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Author Topic: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech  (Read 13208 times)

Goerge Thomas

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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
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Chris Hindle

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #1 on: September 19, 2012, 08:51:28 am »

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

In my experience (QSC EX-4000), it will pass signal. As the volume is raised, it will get hot. It will thermal out, light up all the pretty red lights, and shut down.
Then you will find out that your assigned A-2 has no fusking clue how to hook up more than 1 speaker at a time, and has never worked with more than EON or Wackie S-O-S rigs.
Once the load is corrected, it will hapilly run like normal for another 10 years.
The A-2,  not so much.
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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 #2 on: September 19, 2012, 10:45:00 am »

In general amplifiers use current limiting to protect themselves. This current limit threshold is set so a 4 ohm (or lowest valid load) can put out full power.

Since I am too lazy to calculate actual numbers lets say Amplifier Q is putting out 20A at full power into 4 ohms so current limit will be just over that. The 1 ohm load will draw 4x the current of a 4 ohm load, so it will hit the roughly 20A current limiting at 1/4th of full output voltage.

If it has sophisticated clip limiting, turned on, it will detect this current limiting  as clipping and reduce gain if turned up higher. If not it will current limit, similar to clipping but a little uglier.

Below limiting the amp will work pretty much normally but thermal dissipation in the heat sink will be seriously elevated, so it can thermal out quickly if pushed.

DO NOT OPERATE IT THIS WAY.

JR

PS; I have heard stories of customers operating amps into 1 ohm loads in "show must go on" emergencies. If the amps are robust, well cooled, and you are lucky, you might get away with it.
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Elliot Thompson

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #3 on: September 19, 2012, 11:37:30 am »



You will also be taking little advantage of what the loudspeakers are capable of producing in terms of SPL. Since the amplifier is offering its maximum output @ 2 ohms, operating the amplifier below 2 ohms will just divide the power amongst the speakers even further.

A Crown Macro-tech 5000 offers the following wattage

1300 watts @ 8 ohms = 1300 watts for one 8-ohm driver

2000 watts @ 4 ohms = 1000 watts per 8-ohm driver

2500 watts @ 2 ohms = 625 watts per 8-ohm driver

Under 1-ohm conditions, you can expect each 8-ohm driver to see around 153 watts. Using such a method is a waste of time if your loudspeakers are 1000-watt (Program) rating for you are operating the loudspeakers far below their 1000-watt (Program) rating.

In the case of the QSC PL 6.0 that would 218 watts per 8-ohm speaker under a 1-ohm load in stereo mode.


Best Regards,
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Greg_Cameron

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #4 on: September 19, 2012, 12:25:50 pm »

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 ;)
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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 #5 on: September 19, 2012, 03:51:16 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.
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Yosi Melamed

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #6 on: September 19, 2012, 04:09:59 pm »

A quote from both the Macro Tech i series and the i-Tech HD series data sheet:
"Load Impedance: (Note: Safe with all types of loads)
Stereo: 1/2/4/8/16 ohms.
Bridge Mono: 2/4/8 ohms."

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Chris Hindle

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #7 on: September 19, 2012, 04:28:32 pm »

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 ;)

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.
« Last Edit: September 19, 2012, 04:48:03 pm by Chris Hindle »
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Chris Hindle

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #8 on: September 19, 2012, 04:45:51 pm »

sorry. wrong button.
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Elliot Thompson

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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #9 on: September 19, 2012, 05:29:38 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.

How did you get those figures when you were inquiring about a 1-ohm load?

A 1-ohm load is, eight 8-ohm loudspeakers residing on a single channel.

The best performance from an amplifier is always 4-ohms per channel. This enables the largest amount of power to your loudspeakers with no overheating issues from the amplifier.

Best Regards,
« Last Edit: September 19, 2012, 05:37:23 pm by Elliot Thompson »
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Re: What happens when you load an amp down to 1 ohm? Powerlight/Macrotech
« Reply #9 on: September 19, 2012, 05:29:38 pm »


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