I've been pulling my hair out for the last two days about this pedal.
Everything works, except there is no gain at all. The tone knobs does its thing (brightening and darkening the sound), so does the volume. But no matter what I try, there is no distortion, at all. Just the clean signal (the effect in on, of course). Even the SPST switch works fine.
Oh, one thing I didnt mention. I've actually built this circuit twice, with different components, and I have the EXACT same issue with both.
So far, here's what I've tried:
- 3 different pots for Gain
- Hacksaw everywhere
- Replacing the 2k2 and 18k resistor, and the 68nF cap aswell as the 220 pF cap at pin 1 and 2
- 2 sets of 2n7000, and a pair of BS170 with the correct orientation
- 3 different TL082, checked the orientation too
- Triple checked placement of components and their orientation and the cuts
- Checked the value of all the components
Here are my voltages for the IC:
1: 4.5v 8: 9v
2: 4.78v 7: 4.5v
3: 2.77v 6: 4.5v
4: 0v 5:4.5v
I'm running out of idea.
Pictures (with the BS170 instead of the 2n7000, for the orientation)
Ok, something is definitely funky with that 470k Resistor. I get 4.5v from S of Q1 going into it, but when I measure the other end of the 470k going into pin 3 of the IC i get 2.27v. Is that normal ? I've replace that resistor twice now.
Be methodical in your testing and always troubleshoot with a schematic in front of you.
1. Visual examination Compare the layout with your build, looking for misplaced components, wrong values, missing cuts/links etc
2. Continuity test Set a multimeter to Continuity mode (or resistor mode if it doesn't do continuity) and probe each connection by following the schematic. Place the probes on the component legs, not the solder. This will help find any cold joints. This also includes any wiring
3. Variable components test Test all your pots with a meter. Set to resistance mode, place 1 probe on lug 1 and the other on lug 2. No sweep the pot while checking the meter shows a rising resistance the full way up. The the end of the sweep the meter should show the pots full value (within 20%). Best to do this when the pot isn't connected to the circuit.
4. Voltage test Measure DC at all the important places. The IC, power, vref rail etc.
5. Audio Probe Last resort before throwing the thing out and excepting failure. Follow the schematic and probe for your guitar signal. If its on one side of a component in the signal path but not on the other you either have a bad component for some short nearby. But if you've completed the last 4 steps then the probability is high you've a bad component.
As for the IC socket...I have had a short in one before. A small sliver of copper from the strip board found its way under a socket and it took forever to find as I was probing all over the place. But I follow the above now if I ever have a problem and I haven't been defeated by a build in a long time. (jinxed myself now)
SO...try doing all of the above and if still no joy post some hi res pics of the COMPLETE build (top, bottom, jacks, switches pots etc. Look hard at the pics before you post though...if you can't see what's going where in the pics...we can't see it either.
As for voltages you should see 9V on pin 8, 0V on pin 4 and around 4.5V on the rest. If any of these are different take a good look at what's connected to them.
Sorry if some of this sounds condescending. I've no idea what your skill level is.
Thanks for your help, i appreciate it a lot, but i've put this one on hold. What's bugging me is that i have the exact same issue on 2 different build of this same layout, and i seemed to have made the same mistake twice but can't find it. Oh Well, third time might be the charm.