lame Nurse quacky

[stompbox steve]

Hello people
Does anyone have a quick mod for improving the nurse quacky signal?
thanks, Steve

[Mugshot]

like how? a little more explanation of the problem will give a clearer picture :-D

[stompbox steve]

that would help won't it...  It was late and I thought I had explained further.. I am comparing it to the Q tron + and find its level low.  I am not expecting the same "quack" but an increase in overall level would be nice.  It would be nice if I didn't need to use a clean boost at the same time.  thanks

[Mugshot]

ah i see. you gotta check ROG's. IIRC it used a 3.3M resistor for the envelope section to bring the signal level up.

[stompbox steve]

I appreciate your help and will dive in for change.  Look for my post tomorrow: "dead Nurse Quacky"... 

[Mark Hammer]

While the Nurse Quacky is a nice simple build for those who wish to get into autowahs, I find Jack Orman's Dr. Quack to be better on several fronts.  The JFET front end is a big part of it.  The passive front end of the Quacky has the effect of attenuating the signal a bit, and also loses top end if you aren't already feeding it a buffered signal.

If you want more output level, raise the value of the feedback resistor in the filter stage from 470k to 680k or even 820k.  Or, you can do what the Seamoon Funk Machine did and make it variable, such as a 330k fixed resistor in series with a 1M pot.  Higher resistance increases the gain and output level, but also shifts the centre-frequency downward at the same time.  Not disruptively so, but you WILL notice the difference in overall sweep range.

[stompbox steve]

Hey Mark
How do I know which 470 to change - there are 3 on the board and I have it narrowed down to two.
One is hooked up directly to the opamp.  I am afraid to just try one then try the other as usually when I mess with the pedals I kill them.  Thanks for your help, S 

[Mark Hammer]

It's the one shown going between the output of the op-amp used for the filter, and the "-" pin on that same op-amp.

It is referred to as the feedback resistor because it provides feedback from the output that determines the gain of op-amp.

Op-amps are essentially designed like engines with their accelerator all the way to the floor, and thew only control pedal being the brake pedal.  The feedback from the output is used to determine how hard the brakes are being applied.  If the feedback path is zero ohms (i.e., straight wire connection) then all possible brake pressure is being applied.  If the feedback path is a large resistance, or if the combination of the feedback path and some other connected path to ground results in that feedback being bled off, the gain is also reduced from maximum.

[stompbox steve]

Much Thanks Mark
Tried the 820K, Much much better.  With the attack cranked reminds me of the bass balls (with amp overdrive).  It got a second chance and will have to see how it works with the rest of the fellas.
This Site Rocks, Steve

[deadastronaut]

Much Thanks Mark
Tried the 820K, Much much better.  With the attack cranked reminds me of the bass balls (with amp overdrive).  It got a second chance and will have to see how it works with the rest of the fellas.
This Site Rocks, Steve

just curious. does it quack on all strings now...i built one and it wouldnt do anything on the top b e strings at all...?

its sitting on my 'to mod later ' pile!..

[Earthscum]

[quote author=deadastronaut link=topic=86837.msg732781#msg732781 date=1285508788
just curious. does it quack on all strings now...i built one and it wouldnt do anything on the top b e strings at all...?
[/quote]

I tried the Nurse a while back and got the same thing... I think I determined that it was filtering in the circuit.

I'm a bassist, so in my 5-string I would only get upper notes and higher up on the neck, some of the lower notes would catch. I've noticed this with quite a few envelope circuits, though. More gain just made upper notes have too much and lower notes just barely keeping up, which is what made me start investigating the filtering.

I noticed with bass and lower guitar strings it seems you are getting low enough in the frequency range that envelope filters start getting quirky. I just made up my own t-filter combo and use it now in place of most pre-filtering, and the trick seems to work most of the time. If you can get a steep cutoff high pass at around 30Hz (t-filter with feedback or feed-forward works good for me), and then shape your low pass filter to track the highest notes as well as the lower notes are, if that makes sense. I use another t-filter with FB/FF for this, and works great.

I came up with my filters for doing synth circuit tracking with something universal. Basically, tried them with envelope circuits, and they work great there as well. They actually filter enough to almost return a full instrument range of square waves back into sines... more like compressed sines, but close enough that I don't have any amplitude loss between high and low notes.

[stompbox steve]

you know you are right the high strings are not as quacky, specially the high E.  I tend to like the filtered sound myself so it works for me.