Dr Quack and Nurse Quacky Combo Schematic for Bass

[Ben Lyman]

Here's the Dr. Quack:
EDIT: I just realized this is the Dr Quack schematic I used:
http://www.muzique.com/schem/quack.gif

Here's Nurse Quacky:
http://home-wrecker.com/nurse-quacky.png

Since I'm still just a rookie, I had a hard time reading these the way they are drawn. One way or another I got the Nurse Quacky on the BB sounding great, then sounding even better with Dr. Q's JFET buffer added on. I have read through every thread in this forum pertaining to mods for bass, tried them all and ended up right back at the start.

I've tried to draw up the schematic from my BB but I find the whole envo filter thing a bit confusing.
Anyway, I think it's like this, does it look like it's possible? Have I left out anything or added any unnecessary things?

[slacker]

Your schematic looks good to me, assuming R21 is really a cap not a resistor. You can save a couple of parts, you don't need R8 and you could remove R5 and connect the top of R4 to 4.5 Volts instead of 9 Volts.
If you search the forum I'm pretty sure there's some mods to add a decay control, that might be worth playing with whilst it's still on the bread board.

[rutabaga bob]

What about just making a BassBalls? 

[Ben Lyman]

...assuming R21 is really a cap...

Ah, yes. thanks, just fixed, now it's C12 

..you don't need R8...

That's one of the reasons I drew it up this way, it took me 5 days of boarding before I even realized it was parallel to the 100k pot on both Dr Q and Nurse Quacky, I wondered if there is a reason for it, like maybe it gives the sensitivity control a different feel. Anyway, I'll pop it out and jam on it for awhile, see if anything happens.

...you could remove R5 and connect the top of R4 to 4.5 Volts instead of 9 Volts...

Awesome, thanks, will do. I forgot Jack Orman tells me that everyday! 

...there's some mods to add a decay control...

Yes, checked em, tried em, not really necessary if you ask me. The combo of sensitivity and attack seems to cover all the decay ranges when fiddled with. 500k pot plus 100k across the cap really didn't seem to do much for me but a switch might be better, 10uF and 47uF are two nice, albeit subtle, decay changes.
Thanks!

What about just making a BassBalls? 

I really wanted to because I messed around with a real one and I liked it a lot. I can't remember why I got scared off it when googling schematics but there was something about it. I will have another look at it later. Does anybody have a clearly written, easy to read schematic for it?
Thanks!

[Mark Hammer]

A couple of things.

1) Optimizing an auto-wah for bass generally involves increasing the value of the filter-range caps so that the range of sweep shifts down by an octave or so.  In this case, optimizing for bass would suggest that C9/C10 be at least 6n8 and more likely 10nf.

2) While R13 does vary the attack time (time for the filter to start sweeping upward), and I was probably the guy who got people started including that sort of control, I've grown disappointed with that sort of control, since increasing the resistance of R12+13 not only increasing how quickly C7 charges up (the basis for slower attack), but it also reduces amount of sweep, and requires that the sensitivity control be turned up to compensate.  Unfortunately, the amount of resistance R13 would need to add to provide a noticeably slower attack is such that there'd be very little sweep to notice.  So, a simple toggle that switches between 51R and maybe 220R is about all you probably want to have.

3) What often makes a much bigger difference than negligible increments to attack time is decay or "settling" time.  Fast decay general produces a more synth-like "bwow", rather than "bwaaaa-oooh" sound.  This can be especially important for bass, since auto-wah on a bass makes it more of a percussion instrument, so that you want it to emphasize the beat by having a quick sweep.  This is achieved by placing a resistance in parallel with C7 so that however fast it charges up, it drains off very quickly.

You will note that the Dr. Q has a diode in between the trimpot and the equivalent of C7.  That same diode is missing here in your drawing and in the Nurse Quacky.  Since the trimpot also provides a way for C7 to drain off, inserting a diode, as shown in the DQ, will effectively isolate your "drainoff" from the trimpot and allow variations in decay time with the suggested parallel resistance.  Although a wider range can be achieved in decay time than can be achieved in attack time, it still isn't an exceptionally wide range of decay, such that you'll find yourself setting the dial to 7:00 or 5:00 and pretty much ignoring everything in between.  A more useful solution is to use a 3-position toggle to select between 3 very different resistance settings.  Your toggle would connect nothing to ground in the middle position, 470k in one side position, and perhaps 39k in the other side position for long, medium and short decay, respectively.

Using Jack Orman's Dr. Quack modifications, the LED on the output of U1A is intended to subtract a bias voltage.  Given that we're going to add another diode to make variable decay possible, we'll need to replace that LED with two silicon diodes in series (1N4001, 1N914/4148, your choice), so that when we add the diode just before the trimmer, what is subtracted - in total - is in the right ballpark.

