Fender CHAMPION 30 DSP Service Manual - Champion™ 30 Dsp
CHAMPION™ 30 DSP
(This is the model name for warranty claims)
5
CIRCUIT DESCRIPTION
This section provides an overview of any new or
unusual circuitry incorporated into this amplifier
model. The purpose is to aid the service technician
by providing insight into the design areas most
likely to present a challenge in troubleshooting.
This overview is focused for the efficient use and
security of Fender® proprietary information.
PRE-AMPLIFIER
The guitar input signal is fed into the high pass filter
at U1–A before splitting into two signal paths. The
normal channel signal path (U1–B to U3–B) is ac-
tive until FETs Q1 and Q2 are turned on activating
the drive channel signal path (U2–A to U3–B). Dif-
ferential amp U4–A and follower U4–B adjust the
signal level and provides +1.65VDC bias voltage to
the uDSP effects card. The preamp is in series with
the digital effects card, therefore, disconnecting the
card breaks the overall signal path. The low pass
filter at U5–B recovers the signal from the uDSP
card and sends it to the headphone jack and the
power amplifier.
POWER AMPLIFIER
The LM3876 power amp chip (U8) is used. Load
sense resistor (R69) provides negative current
feedback. This circuit makes use of the on-chip
mute function. During normal operation, transistor
Q4 is on drawing current out of U8 pin 3 through
R85. Zener Diode D27 sets the voltage at which
Q4 turns on. Plugging headphones into J4 re-
moves ground from the cathode of D24 turning Q4
off which mutes the power amp.
POWER SUPPLY
Standard bridge rectifiers, with zener regulation
(D17–18) for the +/–15V supplies. The 7805 regu-
lator (U7) taps off the +27V supply to provide +5V
for the uDSP card and digital user–interface.
DIGITAL USER INTERFACE
The uDSP effects card generates clock signal
DSP_HD1 (~45Hz) which controls the 4053 CMOS
switch to read pots R45 and R81. The DC level (0–
5V) of the pots controls the FX LEVEL and FX SE-
LECT.
DIGITAL NOISE
The uDSP effects card generates some high fre-
quency noise (>50kHz), which is a normal product
of DSP processing. This noise is not audible and
does not effect amplifier performance, but may be
visible when observing the output of the amplifier on
an oscilloscope.