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Simple Amplifier with Bass-Boost

High Quality, very simple design, No preamplifier required
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 at 50Hz. In any case, even when the bass control is rotated fully counterclockwise, the amplifier frequency response shows a gentle raising curve: +0.8dB at 400Hz, +4.7dB at 100Hz and +6dB at 50Hz (referred to 1KHz).
10W Bass Boost Amplifier Circuit Diagram

10W Bass Boost Amplifier Circuit Diagram

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______________N4148 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 Circuit Diagram

Power Supply Circuit Diagram

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
  • 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 will ensure a more linear regulation of bass-boost.
  • Do not 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 to 25mA.
  • Wait about 15 minutes, watch if the current is varying and readjust if necessary.
  • A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 &C4;. Connect C9 to the output ground.
  • Then connect separately the input and output grounds to the power supply ground.
Technical data:
Output power:
10 Watt RMS into 8 Ohm (1KHz sinewave)
115 to 180mV input for 10W output (depending on P2 control position)
Frequency response:
See Comments above
Total harmonic distortion at 1KHz:
0.1W 0.009% 1W 0.004% 10W 0.005%
Total harmonic distortion at 100Hz:
0.1W 0.009% 1W 0.007% 10W 0.012%
Total harmonic distortion at 10KHz:
0.1W 0.056% 1W 0.01% 10W 0.018%
Total harmonic distortion at 100Hz and full boost:
1W 0.015% 10W 0.03%
Max. bass-boost referred to 1KHz:
400Hz = +5dB; 200Hz = +7.3dB; 100Hz = +12dB; 50Hz = +16.4dB; 30Hz = +13.3dB
Unconditionally stable on capacitive loads

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