helios-inspired circuitry with the controls and format needed for modern recording workflows.