MJ11015 & MJ11016 Guitar Amplifier 60W

Guitar Amplifier general description:

     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.

Guitar Amplifier features: 

Sensitivity: 35mV input for 40W 8 Ohm output42mV input for 60W 4 Ohm output
Frequency response: 50Hz to 20KHz -0.5dB; -1.5dB  40Hz; -3.5dB  30Hz
Total harmonic distortion 1KHz and 8 Ohm load: Below 0.1% up to 10W; 0.2%  30W
Total harmonic distortion 10KHz and 8 Ohm load: Below 0.15% up to 10W; 0.3%  30W
Total harmonic distortion 1KHz and 4 Ohm load: Below 0.18% up to 10W; 0.4%  60W
Total harmonic distortion  10KHz and 4 Ohm load: Below 0.3% up to 10W; 0.6%  60W
Treble control:+9/-16dB 1KHz;  +12/-24dB 10KHz
Brightness control:+6.5dB 500Hz;  +7dB  1KHz; +8.5dB @ 10KHz
Bass control:-17.5dB 100Hz ; -26dB 50Hz; -28dB @ 40Hz

Guitar Amplifier circuit diagram:

Guitar Amplifier circuit diagram

Guitar PreAmplifier circuit diagram:

Guitar Amplifier notes:

• The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice.
• 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 unconnected.
• 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.

Guitar Amplifier partlist:

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 partlist:

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