Vega C-6124, Техническое руководство

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53 Vega’s C-
6124
6.4.2.1 RECEIVE INPUT LEVEL
RV1 adjusts the gain of the input amp directly off the line. RV1 offers a gain range of +13db to –50db. The
resulting audio from this amp stage is fed into the LAM circuit and the Automatic Level Control (ALC)
circuit.
6.4.2.2 AUTOMATIC LEVEL CONTROL (ALC)
The receive side audio path has an ALC circuit. The knee of compression is set by adjusting RV5 and
measuring at TP4. The maximum output of the ALC circuit is set at 0.775V. When the signal at TP4 is
around 0.775V the circuit is in compression. The knee of compression starts at about 0.588V at TP4.
6.4.2.3 LINE ACTIVITY MONITOR (LAM)
RV9 sets the level at which the LAM light on the Switch Bus Module activates. The LAM light is the green
LED in the Unselect button. It will blink when a minimum signal level is detected. This parameter may be set
by adjusting RV1 to its desired location (See 4.2.1) and then inserting a signal at the minimum detect level. If
the LAM light is on, adjust RV9 counterclockwise until the LAM light goes off. Carefully turn RV9
clockwise until the LAM light goes on. If the LAM light is off do the same adjustments, but reverse the turn
directions.
6.4.2.4 TRANSMIT MONITOR
The transmit monitor provides a portion of the transmit audio to the receive path. This allows the console
operator to listen to the transmissions of parallel console operators. To set this level have a parallel console
operator intercom on the line to be set. Adjust RV2 until the level is comfortable in the handset/headset
earpiece or the speaker.
6.4.2.5 BUS OUTPUT LEVEL
RV3 controls the output level to the internal bus. The factory sets this level for 770mv at TP11 for a 600mv
signal at TP9.
6.4.2.6 RECORDER OUTPUT
Adjust RV14 until the desired output level is reached at the recorder jack.
6.4.2.7 NOTCH ADJUSTMENTS
The notch filter is designed for a center frequency of 2175Hz. TLM cards are shipped from the factory set at
a 2175Hz notch. The notch adjustments are then “potted” with a compound so the potentiometer will not
change value. The notch circuit should be adjusted only if a different notch frequency is desired.
Adjustments are designed into the circuitry in the first place so that the factory can compensate for
component tolerances.
To adjust the notch filter insert the desired notch tone on the RX pair of the line jack. The input level should
be as high as possible without measuring clipping at TP4 on the TLM. Adjust RV13 for the greatest
amplitude at U8.8. Next adjust RV12 for the smallest amplitude at TP2. Make fine adjustments to both RV13
and RV12 for the lowest possible amplitude signal at TP2.