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Old 11th July 2005, 05:00 PM   #11
Eva is offline Eva  Spain
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Toroids are almost allways bifilar wound, so close matching between secondaries may be assumed. Otherwise, they would tend to saturate even when operated in the usual way.

For the sake of simplicity, I would just connect in paralell the secondaries of each toroid and use each transformer to supply one rail through a diode bridge.

Also, there is a trick to further reduce PSU voltage drop and ripple in stereo LF arrangements. This is achieved by inverting the input signal of one of the channels and reversing the polarity of the load. As a conequence of that, both channels will seldom be drawing current from the same supply rail at the same time and PSU efficiency will be improved.
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Old 11th July 2005, 09:04 PM   #12
Raka is offline Raka  Europe
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Buenas noches,

Eva, thanks for this good idea. I'll think about it, seems that has no drawback whatsoever.
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Old 12th July 2005, 09:59 PM   #13
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Default Re: Thanks for your reply

Quote:
Originally posted by Raka
The toroids I have are identical, at least they are the same RS code and were bought at the same time. So they will be more identical than different.


Does anyone has a different suggestion?

Watch out! toroids may look be identical....but could be made by different vendors using same RS label. Check off load secondary winding voltages first. If the primary has taps, DON'T parallel them. Why you might ask ? A manufacturer might round up the taps to next integer turn and with thinner wire can overheat if connected in parallel with another tranny.
There's nothing wrong in parallel operation so long the voltages are identical.

Hang on.......Mains toroid transformers are NOT wound Bifiliar.....no interwinding screen ...eh ? Manufacturer wouldn't get isolation and creepage approval. Some are wound so badly that the leakage inductance is way worse than EI types.

richj
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Old 13th July 2005, 01:26 AM   #14
Eva is offline Eva  Spain
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Dual secondaries are wound bifilar.
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Old 13th July 2005, 07:49 AM   #15
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okay.....secs. .......was getting late.

richj
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Old 14th July 2005, 07:23 AM   #16
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If the transformers have a orange label with either nuvotem or Telmag as a manufacture name, then the secondaries will definately be bifilar wound and you will have no problems paralleling them.

It would probably be best to use one transformer for each rail though.

Chris
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Old 14th July 2005, 08:15 AM   #17
Raka is offline Raka  Europe
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Yes, mine are from Nuvotem, and the reference from RS is 223-8897. Will be easy now to check if for this application is best to use one single PS (with 500+500VA) or to use two separate PS (500VA each).
The amplifier power is not going to be very high, as the voltage of the transformers is just 25V, but I'm more concerned about the current delivery needed for the paralleled XLS10.
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