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
SPKR___________One or more speakers wired in series or in parallel
Total resulting impedance: 8 Ohm
Minimum power handling: 5W
Best types showed THD figures of 1.8% @ 3W and 0.8% @ 2W.
An optional bass-boost facility can be added, by means of R5 and C5.
A thorough description of both circuits and the results of subjective test comparisons made by this distinguished Author appeared on AudioExpress magazine: February, March and April 2005 issues.
(measured on 8 Ohm resistive load unless otherwise specified)
230mV input for 1.5W output
380mV input for 3.5W output
560mV input for 5.6W output
Sensitivity with bass-boost:
400mV input for 1.5W output
630mV input for 3.5W output
850mV input for 5.6W output
Sensitivity with 8 Ohm nominal, loudspeaker cabinet load:
210mV input for 1.5W output
325mV input for 3.5W output
477mV input for 6.9W output
100Hz to 20KHz 0dB; -3dB @ 40Hz
Frequency response with bass-boost:
+5dB @ 100Hz; +3.9dB @ 200Hz; +2.5dB @ 400Hz; -1dB @ 10KHz and 20KHz
Total harmonic distortion @ 1KHz:
0.3% @ 0.5W; 0.45% @ 1W; 1% @ 5.6W
Unconditionally stable on capacitive loads
- 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.