Electro-Voice 7300A - Compression Driver Protection Capacitors; Octal Accessory Sockets

Operating and Service Instructions for the Electro-Voice 7300A Power Amplifier
Figure 6 High-voltage Distribution System
tect loudspeaker ^sterns (or the
amplifier). It is difficult, however,
to determine the proper fuse value
with the correct time lag and
overload characteristics to match
the limitations of a speaker sys¬
tem. The values shown in Table II
should serve only as a guide. To
use, determine the power rating
and load value. Then, select a
standard value fuse of the next
smaller value to the one listed in
the table.
Table II Calculated Output Fuse
Values
Power 4ft
8ft 16 ft
(watts) Load
Load Load
100 3.70
2.62 1.85
150
4.54 3.21
2.27
200
5.24 3.70
2.62
300
6.42 4.54 3.21
400
7.41 5.24
3.70
600
9.07 6.42
4.54
The values are calculated for fast-
blow fuses which carry 135% of
their current rating for an hour
but will blow within 1 second at
200%. Other fuse values may be
calculated for different power
levels from the following equation:
Fuse value =
(Pout X ZL) ^ amps
ZL X 1.35
where
Pout is the output power
rating of the amplifier;
and
ZL is the load impedance.
Use 32 volt fuses if possible; they
typically have the lowest internal
resistance which will help mini¬
mize deterioration of the damping
factor at the load. Refer to the
example in Figure 4.
3.7 Compression Driver
Protection Capacitors
Compression drivers, used
for mid to high frequency sound
reproduction, are much more sus¬
ceptible to damage from low freq¬
uencies than large cone loud¬
speakers. Even though an elect¬
ronic crossover may be employed,
problems may arise in the cables
between the crossover and the
power amplifier, or from mis-
adjustment of the crossover.
Either of these situations could
apply low frequency signals or
hum to the driver and cause
damage. To prevent a potential
mishap, Electro-Voice re¬
commends using a capacitor
between the amplifier and the
compression driver to suppress
low frequencies and possible DC.
Refer to the example in Figure 4.
In choosing a value, one must be
careful not to interfere with the
crossover frequency. As a general
rule, select a capacitor whose
break frequency, with respect to the
load, is 3 dB down at approximat¬
ely V 2 of the high pass comer fre¬
quency.
Mylar capacitors with at least a
100 volt ac rating are recom¬
mended. Table III shows the re¬
commended capacitor values for
use with 8 and 16 ohm drivers at
popular crossover frequencies.
Table III Compression Driver
Protection Capacitors
Crossover
8ft
16ft
Frequency Driver
Driver
500 Hz 80 ^iF 40 liF
800 Hz
50 |iF 25 liF
1000 Hz
40 ii? 20 ^lF
1250 Hz
33 jiF
16 nF
2000 Hz 20 |iF 10 ^iF
3150 Hz 12 ^F
6 |iF
4 OCTAL ACCESSORY
SOCKETS
Two octal sockets permit a
variety of plug-in accessories to be
used with the amplifier. Normally,
one “U” jumper is inserted be¬
tween octal socket pins 8 and 1,
and another between pins 7 and 6.
These jumpers must remain in
place for the amplifier to operate
when not using any accessory
modules. To use with an accessory
Electro-Voice © a Mark TV Company
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