Jbl sg 520 service manual

Page 2

Figure 1-1

Section 1
FUNCTIONS OF CONTROLS AND CONNECTIONS

1.1 PRIMARY FRONT PANEL CONTROLS

1.1.1 POWER-The POWER pushbutton is an alternate switch: push it once to turn on the system -
push it again to turn the system off. When power is applied, the buttons which happen to be
depressed in the MODE or SOURCE bank are illuminated. The main on-off switch controls not
only the Graphic Controller but also the back panel switched AC outlets.

1.1.2 TONE CONTROLS. - The tour vertical straight-line controls at the left of the front panel
permit the operator to emphasize or diminish bass and treble frequencies independently. Most of
the time these are used as ganged controls. By grasping both bass controls at once, for exam-
ple, they can be moved up and down at the same time so that exactly the same tone control set-
ting is supplied to both channels. On the other hand, to give more-bass boost to one loudspeak-
er than the other, only the desired control is used.

When the markers are centered at the 0' position, the response curve of the 86520 is flat.

1.1.3 SOURCE PUSHBUTTONS.-The top row of eight pushbuttons selects the program source which
will be used. Some of these are designed for high-level inputs: devices which provide at least V4-
volt of signal. Others supply additional amplification for low-level devices such as microphones
or phonograph pickups. Individual input sources are described in paragraph 1.4.

1.1.4 MODE PUSHBUTTONS.--The six pushbuttons in the lower row control the manner in which the
stereo channels are fed to the loudspeakers. The TEST button is used in conjunction with the F-22
Remote Relay assembly to permit rapid balance of the entire electrical components. A detailed de-
scription of the F-22 operation and TEST switch will be found in Sect. 3.5.

1.1.5 BALANCE CONTROL-Sliding the BALANCE control toward the left shifts the emphasis to the
left-hand speaker; moving it toward the right shifts the emphasis to the right-hand speaker. When
the BALANCE control is at the 0' position (and all of the secondary controls have been properly
adjusted) the two channels (A and B) will have identical gain.

1.1.6 VOLUME CONTROL-The VOLUME control is also a straight-line attenuator. lt controls the level
of both channels simultaneously.