Capacitors.

[BassJunkie]

This is probably just for car audio, but, can anyone tell me what a capacitor is used for, pros/cons of having one, the importance, or how necessary it may be?

Thanks all.

-BassJunkie

 

[tattoo_Dan]

This is probably just for car audio, but, can anyone tell me what a capacitor is used for, pros/cons of having one, the importance, or how necessary it may be?

Thanks all.

-BassJunkie

it helps stabilize the voltage in a vehicle.

you could also get a second battery and/or a high output alternator.

 

[jliedeka]

In the signal path, a capacitor will roll off low frequencies proportional to the amount of capacitance. In a cheap speaker, the entire crossover may be a capacitor to protect the tweeter from low frequencies. In a passive crossover circuit, you may see capacitors used for more than high pass. For example, a Zobel, an impedance flattening circuit, uses an inductor, a capacitor and a resistor. Capacitors are also used in notch filters.

One really creative use of capacitors I saw recently was in the Aviatrix speaker design. Curt Campbell used a capacitor on the woofer to lower its mid bass peak. He was able to trade sensitivity for extension using that trick. So 5 inch woofers could go fairly low.

Jim

 

[3db]

A capacitor has many different uses and behaves differently depending on whether or not the voltage applied to it is AC or DC. In what context are you asking about a capacitor?

 

[highfigh]

This is probably just for car audio, but, can anyone tell me what a capacitor is used for, pros/cons of having one, the importance, or how necessary it may be?

Thanks all.

-BassJunkie

If it's used as a "stiffening cap", it's connected to the positive power cable, as close to the draw (amplifier) as possible to minimize voltage drop caused by the demands of the amp during musical peaks. This does little on the strongest, prolonged passages, though. If you connect a small light bulb to a cap and let it discharge, you'll see that it doesn't take long. That's the bad thing. The good thing is that it recharges very quickly but it's still not capable of storing or providing as much energy as a second battery.

If you think of the DC voltage as a clothes line that's suspended at each end, an amplifier is like a coat hanging from the line. It will sag most at the middle with one coat and for every coat you add, it will sag more. Increase the tension on the line and it won't sag as much and you can hang more clothes with less sag. If it really starts to sag because the tension (voltage) can't be increased further, adding a clothes pole (battery or cap) near the load will support it and remove most, if not all, of the sag.

A stiffening cap is like a skinny clothes pole and it has less ability to stabilize the voltage sags from a high power, high current draw amp like a Rockford Fosgate. The amps that will draw a lot of current are easily detected- they have the most dynamic headroom, largest heat sinks and power supply terminals when compared with others of the same average power output.

 

[yepimonfire]

Since we're on the subject, what is the purpose of a capacitor in a receiver/amplifier? I always see people talking about microfarad ratings and capacitor size in receivers and amplifiers, usually gloating about large caps with high microfarad ratings. Someone once told me that it is the amplifiers "power reserve" and the higher the microfarad ratings the more peak output an amplifier in theory could put out.

 

[dem beats]

Since we're on the subject, what is the purpose of a capacitor in a receiver/amplifier? I always see people talking about microfarad ratings and capacitor size in receivers and amplifiers, usually gloating about large caps with high microfarad ratings. Someone once told me that it is the amplifiers "power reserve" and the higher the microfarad ratings the more peak output an amplifier in theory could put out.

The best way I was explained of what a capacitor is/does is that it's like a battery. In the amplifier world it's a super ultra fast battery. It can't hold as much juice(measured in farads) as a battery, but it can dump all it's stored energy in fractions of a second. It stores electrons untill they are needed and then in an instant it dumps it all. Like the flash in a camera.

 

[TLS Guy]

Since we're on the subject, what is the purpose of a capacitor in a receiver/amplifier? I always see people talking about microfarad ratings and capacitor size in receivers and amplifiers, usually gloating about large caps with high microfarad ratings. Someone once told me that it is the amplifiers "power reserve" and the higher the microfarad ratings the more peak output an amplifier in theory could put out.

You ask too many questions!

There are hundreds of capacitors in a receiver with very diverse functions.

I think however you are referring to power supply caps, properly known as smoothing capacitors.

First you have to convert the AC line input to the various AC voltages required in the device. This is done with multiple secondary transformer taps.

Now lets just take a single voltage. The first step is full wave rectification.

Half wave rectification is not very useful

Here we have an AC line voltage and one rectifier. If you look at the scope you see only the positive parts of the wave have been rectified and there is a gap between the positive deflections on the scope.

There are basically two common ways of using both halves of the AC input.

The bridge rectifier.

The other is the center tapper balanced almost always used with tube circuits.

Now you will see in both these examples on the scope you see all positive deflections, but the are positive waves one after the other.

Now we want an elevated straight line, like you would get from a battery.

So a smoothing capacitor is added, like this.

A capacitor will store a charge, and so it smooths the undulations.

Now the capacitor has to have enough capacity to supply the load between the the dips and peaks of the undulating waveform. If it is inadequate, then power ripple will occur, which is highly undesirable.

