What are the most efficient amplifiers, either available or experimental, regardless of fidelity? I know that Class D/T is quoted to go 90%. Is there any that are known to beat this figure and reach 99%? Or is Class D as good as it gets?
I would say, a carefully set up class D amp with a switchmode power supply is as good as it gets.
"Regardless of fidelity" means that you can use an amplifier which is switched off. No power consumption; no fidelity; high efficiency.
Class D can theoretically do 100%. You can't do better than that for audio.
For RF there are also Class E and F, in various forms; also 100% in theory. No fidelity, and not much use for audio.
Class D can theoretically do 100%. You can't do better than that for audio.
For RF there are also Class E and F, in various forms; also 100% in theory. No fidelity, and not much use for audio.
Class D at a relatively low power level (less than 500 watts - above that, things get lossy and exponentially harder to design/build) with a conventional but oversized power supply would yield the highest efficiency. People tend to think switchmode supplies are higher efficiency, but in fact are not. Regulation is better, making a backed-off class AB amp more efficient, but has less effect on a 90% efficient amplifier core. An under-loaded 60 Hz toroid trafo is VERY efficient and can be overloaded by 10X temporarily where a switcher would either go into hard limit, or heat up and explode.
RF class E and F don't get above 90-ish% in practice, either.
RF class E and F don't get above 90-ish% in practice, either.
If the input signal is zero, then it's also the highest possible fidelity. And signal to noise ratio too 🙂
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.
From your post, I'd get the impression you are making a comparison between conventional class AB and non-conventional class D.
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.
What's wrong with a 240Vac PWM inverter, followed by a 240/120Vac (24Vac) transformer (autoformer)?
A 3d generation Siemens inverter (120W Vector model) costs up to $1000 new, $500 for a refurbished one
On the web, a second-hand Siemens Vector goes for less than $75, sometimes under 40.
A general overhaul with new electrolytic caps, and they're as good as new.
A new preset 50Hz to 60hz converter costs less than $100, and lots of circuits on the web to build one yourself.
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Nothing per se, but you are asking me this on a forum called diyAudio and I have a strong urge to DIY. Plus 100watts is overkill for a 4 watt motor. I am trying to figure out low powered solution to this that won't take up a lot of space. Also the aspect of adjusting the frequency at will won me over whereas the inverter is a fixed frequency.
You have links to the ones you like?
Yes! That is class aAG. Currently used for cellphone transmitter, not yet applied to audio. It has theoretically Class A sound, yet extremely high efficiency.
Also "regardless of audio quality" results in the lowest efficiency possible; and, that is because efficiency in audio comes from defining an average ear as the Receiver and then delivering a Suitable signal, which is the only real Purpose for the device to consume electrical current (otherwise, you're wasting your time And your electricity).
So, for practical efficiency, we will be in need of a defined receiver and a defined purpose!
For example, us humans have great difficulty receiving clean bass with speakers and with ears but there are certain harmonics that make it more hear-able and therefore more efficient, practically. And also music is a highly asymmetric signal, so there is more efficiency to be had by forcing symmetry via reducing the amplitude of the errant peak rather than allowing it to cause a clippy sticky output noise (in which case a signal modification is better quality than a really bad noise--this modification to be done only "at the last minute" as if emergency basis and only as a substitute for a worse noise). The relevant literature is really very common to transmitters, but rather rare for audio amplifiers.
P.S.
If you're thinking that you couldn't go far over unity, then you've limited your thinking and probably didn't consider the receiver, which is flesh and variable, but also quite thoroughly documented. After all, a desirable signal is an order of magnitude more efficient than an undesirable signal.
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If you want fixed frequency, rather than an audio amp, then Class E and F become possibilities. At 50Hz almost all the loss will be in the tuned circuits! On balance, Class D may still be the best bet.
Tuned circuits are pretty lossy at 50 Hz. Not to mention huge. If all you need is 50 Hz, class D can be made about as efficienct as it will get. If you could stand the mechanical noise in the output filter, run the switching frequency down to a kHz or two. Switching losses and critical dead-time issues would be gone. You wouldn't need a sophisticated driver circuit - you wouldn't even notice a 200ns fall time on dissipation. Or compromise a bit and run it at 25 KHz - not enough for high quality audio, overkill for 50 Hz, but high enough where you won't hear the output cap/inductor squealing.
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