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Old 28th June 2013, 07:26 AM   #21
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Chane the resistors(adj to gnd) to get 12 volts. If you leave it in the condition as is, you will get unregulated output. NE5532 will have no problem working on 12V or 14.52V

Gajanan Phadte
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Old 28th June 2013, 07:35 AM   #22
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The diodes across in/out are for preventing damage to the LM3x7s incase the output voltage is more than the input.

Diode from adj to gnd is necessary if the cap used is more than 10microF

Gajanan Phadte
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Old 28th June 2013, 09:21 AM   #23
AndrewT is offline AndrewT  Scotland
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The NE5532 has a voltage range of 10Vdc to 30Vdc.
The 5534 usually has a voltage range of 10Vdc to 40Vdc
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Old 28th June 2013, 09:47 AM   #24
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@gajan
i have only used the stock values fr7 diodes for rectification and 1% resistors except c17 and c18, they are 100mfd 25v. the voltage at the output is 14.52 volts with sometimes changes in the most significant left hand digit i.e 14.5'2'-14.5'3' i have no clue to check if the output is regulated as i dont have a scope with me. the calculations are right, the regulator SHOULD PUT OUT 15.1 VOLTS BUT I DONT KNOW WHY IS IT SHOWING ONLY +-14.5.

@Andrew i have found a little transformer 18-0-18 in a very small EI cored package, the bobbin size is 2x4 centimeters. i am unsure about the current of the transformer but i am sure it can atleast put out 250mA of current so it is perfectly suited for this application.

Update- this transformer puts out 18 volts at 500mA.which is more than sufficient for all the 5532 dual op amps(only 3 though 2 for project 88 and 1 for subwoofer filter)

Last edited by godslayer; 28th June 2013 at 10:09 AM. Reason: transformer details
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Old 28th June 2013, 10:29 AM   #25
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by godslayer View Post
....... a little transformer 18-0-18 in a very small EI cored package, the bobbin size is 2x4 centimeters.............. i am sure it can atleast put out 250mA of current.........
250mAac from a 18-0-18Vac transformer requires it to be 9VA.
250mAdc from a 18-0-18Vac transformer requires it to be 18VA.
Neither of these is small.

I suspect your MAXIMUM continuous DC output <<100mAdc.

If it is 3VA then it's AC rating is 83.3mAac. It's DC rating is 42mAdc and I would recommend that you do not try to draw any more than 20mAdc continuous from a 3VA.

How can you be "sure" of >=250mAdc?
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Last edited by AndrewT; 28th June 2013 at 10:46 AM.
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Old 28th June 2013, 12:45 PM   #26
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You r getting 14.x volts because of the low input voltage to the regulator, that means it is not regulated. Reduce the resistor from adj pin to ground to reduce the voltage to 12 volts.

Gajanan Phadte
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Old 28th June 2013, 02:04 PM   #27
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Quote:
Originally Posted by AndrewT View Post
250mAac from a 18-0-18Vac transformer requires it to be 9VA.
250mAdc from a 18-0-18Vac transformer requires it to be 18VA.
Neither of these is small.

I suspect your MAXIMUM continuous DC output <<100mAdc.

If it is 3VA then it's AC rating is 83.3mAac. It's DC rating is 42mAdc and I would recommend that you do not try to draw any more than 20mAdc continuous from a 3VA.

How can you be "sure" of >=250mAdc?
I had used a multimeter to measure the AC current through the transformer secondaries, it showed me .52 amperes of current.i am not sure if the way of measuring the current is right or wrong.i did it only for a short period.

@ gajanan, the value mentioned in the first post is 1.33k and i have used two resistors 1k and 330ohms in series to give 1.33k from ground to adj pin. this value is suited for +-15v i feel the suppy is completely regulated, because no matter what i feed it, 13-0-13Vac, 18-0-18Vac or even 25-0-25Vac the voltage is the same... 14.5

Last edited by godslayer; 28th June 2013 at 02:16 PM.
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