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Old 22nd November 2006, 09:48 PM   #1
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Default BZLS transformer rating

I see here some guys using huge oversized transformers for their BZLSs or some other pass preamp.

So I would like that somebody here could explain me, why I should use 160 VA toroid pro channel when my preamp draws constantly only 80 mA pro channel?

We could use one 30 VA transformer for both channels and still get 30 % for reserve and power sag..
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Old 22nd November 2006, 10:31 PM   #2
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I used a 50VA trafo when building mine and all works perfectly well. I suspect some used larger because they happened to have an extra one lying around of that rating, and others used the more is always better approach. But in reality you are correct. I went with a 50VA because the price difference was negligible.

Cheers, Terry
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Old 22nd November 2006, 10:44 PM   #3
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Hello Terry.

Yes, 30 - 50 VA should be absolutely fine for this application. Also for esthetical reasons...

With 160 VA transformer you should get also much more mechanical and electromagnetic noise than with smaller one.
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Old 22nd November 2006, 10:56 PM   #4
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I'm using one Avel 160VA 55+55 and 2 PSU modules with terrific success. Absolutely no hum.

Agreed that 160VA was extreme overkill, but I got a great price on it. For a couple of extra bucks why not go with a 100VA?

-David
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Old 23rd November 2006, 04:48 AM   #5
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Hi ....

I used one 110 VA for two channels.

You are right that a larger transformer gives you a larger magnetical field, but the mechanical noise actually increases with smaller transformers.

My transformer is both potted and shielded. This kind of protection is not easy to get on smaller transformers. When I checked the strength of the magnetic field later, the specially made 110VA "audio" transformer had less radiation than the 30VA "standard" transformer.

Still, you can buy a lot of extra material for the differences in price...

Greetings, Harry
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Old 23rd November 2006, 01:44 PM   #6
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Quote:
Originally posted by harryeng


You are right that a larger transformer gives you a larger magnetical field, but the mechanical noise actually increases with smaller transformers.
Hm. I cannot agree on that except if the smaller transformer is overdriven. Smaller transformer is less efficient, that means that his voltage sag under the load will be higher and his work temperature without load would also be a bit higher due to ferr. core losses. But the smaller transformer cannot have more noise than bigger one.

Quote:
Originally posted by harryeng

My transformer is both potted and shielded. This kind of protection is not easy to get on smaller transformers. When I checked the strength of the magnetic field later, the specially made 110VA "audio" transformer had less radiation than the 30VA "standard" transformer.

I agree with all that. But sometime where small case is an issue it is easy to acomodate smaller trasnformer than bigger one...
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