Nurse Quaky very low output problem

[hilbi]

My nurse quaky has very low output, not even 5% of unity again, what can be wrong? The leds are burning (one blinking). I hear it quaking, only the volume is very very low

I built it according the torchy vero layout.

Does anyone have the voltage readings?

Any idea what can be wrong?

[Torchy]

I had exactly the same problem, with 4 different layouts. I even asked the ROG guys. Mine was about 50% volume drop. I gave up, as I couldnt see it as a layout problem ... maybe someone has an idea ?

[RDV]

Perfed mine using this, and it works fine. Most likely a wiring or tranny pinout problem.

RDV

[hilbi]

I used torchy's vero wich is based on the same schamtic i think.

Funny thing is if I pick up the signal after the Opamp pin 7 it is still unity gain and quaking.

[Mark Hammer]

What hasn't been made clear is whether it sweeps or not.

[hilbi]

Do you mean if you can change the sweep with the range pot?

All the pots are working and changing the sound.

I still don't understand why the last capacitor (0,1) and resistor (470k) change the volume so much.

Before those two parts it is ok.

[puretube]

look/measure, if 470k is 470 ohms, accidentally...

[hilbi]

yes that's what i thought as well, but that resistor is 470k (measured disconnected from board), but if i remove that resistor and measure the resistance at that place where it was sitting i measure 20k, is that ok?

What is the function of this resistor/capacitor right before the output? Just a sort of filter? Is it an option to leave it out?

[Transmogrifox]

You measure 20k??  That's not ok.  If the jack is unplugged, the capacitor out, and the 100k R gone, it should measure "OL" or several megs or something to indicate that it isn't connected to anything.

If it measures 20k while plugged into the amp, that means the input (static) impedance of your amp is 20k, which means the capacitor is working as a high pass filter with a much higher pole: that would lower the apparent volume.

If you measure 20k with the voltmeter contacting the pin of the op amp with the circuit on, that measurement doesn't tell you anything conclusive.

If you measure 20k at the op amp pin with the circuit off, you likely have a connection wired wrong, shorting somewhere or a bad op amp.


A good first try for debugging is to replace the capacitor with a something like a 47 uF or something.  That will rule out low input impedance on your amp or mixer (mic inputs on a mixer are generally low impedance).

The resistor capacitor combo is just a good "utility" measure.  The capacitor blocks DC (thus protecting the inputs of other pedals and amps), and the resistor sets a ground reference on the capacitor output to reduce switch pop.

It's best not to do away with the capacitor--most pedals and amps are capacitively coupled on the input, but few things are more disappointing than a little 4.5 VDC to toast your computer sound card.

[hilbi]

If i disconnect everything (power, in, out), I remove the C6 and R9 (the output resistor/capacitor combo) and then I measure the output connection to the ground I measure 3k, this can't be good i think, because the output is completely isolated from the rest of the circuitboard.

[puretube]

for the 47µF : plus to the circuit-side, minus towards output...  :wink:

[hilbi]

Found the problem, there was a small shortage between the cut circuitboard at R9 and the ground.

It is working now. Thanks guyes, really appreciated!

Gonna go quaking now