Electro-Voice 7300A - Checking Short Circuit Current

operating and Service Instructions for the Electro-Voice 7300A Power Amplifier
the unit is in the Dual
mcxie with 8 fl loads con¬
nected to each channel.
their full clockwise posi¬
tions.
2. Remove the eleven screws
securing the top cover.
Refer to Figure 1 for the
screw locations.
3. Connect the sinewave
generator output of the
analyzer to the input of
Channel 1. Rotate the
input level control of
Channel 1 to its full
clockwise position. Rotate
the input level control of
Channel 2 to its full coun¬
ter-clockwise position.
4. Apply power to the amp¬
lifier and adjust the
sinewave generator for a 1
kHz, 0 dBu (0.775 V rms)
output level. For this ad¬
justment, it is not nec¬
essary to maintain a con¬
stant 120 V ac line input
voltage under load.
5. Find R26 on the compon¬
ent layout in Figure 12.
Rotate the shaft of R26
slowly clockwise until the
spikes are minimized in
the distortion waveform
as shown in Figure 9.
6 . Repeat steps 3 through 5
for Channel 2.
7. Check the ac idle current
draw. With both channels
at idle, the ac line current
should be approximately
0.6 amps rms. If the idle
current draw is signifi¬
cantly greater, rotate R26
counter-clockwise slightly
on both channels until the
idle current is approx¬
imately 0.6 amps rms.
8 . Turn off the generator’s
output signal. If you have
concluded with the test
and alignment procedures,
disconnect the amplifier
from its power source and
re-install the top cover
with the eleven screws
previously removed.
9.5 Adjusting R23 and R24,
the Negative and
Positive Current Limit
Trimpots
Shown in Figure 11 is an
asymmetrically clipped waveform
caused by an improperly adjusted
positive current limit as deter¬
mined by R24. Had R23 been im¬
properly adjusted, the negative
half of the waveform would be clip¬
ped as well, but its degree of
clipping is a function of R23 only
and is independent of R24.
In the following procedures, you
will be adjusting the current limit
thresholds by varying R23 and
R24 in such a way so as to insure
symmetrical clipping.
1. Turn power off and dis¬
connect unit from power
source. Make sure the
unit is in the Dual mode
with a 4 n load connected
to the channel under test.
2. Remove the eleven screws
securing the top cover.
Refer to Figure 1 for the
screw locations.
3. Connect the sinewave gen¬
erator output of the anal¬
yzer to the input of Cha¬
nnel 1. Rotate the input
level control of Channel 1
to its full clockwise posi¬
tion. Rotate the input
level control of Channel 2
to its full counter-clock¬
wise position.
4. Find R23 and R24 on the
component layout in Fig¬
ure 12. With a small non¬
conducting screwdriver,
rotate R23 and R24 to
5. Apply power to the amp¬
lifier and adjust the sine¬
wave generator for a 1
kHz, -10 dBu (0.245 V
rms) output level. For this
adjustment, it is not nec¬
essary to maintain a con¬
stant 120 V ac line input
under load.
6 . Increase the level of the
generator until the output
of the amplifier reaches
34.6 V rms (which corre¬
sponds to 300 watts out¬
put into the 4 O load).
7. While monitoring the dis¬
tortion waveform on the
oscilloscope, rotate R23
counter-clockwise until
the negative half of the
waveform just begins to
visibly clip (more pro¬
nounced spikes will ap¬
pear on the distortion
waveform). Then, rotate
slightly clockwise just
until the visible clipping
disappears and the spikes
in the distortion waveform
reduce to their pre-clip
level.
8 . Repeat Step 7 for the posi¬
tive current limit pot R24.
You may have to slightly
re-adjust R23.
9. If R23 and R24 are pro¬
perly adjusted, the cha¬
nnel should clip symmet¬
rically (@ 1% THD) at ap¬
proximately 450 watts as
shown in Figure 11.
10 . Repeat Steps 3 through 9
for Channel 2.
11. Turn off the generator’s
output signal. If you have
concluded with the test
and alignment procedures,
14
Electro-Voice ® a Mark IV Company