Most efficient amp

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#21
wg_ski said:
This is where class D is at its best. With the volume down. Class AB may be 60-70% efficient - at full power. At typical listening levels efficiency may be 10%. Class D is 90% at full power, and well over 50% all the time. That's huge in terms of battery life.
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Class AB is very very far from 60-70% efficient at full power. That's the peak efficiency. With the typical crest factor in music being about 10-12dB (meaning the average output level is 6-10% of peak a class AB amp will struggle to even reach 20% efficiency, whereas a class D amp happily achieves 80% efficiency under the same conditions. It gets even worse at lower listening levels.

In portable audio we have done many tests putting class AB and class D amps against eachother and measuring battery run time under typical use conditions and class D amps typically runs the same battery with the same output power in mixed usage with real recorded music 12-14 times longer.
 
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#22
cspirou said:
Also the aspect of adjusting the frequency at will won me over
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For the TT motor, why make life so difficult for a few percent gain.
Example of an all-in-one solution (for a 2-phase servo motor) : http://www.norre.dk/TTPSU/TTPSU.html

If you desire adjustability, you need a display, IEC inlet, switches, buttons.
20VA transformers require only a few inches of space, cost $10.
Lots of pretty and small boxes to put it in.

(NL is the undisputed leader in the conveyor belt market, think flowers/fruit/vegetables. Much easier/cheaper for me to convert used, instead of building new)
 
#24
:up:
cspirou said:
Partly because I wanted to think about an amp from the standpoint of efficiency and then think about what tweaks I can apply until it becomes acceptable. So I was wondering if there is a particular exotic topology that has yielded high efficiency but wasn't used for audio amps.

The other reason is just for my DIY electronic interests outside of the audio itself, in particular to power an AC motor. I have been brainstorming of an affordable and efficient way to power my American turntable that I brought over to France. AC-AC frequency converters don't really exist aside from large installations at power plants. The other solution would be to convert 240V/50Hz to 12V DC and then convert this back to 120V/60Hz AC with a car power inverter but that just ends up costing a lot as well.

Eventually I started thinking about how audio amps play any frequency you want as long as you feed it with the appropriate signal through a signal generator or DAC. You can easily find amps with power rating of 200-1000 watts which is much more power than I need to power a 4-12 watt turntable motor. The main argument against this was that I always assumed that audio amps were really inefficient.

At 90% efficiency, Class D is actually a pretty viable option. For electrical power the signal doesn't have to be anywhere near as clean as it does for speakers so I was wondering about some more efficient but dirtier sources that would work for this project. My turntable motor is 24VAC which are voltages that aren't unheard of for speakers. There are many low cost Class D amps which means I can experiment and risk burning out a few amps to see what works. Long term I see this as a way to make fine adjustments to the speed so the platter to spins exactly right.
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Perfect example of "Lateral Thinking"
 
#27
Bridge rectify 240Vac, and with a converter circuit one can go straight from 240Vac/50Hz to 120Vac/60Hz.
Safety reasons make it advisable to use some sort of isolation transformer.
Would fit in the palm of your hand.

Thinking lateral costs a lot more, takes up way more space, in return for saving pennies.
(I've had classes in lateral/paradoxical/innovative thinking at tech-u, thank you)
 
#28
cspirou said:
I have been brainstorming of an affordable and efficient way to power my American turntable that I brought over to France. AC-AC frequency converters don't really exist aside from large installations at power plants. The other solution would be to convert 240V/50Hz to 12V DC and then convert this back to 120V/60Hz AC with a car power inverter but that just ends up costing a lot as well.
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You think you're the only one having that issue? Think again and realize that eBay is filled with convertors doing exactly what you want for a mere few dollars (or euros for that matter).

100W Step Up Down Voltage Converter 220V EU UK to 110V US | eBay
 
#29
SSassen said:
You think you're the only one having that issue? Think again and realize that eBay is filled with convertors doing exactly what you want for a mere few dollars (or euros for that matter).

100W Step Up Down Voltage Converter 220V EU UK to 110V US | eBay
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What I want to change is the frequency. The voltage convertors you mention only change voltage which is definitely not an issue for me. You find me a converter that changes power from 50Hz to 60Hz for only a few euro and I'll buy it without hesitation.
 
#30
I get this: he wants to produce a high-quality 120VAC 60Hz sine wave to power his turntable. Possible, but it'll be tough with the parts available to made a Class D amp do this, problem being +/-170.

How about +/-85V and a 2:1 transformer?
 
#31
EchoWars said:
I get this: he wants to produce a high-quality 120VAC 60Hz sine wave to power his turntable. Possible, but it'll be tough with the parts available to made a Class D amp do this, problem being +/-170.

How about +/-85V and a 2:1 transformer?
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Actually I want 24VAC 60Hz power since the turntable AC motor takes 24VAC. So all I need is +/- 18V and a 2:1 transformer. This means I just need a cheap switch mode supply to go with a class D board.
 
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