Crown DC-300A - 5.7.1 TURN-ON PROCEDURE; 5.7.2 INPUT;OUTPUT OFFSET VOLTAGE CHECK

20
Example:
Z=80,
Peak
Power:75W
Answer:
Fuse:
15A
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FIG. 3-3
FUSE SELECTOR NOMOGRAPH FOR
LOUDSPEAKER PROTECTION
Another form of load protector is shown schematically
in Fig. 3-4. Whenever the load is overdriven, a relay
switches a lamp in series with the load, smoothly
relieving the overload. The lamp then doubles as an
overdrive indicator as it glows. If overdrive is unreason-
ably severe, the lamp will serve as a fuse. By adjusting
the relay tension adjustment and the protection level
control, this system is useful from 25 to 200 watts for
a typical 8 ohm load.
#307 (or two #309 in series)
OVERLOAD
INDICATOR Output
to Load
(4) | ;
1N4002
From
Amp
Output
Lin PROTECTION LEVEL
FIG. 3-4
RELAY CONTROLLED PROTECTOR
WITH OVERLOAD INDICATOR
Output LEVEL
GND
Another more sophisticated form of overload protector
relieves the overload by controlling the amplifier’s input
signal which is creating the overload. This form of pro-
tector not only saves the load but also eliminates amplifier
overload. With this device, it is possible to operate the
amplifier at its maximum level with a minimum of
clipping. This device is shown schematically in Fig. 3-5.
It features an overdrive indicator, distortionless photo-
optical control, and a Protection Level control giving
adjustment from 1W to 200W when driving 8 ohms.
From
PROTECTION OVERLOAD WW7 vac
INDICATOR
Leecraft
Amp
FIG. 3-5
PEAK POWER LIMITING COMPRESSOR
WITH OVERDRIVE INDICATOR
A common problem which causes damage and irritation
is the turn-on thump problem typical to many signal
sources. Fig. 3-6 shows the schematic of a muter which,
when inserted in the input signal line, mutes for several
seconds before connecting the source to the amplifier,
thereby eliminating turn-on transients. It also removes
turn-off transients occurring after the relay drops
open (=0.1 sec.).
4a7K 1N4004 1.2K
H7 VAC
input
(phase for
P-B KHPI7DVI minimum
110 voc noise)
{shown relaxed)
Tos
meat
in_—__“]|
A
|
From
ee Source
Inputs
FIG. 3-6
TURN-ON-TRANSIENT MUTER FOR
LOAD PROTECTION