9762A
– Preamplifier
Owner’s Manual
Page 12
RTZ Professional Audio
6.3
Polarity and Impedance Selection
The POL polarity switch inverts the polarity (or phase) of the line output
transformer. When the POL switch is depressed a relay inverts the line
output transformer polarity. In most situations the polarity will be used in
normal phase with the POL switch in the non-depressed state.
Low impedance microphone operation is enabled when the LO-Z
impedance switch is in the depressed state. In most cases low
impedance is desired for 50-Ohm impedance microphones. Most modern
micro
phones expect a bridging load and the 9762’s input circuitry
accommodates this when the impedance switch is OUT.
Experiment with the LO-Z feature using a variety of microphones to
obtain the best sound and tonal qualities. Note that the signal level is
affected by roughly 5-6 dB when switching ratios. Adjust the GAIN switch
to compensate for the level change and to avoid masking tonal changes
as compared to the signal level change.
6.4
Using 48V Phantom Power
Notice the 48V LED gradually lights or dims when power is applied or
removed. Special ramping circuitry ramps the voltage up and down when
power is applied or removed to reduce large pops or bangs in the signal
output. Allow a second or two for the phantom power to reach full voltage
when enabled.
The phantom circuitry is protected against shorts for extended durations
and provides up to
14 mA of current for each channel. However, you
should
always ensure the microphone or other phantom powered device
is working properly when using phantom power. Improper use of
phantom power may damage some microphones or other devices
connected to the microphone input that are not intended for use in the
presence of phantom power
.
6.5
Line Output Transformer Termination
Jumper JP1 (see the Hardware Configuration Features section) on the
lower PCB is used to enable or select the termination resistor on the line
output transformer secondaries. In most situations termination should be
enabled to assure the flattest frequency response. However, you may
also disable termination to affect the sound in different ways depending
on the source impedance. In many cases removing termination adds a
slight amount of “air” to the signal due to the gentle HF rise property of
the output
transformer when operating un-terminated.
