The Fredenstein HD Reference microphone preamplifier introduces a completely new approach to microphone level amplification. While many engineers now track at 96 kHz or 192 kHz sampling rates, much of the equipment in use cannot provide the extended frequency response or bandwidth needed to match the capabilities of modern A/D converters. The Fredenstein HD Reference overcomes these limitations, delivering a new level of sonic quality. On wider bandwidth sources such as acoustic instruments, voices and drums, the HD Reference is unmatched and has become a preferred choice for classical recordings.
The Fredenstein HD Reference was preceded by the HD Pre, designed for 500 Series racks. Although the HD Pre set new benchmarks for performance, that format imposed limits on voltage, current and physical space. The HD Reference surpasses it by utilising higher voltage power supplies at ±24 V instead of ±16 V, greater current delivery, and more discrete transistors, increasing from 54 in the HD Pre to 64 in the HD Reference.
A key advancement is the addition of the Commander remote control, which provides access to all functions normally found on the front panel. The HD Reference and Commander connect via a standard XLR cable that can also be routed through a patch bay if required. With bandwidth reaching 920 kHz, it makes sense to place the HD Reference close to the microphones and use short mic cables, preserving signal integrity before sending a robust line level signal over longer distances to consoles or converters.
Practical improvements include a display showing gain in dB next to the control knob, allowing precise gain adjustments in 1 dB steps, which is particularly valuable for stereo setups. Additional choices have also been added for the high pass filter (Off, 39 Hz, 82 Hz) and input impedance (200 kΩ, 1 kΩ, 300 Ω, 232 Ω). Sonically, the HD Reference is fast, clean and faithful to the source, with extremely low noise. Importantly, it maintains its performance at any gain setting without negative feedback, a rare achievement.
The preamplifier features a fully discrete signal path and a Class A balanced output stage. Its revolutionary current amplification circuit neutralises internal transistor capacitance (Miller Effect), which traditionally limits frequency response and slew rate in voltage amplifiers. As a result, the Fredenstein HD Reference achieves unprecedented bandwidth of more than 900 kHz. To support this design, the HD Reference includes moderate sized heat sinks more commonly seen in small power amplifiers, as the true Class A output stage operates on 48 V, driving +29 dBm (60 volts peak to peak) and generating significant idle current. This ensures strong current delivery and effortless long cable driving capability.
Unlike many preamplifiers, the Fredenstein HD Reference does not use input or output transformers, as these would restrict its performance. By comparison, other Fredenstein models such as the F601A, F609, F676, F200, V.A.S and Artistic Mic Pre include transformers and are designed for specific tonal applications where they excel, often competing with respected vintage units.
Features
- Dual-channel mic preamp with fully discrete true Class A, zero-negative-feedback design
- Current mode topology using 64 discrete transistors and ± 24-V rails
- Stepped gain control in 1 dB increments from 0 dB to + 64 dB via LED encoder
- Selectable high-pass filters: Off, 39 Hz, 82 Hz
- Selectable input impedance: 200 kΩ, 1 kΩ, 300 Ω
- +48 V phantom power and polarity reverse switch
- Automatic muting during phantom power switching
- Dual direct input (DI) with low-noise JFET, 2 MΩ impedance, 0–40 dB gain
- Commander remote control with full feature access and lock function