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Old 10th September 2011, 10:34 PM   #1
Serow is offline Serow  Canada
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Default 2-ohm stable, but low power, amp?

Hi all, I'm trying to find an amplifier for a 2-ohm speaker load, but it only needs to be about 10-15W. I'm not sure if I should be posting here, or in the solid-state and/or chip amp forum, so please point me in the right direction

The speaker in question is a pair of HK Soundsticks that I got for free, ATPM 10.04 - Review: Harman Kardon Soundsticks II

They are 4-speaker mini line arrays, with a nominal 2-ohm impedance.

If anyone knows of one of the inexpensive commercially-available digital amps could handle a 2-ohm load, that would be ideal It wouldn't need to put out a lot of power...

Thanks for your help,
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Old 13th September 2011, 10:21 AM   #2
Eva is offline Eva  Spain
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Class D amplifiers just have a current and a voltage output limit. Keeping the same peak output current level, output device dissipation does not increase for lower load impedances.

If you take a 100W 4 ohm class D module and use it at 50% to 70% of rated supply voltage (or just at 50% to 70% the rated signal level for full power), it will become a 25W to 50W 2 ohm amplifier (depending on design margins). The reduction in supply voltage is optional, just to avoid current limiting in modules that would shut down otherwise, and it only makes sense with modules that are still capable to work with the lower voltage.

So in other words, any class D amplifier can drive 2 ohms properly if either supply voltage or input signal are kept under control.
I use to feel like the small child in The Emperor's New Clothes tale

Last edited by Eva; 13th September 2011 at 10:27 AM.
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Old 13th September 2011, 12:02 PM   #3
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Those speakers probably have four 8ohm drivers connected in parallel for a total of 2ohms. You could just re-wire them series/parallel for 8ohms total.

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Old 13th September 2011, 02:47 PM   #4
ssanmor is offline ssanmor  Spain
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True but... some class-D amplifiers will exhibit a lower higher cutoff frequency when used at 2 ohms. So use a post-filter feedback amplifier or you will have to touch the output filter values for full-range operation at below the nominal load.
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Old 13th September 2011, 04:19 PM   #5
Eva is offline Eva  Spain
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It's no longer 2 ohm at 20 khz...
I use to feel like the small child in The Emperor's New Clothes tale
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Old 14th September 2011, 12:55 PM   #6
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Originally Posted by Serow View Post
The review is great!
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Old 14th September 2011, 02:04 PM   #7
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Back to the original question.

Any TA2020 based amp will drive 2 ohms speakers as long as you keep supply voltage at around 12V. That will give about 36Wrms per channel.
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Old 15th September 2011, 11:53 AM   #8
tinitus is offline tinitus  Europe
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it just so happened that I actually heard those speakers the other day
I was shocked by the power
and it actually sounded quite nice too
even an old hifi geek like me was impressed

'ordinary' people probably just think... nice
but knowing just a bit about speaker design, you also know that this shouldn't be possible at all

those are just tweeter cones, with low Fs
looks like the small 1" Tangband

I doubt you can do this without the sub woofer module

all the electronics is in there
I reckon its 'stuffed' with EQ
funny thing is, even if the sub is made of clear plastic, there's not much to see in there either
its close to a mystery
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