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Old 25th January 2008, 08:45 PM   #1
geminni is offline geminni  Yugoslavia
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Default Transformer with uneven ac out

I need 2x15v supply for preamplifier. I have a transformer with two output. One is 23v and second is 30v. Two windings are connected together.
Can i connect it to a rectifier? Will this voltage difference bother?
If it is ok then i will also use zener, transistor to lover voltage at 15v dc.
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Old 26th January 2008, 04:44 AM   #2
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You can use 15V zener regulation to get your needed +/-15VDC with no problem as long as both the 23 and 30VAC outputs can deliver the Current you need
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Old 26th January 2008, 11:50 AM   #3
AndrewT is offline AndrewT  Scotland
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or add the 7Vac winding to the 23Vac to match the 30Vac.

Check which winding has the smallest wire diameter. This becomes the effective limiter of your output current.
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Old 26th January 2008, 12:40 PM   #4
geminni is offline geminni  Yugoslavia
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So, the voltage difference will not make things go bad
Ok, i'll try that and adding that 7 volt in seres with 23v.

Thanks guys!
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Old 31st January 2008, 05:13 PM   #5
geminni is offline geminni  Yugoslavia
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It's working!
Now i have +-40,5V. How can i make +-15V for preamp?
I have been looking in LM317 data sheet, looking on net and found that its maximum input voltage is 40v.
Would the classic zener-transistor combination be enough for preamp?
I ask because i have made same setup for amplifier with TDA1516q and it distorted very bad on higher power output. When i replaced zener-transistor with 7815 it worked very nice. No distortion on louder volume.
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Old 31st January 2008, 08:45 PM   #6
jaycee is offline jaycee  United Kingdom
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Use the transistor-zener as a "pre regulator" to drop down to about 25V or so... then use LM317/337 or 7815/7915 to supply the preamp.

Alternatively build something like the Jung or Sulzer discrete regulators, but that's a lot more complex.
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Old 1st February 2008, 05:52 AM   #7
geminni is offline geminni  Yugoslavia
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Thanks! I'll try that with 2 stage voltage drop
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