Fender Musical Instruments Corp. 7975 North Hayden Road Scottsdale, AZ 85258
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DELUXE 112 PLUS
(This is the model name for warranty claims)
SERVICE MANUAL
APRIL 1995 REV A
IMPORTANT NOTICE:
The information contained herein is CONFIDENTIAL and PROPRIETARY to Fender Musical Instruments Corp. It is
disclosed solely for use by qualified technicians for purposes of equipment maintenance and service. It is not to be
disclosed to others without the expressed permission of Fender Musical Instruments Co. All specifications subject to
change without notice.
For warranty repair service, only Fender specified part numbers are to be used. It is recommended they also be used
for post-warranty maintenance and repair.
Parts marked with an asterisk (
and SAFETY requirements. DO NOT USE A SUBSTITUTE!
A coded naming convention is used in the description of certain parts. The codes and what they mean are as follows:
CAPACITOR CODES HARDWARE CODES
CAP AE=Aluminum ElectrolyticBLX=Black Oxide
CAP CA=Ceramic AxialCR=Chrome Plated
CAP CD=Ceramic DiskHWH=Hex Washer Head
CAP MPF =Metalized Polyester FilmM=Machine Screw
CAP MY=MylarNI=Nickel Plated
CAP PFF=Polyester Film/FoilOHP=Oval Head Phillips
RESISTOR CODES
RES CC=Carbon CompSMA=Sheet Metal "A" Point
RES CF=Carbon FilmSMB=Sheet Metal "B" Point
RES FP=Flame ProofSS=Stainless Steel
RES MF=Metal FilmTF=Thread Forming
RES WW=Wire WoundZI=Zinc Plated
*
) indicate the required use of that specific part. This is necessary for RELIABILITY
PB=Particle Board
PHP=Pan Head Phillips
PHPS=Pan Head Phillips Sems
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DELUXE 112 PLUS
SPECIFICATIONS
Product Release No.:PR 291 (This is not a model number)
Part Number:120V Version :22-6702
100V :22-6772
230V:22-6762
Power Requirements:180-120VAC, 50-60 Hz, 360W max.
230-240VAC, 50 Hz, 360w max.
Input impedance:Input 1: 850kΩ
Input 2: 66kΩ
Power output:94 watts RMS into 4Ω at 5% THD
Effects Loop:Preamp Output Impedance: 1kΩ
Power Amp Input Impedance: 44kΩ
Power Amp Sensitivity: 1.0V for Clipping
Dimensions:Height:16 1/2"(41.9 cm)
Width: 20 5/8"(50.5 cm)
Depth: 9"(22.9 cm)
Weight:33 lbs.(14.9 kg)
Product specifications are subject to change without notice
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DELUXE 112 PLUS
THEORY OF OPERATION
Input 1 is a high sensitivity input. Input 2 is a low sensitivity input. Inputs 1 and 2 contain series switches
that connect to +16Vdc via a third series switch located within the Power Amp in jack (J5). From the input
jacks, this series circuit terminates at the gate of JFET Q7. Q7 is part of a muting /turn on delay circuit for
the input of the power amp. Therefore the input signal to the power amp will remain muted until a plug is
inserted into either Input 1,2 or the Power Amp in jack.
The first stage (U2A) sets up the initial response of the amplifier. It provides a second order high pass filter
with a 3dB down point at 60Hz, and a gain of about 3.8. The output of U2A splits to feed the clean and
overdrive channel. For the clean channel, the signal feeds the Treble, Bass and Mid controls that provide
boost and cut respectively. The signal then flows to U7A. U7A is a buffer for the adjustable high pass filter
made up by C59, C60, R108 and R109. The inverted signal at U5A is sensed through R109 and fed back
to the junction of C59 and C60. As the Volume control is turned up, the feedback from R109 provides
–6dB of attenuation at 30Hz. This prevents the speaker from flapping at very low frequencies. U2B is an
Auto-pad circuit. It provides excellent headroom and low noise.
The signal split from U1A feeds the overdrive channel through a special tone shaping circuit located just
prior to U2A. This circuit is a third order bandpass filter with a peak boost at 2.2kHz. It provides the
optimum frequency response for the following distortion circuit. U2A provides the variable gain adjustment
that drives the distortion circuit. It also acts as a bandpass filter with 3dB down points at 90Hz and 4kHz.
U2B is the distortion circuit. LD1 and LD2 provide diode distortion.
The Contour control adjusts the overall tone quality of the overdrive channel by emphasizing or notching
the mid range frequencies. In the fully CCW position the response is fairly flat up to about 2kHz, where a
gentle roll-off occurs. In the fully CW position, the circuit provides a –20db notch at about 1kHz. The
signal then feeds the overdrive volume control and the treble and bass controls.
The signal from the Clean and Drive channels sum at U5A via JFETs Q4 and Q5. The output from U5A
feeds the reverb drive circuit (U6A) and summing amp U5B. U6B is the reverb sensing circuit. The output
of U6B drives the Reverb volume control and then sums with the dry signal at U5B. The output of U5B
drives the preamp out jack, is normalled through the power amp in jack, and feeds the power amp input.
CHANNEL SWITCHING
The AC voltage from the power transformer secondary is tapped off through resistor R82, and presented to
the footswitch jack (Approx 20 V RMS). By rectifying the positive or negative side of the waveform, we
create a DC control voltage that is sensed by comparators U4A and U4B. Diode’s CR20 and CR21 set up
the reference voltages for the comparators. Therefore the control voltage must toggle between +15Vdc
and –15Vdc. The comparator output controls the JFETs and the indicator LEDs. Without the footswitch
connected to the footswitch jack, CR15 rectifies the negative half of the waveform. U4B senses the DC
control voltage, and provides –15Vdc to the gate of Q6, allowing the reverb output to function.
POWER AMP
U1 is a high voltage op-amp that provides voltage gain for the power amplifier. CR3 and CR4 act as
differential protection diodes that prevent the positive and negative inputs of U1 from becoming more than
0.6 volts apart. Bootstrap Capacitors C37 and C38 sense the output through R69. This provides more
voltage swing for the opamp with respect to ground.
Diodes’ CR5-CR8 (BYV26D) make up the Fixed Bias circuit for the output transistors. The Bias Diodes
mount through a hole in the transistor heatsink. This ensures the Diodes will properly track the
temperature of the output transistors. These Diodes were selected because they exhibit a 2mV decrease
in Knee Voltage for every 1 degree (Celsius) increase in temperature. Pin 6 of U1 is at 0 Vdc. Therefore
the Bias Diodes provide 2 voltage drops (+/- 1.2volts) to the Base of Darlington Transistors Q1,Q2, Q10
and Q11.
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DELUXE 112 PLUS
THEORY OF OPERATION (CONT)
Diodes’ CR9-CR12 make up a voltage clamp protection circuit. Q8 and Q9 make up a current limiting
protection circuit. If the output is shorted, the voltage at the emitters of Q10 and Q11 will increase. This
voltage is sensed through R100 and R107 and presented to the bases of Q10 and Q11. When Q10 and
Q11 turn on, the drive current and bias to the output transistors is removed, which shuts down the output
section of the amplifier.
The output signal feeds through the Headphone jack circuit, before driving the speaker. With headphones
connected to the headphone jack the speakers are muted.