1 ohm amp heating up more into 4 ohms

Have you ? Seems to go against physics if there was one out on the market.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Nope never seen an amp run hotter when driving a 4ohm load vs. a 1ohm.

I guess you could if you cranked the gain up when running the 4ohm load and had very little gain for the 1ohm load. But thats not what we are talking about here.

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Might be possible based on the following.  The amp is biased to one ohm  with load resisters to keep power suppied maxed out, under light load exess power burnt off as heat.  Usually done in class a amps, which we haven't seen this century. 

This prolly Dont have anything to do with this, But doesnt the Alpine PDX1000.1 mono amps put out 1000 watts rms in bot a 2 ohm and a 4 ohm load?? If so, I could maybe see it happening in this application..

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UNLABELED Custom Car Club President

blackcivichatch wrote:

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This prolly Dont have anything to do with this, But doesnt the Alpine PDX1000.1 mono amps put out 1000 watts rms in bot a 2 ohm and a 4 ohm load?? If so, I could maybe see it happening in this application..

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Not possible. Why buy an amp that is maxed out at 1000 watts at 4 ohms and no expansion capabilities when loaded down to a 2 ohm load ? Whenever you load an amp from a 4 ohm load to a 2 ohm load, it will automatically output more power. Power out put will be more as well as power consumption.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

The JL 500/1 also claims to make the same power anywhere from 1.5 to 4 ohms.  There is nothing in the amp that changes rail voltage depending on what load it has presented to it.  If the voltage does not increase into a highe impedance, how can it make more power if less current is required by the load. 

So what prompted this question?

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From Alpine:

RMS Power Ratings

    * Per channel into 4 Ohms: (@14.4V Ƈ%THD+N, 20Hz - 200Hz) 1000W x 1
    * Per channel into 2 Ohms: (@14.4V Ƈ%THD+N, 20Hz - 200Hz) 1000W x 1

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UNLABELED Custom Car Club President

blackcivichatch wrote:

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From Alpine:

RMS Power Ratings

    * Per channel into 4 Ohms: (@14.4V Ƈ%THD+N, 20Hz - 200Hz) 1000W x 1
    * Per channel into 2 Ohms: (@14.4V Ƈ%THD+N, 20Hz - 200Hz) 1000W x 1

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What that (or any other legitimate amplifier power rating) means is that the amp will produce the listed watts into the listed load and still meet the listed FR and THD specs.  It does not mean it cannot do more and not meet the specs.

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So At 2 ohms it IS going to have a higher output?
I wasnt trying to Argue, just never seen this before.

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UNLABELED Custom Car Club President

Unless it has a power limiting circuit or it goes into protection, yes, it will produce more output into 2-ohms than it will into 4-ohms with the same input level. And it will get much hotter.

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Here's the way I see it:

Speaking AS an owner of the PDX1.1000, I was AMAZED to find that it does, in fact, run cooler at a 2-ohm load, than it does at a 4-ohm load! After accidentally discovering this, I went to my garage, and (after some searching...) grabbed my trusty 100:1 current transformer, ran the positive speaker wire through it, and proceeded to run some 50Hz sine waves to the woofers I have. First candidate was the stuffed TL in the trunk, with two 10" iso-loaded 4-ohm DVC TCSounds TC-1000 woofers. This was the 4-ohm setup. The second, my new Eclipse 10" Ti woofer, wired in parallel for 2-ohms.

All of the current measurements worked out - without changing ANYTHING on the deck, I got somewhere about 16A into the 4-ohm load, and 23A into the 2-ohm load. These currents correspond to somewhere in the 1050 watts range, a bit short of the 1176 watts the amplifier was birth-sheeted for, but I really didn't notice too much of a rise in current beyond this.

All I can think is that the power supply raises it's PWM FREQUENCY, to optimize the output rails for the attached load. Toroid transformers are very efficient in power conversion, and become even moreso as the input frequncy rises, especially relating to current conversion, meaning they transfer more energy OUT of them for a given energy INTO them, as the PWM driving frequency increases. I've opened this amplifier, and the toroid in it is TINY, (see the red ones on the left of this photo) compared to some others I have seen in this power category. Due to this, something MUST be "smart" in there, else I would never be able to observe this type of behavior.

While doing this, the power supply stage SPECIFICALLY works more efficiently, reducing the thermal output. (As a side note, MOST of the heat generated in any amplifier is in the DC-DC stage, anyway.) The OUTPUT stages in a high-quality Class D amplifier approach 95+%, and don't really change much... Whereas the OVERALL efficiency of a Class D amplifier, (all stages included) are around 80%. I've felt 150watt DC powered (as in high-voltage primary battery - really DC rails) Tri-Path (RIP ) Class D amplifier modules, running at full output and little more than heat-sink modules big enough to cover the module, and less than 1/4 inch thick, and they haven't EVER felt warmer than ambient.

In this case, THIS amplifier will only do 1000 watts into EITHER a 4-ohm load or a 2-ohm load.

If I'm wrong with my "rememberies", PLEASE i am an idiot, call me on it! You're the techie that all thechies *I* know aspire to be when they grow up!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."