The design is made to be universal and IMO should be 'adopted' to the application it must supply.
1: I wouldn't call it a low noise power supply,(SC did though !
a bit lower noise than typical non adjustable regs but not really low-noise.
A. I have never claimed it to be low noise, although it will certainly be far better than a non regulated supply where sensitive circuitry is involved.
2: Given the addition of the extra resistor in the neg rail a lower current draw this value is not fixed but should be calculated depending on the difference between total + load (5V + 15V) and - load
A. Agreed.
3: The series resistor in the 5V rail is there to make sure the 5V reg doesn't overheat and puts a current limit of 70mA on the 5V rails so it will not unbalance the trafo too much (about max 1.5W on primary + side).
A. That is just one version of this PSU. In the case of the PSU for
the Studio Series Preamplifier, the 100R 5W is replaced with a 5.1V 5W Zener diode.I have also fitted a larger heatsink than originally specified for the 7805.
increasing the input value of a (MUCH ?) more heavily loaded '+' side will do nothing for the current difference but only lower the ripple voltage BEFORE the regulator.
That is precisely what I had in mind.
a disadvantage would be 2 of the rectifier diodes get a bigger 'beating' during startup.
A.The diodes are more than adequately rated to cope, provided that the 2,200uF was only replaced with a 4,700uF.
If the 5V needs more current the logical approach would be to use a switching 5V reg.
This would
a: lower heat dissipation,
b: lower current consumption from the +5V rail by a factor 2.5 and the 100 Ohm can be removed.
c: the current consumption for the +5V rail may be considerable higher.
A. I believe that this was adequately catered for by the use of the 5.1V 5W series Zener diode in the Studio Series Preamplifier.
The PSU and 30VA transformer are well within their ratings still.
With one of these PCBs in my SC DAC, the 100R 5W has been replaced by a 7812 with a small heatsink.
For worried audiophiles that can hear a fly crap on their cables, I would say:
simply make a separate linear supply for 5V and use the current PCB for the + and - 15V and if there is a considerable inbalance and you suspect it might be worrying, simply measure both currents and calculate the resistor to the desired value.
If the + rail draws less put the resistor in the + rail...
I would simply use it as above and measure if things are (well) within their minimum requirements if they are not... adopt.
If unsure post the measurements and ask for advice... that's what a forum is for.
A. I have never claimed to be able to hear a fly crap on a cable !
I do however believe that I have a fairly good working knowledge in this area, and simply asked a question about any possible negative effects of a modest increase of the capacitance value on the +VE rail, as I had never seen this done before, although it more than likely has been done previously. It's also a good opportunity to help increase membership knowledge of this important area in DIY.
... that's what a forum is for.
Kind Regards
Alex
P.S.
Thanks for the replies from all concerned.They are much appreciated