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Author Topic: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech  (Read 13195 times)

John Roberts {JR}

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #10 on: September 19, 2012, 05:43:52 pm »

with the powerlight 6.. would each box not see 875 watts with ideal power for the amp?

7000 total/2 =3500/ 4 = 875 per box on a 600 watt program box isn't terribly off is it

I am not intending to do this but it seems less ridiculous than I thought given proper cooling and power.

I only calculate approximately 437.5W per box for  4 x 4 ohm boxes in parallel, but this involves some serious guesswork.

This issue isn't how many watts each speaker gets, but will the amp be happy (no it won't be happy).

DO NOT DO THIS

JR
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Randall Hyde

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #11 on: September 19, 2012, 08:33:52 pm »

Exactly as the title asks.

Let's say someone messes up the wires and load 4, 4 ohm box's onto one side of a macrotech 5000 or a qsc powerlight 6 or 9 and runs it that way. In stereo mode of course. That would be a 1 ohm effective load on one side of a big metal amp.

Do the amps show fault before they even pass signal? Do they function as normal given proper power supply? Does this kill the amp?

What exactly would happen I am curious.

-Goerge

Regardless of whether the amp can handle it (and some can, ITech comes to mind), when running below 4 Ohms the Damping Factor becomes a big issue. Long speaker cables (at one Ohm, "long" is probably a couple of feet) start affecting the sound produced. I never run below 4 Ohms for this very reason.
Cheers,
Randy Hyde
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Tim Perry

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #12 on: September 19, 2012, 09:10:19 pm »

Let  us not overlook the wire resistance in this equation.

let me create an extreme but possible scenario: an amplifier into 100 ft of 16 AWG cable followed by four 4 ohm loads.

As the cable consists of 2 conductors the resistance will be for 200 ft. this will most likely be about .8 ohm (8/10 th). 

This points out that depending on wire size and length that about half the available power will be dissipated in the cable as heat AND that the load that the amplifier sees may be close to 2 ohm's or higher. (remember speaker loads are nominal ratings)

As the wire heats the resistance goes up which increases the ratio of wasted power... you see where this is going? 

Ok, most of us run shorter runs and heaver gauge wire then this example but I hope this may help resolve the unasked question:  "hey I run 8 speakers a side all the time at such and such a show and it works just fine, how come you say the amp will blow up or thermal out?" 
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Goerge Thomas

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #13 on: September 19, 2012, 10:34:48 pm »

Everyone, thank you for the responses!

This is exactly the type of responses I was hoping for. When I searched I found nothing much on the topic and now others will be able to find this pertinent information when they search.

Moral of the story is what will happen and why and why not to do it.

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Jeff Bankston

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #14 on: September 20, 2012, 03:06:22 am »

As far as I know, the only stereo amp rated to actually run at 1 ohm stereo/2 ohms bridged was this pig:

http://www.crestaudio.com/media/pdf/10001_10-15-97.pdf

And it's only 145 lbs! Don't forget you need at least two 20A circuits to run it, probably two 30A if you really want to run it at 1 ohm ;)
well thats almost twice the weight of my QSC 3800 amps that weigh 75 pounds. i'm thankfull i dont have to repair one of those Crest 10001 amps.   
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John Roberts {JR}

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #15 on: September 20, 2012, 11:27:11 am »

Everyone, thank you for the responses!

This is exactly the type of responses I was hoping for. When I searched I found nothing much on the topic and now others will be able to find this pertinent information when they search.

Moral of the story is what will happen and why and why not to do it.

What will happen is it will work at low level but run into current limiting before reaching full output voltage. Don't do it because the amplifier is being operated beyond it's design targets, and will run hot as a firecracker.  Older amps could blow up, modern designs are customer-proof so they just shut down after overheating.

DO NOT OPERATE YOUR AMPS THIS WAY.

JR

PS: While DF and other discussions are true that is not the most important reason not to do it, it's the heat.
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Sam Zuckerman

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #16 on: September 20, 2012, 09:21:49 pm »

It will probably function at very low levels, but as you get loud(er) the amp will most likely go into protect and cease working.

As the volume is raised, it will get hot. It will thermal out, light up all the pretty red lights, and shut down.
If I'm not mistaken, on macrotechs the red lights will go off ;)

At 128 lbs (256 lbs for stereo), there was always the MacroTech 10,000
208 3 phase, 6,000 watts at 1 ohm, 8,000 watts at 0.5 ohm.
Haven't used one since the mid eighties, or seen one since, for that matter.
After I hooked it up on a dare from "the boss", he was scared shitless about the damage it could do if it got hooked up wrong (like if only 1 speaker was attached). Don't forget, this was back in the day of 400 watt woofers. We ran it for a couple of gigs on MTL-4's, (4 on each amp, if I remember) then he sold them off to a club install. Probably boat anchors by now.
I believe there was one on gear source a while back. Not too expensive either... that is if you are judging on price/pound!
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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #16 on: September 20, 2012, 09:21:49 pm »


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