High Quality, very simple design
No need for a preamplifier
P1_________________22K Log.Potentiometer (Dual-gang for stereo)
P2________________100K Log.Potentiometer (Dual-gang for stereo)
R1________________820R 1/4W Resistor
R2,R4,R8____________4K7 1/4W Resistors
R3________________500R 1/2W Trimmer Cermet
R5_________________82K 1/4W Resistor
R6,R7______________47K 1/4W Resistors
R9_________________10R 1/2W Resistor
R10__________________R22 4W Resistor (wirewound)
C1,C8_____________470nF 63V Polyester Capacitor
C2,C5_____________100µF 25V Electrolytic Capacitors
C3,C4_____________470µF 25V Electrolytic Capacitors
C6_________________47pF 63V Ceramic or Polystyrene Capacitor
C7_________________10nF 63V Polyester Capacitor
C9________________100nF 63V Polyester Capacitor
D1______________1N4148 75V 150mA Diode
IC1_____________NE5532 Low noise Dual Op-amp
Q1_______________BC547B 45V 100mA NPN Transistor
Q2_______________BC557B 45V 100mA PNP Transistor
Q3_______________TIP42A 60V 6A PNP Transistor
Q4_______________TIP41A 60V 6A NPN Transistor
J1__________________RCA audio input socket
Power supply parts:
R11_________________1K5 1/4W Resistor
C10,C11__________4700µF 25V Electrolytic Capacitors
D2________________100V 4A Diode bridge
D3________________5mm. Red LED
T1________________220V Primary, 12 + 12V Secondary 24-30VA Mains transformer
PL1_______________Male Mains plug
SW1_______________SPST Mains switch
This design is based on the 18 Watt Audio
Amplifier, and was developed mainly to satisfy the requests of
correspondents unable to locate the TLE2141C chip. It uses the widespread NE5532
Dual IC but, obviously, its power output will be comprised in the 9.5 - 11.5W
range, as the supply rails cannot exceed ±18V.
As amplifiers of this kind are
frequently used to drive small loudspeaker cabinets, the bass frequency range is
rather sacrificed. Therefore a bass-boost control was inserted in the feedback
loop of the amplifier, in order to overcome this problem without quality losses.
The bass lift curve can reach a maximum of +16.4dB @ 50Hz. In any case, even
when the bass control is rotated fully counterclockwise, the amplifier frequency
response shows a gentle raising curve: +0.8dB @ 400Hz, +4.7dB @ 100Hz and +6dB @
50Hz (referred to 1KHz).
Can be directly connected to CD players, tuners and tape recorders.
Schematic shows left channel only, but C3, C4, IC1 and the power supply
are common to both channels.
Numbers in parentheses show IC1 right channel pin connections.
A log type for P2 ensures a more linear regulation of bass-boost.
Don't exceed 18 + 18V supply.
Q3 and Q4 must be mounted on heatsink.
D1 must be in thermal contact with Q1.
Quiescent current (best measured with an Avo-meter in series with Q3
Emitter) is not critical.
Set the volume control to the minimum and R3 to its minimum resistance.
Power-on the circuit and adjust R3 to read a current drawing of about 20
Wait about 15 minutes, watch if the current is varying and readjust if
A correct grounding is very important to eliminate hum and ground loops.
Connect in the same point the ground sides of J1, P1, C2, C3 &C4. Connect
C9 at the output ground.
Then connect separately the input and output grounds at the power supply
power: 10 Watt RMS @ 8 Ohm (1KHz sinewave)
to 180mV input for 10W output (depending on P2 control position)
Frequency response: See Comments above
distortion @ 1KHz: 0.1W
0.004% 10W 0.005%
Total harmonic distortion @ 100Hz: 0.1W
0.007% 10W 0.012%
Total harmonic distortion @10KHz: 0.1W
0.01% 10W 0.018%
Total harmonic distortion @ 100Hz and full boost: 1W 0.015% 10W
Max. bass-boost referred to 1KHz: 400Hz = +5dB;
200Hz = +7.3dB; 100Hz = +12dB; 50Hz = +16.4dB; 30Hz = +13.3dB
Unconditionally stable on capacitive loads