class AB amps for subs

[SYLrules 10+ year member]

hi. i havent worked with any car audio for a while so im a bit rusty on this subject. i got my current setup almost 3 years ago and havent changed a thing since.

its two 12" MA XL's wired in parallel with i think an MA HK1397 running 2 x 700w RMS @ 1 ohm. the amp is a class A/B and im wondering if id be better off with a class D amp? sometimes the amp shuts off and goes into protection mode when it hasnt been running for very long. it all depends on what song im listening to. i guess certain frequencies dont gel well with the amp? i dont listen to rap, only rock and metal, and some nine inch nails (thats usually what shuts off my amp).

would the size of the box have any effect on how hard the amp works at certian frequencies? i need a smaller box anyway, this one would be great for rap (1.25 cu/ft per sub) but the ideal freq. is just a little too low for what i need it to be.

thanks for the help in advance.

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[tcguy85 10+ year member]

class a/b is ok for subs. i have a DD C2a on my sub and i like it. works well.

 

[Lakota 5,000+ posts]

Class D tends to be more efficient than class A/B. As far as hearing a difference, you won't.

 

[tcguy85 10+ year member]

Class D tends to be more efficient than class A/B. As far as hearing a difference, you won't.

nope, you won't hear a difference.

as far as being more efficient. that depends. run a class d down to 2 or 1 ohm and the efficiency isn't so great anymore. class a/b amps usually are only ok down to 4 ohms when bridged and at 4 ohms efficiency isn't a huge concern. most a/b amps should be fairly efficient at 4 ohms.

i'm running 1200 watts all a/b in my car and my stock electrical system doesn't mind it at all.

i'd say if you're gonna run the sub at 4 ohms then get a class a/b. it's cheaper to get the same power at 4 ohms in a class a/b amp than it is to get good power at 4 ohms in a class d amp. you'll find it hard and expensive to get good power at 4 ohms out of a class d amp.

 

[ThatChevyGuy 5,000+ posts]

Prolly wanna run 2 ohm stereo per channel, that will solve the protection issues.

 

[SYLrules 10+ year member]

my bad. i am running it 2 x 700W RMS @ 2 Ohm Stereo

ive also got a 380w pioneer amp powering my components and i never have a problem with the lights dimming or anything. ive kept the stock alternator but i got a better battery though i probably didnt need it.

ive kept all of the wiring the same since may '05. its not that i always have protection issues, just certain songs i guess have loud bass at just the right frequencies and it rattles the cage just right.

 

[Slammed 5,000+ posts]

dont whats up with my freakin 07 Altima

I got Class D Amp that produces 400 watts RMS @ 2 ohms and my lights dim //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[helotaxi 5,000+ posts]

as far as being more efficient. that depends. run a class d down to 2 or 1 ohm and the efficiency isn't so great anymore.

If the efficiency is bad at an impedance into which the amp is designed to be run, then there is a problem with the design of the amp. Class D amps are going to be more efficient in real world use across the board compared to a Class A/B design regardless of impedance. A Class A/B amp is most efficient at full power and even then the efficiency of a really good design well executed is going to be around 70%. At less than full power (where you operate an amp 100% of the time when playing music) the efficiency suffers horribly dropping onto the 30% range. Compare this with a Class D amp that is within a few percentage points of its maximum efficiency regardless of power output. Not that big a deal when talking about smaller amps that are only putting out an average of 30W with music but when you start talking about larger sub amps that are doing a few hundred watts on music, the difference in efficiency is pretty important.
You also have to account for amp footprint unless space is of no concern. I have a very large Class A/B amp from the mid 90's and it is roughly 3x the size of my modern Class D sub amp. Puts out less power, too.

i'm running 1200 watts all a/b in my car and my stock electrical system doesn't mind it at all.

I've run similar setups with mixed results depending on the type of music I was listening to. Rock, country jazz etc. the stock electrical was usually more than adequate. Throw in the bass tracks or heavy classical and the headlights looked like strobes even with an alt 2x the size of the stock one and two batteries. Just because your setup works out OK, the same can't necessarily be said about his.

i'd say if you're gonna run the sub at 4 ohms then get a class a/b. it's cheaper to get the same power at 4 ohms in a class a/b amp than it is to get good power at 4 ohms in a class d amp. you'll find it hard and expensive to get good power at 4 ohms out of a class d amp.

Agreed.

 

[TonyC 10+ year member]

dont whats up with my freakin 07 Altima

I got Class D Amp that produces 400 watts RMS @ 2 ohms and my lights dim //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

(IMO) a Class D amp @ 400 watts shouldn't be causing dim lighting, do you have other stuff hooked up?

 

[theothermike 10+ year member]

ive used both and for some reason i feel the class a/b has a different sound to the design over class d. It did **** more juice but as mentioned efficiency is lost.

 

[Mr. C 10+ year member]

dont whats up with my freakin 07 Altima

I got Class D Amp that produces 400 watts RMS @ 2 ohms and my lights dim //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

Something needs to be checked. My 03 Altima has about 1000w rms and no dimming issues at all. I run all ol' skool US Amps. Pure class a/b power.

Not sure why you're getting dimming issues with that amp.

I may go class d someday, but that's only when my USA 2000's blow up. Only class D amp I'd really like to play with is one of the Stetsom 7k's. They make me wanna upgrade when I can spare the $$$.

 

[bigbangtheory 5,000+ posts]

In my expierence I have had better luck with the class D's. I just run A/B for the cost right now. I miss being able to slam and feel the amp and still be cool. I wouldn't dare touch my A/B amps unless I had a steak to fry up real quick! I also seemed to get less pull from my electrical with a class D.

Not that I don't like A/B amps. I hope my new Autotek does well. Had a cutting out problem like you had with my old school Lanzar.

 

[phantom240 5,000+ posts]

My 'ole Alpine is still kickin *** in my trunk. This amp has gone through... lemme count... my last 5 vehicles, 3 and a half years of service... And still amazes me.

 

[Grinder1989 5,000+ posts]

I'm running a US Amps VLX-400 on a single 15" sub @ 1.4 ohms. I'm getting around 2k out of my amp. I also had a USA-150 on some tweeters and I didn't dim at all with a 140 amp alt and a yellow top. My new setup will be the VLX and a PPI ProMos-450. I've ran a Sundown 1500D on the 140 amp alt and a wet cell and was dimming slightly losing around .2 to .3 volts when the bass hit. I also had a small Targa 4 channel for my coaxials when I had them. I loved my Sundown and if that VLX hadn't come up I wouldn't have got rid of it. I would have loved to see how it did with the yellow top. IMO with the correct electrical, class A/B vs. D doesn't really matter. Yes D is more efficient and excellent for competition or cars with a crazy amount of subs, but A/B, especially the old US amps, PPI, and Orion amps can perform just as good as class D's if you keep them fed. I don't have a preference, but I miss my Sundown. Just get what you can afford and what works for you.

 

[dipitydoo 10+ year member]

SYLrules, you might be having problems with loose connections/wires or a damaged or poorly designed amp.

As for the class a/b vs. class D debate, as stated already, the real world differences are very significant. Even at their lowest rated impedances, most class D amps typically are better than 70 percent efficient, at 1/3 and full power levels. Class A/B amps generally fall into the 30's at best with music.

That said, if you are not experiencing major voltage drops or dead batteries with the current setup, there probably isn't a whole lot to be gained by switching to class D amps, besides reduced heat or a smaller footprint.