Wally wrote:

As some of you may be aware, I have an on-going speaker rebuild fantasy
bubbling away in the background. The plan is to bi-amp, and part of this
involves a second line output on the pre-amp, to send a signal to the bass
amp. The bass/midrange driver will have no high-pass components in the
crossover - I intend to let the bass roll off naturally, and try to match
the low-pass filter feeding the subs to this roll-off. I'm edging towards
trying to make a prototype filter and would welcome comments...

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?

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?


No.

As you know nothing about electronics you should start with this:

http://www.bmm-electronics.com/Product.asp?Product_ID=7

You really are better off with steep high and low pass filters.
trying to match the hf response of a sub to the lf response of a
mid-range box is difficult, and putting a lot of power through the
mid-range below its resonant frequency is asking for trouble.

--
Eiron.