I have just acquired a slightly beat-up Cambridge A75 preamp (thanks Rob!).
Aside from some tidying up, this will form part of my intended system
upgrade to a bi-amped setup with a low-pass filter on the bass end. I'm
attracted to fitting a second stereo output stage and filter to the preamp -
that would let me try various amps for driving the bass speakers without
having to deal with incorporating the filter into each. Although I can
operate a soldering iron and a multimeter, I'm not terribly clued up on
silicon electronics...

I'm sure there are chips that can take an input from the PCB and drive a
second pair of outputs to the same spec as the existing outputs - but what
ones would be suitable? Those low noise mosfet 741-thingies?

Is there a chip that I can use to construct a filter which doesn't introduce
the sort of phase problems that a speaker-side crossover would? How much
scope is there for being able to tailer the slope of the filter, and make
the slope selectable? Can a subsonic shelf be incorporated? It would be good
to be able to switch the filter off and have the second output provide full
bandwidth.

I'd be grateful for suggestions of other ways to approach the filtering,
suitable chips, maybe some web sites that have circuit / schematics.



--
Wally
www.artbywally.com
www.wally.myby.co.uk/music