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Old 8th May 2012, 03:19 PM   #1
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Default DIY Max Power Low Cost Amplifier Design

One of the designs a lot of folks want is the the most powerful amplifier that can be powered from a standard electric outlet.

This would be 20A 120V or 2400W maximum continuous input power for most folks.

The other consideration is the loudspeaker load impedance. As a loudspeaker is allowed to dip to 1/2 the rated impedance an 8 ohm output should be able to handle a 4 ohm dip.

Now at full power most speakers heat up and can almost double their impedance before failure.

So the amplifier should not be damaged by a short circuit. It should not have a power dip or protection kick in on a burst of energy into 1/2 of the optimum output impedance.

The first issue is what is a reasonable design impedance?
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Old 8th May 2012, 03:48 PM   #2
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Old 8th May 2012, 04:07 PM   #3
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In the US the maximum for AC plugs with parallel prongs is 15A. For continuous current draw, the maximum is 80% of that or 12A. A 20A circuit requires a special outlet that will accept a plug with one prong (not sure which one) turned 90 degrees. It is a code violation to install 15A outlets on a 20A circuit.

Most amps rated more than 1000W will not produce that much power continuously. They are rated to produce pulses of power.

The question of reasonable design impedance depends on the intended use which you have not defined. Some amps use switching power supplys that can change voltage outputs to optimize the amp for different load impedances.
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Old 8th May 2012, 04:53 PM   #4
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Originally Posted by Loudthud View Post
In the US the maximum for AC plugs with parallel prongs is 15A. For continuous current draw, the maximum is 80% of that or 12A. A 20A circuit requires a special outlet that will accept a plug with one prong (not sure which one) turned 90 degrees. It is a code violation to install 15A outlets on a 20A circuit.

Most amps rated more than 1000W will not produce that much power continuously. They are rated to produce pulses of power.

The question of reasonable design impedance depends on the intended use which you have not defined. Some amps use switching power supplys that can change voltage outputs to optimize the amp for different load impedances.
A NEMA 5-20 will handle the current. The average current will be under 5 amps. But the design is for real maximum output!
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Old 10th May 2012, 01:59 PM   #5
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There are several real world considerations in building a large power amplifier. The main two are power transformer and power dissipation.

The heat sink can actually be done quite inexpensively! I can get a 3' heatsink 3" wide for under $35.

That's good because the power transformer will run just under $200.00

So if there is any interest I will go on, otherwise not!
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Old 10th May 2012, 02:27 PM   #6
jaycee is offline jaycee  United Kingdom
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Crazy high power amps are now solely in the realm of using efficient SMPS supplies, and class D output. To do it any other way is insane really
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Old 10th May 2012, 02:34 PM   #7
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A nice big iron core transformer and a nice beefy class AB output stage is the only way to do a well sounding high power amplifier.

Class D should never be allowed anywhere near audio, its just so disgustingly horrendosly bad!! PWM belongs in motor drives and nowhere else!!!
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Old 10th May 2012, 03:04 PM   #8
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SMPS are not DIY!
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Old 10th May 2012, 03:19 PM   #9
wg_ski is online now wg_ski  United States
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Originally Posted by Tekko View Post
A nice big iron core transformer and a nice beefy class AB output stage is the only way to do a well sounding high power amplifier.
And the biggest one of those that you can run off standard 15A wall outlet producing full power sine waves would be a stereo version of the Dirty Harry. I've built bigger ones (1500W, 2 ohms) and they will run from a wall socket - barely - with music. Sine wave trips a 20A breaker.

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Class D should never be allowed anywhere near audio, its just so disgustingly horrendosly bad!! PWM belongs in motor drives and nowhere else!!!
That's a matter of opinion. Class D is getting better all the time. At the power levels that make sense for those speaker distortion dominates and you won't hear what's produced by the amp. A pro sound subwoofer stack is more like a motor drive than a speaker, anyway, right?

And even with class D, you might get it up to 500 or 600W per channel producing sine wave output before a 15A breaker on a wall socket trips.
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Old 10th May 2012, 03:46 PM   #10
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A speaker is nowhere close to a motor drive. Even a subwoofer needs a clean low thd signal to sound good, something only a class A/AB amp can do.

Class D in my opinion has no future, and no its not getting any better, its still today the same crap it was back in the 70's when it was first tried.

Who remembers those philips or whatever class d modules from the 70's that were notorious for failing.
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