Use a single secondary x-former as dual PSU? - diyAudio
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Old 8th March 2009, 08:40 AM   #1
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Question Use a single secondary x-former as dual PSU?

Hi
I whant to use a transformer with a 30V secondary winding to a dual +/- 15V rail supply.
I have heard that a 100K-100K voltage devider (virtual ground) is not a good solution, which need DC-blocking coupling capacitors in the signal path.

The psu is for a lowpass active filter using OP270 chips.

Any sugestions for a PSU circuit?

Brgds
/Pix
Sweden
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Old 8th March 2009, 10:46 AM   #2
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http://tangentsoft.net/elec/vgrounds.html

Will give you a circuit to create an active virtual earth for low current applications.

http://sound.westhost.com/project43.htm Will provide you with better information and proper circuits.
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Old 8th March 2009, 12:26 PM   #3
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Default How about this?

Im my case I will have a rather symetric rail load (all op-amps)
And want to made it as simple as possible (-but still good).
The load will be 3pcs OP270 = aprox 15mA and I could easylly have 15mA trough the shunt regulator chain.

I have a lot of LM431 adjustable shunt regulators for the rail regulation.
WouldŽnt this simple circuit work? (regulation and virtual earth all at ones)
The LM431 regulator has a very low output impedance.

Click the image to open in full size.

Brgds
/Pix
Sweden
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Old 8th March 2009, 12:38 PM   #4
AndrewT is offline AndrewT  Scotland
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Default Re: How about this?

Quote:
Originally posted by pixworld
Im my case I will have a rather symetric rail load (all op-amps)
No.
The vast majority of opamps are ClassAB.
the quiescent current is probably symmetric (i.e. no ground current in quiescent state) but not guaranteed.
The output current is non symmetric. It comes alternately from either supply rail.

If Iq=2mA and Imax =30mApk, then the supply rail will vary from 2mA to 32mApk to meet that demand. The other supply rail variation is just as bad.
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Old 8th March 2009, 12:39 PM   #5
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careful with shunt regulators, because you might lose a lot of power that way.
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Old 8th March 2009, 01:29 PM   #6
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Default Re: Use a single secondary x-former as dual PSU?

Quote:
Originally posted by pixworld
Any sugestions for a PSU circuit?
Yeah, get a suitable transformer.

There are no good reasons for doing what you suggest, only reasons for not doing it. IT'S THE WORST POSSIBLE SOLUTION.

w
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Old 8th March 2009, 11:04 PM   #7
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I concur. To get the lowest noise, highest dynamic range and highest quality preamps, do it properly, CT transformer, with 3 pin regulators.
You want your preamp power supply to be amazing.
Op-amps already have a very good power CMMR, but you can never have enough good quality dc.
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Old 9th March 2009, 12:32 PM   #8
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What kind of power will you need to supply? If you are only
needing to power a couple of opamps you might try this
and regulate it down.
Attached Images
File Type: gif psu1-schematic-small.gif (3.8 KB, 142 views)
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