Car Subwoofer Driver

22W into 4 Ohm power amplifier

Variable Low Pass Frequency: 70 - 150Hz

Circuit diagram:

Car Subwoofer Driver


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


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.

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.


Technical data:

Output power (1KHz sinewave):
22W RMS into 4 Ohms at 14.4V supply
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%