6 channel LM4780 question

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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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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.
 
Sangram. as this is a 5.1 set up - the front right and left along with the sub will consume 80% of the power - the remainder is 'effects' and they consume very little.. so overall the transformer will be able to manage, but it is in the realms of commercial sizing, instead of an ideal..

Owen
 
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owen said:
Sangram. as this is a 5.1 set up - the front right and left along with the sub will consume 80% of the power<snip>

Yes, of course, except if you use matrix mode etc.

As said, even 80VA will be enough if it's not belting out at full volume on all channels.

Not like I have superb transformers myself, but It would be a nice-to-have thing I guess.
 
OOPS!

Apologies, Wynand. Re-reading your post, I realise that you already have a transformer. 500VA will be more than sufficient. The actual power consumption of a 6x60W amp in practice is not close to half of 360W, but the extra VA's are required more for the current-supplying ability of the transformer. The current in the transformer is not constant, but actually pulses. At maximum power, the magnitude of the pulses can be higher than the continuous rating. A higher power transformer is specified to minimise I^2R losses (lower winding resistance) in the transformer.

If you ask me, it's not really worth the trouble (i.e., extra VA's). Some think it is, but I suspect that's just because they're trying to squeeze the last watt out of the amp...
 
I would just like to add that your sub channel is underpowered relative to the others.

Maybe build a 5channel amp and a separate subwoofer amp.

Or build 4x60W +1x120W and ditch the centre channel (my experience is that centre channel is a waste of money, but it may be useful for some room layouts)
 
I've biuld some TDA2050 amplifiers and I know that the opinion is that the LM Ic's are superior, but what if I build 4 channels (front and surround) with 2 LM4780 IC's , 1 sub amp with a LM4780 and a centre channel with a TDA2050 ( 32w chip)?

The tda could have a HP filter on and thus require less power and still "fill" its space.
 
Wynand said:
I've biuld some TDA2050 amplifiers and I know that the opinion is that the LM Ic's are superior, but what if I build 4 channels (front and surround) with 2 LM4780 IC's , 1 sub amp with a LM4780 and a centre channel with a TDA2050 ( 32w chip)?

The tda could have a HP filter on and thus require less power and still "fill" its space.

I suggest to keep the TDA2050 for surround sound and build 2 of LM4780 as.. The one for main (front) 2x50WRMS, and the other 1x100WRMS for sub.

Front (main) 1 LM4780 2 x 50WRMS
Rear (surround) 2 TDA2050 2 x 25WRMS
center 1 TDA2050 1 x 25WRMS
Sub 1 LM4780 1 x 100WRMS



;)
 
That sounds like a good plan.

I've thought about it, as I'm planning to build it over a couple of months and spend a bit of cash, I can get another trafo for the VA's im short. My idea was to build an amplifier that I didn't skim on anything because of money.

If the TDA2050's won't affect the overall quality then maybe they'll be used, but just for saving a couple of VA's...... nope.

You're idea does sound good though, thanks.

BTW. I'm planning on controlling the amplifier with an Atmel MCU. If anyones seen a amp like that I'll appreciate a link or something.
 
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