Line Inputs / Hi-Z Input (Channel 1 Only); Stereo Line Inputs; U" Like Unity Gain; Gain - Mackie ProFX4 V2 Owner's Manual

5. Line Inputs / Hi-Z Input (Channel 1 Only)

In addition to accepting balanced mic or line-level
signals using an XLR connector, ProFX4v2 mixers
may also accept 1/4" line-level signals driven by
balanced or unbalanced sources. These 1/4" jacks
share circuitry (but not phantom power) with the
mic preamps.
To connect balanced lines to these inputs, use
a 1/4" Tip-Ring-Sleeve (TRS) plug. "TRS" stands for
Tip-Ring-Sleeve, the three connection points available
on a stereo 1/4" or balanced phone jack or plug.
TRS jacks and plugs are used for balanced signals and
stereo headphones and are wired as follows according
to standards specified by the AES (Audio Engineering
Society):
1/4" TRS Balanced Mono Wiring:
Sleeve = Shield (ground)
Tip = Positive (+ or hot)
Ring = Negative (– or cold)
To connect an unbalanced line to this input, use
a 1⁄4" mono (TS) phone plug or instrument cable.
They are wired as follows, according to standards
specified by the AES (Audio Engineering Society):
1/4" TS Unbalanced Mono Wiring:
Sleeve = Shield (ground)
Tip = Positive (+ or hot)
The channel 1 line-level input may also accept
instrument-level signals if the hi-z switch is
engaged. This allows you to connect guitars
directly into channel 1 without the need for a DI box.
RING SLEEVE SLEEVE RING TIP
TIP
RING
TIP
SLEEVE
SLEEVE SLEEVE TIP
TIP
TIP
SLEEVE

6. Stereo Line Inputs

The stereo line inputs are designed for 1/4" TRS
balanced or 1/4" TS unbalanced signals. They may
accept any line-level instrument, effects device, CD
player, etc.
If you are connecting a mono source, use the left
(mono) input, and the mono signals will appear
on both sides of the main mix.

"U" like Unity gain

ProFX4v2 mixers have a "U" symbol on almost every
level control. It stands for "unity gain," meaning no
change in signal level. The labels on the controls
are measured in decibels (dB), so you'll know what
you're doing level-wise if you choose to change a
control's settings.

7. Gain

If you haven't already, please read the "Getting
Started" section on page 4. Setting the gain correctly
will ensure that the preamplifier's gain is not too high,
where distortion could occur, and not too low, where
the quieter, exquisitely-delicate passages might be lost
in background noise.
The gain knobs adjust the input sensitivity of the mic
and line inputs. This allows signals from the outside
world to be adjusted to run through each channel at
optimal internal operating levels.
For mono channels (mic input with
a mono line input), the gain knob
adjusts the input sensitivity of the
mic and line inputs.
If the signal originates through the mic XLR jack,
there will be 0 dB of gain with the knob fully down,
ramping to 50 dB of gain fully up.
Through the 1⁄4" mono line inputs, there is 20 dB of
attenuation fully down and 30 dB of gain fully up, with
unity gain "U" at 12:00.
This 20 dB of attenuation can be very handy when you
are inserting a hot signal, or when you want to add EQ
gain, or both. Without this "virtual pad," there is more
chance of channel clipping.
For stereo channels (no mic input)
the gain control just affects the line-level
inputs, with 20 dB of gain, and 20 dB
of attenuation.
Owner's Manual
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