Wally wrote:

The pre-amp is a Cambridge A75. The chips it uses are NE5534N op-amps,
evidently low-noise and suitable for high quality audio. My intention was to
use the same chips for my active filter / output stage, on the assumption
that the pre-amp's PSU will be delivering the right voltage(s). However, it
looks like these chips are no longer made - what would be a suitable
alternative?

5534's are very common audio op-amps. You might not be able to find the
exact part number that you are looking for but a search for 5534 opamp
on Farnell's website came up with a few alternatives. You might also
want to look at the dual equivalent - the 5532.

You should also bear in mind that many 5534's are not stable at unity
gain without additional compensation components.

Cheers.

James.