Just 15v, or +- 15v?+- 15VDC
But, maybe I'll just order a powerstation with the Headamp, then I have two extra rails
Have done mine all with opa2604 running from +/-24vdc,so if you're about to build a psu can go the powerstation way.
On the other hand you can use any dual op amp as stated in the thread as long as it is pin compatible and able to drive loads of 600 Ohms or lower.So on +/-15vdc you can check it with NE5532s first since these are good opamps and very cheap or use drop in replacements to your taste.
You can compare the technical specs of the op amps looking for thing like dynamic range,noise,thd ans so on.
Personally I prefer the opas on higher voltages,but that's just my 2ct
Edit:If I may tease you ab little bit go to the "Amp Head" build thread at Joe's homepage and scroll down to the end of the page,you can see my first one there.The psu looks a bit overkill since it was the smallest torroid I had handy,hahaha....but this piece is a great tool.