[sdiy] Power Supplies

[Roman]

Opamps will not introduce DC offset if their supply is not fully symetrical. They have prety large power supply rejection ratio. So if you change supply voltage by 1V, output may change by 1mV in crappy ones, or even a few uV sometimes, which is more than OK for audio circuits. They only need to have some headroom for large amplitude audio signal evenly distributed around 0, hence the need for more or less the same + and -.

As for dual tracking chip, just add power transistors at outputs and several amps are within reach. It's easy since the MC1468 has drive and sense leads.

Or you can make single tracking supply, assuming that usually draw on +rail is much bigger than in -rail. So reference for negative supply is taken from [+] output followed by inverting amplifier of gain -1. Whatever changes on +rail will be then reflected on -rail. Like here on my overkill power supply:
http://sowa.synth.net/modular/zasilacz.gif

Roman


Dnia 10 października 2015 9:26 Rob Spencer <rob at gmsn.co.uk> napisał(a):



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> Hi All,
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> I’ve been thinking a lot about power supplies recently and was after some advice…
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> The first PSU I built was the classic 7812/7912 with a nice toroidal transformer which sat at the back of the nice big case I was using, however I’m now trying to slim things down. I’m also keen to remove mains power from the box completely.
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> I’ve been having a look using buck converters in an inverting configuration so I could use a 15v DC input, however I would prefer to stick to linear, as switching PSUs don’t quite feel right for me in analogue audio applications. I’m now toying with the idea of doing the heavy lifting in a PSU enclosure and then bringing the Dual 12v in through a multipole connector.
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> During my research I stumbled across this post: http://www.electronicspoint.com/threads/what-is-a-dual-tracking-regulator-for.3354/ which talks about a "dual tracking regulator" adjusting both voltages so they remain the same potential difference with respect to ground. If one voltage drops the other will be adjusted by the same amount, which got me thinking….
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> If I have the classic 7812/7912 PSU, then run a 7805 of the +12v, load it up with an assortment of digital and analogue modules from a variety of designers, I would expect the loading on each rail to be different. As I approach the 1A mark, the voltages on each rail will be quite different with respect to gnd. The affect this will have on critical audio op amps will be supply voltages not sitting evenly around zero volts, which, I would have thought, would produce a signal either with a DC offset or some other kind of distortion.
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> It would be great to incorporate a “dual tracking regulator” to ensure the voltages remains the same level to ground, but they all appear to be rated in the 100s of mA. Is it possible to use a power transistor to draw a larger current from rectified, but unregulated supply, limited to the regulated voltage or are there other tried and tested solutions to the overall problem?
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> Many thanks in advance.
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> Rob
> www.gmsn.co.uk
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