45 Watt Class B Amplifier

45 Watt Class B Amplifier Description

45W into 8 Ohm - 69W into 4 Ohm Easy to build - No setup required

45 Watt Class B Amplifier

45 Watt Class B Amplifier Description

The main design targets for this amplifier were as follows:

• Output power in the 40 - 70W range
• Simple circuitry
• Easy to locate, low cost components
• Rugged performance
• No setup

These goals were achieved by using a discrete-components op-amp driving a BJT complementary common-emitter output stage into Class B operation. In this way, for small output currents, the output transistors are turned off, and the op-amp provides all of the output current. At higher output currents, the power transistors conduct, and the contribution of the op-amp is limited to approximately 0.7/R11. The quiescent current of the op-amp biases the external transistors, and hence greatly reduces the range of crossover.

The idea sprang up from a letter published on Wireless World, December 1982, page 65 written by N. M. Allinson, then at the University of Keele, Staffordshire.
In this letter, op-amp ICs were intended as drivers but, as supply voltages up to +/- 35V are required for an amplifier of about 50W, the use of an op-amp made of discrete-components was then considered and the choice proved rewarding.

The discrete-components op-amp is based on a Douglas Self design. Nevertheless, his circuit featured quite obviously a Class A output stage. As for proper operation of this amplifier a Class B output stage op-amp is required, the original circuit was modified accordingly.

Using a mains transformer with a secondary winding rated at the common value of 25 + 25V (or 24 + 24V) and 100/120VA power, two amplifiers can be driven at 45W and 69W output power into 8 and 4 Ohms respectively, with very low distortion (less than 0.01% @ 1kHz and 20W into 8 Ohms).

This simple, straightforward but rugged circuit, though intended for any high quality audio application and, above all, to complete the recently started series of articles forming the Modular Preamplifier Control Center, is also well suited to make a very good Guitar or Bass amplifier. Enjoy!
Notes:
2N3055 and MJ2955 transistors were listed for Q8 and Q9 as the preferred types, but many different output transistors can be used satisfactorily: TIP3055/TIP2955, TIP35/TIP36, MJ802/MJ4502 amongst others.
Discrete op-amp output transistors Q6 and Q7 do not require any heatsink as their cases remain at ambient temperature. Power transistors Q8 and Q9 should be mounted on a black, finned heatsink as usual.

Parts:

R1______________18K  1/4W Resistor
R2_______________3K9 1/4W Resistor
R3,R6____________1K  1/4W Resistors
R4_______________2K2 1/4W Resistor
R5______________15K  1/4W Resistor
R7______________22K  1/4W Resistor
R8_____________330R  1/4W Resistor
R9,R10__________10R  1/4W Resistors
R11,R12_________47R  1/4W Resistors
R13_____________10R    1W Resistor


C1_______________1µF  63V Polyester Capacitor
C2_____________470pF  63V Polystyrene or Ceramic Capacitor
C3______________47µF  25V Electrolytic Capacitor
C4______________15pF  63V Polystyrene or Ceramic Capacitor
C5_____________220nF 100V Polyester Capacitor
C6_____________100nF  63V Polyester Capacitor

D1,D2,D3,D4___1N4148  75V 150mA Diodes

Q1,Q2________BC560C   45V 100mA Low noise High gain PNP Transistors
Q3,Q4________BC556    65V 100mA PNP Transistors
Q5___________BC546    65V 100mA NPN Transistor
Q6___________BD139    80V 1.5A NPN Transistor
Q7___________BD140    80V 1.5A PNP Transistor
Q8__________MJ2955    60V 15A PNP Transistor
Q9__________2N3055    60V 15A NPN Transistor

Power Amplifier 60 Watt supply voltage 30 - 60 Volts

Power Amplifier 60 Watt supply voltage 30 - 60 Volts

This is a simple and low cost 60W power amplifier. The optimal supply voltage is around 50V, but this amp can work from 30 to 60V. The maximum input voltage is around 0.8 - 1V. As you can see, in this design the components have a big tolerance, so you can build it with almost any components that you can find at home. The output power transistors can be any NPN types, but do not use Darlington types.

Capacitor C1 regulates the low frequencies (bass), as the capacitance grows, the low frequencies are getting louder. Capacitor C2 regulates the higher frequencies (treble), as the capacitance grows, the higher frequencies are getting quieter. 

This is a class B amplifier, this means, that a current must flow through the end transistors, even if there is no signal on the input. This current can be regulated with the 500 Ohm trimmer resistor. As this current increases, the sound of the amplifier is better, but output transistors are dispatching more heat. If the current is decreased, the transistors are dispatching less heat, but the sound quality is decreased.

Guitar Amps

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.

Features:

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

Circuit Diagram:

Guitar Amps

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

18W+18W Stereo Amplifier

General Description:

The TDA7265SA is class AB Dual Audio Power amplifier assembled in the @ Clipwatt 11 package, specially designed for high quality sound application as Hi-Fi music centers and stereo TV sets. The TDA7265SA is pin to pin compatible with TDA7269, TDA7269A, TDA7269SA, TDA7265,TDA7499, TDA7499SA. 

Circiut Diagram:

18W+18W Stereo Amplifier

1W Per Channel Stereo Class-D Audio Power Amplifier

Features

• 1 watt per channel with 8-ohm load
• Max. efficiency » 80% with 8-ohm load at 5 volts
• Filterless
• Digital gain control
• Build-in depop circuitry
• Error protection for short circuit and over-temperature
• Mute (shutdown) current < 1µA typical
• Low operating current (4mA at 5 volts without load)
• TSSOP 24L package available 

General Description

The AP130 is an oversampling class-D power amplifier for  stereo audio applications. It provides high power-efficiency for filterless 8-ohm load. Build-in depop, mute and gain control features simplify the applications. BTL (Bridge-Tied-Load) configuration delivers up to 1 watt into 8-ohm load per channel at 5-V supply voltage. It allows direct coupling of the power signal. Reliability is

improved through over-temperature and short circuit protections. The class-D power amplifier enables high efficiency applications for portable devices.

Circuit Diagram

1W Per Channel Stereo Class-D Audio Power Amplifier