User's Manual

Fredenstein HD Microphone Preamplifier
Volts per microsecond.
Figure 2: 106 kHz square wave response
The input impedance of the HD Pre is standard 200 kOhms and can be reduced to 1 KOhm by
activating the LOW-Z function. This high input impedance avoids loading the microphone output
transformers and yields in most cases sonically superior result. In any case, the engineer can switch
between the two settings to find the desired result without any fear of damaging the microphone.
But the HD also performs excellent in more traditional amplifier tests:
Unfortunately, standard audio test equipment is unable to cover the complete range of the HD Pre.
Above is the frequency response of the HD: 20Hz to 20kHz within 0.1 dB, -3dB at 7Hz and 900
kHz.
Fredenstein HD Pre Manual V1.1 May 6, 2015 Page 2