[sdiy] Book on analogue filter design

[Colin f]

> I was thinking something along those lines, except instead of
> desoldering the whole lot, I would leave the the IR3109s and possibly
> RA11 (a resistor array which seems to be in the same arrangement on
> both designs) and desolder all the other parts - IC47, RA12, RA13,
> RA14, various resistors and capacitors - and see if the cascaded
> integrator design could be fitted onto the rest of the original
> circuit board using the empty through-holes and some careful track
> cutting.

Only thing I woudl say about that is that if you hack the PCB a lot, it
could be a lot of work to re-instate the original filter design, should you
ever come to sell the JP6. Of course, it might be a selling point that it
had JP8 filters...

> It may be possible to leave IC47 in situ as well, and use the existing
> HPF/BPF/LPF select signals to select between 12dB and 24dB LPF.

You should be able to adapt the Oberheim Xpander filter mode switching to
achieve a more useful selection of modes. mixing the outputs from different
poles - maybe 12/24 LPF + BPF.

Cheers,
Colin f