71
Vega’s C-
6124
would like Select audio to be muted until the LAM triggers move JP4 to the A position (B position disables). If you
would like Unselect audio to be muted until the LAM triggers move JP3 to the A position (B position disables).
9.5.2.3 Recorder Output
A 600 ohm balanced output provides a summing of the transmit and receive audios for the use of an external
recorder. Jumper options allow the TX path to be summed in with tones (JP14 = B) or without tones (JP14 = A). The
option for including the tones is intended for test purposes. If a system problem is being detected, recording the
tone output may help debug the problem. A jumper also allows crosspatch audio to be included (JP15 = A) or not
included (JP15 = B). To set the recorder insert a .77V signal to the receive pair and adjust RV14 (accessed from the
back) for .77V at the recorder output which is fully loaded.
9.5.2.4 RX Automatic Level Control
With the nominal voice level coming in through the receive pair adjust RV5 until you see a level of .59V at
TP4, the ALC output. It is up to the technician to determine where the “knee” of compression is. Generally, the knee
of compression for the C-6124 ALC starts at .59V and ends at around .77V. The consoles are shipped from the
factory with the assumption that the “knee” is at .59V.
9.5.3
Internal adjustments
To set every level on the TLM you need an extender card (available from Vega) to remote the TLM.
Carefully consider whether changing these settings necessary. All routine level changes are done from the back of
the console.
9.5.3.1 RX Automatic Level Control
With the nominal voice level coming in through the receive pair adjust RV5 until you see a level of .59V at
TP4, the ALC output. It is up to the technician to determine where the “knee” of compression is. Generally, the knee
of compression for the C-6124 ALC starts at .59V and ends at around .77V. The consoles are shipped from the
factory with the assumption that the “knee” is at .59V. The factory sets the ALC by inserting –10V, adjusting RV1 for
.25V at TP9, and then adjusting RV5 (knee of compression) for .59V at TP4.
9.5.3.2 2175Hz notch filter
The notch filter on the TLM is a very steep notch designed to remove the 2175Hz component out of the receive
audio. This prevents the any transmit 2175Hz getting to the speakers when the console is in four wire TX monitor
mode. Each potentiometer is “potted” with an orange substance to keep the pots from drifting during transportation
of the console. To retune the notch filter the now hard orange substance must be chipped off.
The notch filter works by employing a hi-Q state variable bandpass filter at 2175Hz, shifting the bandpass
output by 180 degrees, and then summing it back with the original signal. RV13 adjusts the bandpass frequency and
RV12 adjusts the phase that the bandpass output is summed in at.
To adjust the filter insert the tone which is to be notched out to the receive pair. The tone should be 10 db
into compression to give the maximum signal the circuitry will encounter. For example, if the input levels have all
been set to a .25V reference insert a .77V signal to set the notch filter. Turn RV13 to the smallest level at TP2. Once
this is done, adjust RV12 to take the level at TP2 down a little more. The filter is finished off by performing a
balancing act between adjusting RV12 and RV13 as you go back and forth to try to get the smallest signal level at
TP2.
9.5.3.3 Bus Driver
The internal bus structure is set up for .77V, fully compressed audio. To set up the RX bus driver insert a
tone to the receive pair that will put the TLM receive path into compression (at the factory we use .77V input).
Adjust RV3 for .77V at TP11.
9.6
Switch Bus Module (SBM)
The only receive adjustment on the switch bus module is the individual Unselect volume controls. These
volume knobs are the ones mounted to the front panel of the Switch Bus Module. They can attenuate the line’s
Unselect audio all the way off.
9.7
UIM Analog
