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Old 08-28-2013, 02:43 PM   #2
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Join Date: Jan 2013
Location: Mickleton, NJ
Posts: 1,776
Re: For you stereo guys

Originally Posted by Geos 72 View Post
Hello to everyone, I think I could use an amp in my truck but I never had one. I have a 240w radio in my 72 C10 w/ two 250w "under the seat" speakers and 300w speakers in each of my kick panels. I'd like to give the radio a little help but I'm not sure how many watts the amp should be. I was thinking maybe an 800w amp w/ four channels would work? I'm not sure if I'm on the right track here but I can't afford a top of the line amp. Anyone got any ideas? Sure would appreciate it. Thanks, George
First thing is first-----look for the RMS ratings of your speakers. Depending on who the speakers are made by, that could be anywhere from 25% to 50% of the max rating most manufacturers advertise depending on what ohms were used for the advertising.
Example from an amp I installed recently in a buddies truck:
RMS Power Rating (@ 14.4V):

4 ohms: 450 watts x 1 chan.
2 ohms: 800 watts x 1 chan.
1 ohm: 1100 watts x 1 chan.

This is a monoblock subwoofer amp, and the box states its 1100watts in really big letters. Except at 4 ohms its really 450 watts, but that is at 14.4V, where most alternators are regulated to 13.8 volts. So the wattage thhig can be a bit nebulous.

One thing you should look for is "CEA-2006 compliant amplifier" on the specs. This usually keeps the manufacturer from fibbing too much.

Also take a look at your 240watt radio. Most head units are putting out 15-20 watts RMS per channel.

Then, look for a 4 channel amp that matches up to your speakers RMS as closely as possible. A little over is ok. Most full range speakers are 4 ohm, so if you have a 4-channel amp running 4 speakers (1 output running 1 speaker) you want to look at the 4-ohm ratings.

As far as brands, any of the common name brands make pretty affordable stuff, and they work ok. Not audiophile quality, and definitely not competition worthy, but decent sound for what most people want/need/desire. Stay away from brands like Crunch, Pyramid, Boss, etc. They are right up there with the old Spark-o-matic radios...LOL

I personally have had very good luck with Hifonics amplifiers. Inexpensive, but they work very well.

1970 Chevy C-10 SWB, 350, TKO 600 5 speed
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