Studio Technologies 742A User Manual

Page 20

Issue 1, July 2012

Model 742A User Guide

Page 20

Studio Technologies, Inc.

Audio Mixer

Level Control
The rotary control is used to adjust the

overall gain or loss of the line input’s ampli-

ﬁer circuitry, thus setting the amount of sig-

nal that is sent to the output bus (or buses).

In the fully counterclockwise position the

ampliﬁer gain is set to its minimum, and full

attenuation is achieved. This means that no

signal continues on to the mixing circuitry

that creates the main outputs. As the level

control is rotated in the clockwise direc-

tion the gain of the preampliﬁer increases,

as does the level of the signal sent to the

selected output bus (or buses).

Output Assignment Switch
A 3-position toggle-type switch is used to

assign which of the output buses the sig-

nal will be routed to. In the up position the

signal is sent only to output bus 1. In the

down position the signal is sent only to out-

put bus 2. In the center position the signal

is sent to both output buses 1 and 2.

Master Section/Main Output

Buses

The Model 742A’s master section supports

output buses 1 and 2 with several controls

and switches, compressor circuitry, and

level and status indications. The following

sections provide detailed descriptions

of each of them. (Refer to Figure 15 for

details.)

Master Level Controls
Two rotary controls are used to set the

overall level of output buses 1 and 2. The

controls are “concentric” type, with the

inner knob controlling bus 1 and the outer

knob controlling bus 2. On the front panel,

note the graphic symbol and the letter “U,”

located at the “12-o’clock” rotational posi-

tion. This indicates the correct setting to

provide unity gain through the circuitry,

and is the position where the controls

should normally be set.

Compressor
Studio-quality compressor circuits are

associated with the two output buses.

A yellow LED, located to the right of each

LED meter, will light whenever its respec-

tive compressor is controlling the dynamic

range of the output bus. The operating

threshold of the compressors and associ-

ated LEDs depends on how the Model

742A has been conﬁgured:
• From the factory the compressor

thresholds are set to be 6 dB over the

Model 742A’s nominal output level of

+4 dBu. This correlates to a level on the

main output connectors of +10 dBu.

• The compressors’ conﬁguration can

also be revised so that thresholds of

2 dB over nominal are selected. This

correlates to a nominal level on the

main output connector of +6 dBu. With

this conﬁguration the compressors may

be active quite frequently during typical

Model 742A operation.

• A third conﬁguration is also available

which serves to disable the compres-

sors. In this case dynamic range control

will never take place and the LEDs will

never light.

If the compressors are set to use one of

the two thresholds, i.e., +10 or +6, the

compressor active LEDs should prove

useful. With the input and master level

controls set correctly, the compressor

active LEDs will typically light only when

peak signals are present. In an “ideal”

world where maximum audio ﬁdelity is the

goal, the LEDs should rarely, if ever, light.