Harley Benton GPA-400 User Manual page 16

Connections and operating elements
8 [MUTE]
Switch to mute the device. The white indicator LED lights up when the unit is muted.
9 [PEAK]
Indicator LED (red). This LED lights up when Channel B is overloaded by an excessive input signal.
10 [SIGNAL]
Indicator LED (green). This LED lights up when the device is turned on and a signal is present in channel B.
11 [VOLUME]
Volume control for channel B.
12 [RESONANCE]
Resonance control for channel B.
13 [PRESENCE]
Presence control for channel B.
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stereo guitar power amp