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Old 29th April 2013, 08:15 PM   #21
pdul is offline pdul  Denmark
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After all you need to charge the batteries somehow when mains is illusory
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Old 29th April 2013, 08:56 PM   #22
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Originally Posted by pdul View Post
After all you need to charge the batteries somehow when mains is illusory
Fusion916 has raised a very valid point concerning tx noise when powering class A amplifiers. Ideally he needs low impedance dc which is most easily and cheaply available as lead acid batteries. They do, as you observe, need charging but whereas ac mains is good enough for charging batteries it is a very poor power source for amplifiers.
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Old 29th April 2013, 09:14 PM   #23
pdul is offline pdul  Denmark
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Obviously not for Krell, Mark Levinson, etc.
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Old 29th April 2013, 09:16 PM   #24
pdul is offline pdul  Denmark
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Theres loads of energy present in the mains, its all about shaping it to suit your needs
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Old 29th April 2013, 09:20 PM   #25
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toroids don't like DC on any winding. Now that youve tried a DC blocking filter on the primary, how is the secondary(ies) loaded? Could there be asymmetric loading that gives current going more one way than the other? (During a complete cycle the VA product going positive should equal the negative, so as to give a net sum of zero, if not they will hum).
Another way of getting them to hum is having too high peak charge currents into the cap-battery. Are you using Chuck Norris' capacitors?
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Old 29th April 2013, 09:34 PM   #26
pdul is offline pdul  Denmark
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Chuck Norris' capacitors
Maybe Arnolds.
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Old 30th April 2013, 04:11 AM   #27
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Casing and potting the transformer will help.

Gajanan Phadte
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Old 30th April 2013, 09:35 AM   #28
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Potting might help. But if the hum is due to asymmetric loading you might get problems with mechanical/heat stress. Better to find out why it hums first. Toroids are really intollerant to offsets, doesn't take many mA on even a several hundred VA rated toroid to hum. The hum is a sign it is not happy. 'Fixing' it with force (potting it in epoxy or some other compound) just means the forces need to go elsewhere, which may (or may not) give problems in other areas.
I had similar problems before and found my seconadries unevenly loaded. I balanced it and woila, complete silence. I have also tried potting in epoxy, and it was silent for a few weeks, but slowly the vibrations came back, a tell tale sign those hum vibrations are pretty powerful mechanical stresses.
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Old 30th April 2013, 09:43 AM   #29
FoMoCo is offline FoMoCo  United States
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It doesn't look like anyone has confirmed the actual line voltage. If it's too high, the transformer may be driven into saturation without DC being present.
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