battery powered amplifier project?

Question

i want to build a small battery powered amp that's capable of producing Hi Fi and driving a set of 3-4" speakers. i'm using a small plastic module taken from some kind of stereo filter that i want to house the unit in. the filter has a 12 pin harness attached to it with RCA line ins and speaker wires coming out.
basically i want to build the amp on a blank board cut to the same size as my box. i want to solider the harness to it and hook up a battery pack. i'm thinking 4 Nicd AA cells should do it. and i need the amp to have a built in recharging circuit. first of all where can i find some schematics for a similar amp? also, to drive a set of 3-4" speakers at moderate volume, how much power do i need? will a 6v pack do the trick?

Answer 1

Either purchase one already made (cheaper, safer)



Or, if you're wanting the experience, purchase a kit to build one. (also, cheaper)



Building a high fidelity amplifier that is efficient from scratch isn't for the newbie. And since you apparently know nothing about it, I suggest a kit to get your feet wet. You still won't understand all the WHYs of it, but at least it will work and you won't be discouraged.



http://www.canakit.com/electronic-kits/nobot-audio-amplifiers



http://store.qkits.com/category.cfm/AUDIO



http://www.mcmelectronics.com/browse/Amplifier-Modules/0000000724

Answer 2

A safety comment on recharging batteries in enclosures. Make sure the enclosure is ventilated (holes to the outside) so that hydrogen cannot accumulate inside. Very unpleasant!



A simple low powered amplifier, consider the LM386 as a suitable device, look up the data sheet. Go for a 9V or 12V supply. This is perhaps not total hifi, but considering the speakers are not either, what does it matter? It will sound as good as the speakers. Amplifiers need some sort of heat sink consideration, and these need to have air circulation. To run on batteries, the amplifier output rating is a few watts at most, probably less than 1W. It is a tradeoff, output versus battery life. The efficiency of the speaker is more important than the power rating in this situation.



There are numerous kits and modules and chips that do this. Search for a kit. Collect a few tools, learn to solder. Practice first. The charger and the amplifier are two separate issues, two separate kits. The charger is designed to suit the battery type and size. Look up data sheets of any chips you use. You can find numerous examples of LM386 amplifiers and chargers on the internet.

Answer 3

This seems a tall order as a first project. Whether 6AA NiCad's will be enough depends on a lot of things. If you go with a standard push-pull analog amp(class AB) with conventional power supply, 6V will only get you about 250mW of power. With relatively inefficient speakers, which is what most small size home hi-fi speakers are , this is enough to listen to music on your desk, while your'e at your desk, without too much bass and at moderate levels. If you want bass and want the music to kind of "fill the room" it won't be enough. It might be a good idea to find out how much power you need by experimenting with the speakers you want and some various amplifiers. "moderate" is a vague term. Your definition of moderate may differ from someone else's.

The best thing to do in this case, given the small size you want and power requirements, is to go with a class-D amp. They are the most efficient amps available and can fit in a small size. And even then 6V may not be enough to really drive 8 Ohm speakers to a decent sound level with fidelity and bass. Usually you have to kick the voltage up with switching power supplies. There are many companies that make single-chip, class-D amplifiers. But they need supporting circuitry and a good PCB layout to make them work properly and with good fidelity. So maybe Google "class-D amplifier project" and look for something that not only has a schematic but also a board layout suggestion.

Also, be willing to be flexible on the size and power requirements. Being too restrictive can kill an otherwise interesting and rewarding project. This is about building something and learning as much as it is about having something.

Answer 4

I can only recommend you this site http://www.eeweb.com/project/circuit_projects/300-watt-mosfet-real-hi-fi-power-amplifier.. I don't want to explain more just read and I'm sure your doubts and questions will be answered.. :-)

Answer 5

for an efficient amplifier that will run on the volts you need, look up the tda7052



see here > http://www.electro-dan.co.uk/electronics/TDA7052.html



there are many other similar device that use the bridge tied load technique.



notice the lack of components and no output caps.



you will need two for two speakers (stereo)



for recharging you can add a simple current limiting circuit (resistor) and stick a zener across the pack to prevent over voltage. then drive this from say a 6V mains adaptor (500ma or less).



i suggest you use NiMh and not nicad. you will get longer run time . AA's can do nearly 3AH now .

Answer 6

the recharging circuit is something I have no idea on, but try to search of schematics for a Roland Micro Cube, Line 6 Micro Spider & anything "Fender Mini"...use a single 9-volt...my dad's an electrical engineer, & I've been doing work with him all my life, I'm 27 years-old now...I've picked up a lot...what are you wiring this together with, a bread board?!? & I built a miniature guitar amp out of a single Sony Boom Box speaker, drilled the hole in the side for the 1/4" input jack, no volume control or any control, 9v harness coming out of a hole I drilled in the top to a board that was already "good to go" (so-to-speak)...then I bought a Roland Micro Cube because a friend of mine worked at a Guitar Center & he gave me the employee discount...was awesome...