Nurse Quacky or Dr. Q mod for bass?

[Mark Hammer]

Making the Range trimmer a panel-mount control is not intrinsically "wrong".  Just be aware that only a modest portion of the rotation of that control is actually useful.  If you can live with it, go with it.

For simple envelope-controlled filters like this, and especially for bass, the choice of time constants is tricky.  The DQ uses a half-wave rectifier, which yields more envelope ripple than a full-wave rectifier.  The ripple translates into rapid "micro-sweep" of the filter frequency that many misperceive as "distortion".  If the circuit used full-wave rectification, such micro-sweeps would occur at double the rate, and above the range of audibility. 

Ripple is typically worst as notes decay.  If one expedites the decay (the reason for the additional control), that ripple doesn't get heard, because things settle back before the ripple sets in.  Fast decay also makes bass notes sound more "synth-like".  If the attack time is fast enough, it sounds like the filter sweeps only downward, because the upward part of the sweep is too fast to hear.  So you get "Owww", rather than "Bwoww".  Depending on the tune and rhythm, "Oww" may not be what you want or need.

Use of 33uf, rather than 10uf will smooth out the envelope, but also takes more time to charge up.  That implies that a reasonably percussive attack will require a smaller-value series resistor.  Your drawing shows 120R, which is going to be slow to charge up the 33uf cap.  I'd suggest 47R instead; 68R at most.  And, because use of 33uf means a slower decay, that's also what requires a smaller-value minimum resistance in series with the Decay pot.  You need that to discharge the cap faster, in order to get a fast synth-like decay...when you want it.

[sevrien]

hey Mark,

that 120R is the sum of both resistors in the homewrecker layout.
Any sugestions on the one in series with the decay pot?

geeetings

[Mark Hammer]

22k in series with the 500k decay pot is fine.

If you're fine with the slower attack, stick with 120R.  If not, drop down to something between 47-68R.

[Fancy Lime]

I don't mean to hijack the thread or derail your project, but all the difficulties with the Nurse Quacky / Dr. Q are what drove me to designing the Quackmire in the first place:

https://www.diystompboxes.com/smfforum/index.php?topic=119101.0

And I never looked back. It now comes with strpboard and PCB layouts!

Cheers,
Andy

[Mark Hammer]

It's a better filter, no doubt.  Just more complex than the basic NQ/DQ.
As I'm sure you concluded, using LDRs as control elements, instead of bipolar transistors (like the DQ), results in smoother sweep with much less envelope ripple.

Perhaps the OP may move onto it if the completed working version of the NQ fails to satisfy.

[Mark Hammer]

I will also add that the Quackmire is a lowpass filter, while the NQ/DG is a bandpass.  The former is better for bass, while the latter is suitable for guitar.  Most other autowahs of the era were bandpass.  What made the Mu-Tron so desirable for bassists was that it could provide lowpass filtering, and was relatively unique in that respect (though Musitronics licensed the design to a lot of jobbers.  I had one of the Fernandes Funk Filters that was a different-branded Mu-Tron III)