Home Projects Audio 60W Guitar Amplifier

 
 

60W Guitar Amplifier
source: RED Free Circuit Designs


 

Bass, Treble, Harmonic modifier and Brightness controls

Output power: 40W on 8 Ohm and 60W on 4 Ohm loads

 


Amplifier circuit diagram:

60W Guitar Amplifier



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________47F   63V Electrolytic Capacitors
C3________________100F   25V Electrolytic Capacitor
C6_________________33pF   63V Ceramic Capacitor
C7_______________1000F   50V Electrolytic Capacitor
C8_______________2200F   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




Preamplifier circuit diagram:

Guitar Preamp



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________10F   63V Electrolytic Capacitors
C2_________________47F   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________10F   63V Electrolytic Capacitors
C13_______________220F   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



Circuit 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.

Technical data:

Sensitivity:

35mV input for 40W 8 Ohm output

42mV 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

Notes:

  • The value listed for C8 is the minimum suggested value. A 3300F capacitor or two 2200F 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 from 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 waveform 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.

 

 
 

 

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