Q Control for Dr Quack

[ustompsteve]

How could I add a Q control to the Dr. Quack?

--Steve

[Mark Hammer]

In that sort of filter configuration, the Q and filter gain controls are one in the same.  Increase the value of the 470k feedback resistor in the filter (between output and input) and you will increase the Q.  Unfortunately, you will also raise the gain to objectionable levels, which also necessitates an output level control to offset that.  Bottom line: it doesn't sound all that great to my ears.

What I think is a much better route to getting a more defined, focal, filter sound is cascading identically-tuned bandpass sections.

So, you have two identical filters, just like what is already there now.  Each filter has its own transistor to ground, and the two transistor control elements are fed by a common envelope follower.  You could easily do this with a Baseballs, except the output of one filter would be fed to the input of the other and then to the output jack, instead of two staggered filters in parallel as they are currently configured.

I've cascaded a pair of Dr Quacks in series and I like the sound of it very much.  A really nice edge.  Unfortunately, there are two envelope followers involved so the response of the second is shaped more by the 1st filter output than by the dynamics of the original guitar signal.  Better to have one envelope follower pushing the whole thing.

[R.G.]

Sounds like what's needed is a buffer on the EF driving two filters.

[Samuel]

Sounds like what's needed is a buffer on the EF driving two filters.

Isn't that what the Bass Balls is? Or am I misremembering?

[Paul Perry (Frostwave)]

I've cascaded a pair of Dr Quacks in series and I like the sound of it very much.  .

Why does that not suprise me?
I imagine that if they are tuned to slightly different frequencies, it would be even better! (I call that "Twin Peaks" mode in my Resonator).

[smoguzbenjamin]

Sounds cool. Hey while we're talking about the dr. Quacky, I was wondering how I could get a reverse sweep out of it. I've been thinking hard but nothing came out

[Paul Perry (Frostwave)]

It doesn't look very easy to reverse (at least to me) because the bias on the transistor that does the quacking is inextricably mixed up with the envelope rectifier.
Incidentally, the thread heading "Q control for Doctor Quack" made me think of "Ground Control to Major Tom" and now I can't get it out of my head :roll: