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Old 21st November 2005, 07:13 AM   #1
Wynand is offline Wynand  South Africa
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Default 6 channel LM4780 question

Hi

I'm thinking about doing a 6 channel amplifier using 3 lm4780 chips. I've got a 500VA transformer with the secondaries stripped. I'm planning on rewiring the secondaries but want to know if a 500VA transformer would be enough for this amplifier.

What would the minimum VA rating needed be?
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Old 21st November 2005, 08:00 AM   #2
owen is offline owen  United Kingdom
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500VA a potential 80W per channel feed. I'd say marginal, but on the right side of just ok. Transients will be softened, and dynamics may suffer as a result, but it may sound great....



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Old 21st November 2005, 08:22 AM   #3
Wynand is offline Wynand  South Africa
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Thank you!!
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Old 21st November 2005, 08:49 AM   #4
Nordic is offline Nordic  South Africa
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Just leave a window open, when you crank it up, ok?
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Old 21st November 2005, 09:19 AM   #5
Wynand is offline Wynand  South Africa
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Why
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Old 21st November 2005, 10:00 AM   #6
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Old 21st November 2005, 10:31 AM   #7
Nordic is offline Nordic  South Africa
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So that I can hear it!!!!!!!!!! lol
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Old 21st November 2005, 10:35 AM   #8
Wynand is offline Wynand  South Africa
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What is I get a seperate Xformer for the subwoofer's channel, Leaving 100VA per channel for the rest?
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Old 21st November 2005, 10:49 AM   #9
Nordic is offline Nordic  South Africa
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Wynand will you be doing a bridged or parallel type setup to drive the woofer? I suppose if you throw in another of those chipamps (8 chan. totl), you could use 5 channels for your surrounds and centre, and maybe then use the remaining 3 amps to somehow work together powering your woofer.
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Old 21st November 2005, 10:55 AM   #10
sangram is offline sangram  India
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If the amp's efficiency is 70%, then for an output of 60 watts you need 85 VA energy input. But that is without headroom. with a 3dB headroom for clipping you're talking 170VA. 160 VA is a good indicator of where I'd feel safe per channel, so the rails don't sag at lower loads.

You could run it with 80VA but I guess the rails would sag once the volume goes up, and on dynamic stuff you may drive the amps into clipping due to rail sag (even though it's within chip capability). Would suggest not going below 120-130 VA unless you're desperate.

I have some EI frame transformers of 220 VA (44V CT 5 amps RMS)and each is meant to drive one chip (Two channels), and that is skinny by my reckoning. But EI frames have serious size limitations and that's about the best I could do keeping the height controllable - toroids are too hard to come by around here.
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