Help....My Op Amp has fallen and it can't get up

[Guitarist335]

Hi:

I am hoping someone can help with this. I am building the following. overdrive pedal: (please ignore the notes and drawing on it)




I have wired the whole thing up, except for the diode part of the circuit. I plan to add the diodes part, once I solve the current problem.

The problem is, that I am getting no sound at all. Of note is the fact that I am using a 4558D op amp, which is a dual amp (rest assured that I have remapped the pins, and buffered the second op amp).

Here are my Pin readings in volts:

Pin 1. 1.5
Pin 2. 3.1
Pin 3. 4.26
Pin 4. 0
Pin 5. 1.0
Pin 6. 8.74
Pin 7. 8.74
Pin 8. 9.3

Any ideas as to why I am not getting any sound?

Thank-you

[idy]

Pin 3 and 5, the +inputs, need to both be at midvoltage, around 4.5v. 3 is close, but the other pins (1 and 2) aren't following. And 5 is nowhere close. You are trying to use pins 1,2,3 for the circuit? Is there a path to ground from pins 1 or 2? (power off, check for resistance to ground.) It should show as an open circuit.

You have a 1M resistor from the junction of the two 10k Rs to pin 3, right? It should measure mid voltage at the junction and close to that (but loaded by the meter) at pin 3. That's OK.  There should be a similar resistor to pin 5. And 5 should be that same voltage. Get that fixed because an oscillating opamp can screw things up.

The elegant way to do this (and not waste the other opamp) would be to get one of the opamps buffering the midvoltage and use that to bias the other. So the junction of the two 10k (or could be a pair of 100k, or even 1m) goes to a +input, the -input and output are jumpered together, and then that also is jumpered to the other +input.

[bluebunny]

Looks like your output (pin 6) is shorted to the power supply.

Edit: Sorry, didn't read your dual for single sub.  Need.  More.  Coffee.

As you were.

[bluebunny]

Can you show us some pictures so we can see exactly what you've built please?

[Guitarist335]

Thanks guys. I'm afraid a picture will knit help. I am a novice who is using a PCB and soldering every connection. It will not be decipherable.

This may help:

I am using the 4558 op amp, which is dual. I silenced the second op amp by connecting pins 7 and 6. I rain a wire from the juncture between R33 and R32 to Pin 5 ( which is the second op amp's  + IN).

The lead from the 1M (r41) goes to Pin 3.

As I think about it now, since I have not added the diodes, Pins 2 and 1 are not at all connected. Could that be the problem? Should;d they not be connected to one another?

[GGBB]

As I think about it now, since I have not added the diodes, Pins 2 and 1 are not at all connected. Could that be the problem? Should;d they not be connected to one another?

If you don't have the gain pot, R46, and C28 connected, that's a problem - the opamp will not have any feedback and will try to provide infinite gain and probably lock up.

[merlinb]

Thread title made me snort

[Guitarist335]

Tried to make the title catchy

[ElectricDruid]

Thanks guys. I'm afraid a picture will knit help. I am a novice who is using a PCB and soldering every connection. It will not be decipherable.

Don't underestimate our deciphering abilities! I've seen people on here spot errors in vero layouts that are so tangled that it's utterly impossible to relate to the original schematic and yet someone comes along and says "that resistor should have the lower leg one row further up" and suddenly it springs to life. Honestly, you'd be surprised what a hive mind like this one can pull off.

So...where's that picture?!?

PS: Both sides!

[Guitarist335]

Ok,...you asked for it lol. I have attached both sides. Now, don't tell me that it looks like a dog threw up on it, cause I know lol

The Case of the "My Op Amp Has Fallen and it Can't Get Up" is officially open. Go detectives!!!!

Here are my readings at the Pins. I am using a 4558D Op Amp

Pin 1.  1.4
Pin 2.  2.8
Pin 3.  4.1
Pin.4.     0
Pin 5   4.5
Pin 6.  4.5
Pin 7  4.5
Pin 8. 8.9

[antonis]

Don't get me wrong but multitude of flying jumpers greater than circuit items figure isn't indicated even for breadboard..

[Guitarist335]

Hi guys. I re did this circuit on a. breadboard and all is well.

Thanks just the same.

I did mention that the pictures probably would not help matters much. But in any event, my problem was an incorrect connection. Once I breadboarded it, it became apparent