Where can make power cord be detachable for LS15

I used to have mine done at a local electronics repair guy in Berkeley. It isn't that hard to do. He used to charge me $60 -$80.

Not worth it at all. It's a PIA, will cost, and result in EXACTLY the same sound you have now.

The OP, and those suggesting drilling out the rear panel, might want to take a look at photos of the OP's early version LS15, and of the later version which as Jl35 mentioned had a detachable power cord. (Click on the thumbnails of the photos near the bottom of this page). Notice how the adjacent fuseholder had to be moved to the left on the later version, to accommodate the IEC connector. And consider what, if anything, the fastener near the left end of an IEC connector mounted on the early version might be able to fasten to, given that relocating the fuseholder would leave a hole at that location.

Also, note how all of the nearby lettering was relocated on the later version, including the "warning" and "caution" statements that are above.

I don't necessarily agree with the previous poster that the resulting sound would be exactly the same (although that's certainly a possibility IMO), but I also wouldn't rule out the possibility that it might turn out to be worse rather than better. With the resale value of a nice preamp probably having been destroyed in the process.

Regards,
-- Al

Bojack, why do you persist?

Al, I don't see an issue it's not that close and not that much of a room needed, at most the lettering may be cut-off, but for the upgrade sake...
As another option to drilling for IEC socket, OP may re-solder aftermarket PC