3
Operational Notes
Transformers
The FP23 uses input and output transformers with premium
magnetic core material to achieve high signal handling capability,
especially at low frequencies. This keeps distortion to a minimum.
Transformers offer superior isolation from the adverse and un-
controlled environments of field production. Unlike other balancing
techniques, transformers “transform” signals magnetically without
any direct electrical connection, providing complete galvanic isola-
tion from the driving source. And their inherently high common
mode impedance provides exceptional common-mode noise re-
jection.
Balanced and Unbalanced Connections
Both the input and output of the FP23 accept balanced or unbal-
anced connections. You can convert either the input or output to un-
balanced operation by grounding pin 3 to pin 1. No change in gain
will occur.
Phantom Power
Use one of the two phantom power settings on the FP23 for mi-
crophones that require it. Some microphones need the 48-volt set-
ting, or they will suffer a loss of headroom and an increase in distor-
tion. The 12-volt setting, however, lengthens battery life, and
electret-condenser microphones rated for operation at 12 V or less
generally receive no performance benefit from the 48-volt setting.
Consult your microphone documentation.
Dynamic microphones do not require phantom power. A properly
connected balanced, dynamic microphone is not affected by the
presence of phantom power and does not draw any current. How-
ever, poorly or incorrectly wired microphone cable can cause audi-
ble artifacts in the microphone signal (phantom power can be an
excellent cable tester). It is good practice to turn phantom power off
when not needed.
High Pass Filter
Use either of the two high pass (low cut) filter settings on the
FP23 to remove excess low frequency energy in the audio signal.
Use the 80 Hz position for most applications, such as recording
speech, music, and ambient sound. The 160 Hz position is useful
for enhancing speech clarity. The high pass filter is a single pole de-
sign, 6 dB per octave.
When possible, equalize at the sound source with microphone
selection, placement, use of a windscreen, and onboard micro-
phone filtering. A high pass filter on the microphone and a high pass
filter on the FP23 gives an additive effect, increasing the slope of
the filter.
Limiter
The limiter switch on the front panel activates two peak-
responding limiters within the FP23. The first acts on the input sig-
nal, while the second one limits the output to +17 dBu. This enables
the FP23 to limit in excess of 50 dB, making it very difficult to clip
the unit, regardless of the gain setting. The limiter LED on the front
panel illuminates in proportion to the amount of limiting.
Batteries
Two AA alkaline cells can power the FP23 for approximately 26
hours (with typical signals, phantom power OFF). The audio perfor-
mance of the FP23 does not vary throughout the life of the batter-
ies.
Many factors affect battery life, including battery chemistry, am-
bient temperature of operation, phantom voltage, microphone cur-
rent draw, and output drive level. Use the chart below to estimate
battery life. Experimentation can help determine the battery life for
each individual setup.
NOTE: Nickel-Cadmium batteries are not recommended. These
batteries have lower energy per cell than other types and result in
very short service.
Battery
Type
Microphone
Type
Battery
Life
Duracell AA
MN 1500
Dynamic handheld
26 hrs.
Duracell AA
MN 1500
Electret condenser,
12-volt phantom
18 hrs.
Duracell AA
MN 1500
Studio condenser, 48-volt
phantom
5 hrs.
(Test conditions: 70 degrees F, 42 dB of gain with an acoustic
music source, 600
Ω
load, +4 dBu output)
