I have set of M audio AV30 speakers that had a failed power supply (the transformer). I replaced the transformer with the closest thing I could find. The original transformer had a metal shroud that reduced mains noise, but the replacement transformer was not the same shape. The end result is that the speakers work but I have some mains hum. The speakers require a plus and minus 19 volt DC supply.

I read that one can create a plus/minus supply by joining two floating (laptop) supplies. So plus 19v of one supply joined to '0v' of other supply.

Hence 19v 0v-19v 0v = +19v 0v -19v

I ordered two DELL 19V (ADP-50SB) laptop power supplies, but long story short, I found that the earth pin from mains plug was connected to the 0V of the DC side of the power supply. So the power supplies are not floating.

My questions are .....

  1. Can I simply disconnect the earth in one power supply and so it becomes a floating supply?

  2. In the same power supply, can I connect the earth to the 19V , as this will happen anyway when I connect this 19V to the 0V of the other supply.

  3. Or should I disconnect both earths? ( the mains earth is connected to a copper sleeve around the power supply. The same copper sleeve is connected to the 0v DC pin.)

I do not know enough about side effects of floating power supplies.


  • \$\begingroup\$ Float the negative one. You'll be grounding its +ve output in the amp via the other one. Make sure you can't confuse them somehow. \$\endgroup\$ – user_1818839 Sep 21 '20 at 17:23
  • \$\begingroup\$ laptop power supplies are notoripusly "dirty" in terms of EMI. Chances are you going to get significantly noise either radiated or conductde into your audio signal chain. \$\endgroup\$ – Hilmar Sep 21 '20 at 19:43
  • \$\begingroup\$ I’d give it a try. Report back if you can hear any audible noise after the modification. \$\endgroup\$ – winny Sep 21 '20 at 22:01

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