4) Make sure to install a socket for Q2 and try out a few different NPN transistors to see what yields the most pleasing sweep.  They aren't all the same.  And PLEASE note that R19 is 220 ohms, not 220k.

That should get you a pleasing auto-wah optimized for bass.

[Ben Lyman]

Great stuff Mark, thanks! Looks like I got some more breadboarding to do... and schematic corrections! 

oops, I just realized I posted the wrong Dr Quack schematic, this is the one I was going from:
http://www.muzique.com/schem/quack.gif

Mark, the mods work great, very nice Nurse Quacky for bass. I also found a clearly written Baseballs schematic, thanks rutabaga bob! Baseballs sounds great too!
Now I don't know which one to make  Baseballs is intense but has a very slow decay and the two trim pots are tricky to adjust.
Is it the goal to set the high frequencies to close sooner than the lows? Other way around? Same time? I can't decide, it all sounds pretty cool.

Quacky is not as boomy and powerful but easier to set a fast decay, easier to dial up funk tones or spacey noises.
Maybe I'm just more familiar with it at this point than I am with Bassballs.

Well, I guess there must be mods for the Baseballs too... maybe that's next. trimmers replaced with 10k pots would be okay, but not enough, it needs decay control

Bballs Schem:
http://topopiccione.atspace.com/pjimages/EHBassBalls.sch.gif

1. Is C4 4.7uF the decay cap?
2. If so, must it be polarized or can I go down to 470nF?
3. If not, how can I speed decay up for a super fast and funky bass slapper?

[Ben Lyman]

Update: forget all previous questions, I took a break from the Bballs.
I got something really great on the board now, thanks to Mark for the mods!
I got some new questions though.

1) Is there any reason I shouldn't go above/below a certain value on these mods?
    For attack I like two settings (to be put on a switch), 51r for fast attack and 470r for slow attack. Is that 470r going too far? (aside from preference)
    For decay, also two settings for a toggle, I want no resistor across a 10uF for slow release and a 10k across it for fast. How about that?

2) I'M confused about how to add the extra diode(s) and why. It's late now, I will try to figure it out tomorrow.

Right now it looks like this on the BB and sounds fantastic with bass:

[duck_arse]

for the attack resistors, go crazy. 470R is fine if it gets you slow enuff. and when you say "I want no resistor across a 10uF for slow release", the B25k pot is across, and the biggest decider of slow decay.

if you replaced the 25k pot with a 250k pot to feed the Q base, for instance, and then wired a 100k as a variable resistor across the decay cap, say, you'd get slower slow decay. you might find a higher value you like.

(and you can wire the 470R hard inline, then switch a ~56R across parallel, failsafe.)

the diodes I'll leave to Mark.

[Ben Lyman]

Cool, thanks Duck. I see what you mean. I suppose a 56r switched across the 470r will keep me even closer to the mark.

I see now what Mark was trying to say about the 25k pot and decay cap but fixing it with the diode thing is still baffling me.

Here's the updated schematic

Got the switches sorted, thanks Duck.

Without the 47K across the sensitivity pot there is a difference but I don't think it is such that it warrants an extra part. Maybe in the old days someone ran out of 50K pots and then it became a tradition to make envelope filters with 100K pot and 47K across it... Is there another reason maybe that Dr Quack and Nurse Quacky have that 47K there?

It works as it without changing any diodes around. I guess the range pot will do what it does but since it all works...  again, worth adding more parts? I dunno.

I like the drastic changes on the switches, and that's what I want for my buddy when he throws a switch, big noticeable differences.

[Ben Lyman]

Finally figured out the diode thing, sorry it took me so long Mark 
I kind of miss watching the flashing red LED when I play but oh well.
I haven't had a chance to crank it up yet with the 3 diodes added in there but I will give it a full test tomorrow.

Can that last LED be replaced with a particular diode too?
Just wondering for ease of layout and stuff.

Here's what I think it is supposed to  be with the diodes, at least it works and still sounds great.

Edit: final decision on the schematic

[Mark Hammer]

I see now what Mark was trying to say about the 25k pot and decay cap but fixing it with the diode thing is still baffling me.

Without the 47K across the sensitivity pot there is a difference but I don't think it is such that it warrants an extra part. Maybe in the old days someone ran out of 50K pots and then it became a tradition to make envelope filters with 100K pot and 47K across it... Is there another reason maybe that Dr Quack and Nurse Quacky have that 47K there?

It works as it without changing any diodes around. I guess the range pot will do what it does but since it all works...  again, worth adding more parts? I dunno.

