Hello,
Thank you all for your help. I've tried some of your suggestions and here are my results:
1. What seems to have the greatest influence is the LM317's output bypass capacitors. First I changed all three of them to 10uF so the output capacitance is 30uF. This drastically reduced the noise - see photo below:
2. Next I increased the frequency of the ADM660, this further improved the LM317's noise levels - see photo
3. Next I tried to change the ADM660 capacitors to lower value ceramic ones. However, this only made things worse (maybe the ESR was high - I didn't have the data for the cearmaic caps).
4. Adding an output load resistor to the LM317 and the ADM660 seemed to have no effect at best and sometimes even increased the noise levels.
5. Also, adding a capacitor in parallel to the LM317 feedback resistor had no noticeable effect.
All in all, with the original 10uF tantalum caps and high frequency the +5V rail looks pretty good.
However, the ADM660's -5V output is acting up (it is possible that I've missed this before but I'm pretty sure that the -5V line was stable prior to all the above changes):
As you can see the output has sharp 50mV - 25ns pulses (which are heavily coupled to the op amp's output).
1) Do you have any suggestions for reducing the output noise?
2) Am I wrong to expect a stable output from an unregulated switch capacitor converter?
Thanks again,
Alex