5
External Voltage Mode (Auto-On Switch"External Volt" Position)
The 275 SE/275X3 SE also feature a removable voltage input connector to
connect other electronics with voltage control outputs. When the Auto-On
switch is set to the “Voltage Trigger “(center) position, the voltage trigger mon-
itors the voltage input connector (
Figure 1
, #19) and turns the amplifier ON
when a voltage (either AC or DC) between 5V and 24V is detected.
Bypass Mode (Auto-On Switch "Bypass" position)
When the auto On switch is set to the BYPASS (right-hand) position, the
Auto-On circuit is bypassed. In this mode, the amplifier is active any time the
front-panel Power switch is in the "in" position.
Auto-On Delay Time Switches (
Figure 1, #17)
The Auto-On Delay Time Switches allow you to set Auto-On turn-on delay
times ranging from less than 1 second up to 12 seconds (see the table to the
right as well as
Figure 3
and
Figure 11
). When more than one Sonamp is being
used, the Delay Time settings
can be staggered to allow the
amps to turn on at
different times. This avoids
taxing AC power lines beyond
the capability of the circuit
breaker(s).
Voltage Output
Connector
(
Figure 1, #21)
The 275 SE and 275X3 SE fea-
ture a removable Voltage Output connector that provides 12V DC to control
other devices such as Sonance A/V Automation Products, 12V relays, or other
Sonamps (See
Figure 4
). The current draw on the connection should not
exceed 200mA.
Active LED
(
Figure 1, #2)
This LED shows the amplifier’s operational activity. The first time AC power
is applied to the amplifier the
Active
LED will illuminate for about 1.75
minutes and then extinguish. This is a normal reaction of the Auto-On
circuitry the very first time it receives power.
Thereafter, the 275 SE/275X3 SE are ready for automatic operation. In the
Auto-On mode, the Active LED illuminates at the presence of an audio signal
to the input jacks. When the Auto-On feature is defeated the
Active
LED
functions as a normal on/off power indicator.
Note: Whenever AC power to the 275 SE/275X3 SE has been interrupted, the
Active
LED will illuminate for about 1.75 minutes when the power is first
restored.
AC On LED
(
Figure 1, #3)
This LED indicates that the AC power cord is plugged-into a live AC outlet. If
the amplifier’s main AC fuse ever opens, this LED will extinguish. This LED
must remain ON at all times for the amplifier’s Auto-On features to operate.
The amplifier’s Power switch (
Figure 1
, #1) has no effect on the
AC On
LED.
Speaker Switch — 275X3 SE only
(
Figure 1, #4)
The Sonamp 275X3 SE has three pairs of speaker outputs. Each pair may be
selected individually by one of the three front-panel push-button switches.
The low impedance capability of the 275X3 SE allows connection of up to 3
pairs of 8-ohm speakers directly to the amplifier’s output stage. The amplifier
does not depend on an acoustically-inferior series connection for safe
operation. This eliminates any interactions between speaker systems, in-wall
volume controls, etc.
Input Level Controls
(
Figure 1, #7)
The front-panel Input Level controls are recessed for adjustment by screw-
driver only. This prevents accidental tampering with levels. The Level controls
are factory-set to a nominal level safe for connecting a CD player output
directly to the amplifier’s line inputs. This would be the case in a receiver
Tape
Out
/multiple autoformer-type volume control installation (Plug and Play).
For systems that incorporate in-wall volume controls:
Use the Input Level
controls to achieve the maximum desired listening level. Use the amplifier’s
Overload
LEDs (
FIgure 1
, #6) to assist when adjusting levels to the desired
maximum. Set the input level controls to just below the LED’s flash point. This
practice helps to prevent autoformer saturation, distortion, or burnout of
the in-wall volume control while also improving audio resolution.
For systems that do not incorporate in-wall volume controls:
Use the Input
Level controls to limit maximum safe gain to protect speakers or to optimize
the signal-to-noise ratios between the source components and amplifier.
Many output level controls on source components are overly-sensitive near
their minimum position; by reducing the amplifier’s Input Level control set-
tings, you “compel” the source component’s volume control to operate in its
more uniform adjustment range. You can also use the amplifier’s Input Level
controls to adjust left/right channel balance for off-center listening positions.
Auto-On Sensitivity Adjustment
(
Figure 1, #8)
This control is conveniently placed on the front panel between the left and
right Input Level controls. It is pre-set at its mid rotation setting, which works
for most applications. If the source equipment’s output level is low, rotate the
Auto-On Sensitivity control
clockwise
so the Auto-On circuitry will respond at
the lower level. If the source equipment’s output has some low residual noise,
rotating the Auto-On Sensitivity control
counterclockwise
will raise the Auto-
On trigger level above the noise level, so it responds only to the signal level.
Clipping LEDs
(
Figure 1, #6)
and Protection Circuits
The 275 SE/275X3 SE have independent L and R Clipping LEDs that alert you
when the amplifier’s normal operation has been exceeded. If the Clipping
LEDs are constantly illuminated, a short circuit is most likely present.
The speaker relay will disconnect when a DC offset condition is detected, thus
preventing damaged voice coils.
The 275 SE/273X3 SE employ active-limiting protection circuits. When an
over-current condition is realized, the amplifier will actively limit the amount
of power delivered to the speaker connectors. No longer will annoying relay
clicking get in the way of listening to an audio program.
Note: It is always a good idea to turn off the power switch while you
are trouble-shooting for shorted connections or faults with source
components.
I N S T R U C T I O N M A N U A L
S O N A M P
®
2 7 5 S E / 2 7 5 X 3 S E
S T E R E O P O W E R A M P L I F I E R
