The following DC Power supply circuit is a linear power supply (using transformer). The voltage output of 13.8V power supply is highly regulated, can be adjusted in the moderate range, at up to 20A continuous current. This power supply is suitable for use for amateur radio equipment. DC Power supply is easily constructed and suitable for heavy duty because it is very efficient, small and lightweight.

In the DC power supply presented here, the pass transistors are located in the negative rail and connected in common-emitter configuration rather than as emitter-followers. Thanks to this, the regulator’s minimum voltage drop is extremely low, only about 0.1V for the transistors plus 0.5V for the equalizing resistors.

The other advantage is that the collectors are directly connected to the negative pole of the power supply’s output, which in most applications is grounded. That means that no insulation is required between the transistors and the grounded power supply cabinet! This eases the cooling very considerably. Thanks to the low regulator drop, a low cost 25V filter capacitor can be used.

Some Notes of DC Power Supply Circuit

• Use a transformer for the primary voltage you need. The 3A fuse is for 220 or 240V primaries. If you use something in the neighborhood of 110V, use a 6A fuse.
• The rather high transformer rating of 35A accounts for the losses that occur due to the capacitive input filter. If your transformer is rated for capacitive input, then a 25A value is enough.
• Of course you can make up C1 by placing several smaller capacitors in parallel. Likewise, the 0.1 Ohm, 5 Watt resistors can be made up by several in parallel, for example by 5 resistors of 0.5 Ohm, 1 Watt each.
• The LM336Z-5.0 voltage reference IC should not be replaced by a zener diode. Zeners are not nearly as stable. A different voltage reference IC can of course be used, if R2 and R3 are modified for the different voltage.
• D1 and Q2 through Q6 need heatsinking. Only Q2 needs insulation. D1 dissipates up to 60W, Q2 up to 25W, while the pass transistors dissipate up to 30W each in normal use, but may reach a level of 130W during short circuit! Take this into account when choosing the heat sink!
• R5 exists only to make sure that the transistors can actually be driven off. The 741 is not a single-supply operational amplifier, so it cannot drive its output very low. If a true single-supply opamp is used, then R5 becomes unnecessary.
  

I don’t believe in the tiny sub box theory. If you are looking for tiny sound, get a tiny sub and put it in a tiny box. Be happy. If you are looking for real bass, you need to have a real box.

In order to get true high performance, you have to make the most of the available airspace you have. To do otherwise is wasting your time, energy and money. Don’t try to fit a larger speaker in a box that is better suited for the next size down. The smaller sub in the right space will outperform the larger sub in too small of airspace.

The first step in getting major bass in your vehicle is to allocate the space for your enclosure. If you really want to flex some sheet metal, the old adage applies, “there is no substitute for cubic inches”. The more space you make available, the higher the potential spl.

You don’t have to use a large amount of enclosure space to make a loud system; loud can be done with a single sub. The amount of loud needs to be determined as you figure out what space you plan to give up. Really loud bass, where you have to scream at your passengers, can be done on a single or double woofer setup. Stupid loud bass, where there is no point in trying to communicate in the vehicle, takes more space and bigger/more subs. F@#$ing crazy loud bass, where it is impossible for the car next to you to communicate inside his vehicle, takes even more space, even more subs and a gazillion watts of power.

A few tips on what to pay attention to when determining the box shape:

If you plan to use a rear firing setup in a trunk car, make sure your box doesn’t seal off the trunk from the passenger compartment. You need to leave some space for the waves to pass back into the interior of the car. Either make the box as low as possible so the wave passes over the box and enters the cabin via the seatback and rear deck, or reduce the width of the box so the wave can pass to the side and into the car’s interior. A big, giant box may make your trunk extremely loud, but all you’ll hear is muffled rattle if the box takes up the whole space behind the rear seat and under the rear deck.

If you have a hatchback car, keep the box as far back in the vehicle as possible. Keep the port as far to the rear as possible.