Dan Armstrong Purple Peaker Modifications
With the above filter modifications, the Purple Peaker's LO section frequency is 159 Hz (413 Hz in Aron Nelson's original schematic) and the HI section frequency is 3.18 kHz (4.98 kHz original). The low is less midrangey now, peaking at around the octave of the low E string, rather than the 5th fret of high E. Additionally, whereas the original effect had only two settings, HI or HI+LO, a second switch was added so the LO can be used by itself. The circuit also has been updated to use common transistors and a negative ground power source.
my modified Purple Peaker, which may get a better enclosure someday