WorkingPro 12®™
(This is the model name for warranty claims)
6
wet signal. The gain for the Effects Blend is pro-
vided by U11A.
The Powered Monitor Input signal is mixed in with
the Effects Blend signal when the outputs of U15A
and U11A connect at the Master Volume control.
The Master Volume control is at U11B. The unique
summing configuration for the preamp & monitor
input signals provides the correct taper for this con-
trol. The limiter circuit is also included at U11B, and
compresses the signal at high levels. The amount
of compression is set by R119 (Limiter Adj), and is
adjusted at the factory to a pre-determined level.
When S5 is in the default (out) position, the limiter
is engaged. When S5 is latched, the Limiter circuit
is in bypass mode.
The stage at U15B serves as a gain buffer for the
power amp, and also provides the mute point for
the tuning mute.
The switching circuitry allows control of the mute
and Bass Intensifier functions. The architecture of
the two switching circuits are basically the same.
The circuit looks for a momentary pulse that can be
generated by either the footswitch, or the front
panel switch. Since the two switches are in parallel,
both the front panel switch and the footswitch will
remain operational when the footswitch is plugged
in. The pulses from the switch are debounced, and
then toggle the state of a flip flop, which drives both
the control circuitry and the LED indicators. Mute &
Bass Intensifier functions are controlled by driving
J111 switching FETs in the respective circuits.
The Overload circuit operates simply by monitoring
several stages of the amplifier. If any of the sense
points rise above the overload threshold (approxi-
mately 12V), the Preamp Clip LED will be
illuminated.
Rear Panel PCB
The rear panel PCB is connected to the main
preamp PCB through two 8 circuit cable assemblies
(P1-2 / P201-202). There are five signal circuits
that are routed to the rear panel: Direct, Line,
Headphone, Effects Send, & Effects Return. The
other signals are for power & control.
The Tuner Out comes from the "Direct" signal, and
is not affected by the tuner mute.
The circuitry around U203 is for the XLR &
Unbalanced Out jacks (J204 & J207). S201
switches the Line Out source from "Direct" to "Line".
Two muting points (Q201-202) mute both the XLR
out and the Unbalanced Out jacks. The Pad switch
at S203 attenuates the signal by approximately
10dB. U203B inverts the signal for the balanced
output. The Unbalanced Out also taps from the
output of U203B.
The effects send comes directly from the main PCB,
after the tone section. As described earlier, when a
jack is inserted into J203, the ring is grounded,
enabling the Effects Blend control.
The Footswitch was designed so that it could work
in parallel with the front panel buttons. LEDs on
both the footswitch and the front panel will track the
switching status from both the front panel buttons
and the footswitch.
Power Amp
The SWR200 power module is a self-contained
class-H power amp and power supply. The module
is used in several SWR products, including the
California Blonde, WorkingPro 10, WorkingPro12, &
WorkingPro 15. Different power transformers
account for power output differences in each
product.
All transformer secondary leads connect directly to
the power amp PCB. The class-H power amp
architecture requires two sets of high voltage
suppies. These two high voltage supplies are
included on the power amp PCB, as well as a low
v/-15V supply. This low voltage supply is
made available to the preamp through the 9 pin
preamp header.
The small primary wiring PCB is also part of the
power amp assembly, and breaks away from the
PCB during assembly. This serves as a termination
point for all primary wire connections.
The power amp disperses heat through the
heatsink bracket on the PCB assembly, directly to
the chassis. Adequate ventillation should be
allowed under and around the chassis to prevent
the amp from overheating.
The speaker output is at WJ1 & WJ2, and is
connected to the chassis-mount speaker jack in the
amplifier chassis.
