# quick question on power ratings

Discussion in 'Amps and Cabs [BG]' started by socalpyropunk, Dec 21, 2001.

1. ### socalpyropunk

Jun 13, 2000
Orange County, CA
when an amps rating say for example....2x400watts(@ 4 ohms)..does that mean you run two 8 ohm cabs or two 4 ohm cabs? I'm just curious because I will later be looking for an amp to run an Ampeg SVT410 HE and SVT115. thanks for the help

2. ### PollyBass******

Jun 25, 2001
Shreveport, LA
Well, when you run to 8ohm cabs together. you get a output of 4 ohms. But your head says that it sends out 2 outputs at 400 watts. so im guessing you use 4 ohm cabs.

3. ### Joris

The amp has two channels. Each channel puts out 400 watts when a 4 ohms load is connected. So to get all 800 watts out of it, you have to connect 2 4 ohms cabs. With two 8 ohms cabs you probably have 30-50% (amp dependent) less power.

If the amp has a bridge circuit (usually a switch on the back) you can connect one 8 ohms speaker and you'll get 800 watts out of the amp. But you'll only have one channel, because the two channels work together on one loudspeaker output.

In bridged mode, a bridgeable amp will have a minimal allowable load of twice the load minimum per channel. (2x4 ohms is bridgeable into 1x8 ohms)

4. ### socalpyropunk

Jun 13, 2000
Orange County, CA
thanks for the explination..I wasn't quite sure and didn't want to go buying any amps mistaking their power ratings

will running two 8 ohm cabs in parallel (I think thats it..into one cab then out of that into the next..might have the wrong term) from the bridged circuit draw the 4 ohm load? Is my thinking correct?

5. ### Joris

Yes. Two 8 ohms cabs connected "daisy chained" give you a 4 ohms load, but many amps are not happy with a 4 ohms load in bridge mone. When I say not happy, I mean "likely to smoke"

With one 8 ohms cab on each channel (ie not bridged) you'll be much safer. I personally don't care much for the somewhat lower power in this setup.

6. ### Matthias

May 30, 2000
Vienna, Austria
For what I know from another post the amp in question is an Ampeg SVT-4 Pro which is capable of running 2Ohms at each channel or 4Ohms in bridged mode (at least that's what the specs say)
So two 8 Ohm cabs daisy chained should not be a problem in bridged mode?
Matthias

7. ### socalpyropunk

Jun 13, 2000
Orange County, CA
Joris: This is not an amp that I actually have.. I was just using it as an example.. I made up the numbers.. I will later be looking for an amp was was just trying to understand what to look for because I will have two 8Ohms cabs.
Mathias: You saw the same thing as me. Thats why I was thinking it should be fine.