I like the drastic changes on the switches, and that's what I want for my buddy when he throws a switch, big noticeable differences.

Throwing a 47k across the 100k pot simply changes the taper of the pot, presumably in a manner that makes things more "dialable".

The "diode thing" (and you've drawn it correctly in the last version) is simple a way of providing the same voltage subtraction that an LED would provide, while isolating the trimpot from the C7 averaging cap, so that the trimmer only sets the range of control voltage fed to Q2, and has negligible impact on how quickly C7 discharges.

Do note that placing 56R in parallel with 470R gives you 50R.  I don't know that the 6 ohms makes an audible difference.  Just keep in mind that any adding in of something in parallel does not select between the 2 or 3 values used.

Personally, I'd go with a 3-way toggle, but that's me.  I think we are both on the same page, though, with respect to having instantly accessible noticeable differences, as opposed to futzing around with knob settings.  Besides, as I'm sure your buddy will find out, the settling time of the filter has as much to do with the butt of his thumb touching the strings as it does with the electronics.

[Ben Lyman]

Awesome Mark, thanks! I have settled on the two way attack switch with values of 820r and 68r switched across it parallel for two completely different sounds, the switch can probably be labeled "Buhwow" and "Ow"

Between your mods and Jack Orman's, the first name I thought of was "The Envelope Jackhammer" but I might call it the "Benvelope Filter" 

It's going on the perf today and hopefully have a vid in a few days posted here.
Stand by, and thanks again!

[Mark Hammer]

Looking forward to it, Ben.

[Ben Lyman]

Preliminary test drive, default settings, no switches installed yet

[thermionix]

Throwing a 47k across the 100k pot simply changes the taper of the pot, presumably in a manner that makes things more "dialable".

I'm going to differ here.  Putting a resistor in parallel with a pot (say connected to lugs 1 and 3) lowers the value of the pot, and it doesn't seem to change the taper based on experiments I've conducted.  A 100KA pot with a 47K resistor in parallel becomes a 32KA pot.  I've seen mention of people adding a resistor from one end lug to the wiper to alter the taper, but I haven't read up on that, or tried it.

[Mark Hammer]

Depends where you put the resistor.  If you strap it between input and ground, you're absolutely right.  If you strap it between input and wiper, you change several things about the pot at once, one of them being the taper.  If the wiper is rotated towards ground, yes it becomes functionally identical to what you describe.  With the wiper at midpoint, however, the total pot value becomes whatever pot fraction remains between wiper and ground, AND the pot fraction between wiper and input in parallel with the added resistor.  With the wiper rotated fully to the input lug, the added resistor does nothing.

As is often the case, much is revealed in a GEOFEX document: http://www.geofex.com/article_folders/potsecrets/potscret.htm

[rutabaga bob]

Nice little demo, Ben!  I'm interested to hear this 'full-blown', with all the switches, etc.   

[Ben Lyman]

Thanks Larry, it looks promising. I'll try to get the switches in after I take the kids to school. Then I probably need to disassemble and paint it because it almost seems the main reason my friends want my pedals is for the paint jobs... i think he'd be disappointed if it didn't have a skull on it! 

[Mark Hammer]

Finally plugged the headphones in at work and gave a listen.  Sounds nice.  Once you have the attack and decay options in, you'll have even more fun.

One more suggestion.  The gain of the filter can be changed in useful ways.  The old Seamoon Funk Machine made productive use of that, and you are referred to it to see how it's done.  In the case of this circuit (your DQ/Quacky/Quack hybrid), changing the gain and Q of the filter would involve changing the value of the 470k feedback resistance.

The SFM goes as high as 5M, but I found that excessive and hard to find a pot for as well.  Here, I could see having a 1M-1M5 resistor in the feedback loop, and using a toggle to strap in another fixed resistor or two to lower the effective resistance and Q.

Note that, as the Q/gain is increased, the range of the filter shifts downward.  So, a feedback resistance of 1M5 might make the unit sound like those 10nf filter caps had been change for something like 33nf, with a bit more emphasis at the middle of the passband.  With a fast decay that can sound real nice on bass; very synth-like.  Not that the circuit would ever sound like a Minimoog, but it can be a better match to some kinds of tempos and tunes.

[thermionix]

Depends where you put the resistor.  If you strap it between input and ground, you're absolutely right.  If you strap it between input and wiper, you change several things about the pot at once, one of them being the taper.

Yes, that's exactly what I was saying, so we can agree to agree. 

In Ben's first schematic, the 47K resistor is in parallel from the input to ground (lug 1 to 3) of the 100K pot, essentially giving him a 32K pot.  I suppose the original designer wanted a ~33K pot, but that's not a common value, so...