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Old 12th September 2007, 09:37 PM   #1
00600 is offline 00600  United States
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Default Transformer load on mains circuit

I'm planning on building a 5.1 HT system using gainclone monoblocks. I'm figuring two for the surrounds, bi-amping the center, and tri-amping the main L&R. That's 10 gainclones (7 running full power @4ohms, 3 running ~20% @8ohms for the tweeters.

I was going to plan on running multiple amps off the same transformer, but I've been reading several posts about noise and hum problems.

I'm now thinking about running a seperate transformer/PS for each amp.

The one issue I'm concerned with is the transformer load on the mains supply. I'm limited to 110V 15A circuits, though I could pull an additional circuit from the breaker box and up the amperage to 20A.

If it comes down to it I COULD pull a 220V 50A circuit, though the cost of wire, breakers, and outlets isn't exactly cost effective.

Any thoughts?
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Old 12th September 2007, 09:53 PM   #2
AndrewT is offline AndrewT  Scotland
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Quote:
I'm limited to 110V 15A circuits,
Hi,
that's 1.5kVA. What else is on the circuit?
If you're only feeding the 5.1 then you have plenty of power available.
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Old 13th September 2007, 04:12 AM   #3
00600 is offline 00600  United States
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32" Mitsu CRT TV, Yamaha 7.1 receiver (running the monoblocks off the preamp outputs), DVD player, AC3 decoder, satellite box, and an active crossover/EQ that is yet to be built/purchased.

I can look up the wattage ratings on the back of the other electronics to figure out the total load. I'm just lost on how to figure the load from the transformers for the amps I'm building.

The house is currently wired with 2 outlets on seperate circuits near the location of the electronics, but IIRC there are also some track lights on the same circuit.
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Old 13th September 2007, 09:55 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
just add up the W or add up the VA ratings. Then do a total load on the circuit.
15A @ 110V = 1650VA.

Most of the devices will be ticking over on a small fraction of their rated power. If you feel confident you can load on more than the circuit capacity but you must ensure that any overload is very short term, I'm thinking hundreds of mS, not seconds.
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Old 14th September 2007, 06:55 AM   #5
00600 is offline 00600  United States
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ugh, so I'll need to sync the powersupplies so they don't all turn on at the same time.....

Ok, Thanks
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Old 14th September 2007, 08:21 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
switch on surge is very short lived.
If the distribution board circuit breaker holds in then you are OK.
If it does not hold in, then staggered switch on is required.

Oh, the joys of living in the UK with 20A or 30A @ 240Vac circuits to every room. I have about 100 socket outlets around the house and each plug top can supply <=2860VA.
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Old 14th September 2007, 10:12 AM   #7
00600 is offline 00600  United States
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Quote:
Originally posted by AndrewT
Hi,
switch on surge is very short lived.
If the distribution board circuit breaker holds in then you are OK.
If it does not hold in, then staggered switch on is required.

Oh, the joys of living in the UK with 20A or 30A @ 240Vac circuits to every room. I have about 100 socket outlets around the house and each plug top can supply <=2860VA.

If you guys had an equivalent to the Second Amendment to the US Constitution, better healthcare, and lower taxes. I'd emigrate

Related question, what is the maximum number of secondary windings I can get on a custom wound torrid transformer? (I'd ask the supplier, but this just seems like a dumb question)

Should I go with one or two large transformers (and work out the hums that may occour), or an individual 160VA torrid for each PS?

I'll be building the Transformer/PS enclosure seperately from the amplifiers so I don't have a problem with packaging.
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Old 14th September 2007, 04:49 PM   #8
kubeek is offline kubeek  Czech Republic
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When I had my xformer made, the only limit was the total power, like that when you have 250W core, and want two separate windings 250W each and use only one at a time, they canīt fit the two on one core, so there is no "headroom" for other unused or wire-gauge-overrated windings.
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Old 15th September 2007, 07:15 AM   #9
AndrewT is offline AndrewT  Scotland
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Yes, Kubeek has hit it. The total VA of all the secondaries can exceed, by a large margin, the maximum VA of the primary and core. This improves the regulation of individual windings and maintains separation between channels/controls/etc.

I like a four secondary toroid for a dual channel amplifier. The toroid VA is 300VA but each secondary is rated to 120VA and allows 150W per channel from a more compact/lighter transformer. Otherwise two 250VA transformers would be required for this duty. Scale the numbers to your requirements.
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Old 27th April 2008, 01:26 AM   #10
WJMIII is offline WJMIII  United States
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A side question from this topic.

I have a very nice, small toroid I was hoping to use with a 3886 kit in a small enclosure - a Partridge Family lunchbox, actually.

The toroid is rated @ 120V - 24v secondary @ 1.5A. would that toroid be suitable for a 3886 chipamp kit? I believe it would be, especially since this is more of a novelty and awesome performance is not sought for the amplifier.

What say you all?
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