Whether they can or not is the $64000 question. When you pull 40 amps off an 80V supply (two channels, 4 ohms) for longer than 8.3 ms (the bass hits), from 20,000 uf of cap, do you consider the 16 volt drop between charging cycles "acceptable"?
Such an amplifier might make 800 watts EIA 1kHz, but is only good for 512 from 20-20k FTC. And if you do try to put out 800W at 20 Hz it's going to sound a whole lot worse than if it flat-top-clipped at 512 cleanly.
"If only half the rated voltage is used, then only half the possible maximum charge is stored in it."
Not quite right.
So common sense might suggest that a capacitor, charged to V, has required Q V joules of energy to reach that state, and so Q V joules is stored in the capacitor, ready to be used.
Sadly, common sense is wrong, as usual.
W=1/2CV^2
Not quite right.
So common sense might suggest that a capacitor, charged to V, has required Q V joules of energy to reach that state, and so Q V joules is stored in the capacitor, ready to be used.
Sadly, common sense is wrong, as usual.
W=1/2CV^2
Its quite right - you seem to be confusing energy and charge. Half the charge is stored, but only 25% of the energy. Common sense (based on experience in pushing friends/siblings on playground swings) tells me that the faster something moves the harder it is (the more work is needed) to make it go faster still. This is analogous to charge (which itself is analogous to momentum in mechanics) and energy. Putting an extra unit of charge on a partly charged cap takes more energy than putting the same unit of charge on an empty cap.
+1 ten times over.
Transient peaks should not be clipped if at all possible.
The extra current that flows during transient peaks should not be clipped, if at all possible.
Current clipping is quite different from voltage clipping, one is due to overload where the voltage is limited, the other is due to overload where the current is limited. I don't know if they "sound" different.
Both of these depend on the Power Supply being able to deliver voltage and current to suit the load.
It may not be exactly half, follow the charge/discharge curves of the cap for that relationship. Energy is what is in the cap, charge/discharge is how it is accumulated/distributed. Is anyone defining these differently? Andrew's example between the different types of clipping gives us a practical guide of the distinction between insufficient energy (voltage clipping) and insufficient charge (current clipping). It should be noted that these are not mutually exclusive. In my opinion, voltage clipping is usually a function of poorly manufactured or worn caps, while current clipping is an ESL/ESR issue.abraxalito said:
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20 amps into 4 ohms is 1600watts x2 channels. No one said 20000uf was enough for that kind of power.
The energy stored in a capacitor is actually 1/2 x C V^2.
This comes from integrating the work done storing charge, Vdq, from 0 to Q.
Since V=q/C, this gives 1/C x integral (q x dq) from 0 to Q.
The integral then is 1/C times Q^2/2, or Q^2/2C.
Since C=Q/V, the energy is equivalently CV^2/2.
Er... no. Only at relativistic speeds. It takes exactly the same amount of energy to accelerate a given mass from 1 m/S to 2 m/S as it does the same mass from 0 m/S to 1 m/S. Not counting relativistic effects. Which you'd be unlikely to experience directly.
No, charging a cap is more like compressing air into a cylinder. The more that's in there, the more reluctant it is to accept more.
The Newtonian kinetic energy of a moving body is 1/2 x Mass x V^2.
Since this is nonlinear with velocity, it does indeed take more energy to accelerate a body by 1m/sec at higher speeds, than at lower speeds.
The momentum does increase linearly with velocity, but not the energy.
For example: to go from 0 to 1 m/s we need to supply (1/2 M x 1^2), or (1/2 M x 1) units of energy.
To go from 1 m/s to 2 m/s we must supply an additional amount of energy equal to: (1/2 M x 2^2) - (1/2 M x 1^2), or 1/2 M x 3 units of energy.
In fact, the energy difference required to increase the velocity by 1 m/s steps, as we go up from zero velocity,
is proportional to the sequence of odd numbers, 1, 3, 5, 7, 9, 11, without limit.
We are subtracting the squares of two adjacent integers, and the difference grows with the size of the integers.
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I like the irony in your use of AC/DC to illustrate your points. This and "Highway to Hell" might be an apt description of the turbulence within power amplifier supply systems.
Coincidently, Phil Rudd who was the drummer in the group, and now living here in New Zealand, has been in the news for other than artistic reasons.
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No, it's not. The acceleration is equal to the force divided by the mass. If you pick the right units...
...F=MA, therefore to accelerate a body of 1 kilogram at 1 m/s/s (to increment the velocity by 1m/s) requires 1 Newton.
If you want to think of it in terms of impulse, F*delta_t=M*delta_V. i.e to increment the velocity of a 1 kg mass by 1 m/s requires a force of 1 Newton acting for 1 second.
It's all relative, you see.
It only becomes contingent on velocity at velocities approaching C.
It's not rocket science. Well... ...it is actually.
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Then go back and read what rayma wrote again. You must have missed something important.
Yep, correct so far.
Still fine 🙂
So where do you get to talk about energy rather than force? Do please continue so we can figure out what you're missing.
This is what you said, nye?
It's just not true. It requires exactly the same amount of work to increase it's velocity by, say, 1 m/s, regardless of how fast it's going. It doesn't get harder to make something go faster, until you're going at nearly the speed of light.
How many times?
In a vacuum a body keeps accelerating the same amount at any speed.
In air it is different as you have an opposing force.
This is how space ships get up to silly speeds.
In air it is different as you have an opposing force.
This is how space ships get up to silly speeds.
So the Crown Macro Reference delivering 1500W at 2Ω per channel is a piece of junk (only having a single pair of 6300µF for both channels)?
"The Crown Macro Reference is very possibly the best sound-reinforcement amplifier ever built. I've heard these monster amps drive multiple-woofer towers at extremely high spls at outdoor concerts, without clipping or distortion. In such scenarios, they're without peer. But this type of application doesn't have anything in common with the more refined art of listening to music in the home. "
Stereophile magazine.
"The Crown Macro Reference is very possibly the best sound-reinforcement amplifier ever built. I've heard these monster amps drive multiple-woofer towers at extremely high spls at outdoor concerts, without clipping or distortion. In such scenarios, they're without peer. But this type of application doesn't have anything in common with the more refined art of listening to music in the home. "
Stereophile magazine.
I don't agree, Gootee.
It's the current (running through the spakers), but not the signal.
PSU delivers (more or less) pure DC, without any "signal".
I understand your explanation (PSU current modulated by the
ampflifier), I just disagree with the conclusion.
I know this is a never ending discussion, kind of philosphy thing.
We also need to mention, that this anyway is a different thing on
Class A amps, where current is approximately constant.
😉
On a side note: I use to use big capacitances on both my Class A
and AB amps and CLC filtering with Class A (>200 mF in my AJ).
For those interested in how Crown gets away with using such a seemingly paltry capacitance, review post #80 in this thread. If ticktock used supersymmetry on his Aleph-J, I'd like to know the efficiency he gets from playing full power and the type of coil he used in the pi filter.
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