Built a Nurse Quacky...its very nice!!!!

[AllyP]

Did a quick build of the Nurse Quacky from runoffgroove....Its my 3rd effect on proto board.......it'll vbe my first thats put into a box :wink:

-Very easy to build
-Sounds great!!!

I used a TL072 for the opamp.  
I couldnt get hold of 0.005uF caps so I had to use .0047s.  
No 25K pots so I used 22K (any way to make a 22K a 25K?  Would It make a big difference?)

I only have one problem with it....All is well on the E A D and G strings but the effect does not affect the top two  They just sound like theyve had the high fequencies cut.....

ie.  Its not triggerring the circuit right?

Any Ideas?



Cheers
Ally

[gez]

I don't have the schematic in front of me, but by the sound of things you need a bit more gain in the envelope follower.  Once you've done this you can prevent the lower strings from being over sensitive by making the input cap to the follower smaller.

[B Tremblay]

I'm glad you're enjoying the project.

The lower strings have more volume and therefore trigger the filter more easily.  The .01uF input cap of the envelope follower helps to even out the response, but may not be enough in some cases.

A compressor placed before an envelope controlled filter often helps quite a bit.

I've found that the Dr. Q/Nurse Quacky needs to be "dialed in" for rhythm or lead and that if it is set for one, it may not work well (or at all) for the other.

[AllyP]

So I need an external compressor pedal b4 the NQ?

Im not sure how the circuit works atm.....which bit of it is the envolope follower and how does it work?

How do I increase the gain?  Is that the equation for gain on the opamp? (The two resistors in series with the negative ip of the opamp coming out between them?)  Or is it done by decreasing the ip cap value?


Thanks again, in all your wisdom

[B Tremblay]

If you want to set the Nurse Quacky controls and not have to worry about switching from lead to rhythm, then an separate compressor placed ahead of the NQ may be in order.

The Dr. Q/NQ design is about as simple as you can get with an envelope-controlled filter and as a result, the quality and "playability" are not as wonderful as more complex circuits.

The envelope follower section of the circuit is the op-amp at the bottom of the NQ schematic, with the LEDs.  The gain is set by the 3.3M resistor in its feedback loop.  I don't think anything will be helped by increasing it; the lower strings will trigger even harder.

You may just have to accept the circuit's shortcomings and adjust the controls for different applications.

[petemoore59]

the other day...having an LPB1 in front of it really got it going More'.
 I was running...guitar> LPB > Nurse Quaccky> Sonic Distortion and having bigg funnzies...
 I'd never tried it like this before, therfore it was sitting on the back of the bench for mnths...I decided to pull it out [prompted by the matching doides post for NQ..'?'] it really surprized me and sounds just great!!!
 Still not much Quack with the thin strings up near the 12th fret and higher...that's cool, the effect is just great and I don't HAVE to have it quack up there.
 Really liking the Sonic Distortion I popped together and in the box in very short order...I haven't heard comments about this one [did I miss them?]...here's mine...it was easy and fairly inexpensive for me to build,
no specialized parts [except if you consider a Generic OA 'exotic'], and works great with just the gain and vol knobs!!!

[gez]

A few things spring to mind.  You could simply make the 47k resistor coming off the sensitivity pot smaller, this would give more gain to the highs in particular and you may not need to make the .01u cap smaller to compensate for any increased gain to the lows.  Only draw back is that it reduces input impedance - not a problem if you buffer the input though!  

Another approach would be to increase the 3M3 resistor (OR wire up a resistor in series with it if you can't get larger values), then reduce the .01ucap.

Another thing which 'might' work is to slightly reduce the value of the 220 ohm emitter resistor of the trannie.  This will make it a little more sensitive, then you can reduce the .01u cap if necessary.

[Rob Strand]

Gez is on the mark here - I'd half the 10n cap and double the 3.3M resistor.

The other option is to leave the circuit as is, dial-up the sensitivity, and just change your playing technique to hit the lower strings lighter.

[Mark Hammer]

There are limits to what you can do with increasing the follower gain.  At a certain point there can be instability issues and gain/bandwidth limitations.

The solution is actually pretty simple: a bypass cap on the sensitivity control.   This is the same trick used in Fender amps and guitars to give a little advantage to the high end by letting it pass directly through the cap to the output.  As the pot is turned down, that treble advantage increases, and as it gets turned up, the advantage decreases.  Depending on the cap value selected, the amount and frequency range of the treble advantage can be tweaked.  I'd start with maybe a cap value of .0047uf and work from there.  Higher values will include more midrange and smaller values will provide advantage to only the higehr frequencies.

Compression WILL work but will also reduce dynamic responsiveness.  In some instances this is a good thing, but not what you'd want for a default setting.  Some compressors may also have the side effect of slowing down sweep decay time too.

There are several ways you can implement this sensitivity-balance remedy.  One way is to have a switchable bypass cap.  You'd want to take the cap out when the input signal is so hot that you have to turn the sentivity way down (in which case you'd get sweep for your unwound strings and diddley from your wound ones).

Alternatively, consider sticking on a booster input with variable gain up to maybe 10.  With a hotter input signal the filter output will be louder so stick a 100k log pot on the output for volume control and effect/bypass volume balance.  Since the place/frequency where the treble advantage begins will depend on the sensitivity setting, you'll be able to get different types of envelope response patterns by varying the input boost and sensitivity controls.  No cap switching is used here.  Probably a good idea to drop down the follower feedback resistor to maybe 2.7M or even 2.2M because of the hotter signal.

[AllyP]

I tried both methods(increase 3.3m and lower.01uF cap and the bypass cap) but to no avail!   Neva mind....I knew the circuit was too good to be true.  I will look into building the LPB1 Pete was talking about....

Cheers guys,

Ally

[gez]

Before you throw in the towel, another thing you could try is to lower the value of the 22k resistor connected to the base of the trannie then make the .01 cap smaller.  It forms a divider with the trannie's input resistance and might be sapping too much control voltage.  Perhaps try another trannie too, something with higher gain?

[AllyP]

Thanks again,  Ill see what I can do, but I like it enough to put in a box anyway.....I'm gonna be busy this weekend!  Ive got an Obsidian to proto build and my Nurse Quacky to solder and put in a box!!!!!   YAY!!! :wink:


The joys of being a Stompbox hacker!    

[Ned Flanger]

I am currently working on a Nurse Quacky and from this topic Mark Hammer suggest a high end bypass on the sensitivity pot.  Is this just a cap bridged between the 3 and 2 terminals of the pot?  Is it that simple?