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Old 11th February 2006, 12:29 AM   #1
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Default LM4780 parallel transformer suitability

Part Number:
122-615
AVEL Y236503 160VA 22V+22V TOROIDAL TRANSFORMER

Is this a good transformer for paralleling two chips. I have been told to back down the voltage since I am trying to run Extremely Low Impedence speakers. They are ESL's.

But parts express offers 3 22v transformers with different VA ratings.
What VA should I get? Would one higher or lower than this be better.
I need a higher current.

Dominick
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Old 11th February 2006, 01:36 AM   #2
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Default transformer suitabiltity

Trying to put into the simplist terms, V*A=W,so youve got a rectified voltage of +/- 27V about 1.5A to generate 90 to 110 Watts + or - so your supply will have to produce enough for at least 140 watts per parallel chip, for overhead. That 280watts 160VA wont make the grade on that one. least 330VA more like 500VA.
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Old 11th February 2006, 07:34 AM   #3
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Default Re: LM4780 parallel transformer suitability

Quote:
Originally posted by Dominick22
Is this a good transformer for paralleling two chips. I have been told to back down the voltage since I am trying to run Extremely Low Impedence speakers. They are ESL's.
Just wondering but how low is "extremely low"? 2 x LM4780 = 4 x LM3886 => over 40 A max! ....but with 25 V peak you'll need much less than 1 ohms. If most of the power is bass you don't need to design for max power at 20kHz.
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Old 11th February 2006, 10:18 AM   #4
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I am trying to push the Martin Logan Ascent i ESL's which I am told can drop as low as .1 ohm at high frequencies. I will try to create some kind of choke that will prevent it from going below 1-2 ohms, but I just need a stable circuit for now. I already blew one chip in the standard parallel design with a 25V 330 VA rating. This was just one chip though and now I am trying it with two.

So what you are saing is that I should remain at 22V and get the highest VA rating I can?

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Old 11th February 2006, 10:56 AM   #5
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I suggest that you check with Martin Logan to get real facts. I have also Martin Logan SL3 and a single LM3886 has no problems with them.
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Old 14th February 2006, 08:09 PM   #6
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I called Martin Logan today and they said that the minimal ohm load is 1.5 at 20k.

Considerably better than the .1 some people quoted.

So what should I look for?


22V at 400 VA????


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Old 15th February 2006, 12:19 PM   #7
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I am having a hellatious time finding a 22V Torroidal transformer with dual secondaries rated between 300-400VA.

Any help would be much appreciated.

BTW: I tried digikey, hammond, ebay, altronics, and parts express already.

I need some other website options.

Thanks,
Dominick
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