[sdiy] Neil Johnson 3 pole filter

[David Brown]

This weekend I put together a filter module based on the three-pole 
state variable filter PCB I bought from Neil Johnson.  I wanted to 
try this module out without investing in a panel, potentiometers, and 
knobs so I built it using a spare MOTM panel I had.  It's a very nice 
filter.  The low pass is very solid.  I expected the high pass to not 
be very interesting.  However, with the resonance and inverted 
envelopes it really comes alive.  The band pass is not real 
pronounced but resonance really adds some character.  I like it well 
enough that I'll need to buy some quality potentiometers and knobs 
and finish the module.

For the front panel I simply printed out a FrontPanelExpress file 
that matched the hole pattern in the MOTM panel, glued it on, and 
gave it two coats of lacquer.  The lacquer protects the toner and 
gives it an orange-peel finish so it looks reasonably well.  I'll try 
and get some samples sometime in the future.  Photos at
http://modularsynthesis.com/njohnson/3psv.htm

Dave