In general - 1 ohm Class D's -- same power at 2 ohms?

[n2audio 5,000+ posts]

Came across this at CS.

It's not logical, and was hoping some of the more technical members would be willing to take a few minutes and help me make sense of it...

Remember kids that your amp, especially a class D mono block amp will run full power into a 2 ohm load even though its 1ohm stable or states that it produces full power into a 1ohm load.. I know, this goes against what everyone says, but it's true. Simply adjust the gain properly to the 2ohm load and PRESTO, full power. If you want more info on this please email... Remember that an amp is simply a gain device. Signal in plus whatever +db gain the amp can do = output.

Click to read more...

 

[ultimate157 5,000+ posts]

That was posted by Robot Underground on eBay... Let me get the response he sent me.

Here ya go:

You almost have it. The amplifier has a range of input voltages.. Usually up to 6 or even 8v on most class d car amps these days. That gives you quite a range of input that the amp will accept without going into clipping.
When you load down an amp, any amp, to it's lowest acceptable load, you simply make the amp more sensitive to the input you give it. This will send the amp into clipping sooner than if you ran it at 2ohm. It would also allow the amp to run cleaner.

The input vs output looks like a parabola where a certain range of intputs vs loads will all yield full output.

 

[Ed Lester 10+ year member]

He is not correct although his theory makes some sense.

At optimal signal voltage input, an amp designed to make full power at 1 ohm will make more power at 1 ohm than 2 ohm 100% of the time. Less resistance in the load will allow more current to flow. Voltage output will stay the same. The extra current times the voltage equals what? More wattage (yay!) it's funny how that works.

Now the higher current flow will create more heat which can cause higher distortion and less efficiency, but in most applications it is not enough to make a difference in how we use these amps.

Just go and measure such an amp.

 

[n2audio 5,000+ posts]

Less resistance in the load will allow more current to flow. Voltage output will stay the same. The extra current times the voltage equals what? More wattage (yay!) it's funny how that works.

Right - which is why the claim seemed very fishy to me.

 

[Haunz 10+ year member]

Different amplifiers will behave differently, and it all comes down to how much rail drop you have going from 2ohm to 1ohm....

some amps like the JBL 1200.1 put out almost as much power at 2ohms as they do at 1ohm; while others will put out nearly twice the power at 1ohm....

 

[helotaxi 5,000+ posts]

A Haunz said, rail drop is the key. The statement in general is patently false.

For the amp to make the same power at 2 ohms as at 1, it would have to make higher voltage at 2 ohms. Most amps will make a bit more voltage into the higher load but not enough to allow full 1 ohm power into a 2 ohm load unless the amp is designed to do so.

 

[pawn man 10+ year member]

oh, so my strapped pr of 40.1s will do the same power @2 ohms as they do at .8 strapped. oooo i don't think so. infact i know not. (i ran them this last weekend @ 1.2 ohms did 153.1 w 3 12s. at sbn i ran them @ .8 did 155.9 w 2 12s in the same configuration) you can not argue with those figures.

 

[jdawg 5,000+ posts]

oh, so my strapped pr of 40.1s will do the same power @2 ohms as they do at .8 strapped. oooo i don't think so. infact i know not. (i ran them this last weekend @ 1.2 ohms did 153.1 w 3 12s. at sbn i ran them @ .8 did 155.9 w 2 12s in the same configuration) you can not argue with those figures.

I dont think you understand

 

[pawn man 10+ year member]

i do understand, i have been doing this for some time now. and i have ran the amps at so many dif. loads that i know what they will do. and they will not come even close at 2 ohms to what they do at 1.

 

[LowEndTheory 10+ year member]

I thought he meant that if you adjusted the gain to give full power at 2 ohms you could get the same wattage. He wasn't saying that by leaving all settings the same the amp will put out the same power at 1 ohm and 2 ohms.

 

[pawn man 10+ year member]

what i am saying is that there is no way you can adjust the amps to do max power at 2 ohms.now if you are not wanting to get all you can get out of the amp then yes.