Speaker Matching
the output tap most nearly equal to total speaker
impedance. I f the load impedance falls between two out-
put terminal values, use the terminal of lower impedance.
Speaker Power Distribution
Total power distributed to all speakers should be not greater
than the power rating of the amplifier system. The
distribution outlet permits connection t o a large number of
speakers, each speaker operating at its required
level.
Computing impedance i s not necessary for this
Each speaker i s equipped with a line transformer having
various power taps. Select the tap which yields the power
desired for that speaker.
OPERATION
ADJUSTMENT OF POWER DRIVER BALANCE
CONTROL
The Power Driver Balance Control
on Power Driver
balances the outputs of transistors 0 1 0 4 and
on the PCB. I f this control is not adjusted properly,
frequency distortion results. I f adjustment is indicated, use
the following procedure:
Step 1.
Connect a 16-ohm dummy load across terminals
2 (16 ohms) and 5 (common) of
(see
Figure
Step 2.
Apply a 20 kHz sine wave to terminals 1 and
2
of the INPUT terminal board
Step 3.
Adjust VOLUME control for 100-watt output
(40 volts).
CONTROLS AND INDICATORS
Step 4.
Connect a frequency distortion analyzer
Two operating controls are on the front
VOLUME
ferred) or an oscilloscope
terminals 2 and 5
control and a primary power ON-OFF switch. A pilot
of
(16-ohm speaker output) and observe
is l i t when the power is ON.
output.
F l LTER
A
filter is provided with the
to
protect driver loudspeakers from excessive low-frequency
power demands. Filter use is indicated when high power
output from the amplifier is applied t o driver loudspeakers
not equipped with protective crossover networks.
The
3 dB frequency of the
filter is 400
Hz
Figure
A screwdriver-operated FILTER IN-OUT switch is located
on the rear of the chassis (see Figure 6). The switch is
placed in the OUT position when the
is ;hipped
from the factory.
SERVICE
I f a malfunction occurs, service should be performed by an
ALTEC Qualified Service Representative. For factory ser-
vice, ship the
prepaid t o Customer Service. ALTEC,
Manchester Avenue. Anaheim, California 92803.
For additional information or technical assistance. call
774-2900, or
TWX
910-591-1142.
Main chassis component locations are shown i n Figures 10
and
The
schematic is shown in Figure 12. Com-
ponent locations on the power driver PCB are shown in
Figure 13.
ACCESS
Remove the four screws securing the front panel, then
open and lower the hinged front panel to gain access to the
chassis interior.
I f the ALTEC 42526 Shelf Mount Cover accessory is in-
stalled, remove
by reversing the steps of the cover installa-
tion procedure given i n the associated instructions.
Step 5.
Remove four screws securing front panel, then
open and lower panel.
Step 6.
Adjust R116 on Power Driver PCB (see Figures
5 and
until minimum distortion i s observed
on distortion measuring instrument.
Step 7.
Close front panel and secure with four screws
previously removed.
ADJUSTMENT OF OUTPUT
BALANCE CONTROLS
Output
Balance Controls
and R137 on Power
Driver PCB (see Figure 5) balance the bias current of power
transistors
Q3 and 0 4 . Inadequate adjustment of
these controls may result in distortion and excessive current
drain from
or more power transistors. I f adjustment is
indicated (such as replacement of one or more power tran-
sistors), use the following recommended procedure:
Step 1.
Turn VOLUME control fully counterclockwise
Step 2.
Remove four screws securing front panel, then
lower panel for access to interior.
CAUTION
the chassis i s opened for service. This
procedure should be referred t o a quali-
Step 3.
Turn Output
Balance Controls
and
R137 fully clockwise (see Figure
Step 4.
Turn on power and allow a 5-minute
period.
