Description
This microphone preamplifier is housed in a 1U rack mount chassis. It is a two channel mic
preamp with individual controls for each channel.
Front panel controls include; Mute switch (mutes output), polarity reverse switch (relay),
phantom power, 24 position rotary gain switch, and dual color LED signal level indicator (green
@ -5 dBu, Red @ +22 dBu).
There are two inputs per channel. One has +48 volt phantom power supplied to it (when
phantom power is switched on) and its signal passes through very high quality capacitors to
block the phantom power DC voltage from the input stage of the preamplifier. The other input is
connected directly to the input of the preamplifier, bypassing the phantom power blocking
capacitors. You can use this “direct coupled” input when you are using microphone that do not
require phantom power, such as vacuum tube mics, ribbon mics, and dynamic mics. You can
only use of these inputs at a time. Do not connect the unused input to anything cable of
microphone. The connector in the middle is the Direct Input. Input and Output connectors are
XLR-3 wired pin #2 hot.
The front panel mounted bicolor LED will light green when an output signal level of –5 dBu or
greater is present, and this LED will turn red when the output signal level reaches +22 dBu. This
is approximately 2-3 dB before output clipping on the 2 channel preamp.
Circuit description
Class A discrete JFET front-end coupled to three discrete JFET opamps. No IC opamps are used
in the direct signal path, but an IC opamp is used as a servo amp (DC offset control) on output.
The signal path is entirely DC coupled except for the phantom powered inputs. +48 VDC full
current phantom power supply. +/-22 VDC power supply rails.
Contact Information:
Forssell Technologies Inc
235 Wild Horse Trail
Sandpoint, Idaho 83864 USA
208-263-0286
www.forsselltech.com
