Hafler TRM10S, TRM12S manual Qualified Service Personnel Only, Circuit Calibration, Bias

CIRCUIT CALIBRATION

Bias:

!Qualified Service Personnel Only

The bias control establishes the quiescent Class AB output current of the amplifier. The bias should not need readjustment from the factory setting: however, if the amplifier is repaired and the output devices have been changed, calibrating the bias is necessary. Disconnect the power to the amplifier before removing the heatsink assembly from the speaker cabinet. To adjust the bias, remove the jumper TP1 and connect an ammeter across the exposed pins. Adjust trimpot R9 fully counter-clockwise before reapplying power to the unit. After the Soft Start turn-on has settled, note the ammeter reading. Adjust R9 until an additional 50mA is added to the ammeter reading. Replace jumper TP1. If the green power LED is not illuminated, apply a low frequency input signal to the amplifier input to activate the signal sensing turn on circuit. Be sure to remove the signal before adjusting the bias.

WARNING: Only a competent technician should attempt the above procedure.

– 20 –