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Old 31st May 2015, 04:02 AM   #1
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Default Diy class a 5W amplifier

Hello all, new to the forums.
I was wondering if the attatched schematic would work as an amplifier for a 5W 8ohm speaker. The application of this amplifier is for a bluetooth portable speaker.

Im not aaking for great aound quality, butnif anyone can give me advice on how to makemit better I will consider it.
Thanks!
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Old 31st May 2015, 05:35 AM   #2
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Class A and portable generally don't go together well. The heatsink will be as large as a small speaker box by itself. Look into a small chip amp instead.
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Old 31st May 2015, 06:54 AM   #3
Mooly is offline Mooly  United Kingdom
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It should work, but its a bit to simple to be very good. If you want Class A then you may as well aim a little higher, otherwise a simple chip amp as jerluwoo mentions will be far better.

Check out the original JLH69 amp. There are loads of threads about that. Its very simple and very good.
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Old 31st May 2015, 07:08 AM   #4
MarianB is offline MarianB  Romania
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Portable means battery powered, or at least it does to me anyway... Class A is probably the one you should avoid the most because of it's very low efficiency. But even if you will not power it from batteries, still as it has been said, the heatsink should be quite large. I think the best way to go, especially if you intend to power the amp from batteries, is class D, that way you get the most power from the energy invested in it, and thus a small heatsink ( or rather very small in some cases, or none at all at low power ).

Cheers.
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Old 31st May 2015, 12:08 PM   #5
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Can anyone point me in the right direction to a simple class d amp, I would like to use discrete components of possible.
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Old 31st May 2015, 12:16 PM   #6
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I know that class d uses a own signal, is there a possibility i could use an atmega328, like an ardu8no or an attiny chip?
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Old 31st May 2015, 12:39 PM   #7
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*pwm signal
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Old 31st May 2015, 06:06 PM   #8
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Quote:
Originally Posted by dbutler6259 View Post
Can anyone point me in the right direction to a simple class d amp, I would like to use discrete components of possible.
You'll get a much better idea of what class D is and why discrete component builds are impractical here: Class D - diyAudio
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Old 31st May 2015, 06:40 PM   #9
MarianB is offline MarianB  Romania
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Class D owes it's efficiency to the way the power stage is operated, it is sort of a buck sincron regulator, it uses a square carrier wave of high frequency, with it's duty cycle modulated by the audio signal on the imput, the power switches on the output are always either fully ON or fully OFF, thus power loss is very small, the musical signal is filtered out before the speaker with the help of an LC low pass filter.

That would be the very short version of it, building a class D power amp only with discrete components is a tough order, but i think there should be a class D chip amp suited for your application, you first need to work out the fine details, how do you intend to power it up, what speaker impedance would you use, is size an issue, and other stuff like that...
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Old 31st May 2015, 10:45 PM   #10
bwaslo is offline bwaslo  United States
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And don't confuse class d with digital. Most class d amps are completely analog. They switch, but nothing is quantized (no bits or clock involved)!
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