Car Audio – More on amplifiers and SMPSU

Some links to car audio circuits

If you read the previous article on how quickly we can become deaf through negligence or just plain stupidity (like this scribe) I have managed to get some gems together for the DIY types.

MTX Audio Thunder754-400w-rms-4-channel-class-ab-amplifier
            MTX Audio Thunder754 400W 4 Channel class AB amplifier

Firstly, for those wanting to repair car amplifiers, Perry Babin has done an incredible job in keeping to the facts and make his tutorials available for free or chargeable as a download.  There has been a lot of time and effort going into this so full marks to the author for doing such an amazing job.  I guess the best way to get started is from this link:  Basic Car Audio Electronics.

Your car audio amplifier may be a full range unit or a thumping bass amplifier with roll off from about 200Hz.  But the one thing that stands out with car audio will be in the PSU – whereas your domestic unit steps down the supply rail supply voltages your car amplifier steps up the rail voltages and usually splits the DC to equal (pos) and (neg) voltages with a common.  Car audio amplifiers follow the same topologies as the commercial domestic units except for the PSU and input filters. Of course when one looks at the lower voltages and high power outputs of car audio we can rely on one fact: They require a huge current from the battery supply to deliver the high voltages from the switching supply.  Be careful! A flashy bit of jewellery on a finger getting caught between two poles with a potential to deliver 100A may lead to an amputation.

So there you have it – 220V kills, very high currents cause burns and fires.

Switching Supplies

As we progress through the world of electronics and start thinking we get smarter in comes two reality checkers:  UHF and switched mode power supplies. As UHF is not in the scope of this article let’s move on to SMPSU or switching supplies.

Stepping up the risk

The car audio variety is a good way to learn about inductances and transformer winding because of the lower input voltages.  Mains wired switchers are not the advisable route to take when designing your own. In most cases Meanwell take care of your needs, at a cost. Step up switching supplies are relatively easy to construct from trustworthy sources as in Rod Elliot’s pages: Switchmode Power Supply For Car Audio – Sergio Sánchez Moreno and Rod Elliott. I have built the design shown in figure 9 and it worked first time but take heed at what is recommended for core turns. What most of us like about these toroidal type supplies is the ease at which one can modify the output voltages.

At the author gives a really good explanation as to design and the operation of his audio amplifier along with preamplifier, possibility of bridging and the power supply which uses the very common 494.  The design is around the Kenwood KAC-718 subwoofer power amplifier. For anyone just starting out I would recommend getting to grips with the circuity in the three links above.




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