Where to put a tone control for better Blue Box tracking?

[Solidhex]

I wanted to build the Tone Pad "Caja Azul" and put a simple low pass filter to emulate the way the pedal tracks notes when the guitar tone knob is rolled off...I wanted to find a spot in the circuit where the filter would effect the signal going into the octave but not the regular guitar signal that you blend the octave back in with.. Any ideas? Here's a link http://www.tonepad.com/project.asp?id=33 with the shem
  I'm sure someone has probably done it but I couldn't find the specific info while searching the threads...

--Brad
 

[SonicVI]

Sounds like a good idea.  I'm thinking maybe between C2 and IC1b?

[Mark Hammer]

C3 helps to create a rolloff starting around 1130hz.  Increasing it to 390pf would bump that rolloff downwards to around 870hz.  Note that some high end still gets through, because the rolloff is only 6db/octave.  You could consider replacing C3 with a 470pf unit and placing a trimpot (let's say 250k) between the cap and the output pin on IC1a.  That would provide variable rolloff point, while leaving gain largely unaffected.

[Solidhex]

C3 helps to create a rolloff starting around 1130hz.  Increasing it to 390pf would bump that rolloff downwards to around 870hz.  Note that some high end still gets through, because the rolloff is only 6db/octave.  You could consider replacing C3 with a 470pf unit and placing a trimpot (let's say 250k) between the cap and the output pin on IC1a.  That would provide variable rolloff point, while leaving gain largely unaffected.

So that would make a variable low pass filter that would only affect the octave signal not the regular guitar signal?

--Brad