22 Watt Car Subwoofer Amplifier

22W into 4 Ohm power amplifier, Variable Low Pass Frequency: 70 - 150Hz

This
unit is intended to be connected to an existing car stereo amplifier,
adding the often required extra "punch" to the music by driving a
subwoofer. As very low frequencies are omnidirectional, a single
amplifier is necessary to drive this dedicated loudspeaker. The power
amplifier used is a good and cheap BTL (Bridge Tied Load) 13 pin IC made
by Philips (now NXP Semiconductors) requiring a very low parts count
and capable of delivering about 22W into a 4 Ohm load at the standard
car battery voltage of 14.4V.

Parts:

P1_____________10K Log Potentiometer
P2_____________22K Dual gang Linear Potentiometer
R1,R4___________1K 1/4W Resistors
R2,R3,R5,R6____10K 1/4W Resistors
R7,R8_________100K 1/4W Resistors
R9,R10,R13_____47K 1/4W Resistors
R11,R12________15K 1/4W Resistors
R14,R15,R17____47K 1/4W Resistors
R16_____________6K8 1/4W Resistor
R18_____________1K5 1/4W Resistor
C1,C2,C3,C6_____4µ7 25V Electrolytic Capacitors
C4,C5__________68nF 63V Polyester Capacitors
C7_____________33nF 63V Polyester Capacitor
C8,C9_________220µF 25V Electrolytic Capacitors
C10___________470nF 63V Polyester Capacitor
C11___________100nF 63V Polyester Capacitor
C12__________2200µF 25V Electrolytic Capacitor
D1______________LED any color and type
Q1,Q2_________BC547 45V 100mA NPN Transistors
IC1___________TL072 Dual BIFET Op-Amp
IC2_________TDA1516BQ 24W BTL Car Radio Power Amplifier IC
SW1____________DPDT toggle or slide Switch
SW2____________SPST toggle or slide Switch capable of withstanding a current of at least 3A
J1,J2__________RCA audio input sockets
SPKR___________4 Ohm Woofer or two 8 Ohm Woofers wired in parallel

Circuit description:The
stereo signals coming from the line outputs of the car radio amplifier
are mixed at the input and, after the Level Control, the signal enters
the buffer IC1A and can be phase reversed by means of SW1. This
control can be useful to allow the subwoofer to be in phase with the
loudspeakers of the existing car radio. Then, a 12dB/octave variable
frequency Low Pass filter built around IC1B, Q1 and related components
follows, allowing to adjust precisely the low pass frequency from 70 to
150Hz. Q2, R17 and C9 form a simple dc voltage stabilizer for the input
and filter circuitry, useful to avoid positive rail interaction from
the power amplifier to low level sections.

Notes:

• IC2 must be mounted on a suitable finned heatsink
• Due
  to the long time constant set by R17 and C9 in the dc voltage
  stabilizer, the whole amplifier will become fully operative about 15 -
  30 sec. after switch-on.

Technical data:

Output power (1KHz sinewave):
22W RMS into 4 Ohms at 14.4V supply
Sensitivity:
250mV input for full output
Frequency response:
20Hz to 70Hz -3dB with the cursor of P2 fully rotated towards R12
20Hz to 150Hz -3dB with the cursor of P2 fully rotated towards R11
Total harmonic distortion:
17W RMS: 0.5% 22W RMS: 10%