7
QA4150 / QA4300
Protection
Every model in the QA Series incorporates
protection features. The front panel Protection
LED indicates the activity of the relay speaker
connection circuitry in each channel. When
the protection LED turn on, this circuitry is ac-
tive, and all connected speakers are muted.
Initial power-up ; For approximately five
seconds after initial power-up, the protection
circuitry is activated and the speaker outputs
are muted. If everything is operating normally,
you will hear an audible click at the conclu-
sion of this brief period, as the protection cir-
cuitry is deactivated and the QA Series begins
delivering signal to connected speakers. It is
normal for the Protection LED to fade gradu-
ally after the amplifier is powered off.
Thermal Protection ; Abnormally high heat
sink temperatures will engage the Protect
circuitry for the overheating channel only. An
output relay disconnects the speakers until
normal temperature range is restored. During
this time, the Protect LED will light.
To guard against this problem, make sure the
QA Series receives adequate ventilation on all
sides and that both the front and rear panels
are unobstructed. If the power transformer
gets too hot, its thermal switch will discon-
nect all of the secondary power and discon-
nect both channel outputs.
Short circuit ; If output is shorted due to
faulty wiring, the thermal circuitry will auto-
matically protect the amplifier. If this will oc-
cur, the load will be disconnected by thermal
protection circuitry (also output relay opens).
DC Voltage Protection ; If an amplifier chan-
nel detects DC voltage at speaker output,
the output relay immediately open to prevent
speaker damage.
Current limiting Protection ; At the amplifi-
er’s full power limit, or clipping point, the lim-
iter circuitry will be activated. This is indicated
by illumination of the Clip LED. The channel
gain is automatically reduced, protecting the
speakers from the high power. This circuitry
may be activated by uncontrolled feedback,
oscillations, improper equipment gain setting.
And this circuitry is virtually transparent in
operation and full signal bandwidth is main-
tained.
Any time the Protection LED lights up (except
for initial power-up during approximately five
seconds), there is reason to be concerned. If
this occurs, turn the amplifier off immediately
and check carefully all wiring and external
equipments in order to locate and correct the
condition.
Protection
