WorkingPro 12®™
(This is the model name for warranty claims)
5
CIRCUIT DESCRIPTION
This section provides concise information about
new or unusual circuitry designs incorporated into
this amplifier model. The purpose is to aid the
service technician by providing insight into the
design areas most likely to become obstacles in
troubleshooting. Information is focused for its
effective use while maintaining the security of
Fender® proprietary information wherever possible.
Overview
The WorkingPro series consists of the WorkingPro
400, 700, 2x10C, 15, 12, & 10 amplifiers. These
amplifiers are highly modular, and use several
common PCB assemblies. The WorkingPro 400,
700, 2x10C, & 15 amplifiers share a common pre-
amp, with some minor stuffing differences to
accommodate the monitor input & Wedge EQ in the
combo amplifiers. The WorkingPro 12 & 10 have
unique preamp PCB assemblies, which are based
on the same preamp architecture, only with some of
the features removed.
The circuitry is derived from the classic SWR ampli-
fiers & is designed to deliver the same tone and
performance as the rest of the SWR amplifier line.
New electronic features to SWR include the Bass
Intensifier effect, a tuner mute function, and a new
footswitching scheme. Also, the new combo ampli-
fiers feature a powered monitor input, and a
"Wedge EQ" circuit to compensate for the tonal
change when the cabinet is in its tilt-back position.
There are two basic power amplifier platforms used
in this series. The first is the SWR500/1000 mod-
ule. The "SWR 500" & "SWR 1000" amplifiers are
essentially the same, only the SWR 500 module is
stuffed with 6 output transistors instead of 8, since it
is used in lower power applications. The SWR
1000 power module is used in the WorkingPro 700,
and the SWR 500 power module is used in the
WorkingPro 400 & 2x10C.
The other power module used in this series is the
SWR200 power module. This class-H power ampli-
fier is used in the WorkingPro 10, 12 & 15 amps.
Different transformers account for output power dif-
ferences.
Preamp
The following discussion follows the signal path
through the functional blocks of the amplifier: The
signal is introduced at J1 & sees a 3.9M
Ω
input
impedance. U3A provides input gain, which can be
reduced by the input pad switch S2.
The Aural Enhancer circuit provides part of the sig-
nature SWR tone. U5A provides gain to make up
for the attenuation of the passive Aural Enhancer
circuit. The gain control is at U5B.
The next block consisting of U8, U10B, & U12 is the
Bass Intensifier circuit. The path through U8B is the
direct signal. U10B is a lowpass filter with a vari-
able cutoff frequency set by R73. This feeds a
compressor circuit at U12. The compressed low-
frequency signal is then mixed with the direct signal
at U8A, resulting in an extreme bass boost. Q3
disables the Bass Intensifier when switched from
the front panel or the footswitch.
Next in series is the Wedge EQ circuit. When S4 is
engaged, the Wedge EQ provides a slight bass
boost and a mild mid-high cut @ U9B. The default
position of S4 bypasses this circuit.
The next stage comprising of U7 & U9A is the tone
section. This is the same architecture as any other
SWR amplifier, and boosts each frequency range
by +/- 15dB. The frequency response of this stage
is flat when all of the level knobs are at their center-
detent position.
The Effects Blend control is the standard SWR cir-
cuit. When there is no plug in the Effects Return
jack (J203), the "EFF_RETURN_R" signal, going to
J203 ring, is open circuit, and the
"EFF_RETURN_T" signal, going to J203 tip, is
grounded. Therefore, the effects return control
does nothing if there is no plug at J203. When a
jack is inserted into J203, the "EFF_RETURN_R"
signal is grounded, so the Effects Blend control
wiper is grounded. As the control is turned, the
grounded wiper will attenuate either the dry or the
