Calibration
Meter Zero Adjust
The zero-adjust of the meter is set by the screw-adjust potentiometer located next to the Limit / Compress Switch. To adjust this, put the meter into Gain Reduction mode. Make sure that there is no signal present. Loosen the locking nut and use a screwdriver to adjust this potentiometer until the meter reads zero.
Side-Chain Pre-Emphasis (R37)
The LA-2A was designed for use in broadcast applications. The audio signal in FM broadcasting undergoes pre-emphasis and results in a 17 dB boost at 15 KHz. Due to this increase in signal level, transmitters are subject to over-modulation. The LA-2A provides a control (R37) which controls the amount of high-frequency compression.
This potentiometer is factory set for a “flat” side-chain response (clockwise). Increasing the resistance of this potentiometer by turning it counter clockwise will result in compression which is increasingly more sensitive to the higher frequencies.
Stereo Balance Adjust (R3)
For stereo operation, two LA-2A units are interconnected in order to achieve the same amount of gain reduction from each of the two units to maintain stereo imaging. In order to accomplish this, terminals 6 from each unit should be connected together. Additionally, their grounds (terminal 7) should be connected together.
The interconnecting wire should be less than 2 feet in length and should be shielded. The shield should be used to connect terminals 7 from each of the units together.
To calibrate the units for stereo operation:
!Connect the units together as described previously.
!Turn the Peak Reduction knob counterclockwise (no compression).
!Set R3 on each unit to a clockwise position.
!Set each meter to read Gain Reduction.
!Adjust the Peak Reduction control on the left channel until approximately 5dB of gain reduction is achieved.
!Adjust R3 on the unit that shows the greatest amount of gain reduction until the gain reduction indications are equal.
!When operating, set the Peak Reduction controls to the same setting on both channels.
