67 evil eleanor

If you are looking to keep out noise, then the quality of the wires (shields) that go from the head unit to the amp is very importain. Using cheap shielded wire will allow outside noise to enter. Judging by the weight of the capacitors sold for car stereos, I can't imagine that theres too much to them. Heres what a 54uf (actually about the same physical size as the crap they sell for cars) capacitor will do. If it was me, I would put my money in the correct size and quality made wires, a good battery, and the correct size alternator. Check out the video.
http://www.youtube.com/watch?v=BqgxQG1PyfM

Norm Peterson

That conveniently assumes that the power supply to the amplifier is pure DC, which is hardly the case in an engine-running automotive environment where the alternator output (I think it's originally generated as 3-phase AC) ends up being essentially DC with some AC ripple superimposed. Then you add ignition and whatever other electrical noises exist that either feed back to the amplifier power line directly or by induction (even a really inefficient not-quite-zero turn transformer will develop AC power in its "secondary winding").

I would suggest that recording studio equipment uses better power supplies with far better filtering than anything based on automobile alternators. I doubt that the studios call Autozone or Pep Boys in the event of power failure.

Oscilloscope traces of power input to studio and automobile line (both with and without capacitors) might be revealing.

I agree with you in that a capacitor really doesn't make any sense in a series installation, meaning that just about any argument that gets any of the 99.99%-ers away from a useless arrangement can't possibly hurt. That doesn't address the 0.01% with parallel capacitors that certainly aren't "monkey see, monkey do" setups, though.


Norm

65rangoon

first off a capacitor is rated in farad's not caps. cap is just short for capacitor.

secondly, if you are going to spend the $$ on a capacitor buy a deep cycle battery (marine battery) instead and place it in the trunk. it will do the same thing as the capacitor but it will not drain as quickly as a capacitor (ie if the cap isnt sized right the lights will still dim when a heavy note hits)

if you have a system in your car weight is obviously not an issue so the added weight of a battery over a cap shouldnt bother you.

the deep cycle also will not burn up your alt (unsure about the factory one) as they are made to run a boat without an alt wired to it.

fakesnakes

A battery is actually a capacitor. It is not the most efficient capacitor as it has a high internal resistance, but it does act as a capacitor to the alternator, reducing the a/c ripple remaining after the rectifier. The biggest challenge to using a deep cycle battery close to the amp is the high internal resistance inherant in a battery vs. a cap. A battery simply can not respond to the instant demand for power created by audio. Simply said battteries and the rest of the electrical system in a car is set up for DC (constant voltage at a set level - 12v). Audio is AC, just the kind of current flow where a capacitor is at its best. In AC systems resistance is actually measured as capacitive reactance. The reason for this is it varies by the frequency of the alternating current applied. All of the arguments above are based on DC theory, not AC. I guess the next argument is that we are talking about the power supply and that is 12v DC. True, however this power supply is attempting to stay flat under tremendous changes in demand created by a significantly amplified audio signal.

Frankly, I don't know why the consumer accepts amplifier manufacturers claiming huge power outputs, without both installing components in their amps that stabilize the input voltage during big current demands (read as capacitors that you don't have to buy separately) and requiring minimum current output capable alternators for proper operation.

Finally, you can not connect a capacitor in series in a DC circuit. It will not work as it will simply block the current flow. It must be connected in parallel, that is negative lead to ground and positive lead to both 12v source and amp 12v input. I'm not sure where this notion of a series installation came from.

Norm Peterson

I wonder if PR's "series connections" are between a preamp output and the main amp's input??? I seem to recall that the size of one of the capacitors on Radio Shack transistor milliwatt-range amplifier circuit boards was loosely related to the output frequency response, though I do not remember how it was connected.


Norm

kalli

Mark who are you? Alessandro Volta, Mr. Ampere, James Watt or the IEC :-D

Kalli

Adrenolin

I'm sorry I mentioned it now... should have known better to bring up Capacitors on a web forum LOL.

fakesnakes

Very funny!

Actually, I'm an electrical engineer by education, but an HR executive by occupation. I'm not sure which is worse!

By the way my dear Kalli, you forgot Nikola Tesla!