Transformers ???

Although adding a capacitor to a battery charger will significantly reduce hum, you'll get nowhere near as clean of an output as you will with a linear regulator.

Also, bigger is not necessarily better. The bigger the capacitor, the less the ripple it's true. However, when the ripple is small the capacitor has to charge at the peak of the input sine wave, which results in higher peak current through the transformer and rectifier. At some point you'll hit the current limit on the charger and a bigger capacitor won't help. Probably a 1000 MFD capacitor is good enough. That's why power supplies with big filter capacitors also have massive transformers and hefty rectifiers.

I'm looking at 12v (13.8v) power supplies on Ebay - Consumer Electronics> Radios: CB, Ham & Shortwave> Ham Radio> Accessories> Power Supply. It looks like I can get one for about $25. plus shipping.

I guess I want one that is filtered ???
I'll probably want to add an amp/equilizer so I'm thinking 20A ???

My friend owns a car stereo store so used radio is $0.

Car type speakers are cheap. I already have some.

Plastic - Walmart - boom boxes don't last on a construction site.

DeWalt/Milwaukee boxes have poor sound / no volume / poor reception. 3A-5A.

I'm thinking for < $100. I can build a box with decent sound, multiple speakers and good volume that will last.

Any linear regulated power supply will have some degree of filtering, so claims that a given power supply is "filtered" are meaningless. The only way you could compare two power supplies would be to dissassemble them and look at their components. So go for the cheapest one that meets your specs (assume that the specs are exaggerated at least 100 percent).

There are two reasonably cheap ways to get clean dc power:

1. Buy a regulated (linear) DC power supply. This is by far the easiest and simplest way to go. Radio Shack lists a 3 amp 14 power supply for 42 bucks. (Link below.) You might find one cheaper elsewhere. This power supply should be more than adequate for a standard car radio, but it might not be big enough if you intend to put in a booster amp. Either go with a bigger supply, or go to option #2.

2. Hook a small battery charger (2 amp should be plenty) to a small battery, say a lawn tractor battery. This should give you plenty of reserve for a booster amp, but you have the big disadvantage of lugging around a lead acid battery that might spill or explode.

You might ask "why can I get more power out of a 2 amp charger than a 3 amp power supply?" The answer is that your amplifier power demand has a lot of spikes, the battery will supply power for those spikes that a solid-state power supply cannot.

• Radio Shack 3 amp 14 vdc power supply

I would think a lawn & garden battery to run the radio with a 2amp trickle charger to recharge the battery is the way I would go. About 3 to 4hrs of radio playing before a car battery will bite the dust and not start the engine.

An expensive radio for what a boom box would cost new.

You also might want to check out a book at the library on basic electricity. A good time to learn.

T_Bone

For boom boom boxes you are wanting to produce a lot of racket which would require a lot more than 10 watts.....probably 200ish watts if my memory is correct.

So expect to pay a couple hundred for it. Too much power supply is ok.....like it is capable of putting out 200w and you only use 100. Too little (ps capacity) and you will burn it up or continuously blow the line fuses.

Mark