In article , 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?

Erm... despite the magazines, etc, I'd say almost anything would do. :-)

My personal favourite has always been the Hitachi HA12017, but these are
now hard to find, and require more components than most. Despite the
hostility of some of those in audio, you could consider the TL071/81
families as used by Quad in the 34 pre-amp. These are quite easy to use.

I know next to nothing about solid state electronics, but my efforts so
far would suggest that I want to use an integrator and a phase inverter.
The integrator provides the actual filtering effect (I think), but is
180 degrees out at the crossover, decreasing to 90 degrees lower down.
It would seem to be a good thing to try and get the subs to be in phase
at the point where they cross over the natural roll-off of the bass/mid
drivers/cabs. So, I reckon the active filter and a phase inverter will
do the trick - that should give me zero degrees shift at crossover, and
90 degrees lag somewhere low down. (I'm considering a crossover point at
something around 60-80Hz.)

Does this sound like it should work?

Dunno. However I'm not sure what you are thinking of an an 'integrator'. A
genuine integrator has a gain that approaches infinite as you go down to
d.c. and hence is nominally unstable. Its phase lag is 90 deg at all
frequencies.

Have a look at some of the pages on filters in the 'Scots Guide'. This
inlcudes some basic stuff on designing simple filters with ICs.

Slainte,

Jim

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