Dual polarity power supply with a single secondary transformer? - Page 2 - diyAudio
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Old 16th April 2011, 07:42 AM   #11
Elvee is offline Elvee  Belgium
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See the comments in this thread:
"Fake" Split PSU
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Old 15th August 2011, 09:46 AM   #12
Junm is offline Junm  Philippines
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Hi ,I had used this config from my single tap trafo to power up my discrete amp without any transistors just bleeder resistors.I only put 2 15,000 uf filter caps. I just dont know the consequencies of this but luckily until now my amp is operational and does not encounter any breakdown since it was made 3 years ago.

I have another trafo 24vac @ 40 amperes from power supplies and I plan to use it again with the attached rectification and add up capacitances for my circlophone....is there any danger on this? ground is on chassis only since we only have 220Vac -0 line.So line ground or earth is not connected.
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Old 15th August 2011, 11:04 AM   #13
DF96 is offline DF96  England
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Read the thread. Make sure you understand why this circuit is not a good idea. You may have been lucky until now. Don't push your luck by using the same bad circuit again.

Last edited by DF96; 15th August 2011 at 11:06 AM. Reason: complete comment, interrupted by server
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Old 15th August 2011, 11:33 AM   #14
AndrewT is offline AndrewT  Scotland
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I have already reported his post asking the Moderators to consider deleting it.
No action, nor response , yet!
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Old 15th August 2011, 12:26 PM   #15
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Hi Andrew It's difficult sometimes to make decisions about this sort of thing, If he were rectifying the mains directly with no transformer I'd immediately pull it. If the issues are more subtle then in some respects it is good for other members like you and DF96 to highlight those problems so that anyone else contemplating something similar will hopefully see the error of their ways.

Is your main concern that Junm has said that it has been working (possibly encouraging others to do it as well?)

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Old 15th August 2011, 12:44 PM   #16
AndrewT is offline AndrewT  Scotland
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it cannot be working correctly as shown.
There is at least one fatal mistake.
The poster does not have the knowledge to recognise that either, it is not working correctly, or that he has not recognised that what he has posted is unsafe.

There seems no point in discussing it.
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Old 15th August 2011, 01:10 PM   #17
Elvee is offline Elvee  Belgium
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As long as Junm leaves the mains side alone, there is only a material risk: diodes melted or transistors destroyed.

He is talking about 0 - 220V: this is more of concern, since I don't see what it has to do with the topic.

The secondary has to be kept separate from the primary, and the type of mains system should have nothing to do with it.

Anyway, the last schematic will not work, and even if the problem is corrected, there are good chances the amplifier (and loudspeakers) connected to it will blow.
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Old 15th August 2011, 07:14 PM   #18
kevinkr is offline kevinkr  United States
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The first approach shown is a house of cards - if the load current isn't symmetrical an offset appears at the output of the amplifiers - a large enough offset and kiss the chip and speaker goodbye.. (High current bleeder resistors reduce this likelihood but cannot totally eliminate it.)

The second one shown due to the added connection would be half wave.. (Lots of ripple and poor voltage regulation.. I would wire the bridge for half wave bipolar rectification - disconnect the side of the bridge connected to the grounded side of the secondary.) No safety issue here, just not a very good way to do it.



Proper transformers aren't really that expensive, and the proper center tapped transformer is recommended.
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Old 16th August 2011, 01:51 AM   #19
Junm is offline Junm  Philippines
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hello, i had posted and asking for any danger or risk so that i can avoid doing it again.... I did it and happened to work for 3 years now...thats why im wondering why this kind of circuit works. Mains are not connected to chassis ground and secondary is 24 v ac. As i see it, it is a doubler with a bridge diode. AFAIK i've seen it on a book before thats what i tried and work so just asking...don't get mad pals....that why this forum is here to talk what to do or dont....
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Old 16th August 2011, 01:58 AM   #20
Junm is offline Junm  Philippines
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Can someone give highlight why this circuit is BAD and to be avoided and explain the flow of current during positive and negative cycle?

I don't encourage anybody to do this i just want explanation....so that i can redo what ive done...thanks..
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