Capacitors and Amps, Value, Brands?

Hello folks new to the 12 volt just registered.  I have been doing some looking around on this site  and have few brand/quality/value questions. I know when it comes to amps you can figure by the watt/price what youre going to get, what about caps farad/ price equation?

what is the performance dif between a cheap name  vs big name cap? huge price difference, are they cheating the numbers?

On amps, are digital mono amps worth buying? the increse in distortion makes me think I could save bucks with a cheaper  amp w/ similar numbers. ( I like savin money)

Last, I humbley request a recommendation; Infinty 12/reference series 300rms/1200max sealed box (probobly too small got it at wal-mart (go ahead and laugh))  what amp for this sub- I want to spend about 150. its getting about 165 watts now and I need some more.

Thanks

As far as the caps go, there are actually very few companies that make capacitors.  Most of them just buy from distributors and stick on their own label.  I don't know of any company that lies about the capacitance numbers.  Some will charge a premium for 20-volt caps as compared to 16-volt caps, but that's a waste of money.  What do you want the cap to do?  In my experience, they're only good for certain specific applications.

Digital mono amps are certainly the best bang-for-the-buck, but I don't know enough about the sound quality to make a recommendation.  I'm kind of an old-school Class AB amp guy myself.  I don't even use amps that have built in signal processors or crossovers.

As for your amps/box.  Measure how big the box is.  If it's only a little undersized, you can put in some polyfill to "fool" the speakers into thinking they're in a slightly larger box.  One pound of polyfill per cubic foot of enclosure space is the rule of thumb.  Be sure to pack the polyfill loosely, like cotton candy.  It doesn't work if it's all wadded up in the back corner of the box.

Scott Gardner

The cap is to keep the headlights from dimming and to keep me from spending hundreds for an alt  75$ vs 300$. I put the stereo in a little at a time, on a budget. I don't want the very best I'll settle for less. but I do want the most for what I am spending. the cap i'm looking at claims 2.25 farad- I'm runnng five amps and need a little boost to my juice,lights get dim and the vm moves w/ the beat when the sub hits.

Box had the polyfil  installed already when I bought it. Whats the dif between the classes of amps, or where can i find the info ?

Okay, I just wasn't sure if you wanted the caps to make your bass hit harder, your amps to run cooler, or the sound to be tighter.  Too many people have unrealistic expectations of what they want a capacitor to do for them.  For buying the cap, you can pretty much do a dollars-per-Farad comparison.  Most of the specifications are pretty much the same from model to model.  They just vary on the amount of capacitance.

As for the different classes of amplifiers, their are class A, AB, B, C, and the new digital-switching amps that some manufacturers call "Class D".  Pure class-A amps are pretty much only found in home audio, generally have the best sound quality, but have atrocioius efficiency numbers, down around 5-10%.  Class AB is the most common amp type, both for home and car use, has better sound than class B or C, and better efficiency than class A (AB efficiency is usually around 50%).  Class B and C amps aren't really suitable for amplifing music.  "Class D", or digital-switching amps, have awesome efficiency numbers (around 75-90%), so there's less drain on your electrical system for a given number of watts, but most of them are bandwidth-limited, making them only suitable for subwoofer amps.  I've heard that one company (Infinity?) has a full-range digital-switching amp, but I've never heard it.

Scott Gardner

Thanks for the info about amp classes. how about a little clarifaction on caps? $/farads equation doesnt seem to make much sense when a fosgate .5 costs as much or more as a no name 1 farad. I am looking at several on ebay ; 3 farads for 80$ or 2.25 for 60$or so.

I doubt Rockford Fosgate has a capacitor-manufacturing plant, so I think they just put their labels on someone else's caps and jack up the price.  Their prices actually seem pretty typical to me - $35 for .5F and $55 for 1F.  I hadn't realized how much prices had dropped.  I really think you'll be okay with a no-name, though.  Unless they're outright lying about the capacitance, they should perform as well as any other brand.  One thing to look for is the size.  If it's a traditional cylindrical capacitor, and it says it's 2F, but it's the size of a Coke can, they're probably full of it.  Keep in mind that this is only true for the traditional-style caps.  There are new "super capacitors" that have 2500F of capacitance (yes, that's two thousand, five hundred Farads) and only weigh about five pounds.  They're not really suitable for car use, though.

Scott Gardner

I've never used Batcaps, but they're not really capacitors.  They're a type of battery that has a very low internal resistance.  The theory is that using the Batcap battery means that you don't need a capacitor, since the Batcap will discharge its stored energy as quickly as a capacitor would.  There's no reason to believe they would have a short service life or any other problems.  The "lifespan" of a capacitor should be the same as any other electrical component, when used within specifications.  If it lasts the first 90 days, it will probably last the lifetime of the vehicle.

A "mono only" amplifier is just a single-channel amp.  Rather than having a left and right channel, it just has a single channel.  In cars, they're used mostly to power subwoofers.  In home audio, some high-end amps are mono, meaning you have to use two of them for stereo.  The idea is that by giving each channel its own amp, in its own chassis with its own power supply, that crosstalk between channels can be minimized.

Mono amps can be digital-switching, or they can be any of the other classes (A,AB,B,C) as well.  MOSFET is an acronym for Metal Oxide Semiconductor Field Effect Transistor.  This is just  a type of transistor.  Most digital-switching amps use MOSFETs in their power supplies, but many other types of amplifiers use them, too.  The reason that digital-switching amps use MOSFETs in their power supplies is the power supplies work by switching on and off very quickly, and MOSFETs are known for their fast switching rates.

Scott Gardner