Fredenstein HD Reference 2-Channel Microphone Preamplifier

The preamplifier provides extremely low noise and low distortion with an ultrawide frequency response (1 Hz to 920 kHz, -3 dB) at all gain settings. The preamp sports a combination of high-end specifications to provide a smooth transition into saturation. This is due to the absence of negative feedback and the fast recovery inherent in the topology, which allows the sound to go from pristine and three-dimensional through rich and powerful depending on how hard one drives it.

Each channel features a combination rotary encoder that doubles as a push-button mute and gain control with 1 dB stepped operation from 0 to +64 dB (using highly reliable relays). A large 7-segment LED display indicates signal levels and clipping. There are three impedance settings, three high-pass filter frequencies, 48V phantom power, and a polarity switch.

Other notable features include automatic muting when changing phantom power settings to prevent damage to your monitors, and a pair of high-quality Direct Inputs (DI) for use with instruments.

The HD Reference is compatible with the separately sold Commander remote, which allows you to keep the preamp close to the microphone, while being able to make adjustments in the control room. By keeping the mic cables short, the preamp is able to preserve the fragile mic-level signals without degradation or noise and send a robust line-level signal to any reasonably distanced converter, console, or compressor. There is a Lock button, which prevents the HD Reference settings from changing when using the Commander remote.

Controls

Gain Control

Rotary Encoder sets the Gain in 1 dB steps which are displayed next to the knob. Pushing the Knob activates an immediate MUTE. This control as with all others can be remote controlled.

POL Polarity Control

Pushing the POL switch selects the polarity. When lit (blue), the output polarity is reversed. Otherwise the true nonreversed, polarity is selected (normal operation).

Low-Z: 1-Kilohm Low-Impedance Input

When lit (green), the input impedance changes from 200 kilohms to 1000 ohms. Some dynamic and ribbon microphones are most linear when driving a low-input impedance.

Low-Z: 300-Ohm Low-Impedance Input

When lit (green), the input impedance changes from 200 kilohms to 300 ohms.

P48 Phantom Power

Most FET condenser microphones as well as some other microphones with built-in amplifiers require +48V Phantom Power. Setting the P48 switch (red light) enables +48V through the balanced microphone line. Please check your microphone documentation if you are not 100% sure. Enabling P48 on microphones not designed for P48 might cause severe damage to the microphone. The DI input is not supplied with Phantom Power.

Low Cut Filters

Low-Cut 39 Hz: A 39 Hz low-cut filter is activated when lit, avoiding unwanted low frequencies while tracking.

Low-Cut 82 Hz: A 82 Hz low-cut filter is activated when lit, avoiding unwanted low frequencies while tracking.

DI, Direct Input

The most common use for the DI input is to connect instruments like guitars directly to the HD Reference. The input impedance is greater than 2 megohms to insure compatibility with most instrument pickups. After inserting a balanced (TRS, tip-ring-sleeve) or an unbalanced (TS, tip-sleeve) plug, the balanced microphone input through the box or rack is automatically disabled.

The gain range for the DI is from 0 to +40. Turning the Gain knob past +40 will have no effect. When a 1/4 plug is inserted into the DI jack, the HD Reference automatically switches on the DI preamplifier and lights up a LED at the bottom right of the Gain display. If a separately available Commander is used, it will also use that LED to display that the DI is plugged in.

Lock Status

There is also an indicator called Lock Status, which lights up if the Lock button is pushed on the separately available Commander. If this is lit, all controls on the HD Reference are frozen and can only be controlled from the Commander. This is to prevent tampering.