Even allegedly DC coupled amplifiers have servo controls which effectively limit the amp's low frequency bounds, no?It could be used in that way. If the amp is effectively limited from going all the way to DC then the power supply can't be modulated.
Filter Capacitance
Hello Audiogonners!
Perhaps this should be placed in tech talk - not sure....
In my own clumsy way, I'm building more understanding of amplifiers. I have no electrical training, save some very awkward swings of that hot gun that interacts with solder and a PCB, back in High School, about 400 years ago!
So, I see there are two players in the amp game that I do not understand, about which I am studying (more study of other pieces of the system, later): Filter capacitance and transformer size. Until a few days ago, I might have (entirely) mixed the two in my head... now it's only a partial mix... So, I'm interested to see, for example, that the Schiit Aegir has the following hardware, so far as is described on a Schiit-Euro site:
"The power supply is completely linear, with 600VA transformer, over 150,000uF of filter capacitance."
That seems like A LOT of capacitance, and I'm totally confounded as to why this doesn't translate into higher output. As you know, the Aegir is described as 20 watts per channel into 8 ohms, and maybe 40 into 4 ohms. Seems like low wattage for all that transformer and capacitance weight!
The Vidar runs the same size transformer but only 40,000uF of filter capacitance - 20K per side! AND it's a 100w into 8ohm amp - 200 into 4ohms.
I own the STA200 by Nuforce and I cannot find anything describing capacitance, nor transformer size... I'm studying amplifier tech because I'm running into some difficulty when running the STA200 into my Moabs, at high volumes characterized by significant bass extension: think giant BOOM and you get the idea. Most of what I listen to is jazz/acoustic, so it's not a big issue until I move over to something that emphasizes boom, so I'm curious as to how the tech shows up in these applications...
Perhaps this should be placed in tech talk - not sure....
In my own clumsy way, I'm building more understanding of amplifiers. I have no electrical training, save some very awkward swings of that hot gun that interacts with solder and a PCB, back in High School, about 400 years ago!
So, I see there are two players in the amp game that I do not understand, about which I am studying (more study of other pieces of the system, later): Filter capacitance and transformer size. Until a few days ago, I might have (entirely) mixed the two in my head... now it's only a partial mix... So, I'm interested to see, for example, that the Schiit Aegir has the following hardware, so far as is described on a Schiit-Euro site:
"The power supply is completely linear, with 600VA transformer, over 150,000uF of filter capacitance."
That seems like A LOT of capacitance, and I'm totally confounded as to why this doesn't translate into higher output. As you know, the Aegir is described as 20 watts per channel into 8 ohms, and maybe 40 into 4 ohms. Seems like low wattage for all that transformer and capacitance weight!
The Vidar runs the same size transformer but only 40,000uF of filter capacitance - 20K per side! AND it's a 100w into 8ohm amp - 200 into 4ohms.
I own the STA200 by Nuforce and I cannot find anything describing capacitance, nor transformer size... I'm studying amplifier tech because I'm running into some difficulty when running the STA200 into my Moabs, at high volumes characterized by significant bass extension: think giant BOOM and you get the idea. Most of what I listen to is jazz/acoustic, so it's not a big issue until I move over to something that emphasizes boom, so I'm curious as to how the tech shows up in these applications...
Showing 2 responses by atmasphere
How does a person know if they are making a high current, high watt amp, or not?The first thing to understand here is that power, current and voltage have a direct relationship; 1 watt = 1 Amp x 1 Volt That's called the Power formula, and like Ohm's Law, cannot be violated, unlike a speed limit :) So right away, if you work the math, you can see that a 'high current' amplifier is a misnomer. You can read more about that here: http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php One thing about filter capacitance: the amp circuit has timing constants in it, usually a coupling capacitor somewhere, which rolls off at some low frequency that can be calculated. The power supply has timing constants too (it takes a certain amount of time to discharge the filter caps based on how much current can be drawn from them); for best results the power supply should always have a timing constant considerably lower than that of the amplifier, otherwise low frequency instability and/or intermodulations can result. You might be thinking 'what about amps that are direct-coupled input to output?' and its a good question. They will always have the ability to modulate their power supplies! This is why you tend to see excessive amounts of filter capacitance in solid state amplifiers. Now its a pretty good bet that the amp won't see really low frequencies that will get it in trouble, due to the fact of timing constants rolling off in the sub-bass octaves upstream. But if there gets to be any noise or sag in the power supply, in a solid state amp that can be pretty audible as transistors tend to be more sensitive to voltage variations in the supply than tubes (generally speaking of course). So large filter banks are common in such amps. |