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Old 24th February 2006, 11:59 PM   #1
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Default Paralleling LM4780 chips?

I am paralleling 2 LM4780 chips per channel fo my amp.

I have the power wired, but I am unsure of how to wire the signal paths. Both IN AND OUT.

I have ideas but thought I better ask before I see that magic black smoke!!LOL
Do I just run the + signal to one chip and the - to the other and then the corresponding polarity to the output jack?
*A diagram would be nice*

I am using the kits from audiosector.com.

Thanks a ton,

Dominick
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Old 25th February 2006, 01:09 AM   #2
amt is offline amt  United States
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How about the schematic thats on the website, showing the connections?

amt
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Old 25th February 2006, 01:10 AM   #3
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Read LM4780's datasheet.There is a schematic of paralell config.
If the power supply is wired correctly,you shouldn't smoke LMs that easy.
A common problem is when there is no insulation washer between chip and heat sink(chip has -Vs connected to its case). If the sink is grounded , the power supply is usually powerful enough to blow IC in chunks.I have done it by myself once .

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Old 25th February 2006, 01:33 AM   #4
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I dont think that my question was understood.

I have 2 chips already wired in parallel. Now I need to know how to parallel the paralelled chips!!

Dominick
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Old 25th February 2006, 01:38 AM   #5
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If I'm correct, that would give you support of down to 1ohm...any reason to need it that low?
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Old 25th February 2006, 02:35 AM   #6
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Good observation.

That is exactly why I am doing it.

I intend on using this amp on my Martin Logan Ascent i speakers.
I called the company direct and they said that the speakers run at 2.5 ohms @ 20k.

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Old 25th February 2006, 03:03 AM   #7
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2.5 ohms...that would run fine just with a parallel lm4780. 1 x 4780 parallel should give you about 120w @ 2 ohms I'm pretty sure.
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Old 25th February 2006, 05:33 AM   #8
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I already tried it and blew one of the chips in less than a minute!


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Old 25th February 2006, 11:20 AM   #9
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Did you have a heatsink on it? It shouldn't be a problem at all. People use the paralleled lm4780 setup from brian at chipamp.com for 2 ohms.

**edit**
Here is the schematic they use:
http://chipamp.com/lm4780.pdf
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Old 25th February 2006, 12:31 PM   #10
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LM3886s can stand continous short circuit and has lots of protection.
Adding more in parallel may even worsen results , if ICs have DC offsets greater than a few mV.
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