Tuesday, November 17, 2009
This circuit of audio amplifier push-pull single-ended Class A is capable of providing a sound comparable to those valve amplifiers, delivering more output power (6.9W measured across a 8 Ohm loudspeaker cabinet load), less THD, higher input sensitivity and better linearity.
Voltage and current required for this circuit are 24V and 700mA respectively. The only penalty for the transistor operated circuit is the necessity of using a rather large heatsink for Q2 and Q3. In any case, the amount of heat generated by this circuit can be comparable to that of a one-valve amplifier. An optional bass-boost facility can be added, by means of R5 and C5.
Voltage and current required for this circuit are 24V and 700mA respectively. The only penalty for the transistor operated circuit is the necessity of using a rather large heatsink for Q2 and Q3. In any case, the amount of heat generated by this circuit can be comparable to that of a one-valve amplifier. An optional bass-boost facility can be added, by means of R5 and C5.
Component list of audio amplifier kelas A
P1_____________47K Log. Potentiometer (Dual-gang for stereo)
R1____________100K 1/4W Resistor
R2_____________12K 1/4W Resistor (See Notes)
R3_____________47K 1/4W Resistor
R4______________8K2 1/4W Resistor
R5______________1K5 1/4W Resistor (Optional, see Notes)
R6______________2K7 1/4W Resistor
R7,R9_________100R 1/4W Resistors
R8____________560R 1/2W Resistor (See Notes)
R10_____________1R 1/2W Resistor
C1,C2__________10µF 63V Electrolytic Capacitors
C3_____________47µF 25V Electrolytic Capacitor
C4____________100µF 35V Electrolytic Capacitor
C5____________150nF 63V Polyester Capacitor (Optional, see Notes)
C6,C7_________220µF 25V Electrolytic Capacitors
C8___________1000µF 25V Electrolytic Capacitor
Q1___________BC560C 45V 100mA Low noise High gain PNP Transistor
Q2,Q3________BD439 60V 4A NPN Transistors
Notes:
- If necessary, R2 can be adjusted to obtain 13V across C8 positive lead and negative ground.
- Total current drawing of the circuit, best measured by inserting the probes of an Avo-meter across the positive output of the power supply and the positive rail input of the amplifier, must be 700mA. Adjust R8 to obtain this value if necessary.
- Q2 and Q3 must be mounted on a finned heatsink of 120x50x25mm. minimum dimensions.
- Add R5 and C5 if the bass-boost facility is required.
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