Duck learns to talk - NQ mods

[strungout]

Pls keep in mind that I really don't know much about electronics, but I do know what sound I like better

I breadboarded a nurse quacky and started pokin around and changing things here and there, all the while using the very useful "search" link in this forum to get some info about what does what. Here are the mods I did:

-I wanted less highs, so i changed the input and output caps to .1uf and .22uf.

-One of Mark Hammer's post reminded me that trick fender uses to give a bit more advantage to the highs, so I added a 180pf across the input lug and wiper of the sensitivity pot.

-Transmogrifox said in one of his post that added a 1.2k resistor (I went with 1.5k cause that's what I had handy) at the transistor's collector helped with the difficulty of setting the sensitivity and range to be "milked" in a certain frequency. I did seem to help. With the range and sensitivity set to about 50% rotation,
I get much more wah on the E minor with the same picking strenght (quite strong) and the E major is still very sensitive, and goes high real fast unless I pick very softly.

-I wanted a slower attack, even more than the slowest the 51 ohm and 1k pot would give me, so I changed the 51 ohm to 470 ohm. I also tried a 510 ohm, but that cut the wah from the E minor. Seems the slower the attack is, the harder it is to get a wah from the E minor...

-I don't know why the 1N914 diode was taken out, but I put a 1N4148 back in and I liked it.

-gez suggested to someone that lowering the 220 ohm resistor from the transistor emitter would make the transistor more sensitive. I lowered it to 22 ohm with good results.

So, basically, what I was trying to accomplish was to widen the range at which the wah is triggered, so that I'd get as similar a reaction as I could from E minor to E major. I also wanted a slower attack so that I could hear the sound go from low to high and back down. The Nurse quacky went up too fast for my taste. You knowledgable people can validate or not the usefulness of my efforts Maybe I heard what I wanted to hear, but this modded Nurse isn't the same and she "woaow"s more than she quacks (you could do a guitar impression of a pissed off Donald Duck .

And as usual I have some questions:

-What would be needed if I was going to split my signal between two of this circuit, one set for highs, the other for lows? I'm assuming a buffer would be one thing needed.

Ok, well, looks like I have ONE question

Ciao.

[Transmogrifox]

Actually, you have a JFET buffer on the input anyway, so just tap one off for the highs by making the input capacitor smaller (it's a .047, or .0047? whichver it is, make it smaller).  Then for the lows, make the same filter circuit all over again, use the same envelope follower to control the transistor, and use the "bass" input wiring scheme of the DPDT switch (I can't remember if Nurse Quacky does this, but Dr. Quack has this)...and put a capacitor in parallel with the 470k resistor in the feedback loop of the opamp.

Now, if you want to use this basic filter circuit, but have it sound better, use the Morley Pro-Series wah with the LDR deal.  If you need to know how to control the LDR/LED set-up, I can send a schematic of the envelope follower that I inserted into my Bad Horsie to make it useable as an envelope filter...

you may also use this same Nurse Quacky filter and just replace the 2N3904 with a LDR from Rat Shack and control an LED from the envelope follower.  You may need to tweak with the 22k resistor that normally would go to the base of the tranny, but that circuit is pretty easy to set up with a LDR.

[Mark Hammer]

The difficulty with the envelope follower arrangement in the DQ/Dr Quack/Nurse Quacky is that both the attack time and the envelope signal amplitude are affected by the resistor in question.  So, as you increase the attack time by increasing that resistor value, you also inadvertently reduce the amount of sweep.  For the most part, this isn't such a bad thing since modest changes to attack time can be offset by small changes to sensitivity.

As you found, though, asking a little more from the design is not always easily compensated for by tweaking the existing controls.

One solution is to use something like a rotary or multi-position toggle switch that simulatneously adjusts envelope-follower gain and attack time resistance.  So, as the attack resistor is increased (limiting current in the envelope path), the feedback resistor is also increased to goose the gain a bit.  That way, you sort of disconnect attack time from wherever you happened to set the sensitivity control.

A second type of solution is to tinker with the cap to ground.  The attack time is a reflection of how long it takes to charge up that cap.  With a bigger resistor it take longer to fill it up, but it also takes longer if the cap is a larger value, too.  The problem this creates is that bigger caps take longer to discharge so to substantially increase attack time by means of increasing that cap, you'd be stuck with a decay time that is simply too long to be practical.  Fortunately, if you stick a resistor in parallel with the cap, it will discharge more quickly since it now has a path to ground.  

My suggestion would be to adopt a combination of two approaches.  Use a  small-value (1k) pot for the attack resistor, and have a switchable decay cap that would double or triple the range.  An example might be a 10uf cap and a 22uf-33uf cap that could be added in parallel.  The extra larger-value cap should have a resistor in parallel with it, say maybe 100k-220k or so.  This way, when you switch in the extra cap, attack time goes up by 3-4 times, but decay time is not all that dramatically lengthened.  Be sure to switch the cap using the positive end rather than the ground end.  The parallel resistor providing a path to ground will assure that the cap is generally well-drained, yielding relatively pop-free switching.  If you switch the cap using the ground end, it will have no opportunity to drain when you aren't using it, so it will pop when you bring it back in circuit.

[strungout]

Thanks for the answers.

I could use that schematic, Transmogrifox, my email's at the bottom. I'm not sure why but that LDR thing is intimidating me. I have a bad experience with so-simple concepts that turn evil in adjusting them But anyway, ppl take polar dips, so I'll just jump in.

Mark: I'm definately gonna try the switched settings arrangement for the attack/decay, and the switchable cap to ground. I should have enough parts to rebuild a Nurse (I perfboarded the one I had to free my project board, oh well ).

Ciao.

[Mark Hammer]

There are enough of you in the Quebec area (Gilles Caron and I think one other besides yourself) that you guys should connect.

[Transmogrifox]

Give me a couple days, and I'll find that schematic and scan it for you.

take care...