Setting the gain on the amplifier
• Gain setting is done for one channel at a time, so disconnect the other channel inputs and speaker connections during this.
• Turn off the Equalizer, crossover settings, bass boost on the HU. Turn up the volume till 3/4 th of the upper limit.
• On the amplifier, turn the gain screw anticlockwise fully, make the crossover filter settings to OFF/ FLAT. Turn off the bass boost.
We will start with the subwoofer bridged channel. Disconnect the RCA input cables from the front input(ONLY) and all speaker wires from the amplifier.
• Now Set the multimeter to 'AC Voltage' mode and ‘200V’ range. (IMPORTANT: NOT DC Voltage, otherwise it may damage the multimeter)
• Connect the red probe of the multimeter to the + terminal of the bridged channel and the black probe to the - terminal of the speaker connectors.
• Insert the 50Hz sound CD/ USB and play the sound file. Make sure the HU volume is turned up 3/4th or more.
• Now observe the reading in the Multimeter screen. The amplifier will have pots for adjusting the gain/ input level. Adjust the pot by turning it clockwise gradually with a screw driver till it reaches the 28.29V level. (As calculated above. May be different in your case).
• Repeat the procedure for front channel and play the 1 KHz sound file. Disconnect the RCA input cables from the rear/sub input (ONLY) and leave speaker wires as disconnected as before. Adjust the pot till 16.74 in front channels. Check the Voltage reading in both FR, FL channels.
Now put the RCA and speaker connections back. Set the Equalizer, crossover, bass boost on the HU and crossover, bass boost settings on the amplifier as it sound sweeter to your ears. Now We are good to go, enjoy your favourite music.
The HU used here is Sony XAV62 (3V preout) and 4Ώ JBL subwoofer and component speakers connected to the JBL GT X646 amplifier.