60 Watt Guitar Amplifier

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Bass, Treble, Harmonic modifier and Brightness controls
Output power: 40W into 8 Ohm and 60W into 4 Ohm loads

This design adopts a well established circuit topology for the power
amplifier, using a single-rail supply of about 60V and
capacitor-coupling for the speaker(s). The advantages for a guitar
amplifier are the very simple circuitry, even for comparatively high
power outputs, and a certain built-in degree of loudspeaker protection,
due to capacitor C8, preventing the voltage supply to be conveyed into
loudspeakers in case of output transistors’ failure. The preamp is
powered by the same 60V rails as the power amplifier, allowing to
implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

60 Watt Guitar Amplifier Circuit

60 Watt Guitar Amplifier Circuit Diagram

Amplifier parts:

R1___________6K8 1W Resistor
R2,R4________470R 1/4W Resistors
R3___________2K 1/2W Trimmer Cermet
R5,R6________4K7 1/2W Resistors
R7___________220R 1/2W Resistor
R8___________2K2 1/2W Resistor
R9___________50K 1/2W Trimmer Cermet
R10__________68K 1/4W Resistor
R11,R12______R47 4W Wirewound Resistors
C1,C2,C4,C5__47µF 63V Electrolytic Capacitors
C3___________100µF 25V Electrolytic Capacitor
C6___________33pF 63V Ceramic Capacitor
C7___________1000µF 50V Electrolytic Capacitor
C8___________2200µF 63V Electrolytic Capacitor (See Notes)
D1___________LED Any type and color
D2___________Diode bridge 200V 6A
Q1,Q2________BD139 80V 1.5A NPN Transistors
Q3___________MJ11016 120V 30A NPN Darlington Transistor (See Notes)
Q4___________MJ11015 120V 30A PNP Darlington Transistor (See Notes)
SW1_________SPST Mains switch
F1___________4A Fuse with socket
T1___________220V Primary, 48-50V Secondary 75 to 150VA Mains transformer (See Notes)
PL1__________Male Mains plug
SPKR________One or more speakers wired in series or in parallel Total resulting impedance: 8 or 4 Ohm Minimum power handling: 75W

Guitar Preamplifier Circuit

Guitar Preamplifier Circuit Diagram

Preamplifier parts:

P1,P2__________10K Linear Potentiometers
P3_____________10K Log. Potentiometer
R1,R2__________68K 1/4W Resistors
R3_____________680K 1/4W Resistor
R4_____________220K 1/4W Resistor
R5_____________33K 1/4W Resistor
R6,R16_________2K2 1/4W Resistors
R7_____________5K6 1/4W Resistor
R8,R21_________330R 1/4W Resistors
R9_____________47K 1/4W Resistor
R10____________470R 1/4W Resistor
R11____________4K7 1/4W Resistor
R12,R20________10K 1/4W Resistors
R13____________100R 1/4W Resistor
R14,R15________47R 1/4W Resistors
R17,R18,R19____100K 1/4W Resistors
C1,C4,C5,C6____10µF 63V Electrolytic Capacitors
C2_____________47µF 63V Electrolytic Capacitor
C3_____________47pF 63V Ceramic Capacitor
C7_____________15nF 63V Polyester Capacitor
C8_____________22nF 63V Polyester Capacitor
C9_____________470nF 63V Polyester Capacitor
C10,C11,C12____10µF 63V Electrolytic Capacitors
C13____________220µF 63V Electrolytic Capacitor
D1,D2__________BAT46 100V 150mA Schottky-barrier Diodes (see Notes)
Q1,Q3__________BC546 65V 100mA NPN Transistors
Q2_____________BC556 65V 100mA PNP Transistor
J1,J2___________6.3mm. Mono Jack sockets
SW1,SW2______SPST Switches

35mV input for 40W 8 Ohm output
42mV input for 60W 4 Ohm output

Frequency response:
50Hz to 20KHz -0.5dB; -1.5dB at 40Hz; -3.5dB at 30Hz

Total harmonic distortion at 1KHz and 8 Ohm load:
Below 0.1% up to 10W; 0.2% at 30W

Total harmonic distortion at 10KHz and 8 Ohm load:
Below 0.15% up to 10W; 0.3% at 30W

Total harmonic distortion at 1KHz and 4 Ohm load:
Below 0.18% up to 10W; 0.4% at 60W

Total harmonic distortion at 10KHz and 4 Ohm load:
Below 0.3% up to 10W; 0.6% at 60W

Treble control:
+9/-16dB at 1KHz; +12/-24dB at 10KHz

Brightness control:
+6.5dB at 500Hz; +7dB at 1KHz; +8.5dB at 10KHz

Bass control:
-17.5dB at 100Hz; -26dB at 50Hz; -28dB at 40Hz


  • The value listed for C8 is the minimum suggested value. A 3300µF
    capacitor or two 2200µF capacitors wired in parallel would be a better
  • The Darlington transistor types listed could be too oversized for
    such a design. You can substitute them with MJ11014 (Q3) and MJ11013
    (Q4) or TIP142 (Q3) and TIP147 (Q4).
  • T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V
    or 50V center tapped). Obviously, the center-tap must be left
  • D1 and D2 can be any Schottky-barrier diode types. With these
    devices, the harmonic modifier operation will be hard. Using for D1 and
    D2 two common 1N4148 silicon diodes, the harmonic modifier operation
    will be softer.
  • In all cases where Darlington transistors are used as the output
    devices it is essential that the sensing transistor (Q2) should be in as
    close thermal contact with the output transistors as possible.
    Therefore a TO126-case transistor type was chosen for easy bolting on
    the heatsink, very close to the output pair.
  • R9 must be trimmed in order to measure about half the voltage
    supply across the positive lead of C7 and ground. A better setting can
    be done using an oscilloscope, in order to obtain a symmetrical clipping
    of the output wave form at maximum output power.
  • To set quiescent current, remove temporarily the Fuse F1 and
    insert the probes of an Avo-meter in the two leads of the fuse holder.
  • Set the volume control to the minimum and Trimmer R3 to its minimum resistance.
  • Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
  • Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Author: http://www.redcircuits.com