6 channel LM4780 question

Wynand · 21st November 2005, 07:13 AM

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?

owen · 21st November 2005, 08:00 AM

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....

Owen

Wynand · 21st November 2005, 08:22 AM

Thank you!!

Nordic · 21st November 2005, 08:49 AM

Just leave a window open, when you crank it up, ok?

Wynand · 21st November 2005, 09:19 AM

Why

rampage101 · 21st November 2005, 10:00 AM

For the fire in case it crashes and burns.

Nordic · 21st November 2005, 10:31 AM

So that I can hear it!!!!!!!!!! lol

Wynand · 21st November 2005, 10:35 AM

What is I get a seperate Xformer for the subwoofer's channel, Leaving 100VA per channel for the rest?

Nordic · 21st November 2005, 10:49 AM

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.

sangram · 21st November 2005, 10:55 AM

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.

21st November 2005, 07:13 AM	#1
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	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?

21st November 2005, 10:00 AM	#6
rampage101 diyAudio Member Join Date: Apr 2004 Location: NSW Australia	For the fire in case it crashes and burns. __________________ What's a signiture?

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21st November 2005, 08:00 AM	#2
owen diyAudio Member Join Date: Mar 2004 Location: Shilton	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.... Owen

21st November 2005, 08:22 AM	#3
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	Thank you!!

21st November 2005, 08:49 AM	#4
Nordic diyAudio Member Join Date: Sep 2005	Just leave a window open, when you crank it up, ok?

21st November 2005, 09:19 AM	#5
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	Why

21st November 2005, 10:31 AM	#7
Nordic diyAudio Member Join Date: Sep 2005	So that I can hear it!!!!!!!!!! lol

21st November 2005, 10:35 AM	#8
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	What is I get a seperate Xformer for the subwoofer's channel, Leaving 100VA per channel for the rest?

21st November 2005, 10:49 AM	#9
Nordic diyAudio Member Join Date: Sep 2005	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.

21st November 2005, 10:55 AM	#10
sangram diyAudio Member Join Date: Sep 2002 Location: India	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.