Pedal problems

[petemoore]

Op amp 1; + input = 4.04V
- input = 4.23V
Ouput = 4.22

Op amp 2; + input = 4.18V
- input = 4.22V
output = 4.21V
  All your pins are some percentage of the supply voltage. What percentage they are of the supply voltage allows a reader to make comments that are based on...percentages of supply voltage.
  For sure the supply V is >4.23vdc, probably 8 or so.
  And the Gnd. is either 0.0vdc or something else.
  If then...the insies and outsies looke to be around 1/2v and so opamp bias might be a problem. But I doubt it. When I see the pin voltages like this:
1: 4.5v     8: 9vdc
2: 4.5       7: 4.6
3:  4.4      6:  4.6
4:  4.1      5:  4.4
  Reasoned conclusions can be made.
  Kinda looks from what you did disclose that the opamp could be biased and the problem is with the signal flow.

[will_raymo2000]

Op amp 1; + input = 4.04V
- input = 4.23V
Ouput = 4.22

Op amp 2; + input = 4.18V
- input = 4.22V
output = 4.21V
  All your pins are some percentage of the supply voltage. What percentage they are of the supply voltage allows a reader to make comments that are based on...percentages of supply voltage.
  For sure the supply V is >4.23vdc, probably 8 or so.
  And the Gnd. is either 0.0vdc or something else.
  If then...the insies and outsies looke to be around 1/2v and so opamp bias might be a problem. But I doubt it. When I see the pin voltages like this:
1: 4.5v     8: 9vdc
2: 4.5       7: 4.6
3:  4.4      6:  4.6
4:  4.1      5:  4.4
  Reasoned conclusions can be made.
  Kinda looks from what you did disclose that the opamp could be biased and the problem is with the signal flow.

From what I can grasp from your post. you are saying the op amp is reading the right values however somewhere along the signal flow from the output of the second clipping stage to the output pot.. the signal is being lost somewhere?

[petemoore]

1: 4.5v     8: 9vdc
2: 4.5       7: 4.6
3:  4.4      6:  4.6
4:  4.1      5:  4.4
  Voltage divider circuits like this should have all the pins as they are, except pin4 should be connected to ground.

[will_raymo2000]

1: 4.5v     8: 9vdc
2: 4.5       7: 4.6
3:  4.4      6:  4.6
4:  4.1      5:  4.4
  Voltage divider circuits like this should have all the pins as they are, except pin4 should be connected to ground.

It is indeed connected to ground and is reading 0V. I shall do some probing of the circuit and find out where the signal is going then.

From my readings of the AC it seems that the signal goes down to 0.05V between the 390pF cap and the top end of the tone pot. Yet the signal is then hugely low over the 0.1uF cap on the other side of the tone pot. hmmm 

[will_raymo2000]

Sorry for the double post. Just a slight update.. I have just downloaded Visual Analyser 2009 (very good program if you want freeware oscilloscope software!)

I then took the output wire from the pot and poked it around the circuit a bit.. the only place i could find a distorted signal was in the middle of the pairs of diodes. I then plugged the thing back in again and measured the distortion. it was roughly 1% distorted from a 10Hz signal through to a 5000kHz.

I am at the stage of giving up on this. although i am curious to know why people have built it before and it works but mine does not. for no apparent reason either!

[frokost]

Probably because you've done something wrong  .

Which layout did you use? Are you certain there are no cold solder joints, no solder bridges, and that your wiring is correct?

[will_raymo2000]

Probably because you've done something wrong  .

Which layout did you use? Are you certain there are no cold solder joints, no solder bridges, and that your wiring is correct?

Haha yep i'm pretty sure something has gone wrong somewhere!

I have perfboarded the original schematic (in my own layout  ) however I wouldnt have thought it would be that dependant on layout should it?

I have reflowed about 70% of the joints and checked continuity in all of them. This has to be the most confusing thing I have ever built!

[frokost]

Well, the layout could be incorrect. Could you post it?

[will_raymo2000]

Well, the layout could be incorrect. Could you post it?

Im not sure I even want to post this;





Yes, one of THE most messy things ever created!

Can someone suggest an alternative layout?!

[slacker]

It's a bit hard to see what's going on, because of that red jumper wire, but it looks like pins 1 and 2 of the opamp are shorted together. That would explain why you're not getting any boost in volume out of that part of the opamp.

[will_raymo2000]

Nope, although it looks like it is, none of the pins are shorting..

I tried to build it so that the signal flowed from one side to the other in a linear form. Is this the right way to go about things?

[slacker]

It doesn't really matter how you lay it out, so long as it matches the schematic it should work.
I would try and split the circuit up into blocks to debug it. Remove the 10k that's between the opamp stages and temporarily connect the volume pot to the negative side of the 4.7u cap. That isolates just the first stage, so you can try and get that working without worrying about everything else. That should give you a volume boost and a fair amount of distortion. Once that's working reconnect the rest of the circuit and disconnect the tone control by taking the output from the negative side of the 10uF cap off the second stage. That should give you even more volume and distortion. Once that works reconnect the tone controls and hopefully it will work.

[will_raymo2000]

That is a shot of the output from the negative side of the 4.7uF electro from the first stage... hmmmm!

[frokost]

How does it sound with a guitar?

[will_raymo2000]

How does it sound with a guitar?

Like a quieter version of the guitar.

Cheers for all your help guys but I can't be bothered to try and debug this anymore!
I shall move on to other things that will hopefully work first time!