Troubleshooting Nurse Quacky

[greenacarina]

I seem to be having gating problems with Nurse Quacky...I think.
Built it according to- http://aronnelson.com/gallery/album28/Nurse_Quacky
Only substitution I made was the 2 LED's...I used 2 small rectangular ones instead of 3mm round.

Voltages that I read-
Batt- 8.27
TL072
Pin 1- 1.52
2- 1.52
3- 1.75
4- 0
5- 1.90
6- 1.75
7- 2.08
8- 7.87

I notice when the battery is attached, LED 1 glows faintly all the time. LED 2 lights with the gating effect which is more prominent when the Range pot is toward the treble end of things. The other 2 pots don't seem to do much. What should I check?
Thanks!
Chris

[Mark Hammer]

The LED shape makes no difference whatsoever (colour does, though), and the illumination behaviour you describe (one on, one flashing) is normal.  Not sure what you mean by gating,

[greenacarina]

One LED is green, one is yellow. Didn't figure color would make a difference. The main symptom I'm having is not getting any sound through the pedal without a very vigorous strum. More-so on the treble end of the range pot, less-so on the bass end.
May I ask why color makes a difference with these LED's? Inquiring minds want to know.

[Mark Hammer]

If my understanding is correct, red LEDs have a lower forward voltage than green or yellow, which is why they are used and specifically recommended in distortion circuits.  Jack Orman's adaptation of the Dr Q, which permits use/choice of more op-amps than the 1458 (which the Dr Q requires), involves the complementary effects of the red LEDE at the noninverting input of the op-amp, and the red LED at the output.  Critical to this is not just the colour of the LEDs but the identical forward voltages, such that what one adds the other subtracts.

Switch LED colour and I suspect you may have a functioning effect.

[greenacarina]

Great! I'll swap those LED's out with some red ones tonight and see what happens.

Chris

[Barcode80]

by the way, if you are wanting to know exactly why voltages differ from different colors, it is because each LED is made to emit a certain color (housing of the LED is afterthought) inside, and different voltages and frequencies in (determined by the material inside the LED) are what supply the different spectrum wavelengths to generate each specific color. this is probably an over-simplification though, more info here:

http://en.wikipedia.org/wiki/LED

[greenacarina]

OK, one more question on LED's...does the size matter? I put in the red ones but they are 5mm and I seem to get about the same result as before.
Chris

[Mark Hammer]

Size should probably make no difference in the voltage drop, but may make a difference in how bright they get, given the current fed to them.  If your plan was to have both LEDs inside the box and non-visible, then size would not matter.  If your plan was to have one or both visible for some cutesy packaging reason (e.g., calling the box a "Wink of Sweep" and using one LED within a blinking eye graphic), then you probably want to think about size a bit.

LEDs *are* diodes, and like any of those black-with-white-stripe 1N400x diodes, they will vary in current handling.

[greenacarina]

I'm still stuck on this thing. Swapped out the LED's for red ones, triple-checked all my circuit traces looking for solder bridges and/or places where I hadn't broken the trace properly...looks OK. My voltages at the IC all measure the same as before.  Any clues as to where I should be looking next?
Thanks!
Chris

[Mark Hammer]

Just out of curiosity, have we confirmed that the pinout on the actual transistor itself is the same as on the PCB?

[greenacarina]

Just out of curiosity, have we confirmed that the pinout on the actual transistor itself is the same as on the PCB?

Visually looks OK to me. Is there a test I can perform to verify?
Thanks.
Chris

[Mark Hammer]

Just look up the datasheet for the transistor being employed.  They always provide an indication of the pinout.

[greenacarina]

Just look up the datasheet for the transistor being employed.  They always provide an indication of the pinout.

OK, just looked up the data sheet thru Mouser (part # I'm using is 512-2n3904ta) and it looks like the pinout is correct. Maybe I fried the little guy when installing?
Chris

[Mark Hammer]

Frying happens, but doesn't happen all THAT often.  Usually, it's more likely to be a forehead-smacker, one of those "Dear lord, do I have to confess THIS in front of all these people?".  Something like a diode installed backwards, a solder-bridge, a transistor pinout,, etc.  In my case, the first perfed Dr.Q I made had fractured wire inside intact insulation going to the bass/normal switch.  The second one, made with a PCB, was etched backwards such that I had to bend the IC pins backwards and flip the chip over to get it working.

Yep, enough forehead smacks to risk frontal lobe damage (which may well be the source of all those errors, come to think of it).

Right now, there are two things you wish to know:
1) if you disconnect the sidechain circuit from the filter itself (and that includes the transistor tied to the pair of .0047uf filter caps and 47k resistor), does the filter pass audio signal and will adjustments to the resistance to ground (the 47k) vary the filter frequency?  In principle, it should work as a manually tunable filter.

2) Is the sidechain following the instrument signal appropriately?  That means not only whether the LEDs appear to light up appropriately, but also whether you are getting an appropriate envelope signal.  You *should* be able to see a couple of volts AC on the output of the op-amp that feeds the second LED.  The second LED will subtract about 1.5V of that, such that you can measure something like a volt or so (AC) at the junction of the Attack pot and 22uf cap.

Generally identifying which functional half of the circuit is behaving or misbehaving will help track down the specific weak spot.

[greenacarina]

Frying happens, but doesn't happen all THAT often.  Usually, it's more likely to be a forehead-smacker, one of those "Dear lord, do I have to confess THIS in front of all these people?".  Something like a diode installed backwards, a solder-bridge, a transistor pinout,, etc.  In my case, the first perfed Dr.Q I made had fractured wire inside intact insulation going to the bass/normal switch.  The second one, made with a PCB, was etched backwards such that I had to bend the IC pins backwards and flip the chip over to get it working.

