Altec 1594B Operating Instructions Manual page 7

Speaker Matching
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 70.7V
distribution outlet permits connection t o a large number of
speakers, each speaker operating at its required powt!r level.
Computing impedance i s not necessary for this application.
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
CONTROLS AND INDICATORS
Two operating controls are on the front pane1:a VOLUME
control and a primary power ON-OFF switch. A pilot indi-
A two.section highpass filter is provided with the 15948 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.
3 dB frequency of the highpass filter is 400
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 15948 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 15940 prepaid t o Customer Service. ALTEC,
For additional information or technical assistance. call
TWX
910-591-1142.
Main chassis component locations are shown i n Figures 10
and 11, The 15948 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.
ADJUSTMENT OF POWER DRIVER BALANCE
CONTROL
The Power Driver Balance Control (R116 on Power Driver
on the PCB. I f this control is not adjusted properly, high-
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 TB2 (see
Figure 121.
Step 2. Apply a 20 kHz sine wave to terminals 1 and
of the INPUT terminal board ( T B l I .
Step 3. Adjust VOLUME control for 100-watt output
(40 volts).
Step 4. Connect a frequency distortion analyzer (pre
ferred) or an oscilloscope t o terminals 2 and 5
of TB2 (16-ohm speaker output) and observe
output.
Step 5. Remove four screws securing front panel, then
open and lower panel.
Adjust R116 on Power Driver PCB (see Figures
Step 6.
5 and 12) until minimum distortion i s observed
on distortion measuring instrument.
The
Hz
Step 7. Close front panel and secure with four screws
previously removed.
ADJUSTMENT OF OUTPUT "Q" BALANCE CONTROLS
Output Balance Controls R136 and R137 on Power
Driver PCB (see Figure 5) balance the bias current of power
transistors 01, 02. Q3 and 0 4 . Inadequate adjustment of
these controls may result in distortion and excessive current
drain from one or more power transistors. I f adjustment is
indicated (such as replacement of one or more power tran-
sistors), use the following recommended procedure:
Turn VOLUME control fully counterclockwise
Step 1.
Remove four screws securing front panel, then
Step 2.
lower panel for access to interior.
the chassis i s opened for service. This
procedure should be referred t o a quali-
Turn Output
Step 3.
R137 fully clockwise (see Figure
Turn on power and allow a 5-minute warmup
Step 4.
period.
CAUTION
Balance Controls R136 and
2