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Old 23rd July 2005, 08:56 PM   #1
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Default output resistor matching for LM4780 paralleled

I really did search on this.... and couldn't find my answer

for paralleling a pair of LM4780 where should the output resistor be placed for matching?

also is there any set resistance for these chips for paralleling them? I know they need to be 0.1% tolerance but is there any specific ohm? What about watt capabilities (1/16 watt, 1/8watt, etc)

I'm refering to the supposed extra resistors needed in the outputs for paralleling...
not the resistors that are already in the schematic
thanks
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Old 23rd July 2005, 09:34 PM   #2
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0.1-0.3 ohm should work fine, 3-5 watts. they don't need to be 0.1% tolerance though...
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Old 23rd July 2005, 10:34 PM   #3
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Quote:
Originally posted by bigmike216
0.1-0.3 ohm should work fine, 3-5 watts. they don't need to be 0.1% tolerance though...

1% tolerance is ok?

also these are placed in line with the output to the speaker terminals? or elsewhere?
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Old 23rd July 2005, 10:57 PM   #4
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They are placed after the output pins of each chip.then the other end of the resistors are connected together in parallel for your parallel amp.
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Old 24th July 2005, 12:21 AM   #5
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Quote:
Originally posted by bigmike216
They are placed after the output pins of each chip.then the other end of the resistors are connected together in parallel for your parallel amp.

many thanks
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Old 25th July 2005, 07:37 PM   #6
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It is more important that you match the gain of each amolifier and take care of DC-offset (if you have such). A "bigger" output-resitor will to soem extent take care of the last issue

Have fun

Thomas
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Old 6th August 2005, 09:40 PM   #7
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can these resistors be non-inductive/wirewound???
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Old 7th August 2005, 07:36 AM   #8
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Yep. Those are pretty much your best bet. Mouser has a nice selection of the Dale non-inductive wirewounds.. Check the LVR3 series.
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Old 7th August 2005, 10:03 AM   #9
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Look at www.czechaudio.com - at my PA 03, some photos are there .
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