Yep, enough forehead smacks to risk frontal lobe damage (which may well be the source of all those errors, come to think of it).

Right now, there are two things you wish to know:
1) if you disconnect the sidechain circuit from the filter itself (and that includes the transistor tied to the pair of .0047uf filter caps and 47k resistor), does the filter pass audio signal and will adjustments to the resistance to ground (the 47k) vary the filter frequency?  In principle, it should work as a manually tunable filter.

2) Is the sidechain following the instrument signal appropriately?  That means not only whether the LEDs appear to light up appropriately, but also whether you are getting an appropriate envelope signal.  You *should* be able to see a couple of volts AC on the output of the op-amp that feeds the second LED.  The second LED will subtract about 1.5V of that, such that you can measure something like a volt or so (AC) at the junction of the Attack pot and 22uf cap.

Generally identifying which functional half of the circuit is behaving or misbehaving will help track down the specific weak spot.

OK, I'm a little lost so please bear with me.

1) Not sure what components comprise a sidechain circuit or the "filter itself"...I get the idea that it's related to the transistor but otherwise I'm like a deer in headlights.

2) I am reading about 1.7 volts DC (not AC) at the output to the 2nd LED (pin 3),  and a hair over 2 volts DC at the 22uf cap.

LED 2 is on all the time (while the input is plugged-in)...not sure if this is how things should be. I'm guessing part of my problem may be the lack of AC as I am reading DC voltage all over the place? Should I flip my battery back-and-forth real fast?
Thanks!
Chris

[Mark Hammer]

1) To clarify, looking at the Home-Wrecker website (http://www.home-wrecker.com/nurse-quacky.png), all that stuff when you turn south on the IN point is the sidechain - the part that extracts an electronic representation of the signal amplitude.  In fact, if you extended the long horizontal line that reaches back from the transistor collector, such that it went all the way across the drawing, everything above the line is filter, and everything below is essentially sidechain.  The transistor, I suppose, might be treated as the "communicator" or "translator" between sidechain and filter.

2) Although the second LED has the effect of "chopping" off half the waveform, such that the voltage swings only in one direction, up until the point where the 22uf cap smooths everything out, what you have is essentially a kind of AC voltage, swinging back and forth between midpoint and peak, as opposed to peak to peak.  So yeah, I suppose it IS a sort of DC, but not the sort that sits still long enough to register accurately on a meter.  The 22uf cap "smudges" those rapid, audio-frequency changes, so that they more closely approximate a slowly changing DC voltage.

3) As noted, of the two LEDs, one of them (the one tied to the + input of the opamp) should be on always, and the other one should really only be visible and flash when you strum.  Apart from that, the "2nd" one should stay off since the anticipated voltage and current feding it should not be enough to illuminate it.  Now I'm wondering if the reference voltage is off somehow.  Check the op-amp pin shown in the diagram as "4.5v".  It should read around half of whatever the battery reads (given the margin of error built into the two 47k resistors used to divide down 9v into 4.5v).

[greenacarina]

1) To clarify, looking at the Home-Wrecker website (http://www.home-wrecker.com/nurse-quacky.png), all that stuff when you turn south on the IN point is the sidechain - the part that extracts an electronic representation of the signal amplitude.  In fact, if you extended the long horizontal line that reaches back from the transistor collector, such that it went all the way across the drawing, everything above the line is filter, and everything below is essentially sidechain.  The transistor, I suppose, might be treated as the "communicator" or "translator" between sidechain and filter.

2) Although the second LED has the effect of "chopping" off half the waveform, such that the voltage swings only in one direction, up until the point where the 22uf cap smooths everything out, what you have is essentially a kind of AC voltage, swinging back and forth between midpoint and peak, as opposed to peak to peak.  So yeah, I suppose it IS a sort of DC, but not the sort that sits still long enough to register accurately on a
meter.  The 22uf cap "smudges" those rapid, audio-frequency changes, so that they more closely approximate a slowly changing DC voltage.

3) As noted, of the two LEDs, one of them (the one tied to the + input of the opamp) should be on always, and the other one should really only be visible and flash when you strum.  Apart from that, the "2nd" one should stay off since the anticipated voltage and current feding it should not be enough to illuminate it.  Now I'm wondering if the reference voltage is off somehow.  Check the op-amp pin shown in the diagram as "4.5v".  It should read around half of whatever the battery reads (given the margin of error built into the two 47k resistors used to divide down 9v into 4.5v).

1) Thanks for the link!! The schematic makes more sense to me visually than the vero layout. I understand much better about the sidechain and filter.

2) My meter wouldn't read that voltage as AC, only on the DC scale...so I assumed I must be getting DC where there should be AC.

3) I got my "LED 1" and "LED 2" backward (it's that whole top/bottom thing). My battery reads 8.7v but my reference voltage (at pin 5) is 2.137v... same at the junction of R13 and R14. R13 measures 48 ohms. Where is my voltage going? 

Thanks again for the education, Mark! I greatly appreciate you taking the time with me.
Chris

[greenacarina]

OK, Nurse Quacky is now officially kicking my butt. I know I'm having a voltage problem...but I don't know why. After re-reading the troubleshooting FAQ I realize I have been a little light on information. I ran my voltmeter over the whole board and here's what I came up with-


Thanks.
Chris

[greenacarina]

So, in frustration I completely de-soldered all the components from my board, double-checked my trace connections and breaks, double checked each of my components as I soldered them back into place....all for nothing.
Still getting the exact same symptoms as before...same voltage readings. What should I do next? I'm obviously missing something. My voltage is dropping too low. Any suggestions?   
Chris

[greenacarina]

Anyone.....anyone....Bueller?