Nurse Quacky build, SO close to good... Help!

[Barcode80]

So i put together the Nurse Quacky project with the board and layout on the GGG site. It works, and when it quacks it sounds pretty nice, i just have a couple small problems.

i used the 1458 chip. i subbed (3) 1M resistors in series to approximate the 3.3M. I used a 5k attack pot instead of a 1k. other than that, it is stock.

the problem is that it is not NEARLY sensitive enough. I have to bang the strings to get a quack out of it, even with the controls maxed. could a faulty sensitivity pot be the culprit? i measured from the outside lugs and it showed acceptable tolerance from 100k (around 97 i think, IIRC), but since it isn't very sensitive, i figured that might be the problem.

i'll post voltages in a bit, but any help would be great!


EDIT: Voltages:

1-1.68
2-1.23
3-1.45
4-0.0
5-4.64
6-4.64
7-4.64
8-9.51

[zhx]

My first post here...


I too buid the Nurse a few days ago, but modded for bass.
I noticed, that 1458 doesn't sound nearly as good as the TL072. The 1458 sounded too mild.

I would also try a jumper to bypass the attack pot to see if it has any difference.

Great pedal once you get it to work!

[Barcode80]

sweet! did both those, works like a charm. i'm actually probably going to bypass all pots because it sounds perfect to my ears maxed out. although, i may want to open up the treble a little more. it sounds great, but i get almost no signal in the top range. might not matter, i don't do a lot of autowah up there.

[Hanglow]

I did the GGG one as well, for me there is too much treble in it sometimes, and I have to remove some, especially with the range and sensitivity pots up. It doesn't sound particularly good with both those pots at full...but sounds great with them backed off a bit. I used an LM 358

[Mark Hammer]

Your attack pot was too big.  Note that the attack pot is a series resistance that, among other things, reduces the current drive to the transistor, just the same way it would limit current going to an LED.  There is  normally a tradeoff between attack and sensitivity such that, when the attack resistance gets bigger you need to turn up the sensitivity to compensate.  Personally, I've found that anything bigger than 1k starts to mess with the pedal's ability to respond.  I've also found that adjusting decay time via a resistance in parallel with the 10uf cap to ground tends to yield more variation in feel with much less sonic penalty.  A 10k-22k in series with a 500k-1M pot is probably about right.

If one does want a variable attack time, the MXR Envelope Filter (see Tonepad Agua project) handles that much more effectively.  Indeed, it was the surprising range of attack times available on the unit that led me to buy one in 1978 and again in 1985  The filters may sound a little juicier on other pedals but the feel on the MXR is special.

[solarplexus]

I built one recently and it's not working... I supose it's because I am using a 4558D ?   I hear the guitar, I see the LED blink (the other always on) I hear a very faint effect in the back only when all the pots are maxed out.  Any ideas ?

[solarplexus]

I just took a look at the GGG wiring diagram...

In Torchy's layout, it says to connect input to Lug 1 of Sens... here it says Lug 3.

http://www.indyguitarist.com/torchy/Wah%20&%20Auto-Wah/ROG%20Nurse%20Quacky/Nurse%20Quacky.gif



So mine isn't working with torchy's layout... I guess I need to connect it to Lug 3 ??

[Mark Hammer]

Aside from the usual sorts of build-goofups that people commit, regardless of circuit type, the more common sources of nonfunctioning in this build include:

1) The transistor you ended up using has a different pinout.
2) One of the LEDs (usually the blinky one) is misoriented.
3) There is insufficient signal to push the unit, given the setting of the rectifier gain stage.

One thing you can do is this.  The 25k trimpot should be able to vary the filter frequency on its own.  If twiddling the trimpot does nothing audible, even as minimal as changing the quality of the audible hiss coming out, then you have the transistor set up wrong.  If the trimpot works fine  but you can't elicit sweep, then the envelope/sidechain path is screwed up somehow.

[solarplexus]

3) There is insufficient signal to push the unit, given the setting of the rectifier gain stage.

By that you mean??  Is the 4558D adequate for this circuit?

[Mark Hammer]

No.  ANY dual op-amp is sufficient for the circuit.  The gain is not inherent in the chip but in the component values used with the chip.

However.....what comes out of the 2nd LED has to be big enough to result in changes at the transistor.  Sometimes, failure to sweep is a result of having the trimpot adjusted wrong.  I mentioned that twiddling it will get some "sweep" type sounds. What I didn't mention was that some extreme points in the trimpot rotation will get you NO sound, even though both LEDs are giving you the "thumbs up" indication..

You will note that what your guitar "sees" at the input is two immediate paths to ground: the 47k resistor and the 100k pot.  Right away, that low input impedance means you lose a bit of signal.  Happily, the filter adds some bite so you don't lose that much level (if at all), and the 3M3 feedback resistor in the op-amp adds enough gain that even modest guitar signals (e.g., weak strumming on weak pickups) means that the transistor can still be urged to change state even when the sensitivity pot is not dimed.

If you have a weak-ish input signal, and the 3M3 resistance is replaced with something significantly lower, AND the trimpot is set wrong, it is still possible to have no audible sweep even though everything is wired properly, simply because their combination results in insufficient envelope signal.  That's actually one of the nice aspects of the Orman mods to the Dr Q (implemented in the Nurse Quacky and Dr Quack) - you can SEE when the envelope follower is working properly.

One other test you can use in debugging is to boost the signal in some manner, whether through booster, overdrive, compressor, or whatnot, and see if that evokes a sweep from the pedal as you are adjusting the trimpot.

[Barcode80]

i have no trimpot on my nurse quacky build....

[Mark Hammer]

So, um, what DO you have between the base of the transistor and the rectifier circuit?

[Barcode80]

i dunno, as i'm not really sure which section is the rectifier section, but the GGG prject has no trimpot in it:

http://www.generalguitargadgets.com/pdf/ggg_nurse_quacky.pdf

[slacker]

So mine isn't working with torchy's layout... I guess I need to connect it to Lug 3 ??

If you're having a problem with Torchy's layout it might be because you've wired the attack pot incorrectly because it's confusing on the the layout. It should be like this



I know someone else had that problem, have a look at this thread for more info http://www.diystompboxes.com/smfforum/index.php?topic=52305.20

[oldrocker]

I used a TL072 and two yellow LED's from Radio Shack and mine works and sounds great.  When I tried a 4558 it barely worked at all.   I'll have to put up some sound clips if and when I gat the chance,  (Just started a new job and the overtime and drive time is killing me. 

[solarplexus]

Thanks for the help... but where does the input go?

[Mark Hammer]

i dunno, as i'm not really sure which section is the rectifier section, but the GGG prject has no trimpot in it:

http://www.generalguitargadgets.com/pdf/ggg_nurse_quacky.pdf

Misunderstanding solved.  I was looking at the original ROG schematic which has the trimpot AS trimpot, like the Dr. Q it is based on.  The GGG pdf file has it moved to the front as panel-mount control, which is a recommended practice.  Note that, whether trimpot or knob-pot, not ALL that pot's range is usable, and some settings result in no audible sweep.  One or more of us has to sit down and figure out what combination of a 10k pot and fixed resistance values on each outside lug of it would result in a panel-mount range control that would be usable across its entire range.