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Old 20th May 2010, 06:35 AM   #1
vinodk is offline vinodk  United States
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Default LM3886 & low impeadence loads

I am looking to buy a gainclone amp with LM3886 chip. Can this handle low impeadence loads? I am planning to drive Martin Logan Motif which has nominal impeadence of 6ohms & minimum of 4 ohms.
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Old 20th May 2010, 10:15 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
if that 4ohm minimum is true then, yes.
Look at the datasheet and see why you should use an 18Vac or 20Vac dual secondary transformer to power the chipamp.
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Old 20th May 2010, 12:25 PM   #3
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I'm running a set of low impedance speakers with my LM3886 chipamp power supply has a 20vac dual secondary transformer.

The amp doesn't break a sweat even with the speakers dipping to impedance lows of 3 ohms. I must say I was rather concerned that the chipamp wouldn't cope but it has done so with ease.

Below is the impedance plot of the speakers, the crossover has evolved somewhat since the first measurements which showed dips on both sides of the impedance peak to 2.7 ohms, now roughly 3 ohms.

Tony.
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File Type: png all_impedance.png (16.3 KB, 226 views)
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Old 20th May 2010, 12:49 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi Winter.
One of the worst loads your speaker provides is at 200Hz, ~3.2ohms and ~16degrees of phase.
Very gentle load.
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Old 20th May 2010, 02:18 PM   #5
vinodk is offline vinodk  United States
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I am not too good at DIY projects with complexity such as amps. Is there anybody who makes fully assembled gainclone amps for sale as a hobby? Tim Rawson used to do that on Audiogon but it seems he no longer is active. I also have TEAC AL700P amp that I want to get modded but can't seem to find anybody who does the mods anymore.
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Old 20th May 2010, 05:09 PM   #6
wazzy is offline wazzy  Zimbabwe
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Default low impedance loads

I am running a pair of 4ohm nominal speakers and using a dual 22v transformer. Make sure to have a decent heatsink, I am using the tf package so have pretty large heatsinks, it does get pretty warm at high volumes.
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Old 21st May 2010, 03:12 AM   #7
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Quote:
Originally Posted by AndrewT View Post
Hi Winter.
One of the worst loads your speaker provides is at 200Hz, ~3.2ohms and ~16degrees of phase.
Very gentle load.
Thanks Andrew, good to know! I'd never considered the phase, only the impedance (thinking low was bad) Obviously a lot more to it than I thought!!

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