Zapfilter Mk2 PSU question

[Glenn2]

Hi,

I'm a bit of a noob when it comes to the art of voltage regulation so forgive any stupidity...

I have the Zapfilter2 output stage hooked up to my DAC. It consists of a 15-0-15 toroid, a PSU board and the Zap board itself.

The Zap board has shunt regulators on board, whilst the PSU consists of a a Schottky-diode bridge providing two rails, smoothing caps (2200uF/40V), and finally the series output resistors that are necessary for the shunt regs to work (56R/5W).

The rectified voltage is +/-23V and the output is +/-10V under load (regulated by the shunts).
Also, my mains here in London never drops below 240VAC and is usually up around 250V, not the 230V it was designed for.

I was thinking of adding pre-regulation to the PSU, so the pre-reg can handle the line regulation and the shunts the load regulation. I just want to see if the sound improves or gets worse by doing this.

Currently, with a drop across the 56 ohm resistor of 13V, I make that 230mA and the whole thing gets a bit too hot. LC Audio later increased the resistors I believe to 100 ohm, but some users had to bring them down again to somewhere in-between to counteract line ripple. I read somewhere that 68-75R is optimal.

I briefly switched to a 12-0-12 toroid (18V-10V/56R=140mA) and got a bit of hum myself actually.

I was thinking that if I eat up a few volts with an LM317/337 in series before the resistors I will get the current down to about 180mA and get better line rejection, killing two birds with one stone. I can decrease the resistor of course to bring the current back up again if I need to.

Anyone see anything wrong with that?

Another option (I think) is to use the LM317/337 as a CCS. Is this a better idea? I'd need a bit more guidance as to how to do it though.

Thoughts and flames welcomed.

Cheers!
Glenn