LM4780 4ohm @ +/-40V rails - Page 2 - diyAudio
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Old 13th December 2006, 03:32 PM   #11
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This is something I have always wondered about...

What about CRCLC? You see CLC and you see CRC, how come nothing on CRCLC or CLCRC?

Inquiring minds want to know.
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Old 13th December 2006, 03:36 PM   #12
alexcd is offline alexcd  United States
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You can keep adding poles to the filter as you would any "Low Pass Filter." Measurable gain vs cost would be diminishing near DC.
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Old 13th December 2006, 03:48 PM   #13
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Default CRCLC...

Same overall params I used before:

CRCLC: 34.3v, 110mV ripple

Kind of makes you wish the program had a function where you could give it a budget for components and have it permute the possible components to find the best fit...

ie is it better to have CRCRC, with smaller caps than single big C, or some other variation...bigCRsmallC etc

Stuart
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Old 13th December 2006, 03:52 PM   #14
alexcd is offline alexcd  United States
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Big caps aren't always big $$$ though. Capacitance is cheaper than it used to be but it still pays to use it with intelligence.
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Old 13th December 2006, 04:27 PM   #15
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I'm a bit confused. Reading your first post it and thread title it appears you are going to drive two 8 ohm speakers wired in parallel to be 4 ohms and then configure the LM4780 in parallel mode to drive them? Is this correct? If so you're wasting time, just drive each speaker from one ouptut. No need to do any parallel of anything. The output power will be the same at 8 ohms on each channel as 4 ohms on the channels in parallel. In fact, single 8 ohms per channel is better since you will have resistors to connect the outputs in parallel that drop power and add noise. If I don't understand than ignore all the above.

The chip should not pop just run hot. The LM4780 is recommended to run at +/-35V with 8 ohms/Ch so +/-40V is going to run hotter. Don't expect it to run sine waves all day without over heating but with music and a big heat sink you might get away with it. The other thing to be careful is the 84V (+/-42V) and the 94V (+/-47V) ratings. Exceed those and you're asking for blown chip. Might need to drop a little voltage and maybe add some sort of protection for high line condition.

Good luck,
-SL
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