Panel switch wiring

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.

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.

The easiest way to add low-end punch to your car’s stereo is to install a subwoofer. This guide will cover the installation of one or more subwoofers in a pre-fabricated enclosure. It will also cover the process of hooking up an amp to power the sub.


The first thing to do is to put the woofer into the box. This should be easy as long as you got the right size enclosure. Before actually screwing down the speaker, be sure to connect the included leads to the terminal in the back of the box. Next, screw the woofer down tight into the front of the box and mount the protective grille directly over the speaker.

Put the box in the trunk. For the best sound, the woofer should be facing the back of the car. To keep it from sliding around, consider using high-strength Velcro strips to secure it to the trunk floor. If this is not possible, L-brackets may be mounted to the cargo floor, but be sure not to put any screws through the side of the box. However you decide to secure it, make sure that it is out of the way of anything you put in the trunk.
Now it is time to install the amplifier. Begin by mounting the unit in the desired location. This should be a flat area with a lot of open space so that the amplifier can cool properly. Do not mount the amplifier on the subwoofer enclosure, as the vibrations from the speaker can damage the internal parts.

The next step is to hook the amp up to power. Before doing this, disconnect the negative terminal from the battery. Hook the long positive power cable for the amp to the positive terminal of the battery. If the cable does not have a fuse, you should install one inline within three feet of the battery connection. Consult the amplifier owner’s manual for the size of the fuse. Run the fused positive cable through the firewall and back into the cabin. Remove any trim panels necessary and pull back the carpet so you can run the cable underneath. Once the cable can reach the amp, trim off any excess, strip the end, and connect it to the positive power terminal of the amplifier. For the negative cable, connect it first to the amplifier, then run it beneath the cargo floor of the trunk and connect it to a ground point on the chassis or floor pan.
Next, you need to connect the amplifier to the head unit. You should do this using the subwoofer pre-amp hookup on your stereo. This can be either a stereo (paired RCA plugs) or mono (single RCA plug) connection. Unless you have a mono subwoofer amp, you will need to use a paired RCA cable to plug into the amp. If your head unit has a mono RCA out, this means you will need to use an RCA mono-to-stereo adapter to plug the stereo cable into the mono jack. Run the RCA cable underneath the carpet on the opposite side of the car from the power lines to avoid interference. When you get the cables back to the amplifier, plug them in at the RCA in terminals. Before putting the carpet and trim back, run a small 16-18 gauge wire from the head unit amp remote connection to the remote control terminal on the amplifier. At this point you can replace the carpet and trim panels to make the installation look clean.

The last step is to plug the subwoofer into the amplifier. To do this, use 12-14 gauge speaker wire. If you have a bridgeable stereo amp, you should bridge the amp by plugging the positive wire into the positive terminal for the left output and the negative wire into the negative terminal of the right output. The actual configuration of the bridge will vary from amp to amp, so read the owners manual for specific instructions. If you have a mono amp, simply connect the positive and negative wires. Finally, plug the wires into the back of the sub. If you have more than one sub, you can run a length of stereo from one sub terminal to the other.
Finally, put the negative terminal back on the battery and fire up your system. You will need to adjust the gain and filters on your amp, if it has them. First, turn on the low pass filter (LPF) option. Then, turn the gain all the way down. Turn up your stereo until the speakers begin to distort, then turn it down just a hair until it no longer distorts. With the stereo playing at this volume, turn up the gain on the amp just until the subwoofer begins to distort. At this point, turn the gain down a bit. That’s it; you’re done, and good luck with your new subwoofer.

Here is the circuit diagram of a simple subwoofer filter that can be operated from a 12V DC supply. Such a circuit is very useful in automobile subwoofer applications. The circuit is nothing but a low pass filter whose pass frequency can be adjusted between 60 to 160 Hz. The circuit is designed around the TL072 dual BIFET opamp IC. Out of the two opamps inside the chip, IC1A is wired as a buffer. The left and right audio inputs after mixing is fed to the input of the IC1A using the DPDT switch S1. Switch S1 is the phase control switch which can be used to make the subwoofer in phase with other speakers. When S1 is in position 2, 180 degree phase shift will be induced.POT R7 can be used for controlling the level. IC1B forms the low pass filter whose pass frequency can be controlled by adjusting the dual gang POT R13.