Operating Manual

Fredenstein HD Reference Preamplifier
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, non-reversed, polarity is selected (normal operation).
Low Z 1K – Low Input Impedance:
When lit (green), the input impedance changes from 200 kOhms to 1000 Ohms. Some dynamic-
and ribbon-microphones are most linear driving a low input impedance.
Low Z 300 – Low Input Impedance:
When lit (green), the input impedance changes from 200 kOhms 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 39Hz:
A 39 Hz low cut filter is activated when lit, avoiding unwanted low frequencies while tracking.
Low Cut 82Hz:
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 MOhms to insure compatibility with most
instrument pickups. After inserting a balanced (Tip-Ring-Sleeve) or an unbalanced (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 in the DI
pre-amplifier and lights up a LED at the bottom right of the Gain Display. If a Commander is used it
will also use that LED to display that the DI is plugged in
There is also an indicator called LOCK STATUS, which lights up if the LOCK button is pushed on
the 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.
Fredenstein HD Reference Manual V1.0 Feb 5, 2016 Page 9