Use a single secondary x-former as dual PSU?

[pixworld]

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

[Rainwulf]

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.

[pixworld]

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.
Would´nt this simple circuit work? (regulation and virtual earth all at ones)
The LM431 regulator has a very low output impedance.



Brgds
/Pix
Sweden

[AndrewT]

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.

[Rainwulf]

careful with shunt regulators, because you might lose a lot of power that way.

[wakibaki]

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

[Rainwulf]

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.

[woody]

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.