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Connecting a Signal to the SP™4P
There are a variety of ways to input a signal to the SP®4P.
The inputs (5) provides either a balanced mic- or line-level input, allowing the use of a 1/4" TRS (ring-tip-sleeve)
type phone plug or a male XLR plug.
There is also a 3.5 mm MEDIA IN jack on the Channel 2 input.
The 3.5mm TRS input jack has its own preamp designed for connection to the headphone jack on mobile audio
devices. The Channel 2 Gain control adjusts the signal level from all of the channel 2 input connectors. It is pos-
sible to use both the combo mic or line input and the 3.5mm input by setting the channel 2 Gain control for the
combo input source, and then using the mobile devices headphone volume to adjust its volume.
Note that the 3.5 mm jack mixes a stereo signal down to monophonic, as the SP®4P is a single sound source.
Do not connect cables to the jacks while the unit is ON and the Gain knob is turned up! While a standard
single-ended 1/4" phone plug-equipped cable will work well and the balanced input circuitry will provide some
interference rejection, a balanced cable using either the balanced TRS 1/4" phone plug or the XLR plug will pro-
vide superior interference rejection and performance.
Sometimes, with difficult interference problems, it will be helpful to lift the shield ground ( Pin #1 of an XLR)
of a balanced cable at the SP®4P end. Check any input changes carefully, always turning the Gain control down
before plugging and unplugging cables, or lifting the ground.
Use of high quality, premium cables is recommended for the SP®4P, as these usually have better shielding and
materials and will provide greater long-term reliability. The best option is a shielded balanced cable no longer
than necessary to reach the SP®4P. It is usually a good idea to leave some slack at the input to the SP®4P and
also to tape the cables down or run them under a cable guard to avoid anyone tripping over them or pulling the
SP®4P over when stand mounted.
Gain Control Adjustment
The SP®4P is equipped with Gain controls (6) on the input to facilitate use in many different applications. With
the Gain control adjusted fully clockwise, gain is at maximum and the input sensitivity is 0.42 V RMS for
full-rated output with the line level position of the Mic/Line switch (7). When driving the SP®4P from a mixer, it
may be advantageous to reduce the input sensitivity by turning the Gain control to the halfway point. The SP®4P
will now more closely match a typical power amp.
If the mixing board indicates clipping of its output signals, then all of the SP®4P power capability is not being
utilized cleanly. Clipping the signal before it gets to the SP®4P is not optimal. Reduce the mixer
output level and turn up the Gain control/s on the SP®4P.
The amplifiers in the SP®4P are equipped with DDT™ and there is an indication on the rear panel LCD display
(12) that reads "DDT" whenever the DDT system engages.
If the sound seems heavily compressed, check this indicator; if it is blinking more than occasionally, then the
drive level from the mixer (or the Gain control on the SP™4P) needs to be reduced.
When first turning on the sound system, switch on all upstream electronics first, then the SP®4P with its Gain
control fully counterclockwise (all the way down). Begin checking levels with the mixer output level controls all
the way down, and bring them up slowly with the SP®4P Gain control/s set to the desired setting (one-third way
up recommended to start).
It is not good practice to turn the Gain control/s on the SP®4P all the way up and then try to control level only
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