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Old 16th May 2008, 11:11 AM   #1
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Default how to reduce PSU DC voltage

hi,

i need to know how can i reduce my transformer DC voltage?
now i have in secondary is 43-0-43 ACv. can it be reduce after rectified? like it is 59v dc after rectified. i only need 40v.
is it will be easy to make the circuit? i will need 40-0-40 DC volt.

my transformer is about 10amp.

thank you.
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Old 16th May 2008, 11:23 AM   #2
paulb is offline paulb  Canada
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What are you powering with this power supply? How much current does it require?
You might look at this:
http://www.passdiy.com/projects/zenv3-2.htm
and this:
http://www.passdiy.com/projects/zenv5-7.htm
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Old 16th May 2008, 11:24 AM   #3
Mooly is offline Mooly  United Kingdom
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Hi Space,
You mean the voltage after rectification and smoothing
If it's a Toroidal you can sometimes unwind a few turns off the secondarys. You could use a high power/current regulator but this is very inefficient, lots of heat at high current.
What are you trying to run off it.
Regards Karl
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Old 16th May 2008, 11:30 AM   #4
AndrewT is offline AndrewT  Scotland
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you need 26-0,26-0Vac, to 28-0, 28-0Vac, transformer for +-40Vdc.
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regards Andrew T.
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Old 16th May 2008, 11:50 AM   #5
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hi mooly,

actually it is for amp. i was supecting that i am overdriving the amp by voltage so it's need to reduce about 40+dc. it is not final yet. i am still testing on my amp now. see if there is anythings goes wrong. i already change one transistor for higher voltage as dx sugested. now operating it anschecking the temperature of the sink. it is now moderate volume about 41C. my sink is huge too.
it shouldn not be so hot till this, i still don't know, sound is clear too. i don't know how far the temp will go. what is the limit of the
temp for average amp.


my this transformer is good and heavy duty. it has 10amp power. i have like this two transformer. so i want to use it for amp i made.


thanks
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Old 16th May 2008, 11:58 AM   #6
Nordic is offline Nordic  South Africa
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It is not an overvoltage problem, my test prototype ran with + and - 51VAC = just over 70VDC.
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Old 16th May 2008, 12:14 PM   #7
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Nordic.....wow....so great.

that means i am not operating over voltage. now i am testing for about 2hrs past... i am still operating on 59v....it's showing no problem so far, no extra sound....temp is now quite ok...39c in moderate vol....do you think this is correct temp? the problem was sove caused by thin cable i use for dummy test....also transistor...but that BC547..now BC546 transistor voltage still below 500mil volt....so i will chenk evn more prcly...

thanks nordic....again...
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Old 16th May 2008, 02:02 PM   #8
Mooly is offline Mooly  United Kingdom
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Space, do you have an oscilloscope ? There is an interesting little experiment you can do, kind of related to all this.
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Old 16th May 2008, 10:22 PM   #9
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no, i don't have any osiloscope. i only have one digital meter....ha...ha...thats why so much trouble....
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Old 17th May 2008, 06:20 AM   #10
Mooly is offline Mooly  United Kingdom
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O.K. Well that's that then. I was after you seeing how much power (voltage swing) you really need across your speakers when playing very loud. Probably not as much as you might think !
Put it on your list of things to get
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