amplifier with no transformer

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Gaston

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Why can't you just rectify 120 volts ac and make an 1,800 watt into 8 ohms amp with no transformer?
 
Gaston said:
Why can't you just rectify 120 volts ac and make an 1,800 watt into 8 ohms amp with no transformer?
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Because then every part of the sound system (the input source and the speaker's terminals) could be at 120VAC and electocute anybody who touched it and ground.
 
Yeah, the 1800V shares the same neutral with the wall-supply which also is connected to the ground by the power company and the building's electrician. THe 1800V is high enough to force a current path through your body's resistance when you touch it (which is also connected to the ground you are standing on and therefore at ground and part of the electrical circuit). If you have a isolation transformer, then the neutral to the 1800V becomes separated from the neutral for the 120V and floats at whatever voltage (ie. not the ground that you are standing on).

It's also a lot easier to step up an AC voltage with a transformer than DC so why step it up after rectifying it when you could do it before?
 
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Well if it's 1:1 that then that that is it's only purpose. If it has something different it's probably to step up the voltage while it is AC also.
 
I think you've misunderstood Gaston, He's asking why you need to drop the voltage as you normally do in an amp circuit, Then send it out to your speakers giving you less 'power' when you could theoretically just send your Mains 120Volts to the speakers giving you a 'Mega silly ammount of watts'. His 1800 figure is the figure he's worked out in Watts which would be delivered to the 8 Ohm speaker from a 120V supply.

He hasn't mentioned stepping up the supply voltage to 1800 Volts. I get where he's coming from, but totally agree that it would be just as silly as the 'Mega silly ammount of watts' to even contemplate driving a speaker directly from a mains supply without isolation, Otherwise you have a speaker which is sitting at mains potential! As already stated by Audioguru.

My 2p worth anyway!
 
1800W is only twice as loud as 180W. The average power with music from an 1800W amplifier which clips the peaks is only 90W. With 3dB of headroom then the average power is only 45W.

If you aren't really close to the speaker then it isn't too loud.
 
audioguru said:
1800W is only twice as loud as 180W. The average power with music from an 1800W amplifier which clips the peaks is only 90W. With 3dB of headroom then the average power is only 45W.

If you aren't really close to the speaker then it isn't too loud.
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i understand the part about 1800w only being twice as loud... but you lost me after that. why would the peaks be clipped? I am only talking hypotheticaly and never intend to build an amp of that wattage, however i do have a need for such amps as i have some pro audio cabinets. I have two folded sub horns that handle 2400 watts continuous alone.
 

Check out amplifiers like the Behringer EP2500 series, good reliable powerful amps at a good prices.

And as for only twice as loud, while true, twice as loud makes a hell of a difference! - I've done PA using only 2x100W - using 2x10W is more like headphones than PA
 
An amplifier is at its max power when the peaks clip a little.
The average power with most uncompressed music is about 13dB below the max peak RMS output which is 1/20th the power.

Your hearing's response to loudness is logarithmic so you can hear a very wide range of levels. Double the power sounds only a little louder. Half the power is only a little less loud.
 
i see what your saying A.G. the average level is way lower than the peak without any processing equipment. I thinking of high power levels because of the large mass of air that has to be moved at low frequencies.
 
You also need two power rails, unless it's a bridged amp and you also might want a slightly higher voltage to drive the transistors and a lower voltage for the pre-amp.
 
Gaston said:
isn't there a way to use a single supply if you use a capacitor on the output?
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Yes, but it's generally a poor idea, lower quality, and tends to be more expensive than using a split supply.

Sorry, but the entire idea is completely stupid, use a mains transformer - there are no sensible alternatives!.
 
So it should then be possible to construct a crazy-wattage audio amp (3000+ Watts?) without a transformer (i.e. the most expensive component) if you use the 240V mains (U.S.A.) on a dedicated pair of circuit breakers and directly rectify the mains voltage so you can have a split supply. I.E. two hot 120VAC (180° out of phase) and one common ground between them and also the rest of the building... Just like a typical electric furnace would connect. You may have to do a little house rewiring but for the do-it-yourself crowd this may be a far superior option than shelling out a thousand bucks for a 100 lb transformer. Our homes are already conveniently wired for 240V with a center tap if you go all the way back into the circuit breaker box. Essentially you'd be using the pre-existing huge transformer on the utility company's pole as part of your design. Anyone agree or disagree?
 
If you can find a 50 year old speaker with a high voltage coil then your idea will work. I have not seen one in 45 years. You might find one is a museum. I am pretty sure those old speakers were not rated 8 ohms because the speaker coil was actually the transformer.
 
briang7723 said:
So what is the audio fidelity loss of a transformer in the audio circuit? This troubles me in principle.
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A very high quality audio input transformer will produce very good fidelity. A cheap transformer might make it sound like a telephone.
 
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