From: peter2@hipson.net   
      
   On Sun, 22 Feb 2009 16:43:45 +0000, Stoatgobbler   
    wrote:   
      
   >Jasen Betts wrote:   
   >> On 2009-02-21, Stoatgobbler  wrote:   
   >>> Hi there,   
   >>>   
   >>> I'm building a JL Hood hifi amplifier and to construct the power   
   >>> supplies I've mounted two toroidal transformers in a case, one on top of   
   >>> the other. Each toroid has two secondary windings which I'm going to use   
   >>> to create two separate, independent, regulated +22v - 0 - -22v power   
   >>> supplies. To make these power supplies truly independent (and to reduce   
   >>> the chances of earth loop hum) I've "lifted" each power supply 0v common   
   >>> from the chassis earth via 60ohm resistors.   
   >>>   
   >>> On testing the power supplies I've noticed that the greater the current   
   >>> I pull out of each power supply the greater the potential difference   
   >>> that appears across the 60ohm resistor (chassis earth to power supply 0v   
   >>> line). when I pull 1.1A from the power supply then I have nearly 17v   
   >>> across the 60ohm resistor. This voltage does not seem to vary with   
   >>> raising the upper toroidal away from the lower so I don't think the size   
   >>> of this voltage is to do with interactions between the two (but would   
   >>> stand to be corrected).   
   >>>   
   >>> I've never "played" with this, I did expect a voltage across it (due to   
   >>> eddy currents within the transformer normally "lost" in heating the iron   
   >>> core in a conventional E I type transformer?) but I thought toroidals   
   >>> minimised this and the voltages resulting from this would be   
   >>> nominal....17v across 60ohm is not nominal.   
   >>>   
   >>> Is this normal or is something going on?   
   >>   
   >> somethings going on.   
   >>   
   >> AC or DC ?   
   >> frequency?   
   >>   
   >>> Any advice or comments would be appreciated.   
   >>   
   >> can't make any usefull guesses without knowing what it was and what   
   >> you've done to it.   
   >>   
   >>   
   >Two toroidal transformers, both inputs 250vac 50hz, both outputs +/-   
   >37vdc (no load) regulated to +/-22vdc with a 0v centre. Simple power   
   >supply, split rail regulated, circuit is here >   
   >http://www.tcaas.btinternet.co.uk/jlhlm3x7cb.htm   
      
      
   A full schematic including transformers and circuits would be more   
   useful, but the two grounds (common 0V) are isolated from each other   
   with a total of 120 ohms? Why islolate the grounds from each other?   
   I'd tie the two common 0V points together, then run them together to   
   teh chassies as needed.   
      
   --- SoupGate-Win32 v1.05   
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