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Old 20th May 2011, 04:01 AM   #1
Frosteh is offline Frosteh  United States
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Default Transformer calculations

Hi all. I just want to make sure I have my calculations set. I'm looking to buy one of These on ebay and I want to make sure I have my power supply all set up correctly. I'm looking to buy the 500W 40V toroidal transformer from PE (located here) which seems to satisfy the requirements for this amp (look about halfway down the ebay page where it says "Recommended AC 400W Dual 40V AC power transformer above."). All would be well, except that I messaged the seller and he said that I would need a power supply as well. To my knowledge, this transformer will take 115VAC from the wall and I won't need a separate PSU. Is this correct? I'm confused as to why he told me to get a PSU as well when this will easily just plug into the wall. Could anyone please clarify? Thanks!
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Old 20th May 2011, 06:19 AM   #2
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Yes, you will need a separate PSU as the transformer outputs AC current which must be rectified to DC before being fed to the amplifier module. Some modules have a power supply mounted on-board to change AC into DC however, this one doesn't and you will need a power supply board with rectifier and filter capacitors.

Something like this from the same seller would do and would be up to the voltage rating of your power transformer (it uses 80V capacitors whilst other kits use 50V ones-cutting it a bit fine IMO). The primary side of the transformer is connected as usual with just the live and neutral along with a switch and fuse on the live line. The secondary (where the lower voltages are produced) will connect to the power supply board which in turn will turn your incoming AC to DC and filter it (reducing the ripple). The output of the power supply board will then go to the amplifier module.
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Old 26th May 2011, 04:45 PM   #3
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I like the look of that Capacitor board from ebay, but I usually have some lower capacity caps on there as well. It may not be necessary and is probably overkill but that is how I usually put power filters together.
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Old 26th May 2011, 05:16 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
a single secondary transformer with 40Vac will give you a single polarity ~60Vdc supply.
If the amplifier needs a dual polarity supply then the transformer must have either:
dual 40+40Vac secondaries
or
centre tapped 80Vac secondary.
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