Now if the capacitor is of a value larger than required for smoothing, then the capacitor can make excess current available to the load for very brief periods. This is most useful for providing current to an output stage, to supply the current to provide the apparent power required for loads with negative phase angles. Since this power is given back this is an ideal application for using capacitors of higher value than required to meet true power requirements. However capacitors will not increase the true RMS power of an amp in a meaningful way.

In modern circuits, power supplies are highly regulated. There are thousands of topologies for regulated power supplies.

Here is and example.

If you understand this, I think you will see that any claim for an AC cable or receptacle to improve the sound of an amp is totally bogus.

Also power conditioners are largely bogus.

Regulated power supplies will keep the DC supply voltages in tight limits for brief periods, and for excess voltage within specified limits indefinitely. However they can only handle voltage sags very briefly.

Voltage sags are also highly deleterious to modern microprocessor electronics.
To handle sage requires a battery.

That is why I keep telling you guys, that proper protection requires good surge protection, preferably whole house, and a UPS which has a battery to control sags.

 

[yepimonfire]

if im not mistaken, a ups bypasses the battery unless power goes out.

 

[TLS Guy]

if im not mistaken, a ups bypasses the battery unless power goes out.

Not the ones I use. The batteries do support low voltage. Mine react in 1 to 5 msec as soon as voltage is out of set parameters. Mine supports voltage below 108 volts and shaves it above 132 volts.

 

[3db]

You ask too many questions!

There are hundreds of capacitors in a receiver with very diverse functions.

I think however you are referring to power supply caps, properly known as smoothing capacitors.

First you have to convert the AC line input to the various AC voltages required in the device. This is done with multiple secondary transformer taps.

Now lets just take a single voltage. The first step is full wave rectification.

Half wave rectification is not very useful

Here we have an AC line voltage and one rectifier. If you look at the scope you see only the positive parts of the wave have been rectified and there is a gap between the positive deflections on the scope.

There are basically two common ways of using both halves of the AC input.

The bridge rectifier.

The other is the center tapper balanced almost always used with tube circuits.

Now you will see in both these examples on the scope you see all positive deflections, but the are positive waves one after the other.

Now we want an elevated straight line, like you would get from a battery.

So a smoothing capacitor is added, like this.

A capacitor will store a charge, and so it smooths the undulations.

Now the capacitor has to have enough capacity to supply the load between the the dips and peaks of the undulating waveform. If it is inadequate, then power ripple will occur, which is highly undesirable.

Now if the capacitor is of a value larger than required for smoothing, then the capacitor can make excess current available to the load for very brief periods. This is most useful for providing current to an output stage, to supply the current to provide the apparent power required for loads with negative phase angles. Since this power is given back this is an ideal application for using capacitors of higher value than required to meet true power requirements. However capacitors will not increase the true RMS power of an amp in a meaningful way.

In modern circuits, power supplies are highly regulated. There are thousands of topologies for regulated power supplies.

Here is and example.

If you understand this, I think you will see that any claim for an AC cable or receptacle to improve the sound of an amp is totally bogus.

Also power conditioners are largely bogus.

Regulated power supplies will keep the DC supply voltages in tight limits for brief periods, and for excess voltage within specified limits indefinitely. However they can only handle voltage sags very briefly.

Voltage sags are also highly deleterious to modern microprocessor electronics.
To handle sage requires a battery.

That is why I keep telling you guys, that proper protection requires good surge protection, preferably whole house, and a UPS which has a battery to control sags.

Out of curisity TLS< why is it you show a Euro power supply schematic rather than a NA supply?

 

[TLS Guy]

Out of curisity TLS< why is it you show a Euro power supply schematic rather than a NA supply?

Because that was handy and it makes no difference to the principles.

 

[dem beats]

You ask too many questions!

That is why I keep telling you guys, that proper protection requires good surge protection, preferably whole house, and a UPS which has a battery to control sags.

THis was amazing. Thanks for sharing all that. I use a UPS right now but it's really just one that is used for PC's normally. Do you recomend something more robust?

 

[highfigh]

THis was amazing. Thanks for sharing all that. I use a UPS right now but it's really just one that is used for PC's normally. Do you recomend something more robust?

A UPS made for a computer that may only have a 500W power supply probably isn't going to be rated for a whole A/V system A power supply with true sine wave output is best.

 

[tattoo_Dan]

This is probably just for car audio, but, can anyone tell me what a capacitor is used for, pros/cons of having one, the importance, or how necessary it may be?

Thanks all.

-BassJunkie

I am assuming you are asking about this type of bass cap,for an amplified subwoofer system in a 12v car application ?

http://www.rockfordfosgate.com/products/product_details.asp?cat_id=5&series_id=40&family_id=87&item_id=108313&locale=en_US&p_status=

http://www.crutchfield.com/S-KxuNZe0WMrk/tech/kb146.html

 

[yepimonfire]

A UPS made for a computer that may only have a 500W power supply probably isn't going to be rated for a whole A/V system A power supply with true sine wave output is best.

yeah, i had my receiver and PS3 hooked up to one of those at one point in time and it only outputs DC, you can tell when it comes on because everything with a power transformer in it starts buzzing from the DC current. it also won't last for more then about 30 seconds before the battery dies. needless to say it was pretty much useless.