DR QUACK PROBLEM

[grani79]

I built a dr quack clone. I used a tl072 opamp or Jrc 4558 D.... only sound.. no quack  

I used also two 3mm red led... are they right?

[Michael Allen]

do the LED's light? if they don't you either have a problem with the power or with the orientation. Also, one led should brighten and dim along with the guitar sound. Does that work? That's your envelope detector. Post some voltages and make sure that everything is getting power. Then make an audio probe and trace your way through it.....

Michael

[petemoore]

I did N Quacky ... knobs needed turned before she'd start quacking.
 Also boosting or compressing the input can bring low ouput pickup to a level that triggers the sweep
 I'm not real sure about the Dr. but it's worth a try if you haven't already.

[grani79]

No lights! The led are 3mm 9V.

I use tl072 op amp.

No wah, no light... only my guitar sound....

[Travis]

As I recall, the Dr. Q is VERY picky about having the correct parts.  I believe that you almost have to use a 1458?(whatever the original part was) as the dual OA in this circuit.  

The Nurse Quacky was designed, in part, because of such deficiencies in the original circuit.

[Michael Allen]

If he built the Dr. Quack, then the opamp shouldn't make such a difference and he's used a correct choice anyway. Jack Orman designed the Dr. Quack to be doable with more basic opamps....

If your LEDs are not lit, then you either have the orientation reversed or they're not getting power. Make sure that 1) your power is plugged in. I've left this off a few times  :wink: .  2) Make sure the power is being supplied to the board. Check the connection on the board making sure your solder job is good. Then measure with a DMM to see if your board is getting volts. Pin 8 should have around 9vdc.  If not, then from there you need to trace around and see if anything shorts to ground.

What layout did you use? If it was RG's then it shold be fine and you'll just have to check for solder bridges. If you made your own then you're going to have to run through your whole layout and check that it's right.

Michael

[Mark Hammer]

Michael is correct.

If only one of the LEDs was lit and the other didn't flash, I'd think maybe it was a case of either undersignalitis or something was amiss in the path between input jack and envelope follower (the steady-on LED only reflects the presence of a suitable offset voltage and nothing about input signal).  If the steady LED was on and the second one flashed a bit, I'd think it was either a) undersignalitis, b) a misoriented transistor, c) a misadjusted trimmer.

The fact that the first LED isn't on, though, indicates that the required bias to the op-amp ain't happening.  The other potential sources of difficulty may still be in there (hope they aren't) but until the LED is properly oriented you shouldn't expect to hear much sweep.  

When functioning correctly, there will be one LED that stays on always, and the second one should light up when you strum.  How birghtly it lights will be both a function of the pick attack, the amount of gain in the envelope follower op-amp stage, and the intrinsic brightness of the LED itself.  Although having a bright LED flash provides good confirmation (and monitoring of input if you panel mount it) in many instances, I imagine a flawlessly functioning DQ can occur with a second LED that just gives you a blip you need a dark room to spot.

[grani79]

tl072 is not a problem! It's good for this circuit, only more noisy than the other LC....

The led are ok. In the right position. I think it's a problem of capacitors. I don't have 0,005 and I used 4300 pf ... what do you think about that??

[smoguzbenjamin]

That's 4.3 nF or 0.0043 uF, not that much off. Besides it just changes the sweep sound a bit. Try increasing the resistor in the feedback loop of the envelope detector, maybe that will resolve the problem, if it doesn't try lowering it. The Dr. Q has sucky envelope follower I guess

[Mark Hammer]

Using a lower value cap will not change *whether* it sweeps, just what it sounds like *when* it sweeps.  4n3 caps will sound a little thinner.  6n8 caps will still sound nice for guitar.  10n caps start to become a little better for bass.  15n caps are definitely for bass not guitar.

[grani79]

So what it can be?

[Mark Hammer]

It can probably be anything between about 15n and 3n3 and still get something that sounds good with guitar once you adjust the trimpot.

Although the trimpot is not useful for tuning across its whole range, I've found that for about 30% of its rotation you can alter the start frequency of the filter.  So, you can use 15n caps and tune the filter a little higher, or use 3n3 caps and tune it a little lower.  Will they all be able to sound like a "classic" Dr Q?  probably not, but they WILL sound funky and provide something musically useful.

Although you don't absolutely need matched caps for it to work, the characteristic sound uses same-value caps.  Remember that the caps are simply the same value and do not have to be matched.  Normally, there will be some difference between what it says the cap is on the markings, and what it really is.  Something that says 4n3 *could* be 4n6 and something that says 4n7 or 5n *could* be 4n5.

Also don't be shy about using caps in parallel or series.  If you had a 3n3 and 1n5, soldering them in parallel would give you 4n8.  If you had some 10n caps, two in series gets you 5n.  Actually using a pair of 10n caps would probably be ideal.  Use them both and it's optimized for guitar.  Shunt one cap in each pair and it's better for bass.

[grani79]

ok! I know that... the problem is that I haven't got wah from this pedal... only guitar signal!!! The led don't light.  the circuit is powered. I controlled all the things and they are ok... :-( I'm using a Blade guitar with hnumbuckers p.u. also a Ibanez jem...            

[grani79]

Ok!

Now the led near the chip is lighting. The other isn't! What it can be? Ht eproblem was the transistor GSD....

[smoguzbenjamin]

There are 2 LEDs near the IC. Which one is lighting, the one showing there is a current source or the envelope detector LED?