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Can someone help me build an amp?

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haglered:
I am a relatively inexperienced at building anything electronic but I have had some experience at it.

I would like to build a simple relatively low power amp (between 5 and 20 watts).

I need help in finding a simple but effective design. It needs to be made from parts I can get from Radio Shack or scrounge from old equipment (Like an old speaker I can get from a Thrift store.)

I need help in knowing what to look for.

I am a soundman and want to use this unit as a small portable amp for occasional outdoor use. It will need to be powered by batteries and accept 1 mic. So it will need to include a small pre amp for at least one mike.

I intend to amplify voice so the mid range is the important range to amplify.

I don't have much in the way of equipment. I have a radio shack iron and a few other tools.

 

 

Simon:
perhaps you can find a kit from radio shack ? otherwise there are many many audio amplifier IC's around that will do the job, just remember that wattage to some extent depends on voltage supply. Try the TDA2009 or TDA2035  (I may have got all of those wrong mind you it's a long time sice I used them and apparantrly they are out of date)

david77:
Maybe have a look around here: http://www.sound.westhost.com
I've used some of his circuits in the past with excellent results.

Do you need a stereo amp or would mono be enough, e.g. just for monitoring a sum from a mixer?

I agree with Simon, have a look at the TDA2009's datasheet http://www.datasheetcatalog.org/datasheets/208/378193_DS.pdf
I'd suggest using the circuit shown in Fig. 16, that should give something like 8W power into 8Ohms, if
run from a lead acid 12V battery. You'd need that circuit twice for stereo, obviously.
If weight is not much of an issue you could use two lead acid batteries to increase the power output.

Then you'd only need to add a small preamp to use the thing with a microphone. Have a look at the link
I posted above, he's got it all there.

Zero999:

--- Quote from: david77 on October 21, 2010, 07:09:17 am ---I agree with Simon, have a look at the TDA2009's datasheet http://www.datasheetcatalog.org/datasheets/208/378193_DS.pdf
I'd suggest using the circuit shown in Fig. 16, that should give something like 8W power into 8Ohms, if
run from a lead acid 12V battery.
--- End quote ---
It think that's a little optimistic, especially when usable power and distortion are taken into account.

Although your theory is correct, you haven't allowed for the extra transistor saturation losses.  The graph in figure 4 says the power output is just under 2W into 8R with at 12V supply. Bridging will theoretically quadruple the power to 8W output but the current will be higher so the saturation voltages in the driver transistors so it will be a bit lower. A good guess for bridge is to double the the power output for a 4R load, since it will be using the same current as 4R with 8R at double the voltage, I make it 7W maximum.

Then there's the actual usable power output which will be much lower. Figure 4 is at 10% THD (clipping) which sounds so bad it's useless. Looking at figure 3 will give a better indication of the usable power so going by the double the power for 4R rule of thumb again, we get 6W of power with a THD of 1% which is pretty usable.





DJPhil:
All good advice. The TDA series from ST Micro is all around what you're looking for, and the example circuits in the datasheets will get you rolling on a power amp section.
The best advice I can give is to get a few chips and start tinkering. I got sidetracked reading into the details for far too long before jumping in when I started tinkering with chip amps. It all comes together really quick once you start building them.

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