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Old 9th September 2003, 06:27 AM   #1
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Angry higher voltage PS

I did purchased toroid trans from farnell with 35-0-35 250VA. After passed through bridge rectifer, it access +- 100v which over LM3875 specification. Any one would like to help me on how to modify the PS to reduce the output volatage. Current I managed to reduce it with RC circuit BUT it have distortion when switch on & have some kind like air sound flow from left speaker to right speaker after 10sec switched on the amp.
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Old 9th September 2003, 04:36 PM   #2
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So you bought a 35V torroid, but it's giving you 100V instead? Could this be a result of internal wiring flaw?
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Old 9th September 2003, 04:54 PM   #3
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Default Re: higher voltage PS

Quote:
Originally posted by Steven Koay
I did purchased toroid trans from farnell with 35-0-35 250VA. After passed through bridge rectifer, it access +- 100v which over LM3875 specification.

It's possibly specified for 110VAC primaries. Are your primaries 220 VAC?

Jeremy
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Old 9th September 2003, 05:08 PM   #4
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sounds like you have the secondaries wired together?

35+35=70, 70*1.414 = 99 (or 100 V)

check your wiring.

as is after rectification your going to get 50V from each secondary.
isn't that a bit much for a GC?
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Old 10th September 2003, 05:15 AM   #5
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Is correct, the calculation from 70*1.414 = 100v, which exceeded LM3875 specification which only allow to have 85v. I did include RC circuit in PS to reduce the voltage to 80v ( put the meter probe to + & - point to get 80v. But the sound have distortion like air sound flow from left speaker to right speaker. But the distortion went away IF the remove the RC circuit.
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Old 10th September 2003, 11:29 AM   #6
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Quote:
Originally posted by Steven Koay
Is correct, the calculation from 70*1.414 = 100v, which exceeded LM3875 specification which only allow to have 85v. I did include RC circuit in PS to reduce the voltage to 80v ( put the meter probe to + & - point to get 80v. But the sound have distortion like air sound flow from left speaker to right speaker. But the distortion went away IF the remove the RC circuit.
There's an obvious option: you can build a regulator for your GC.

Some have reported good results from regulating, some say the GC sounded worst. Pedja has a nice regulator on his page.

You will have some heat, from the 7.5v x current on each regulator, but it could be worst.

Not everything is lost.


Carlos
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