Shure FP23 Operational Notes, Transformers, Balanced and Unbalanced Connections, Batteries

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 ªtransformº 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	Microphone	Battery
Type	Type	Life
Duracell AA	Dynamic handheld	26 hrs.
MN 1500
Duracell AA	Electret condenser,	18 hrs.
MN 1500	12-volt phantom
Duracell AA	Studio condenser, 48-volt	5 hrs.
MN 1500	phantom

(Test conditions: 70 degrees F, 42 dB of gain with an acoustic

music source, 600 Ω load, +4 dBu output)

3