Bass Omnidrive - switching the LP filter to the clean side - yes/no?

[auden100]

So I'm messing with some plans to convert the OmniDrive from John Hollis into a bass-ready pedal for a friend. Reading through the other bass omnidrive threads, I saw a few discussing the LP filter present in the circuit, but not in this way. From my understanding, this LP cuts off the highs so that the octave-up section sounds better. I like that, but I also want to incorporate an LP filter into the clean portion of the pedal for just the bass freqs to come through. I'm still a noob, and I don't recognize the way this filter section is set up. So two questions:

1) Since he'll be using this for a bass, is the LP filter for the overdriven signal still necessary to enhance the octave effect? If not, I could just as easily utilize that section for the clean signal. If so, would it be just as well to use a typical R-C lowpass filter on the overdriven signal so I can use the active filter for the clean signal?

2) Is there a way to make the LP section adjustable with a pot? I figure replacing one of the many resistors would do that, but I'm not sure which.

John Hollis' page:
http://www.hollis.co.uk/john/circuits.html

The OmniDrive filter section:

[moosapotamus]

I've never built the omnidrive and have not read of anyone using it on bass, but that doesn't necessarily mean that it not already bass-friendly. Often a clean blend feature is all that's needed to get good results, and the omni already has that. If there is no low end loss in the clean signal, it might be good to go as-is.

Another possible mod to consider might be adding another toggle switch to switch the low pass filter into the clean signal path, and leaving the low pass switch for the drive side as-is, so you would be able to feed both the drive and clean sides with the one filter simultaneously.

To make the cutoff for that filter adjustable, I think you need a dual ganged pot in place of R6 and R7. Not sure what the best value would be, maybe 500K?

~ Charlie

[PRR]

In general, to adapt frequency response for the octave-down Bass, double most of the capacitors.

Yes, resistors also change frequency, but they affect gains and biases too. You can figure that out. But caps only affect frequencies, so changing them is less hard thought. You may not need to double all of them; some are bulk power, some may already be generous.  But for a one-off the cost of oversizing an extra cap is trivial.