Why isn't my clipping stage working?

[drainyoo]

Hey folks, I'm new here. This is my first post and my first pedal circuit design.

I'm making a transistor-based overdrive pedal with a second clipping stage at the end that can be switched in. I spent a lot of time designing it in Falstad, and it works great in the simulation, but it's not working properly on my breadboard.

When it's switched off, the circuit sounds great. I'm getting a nice crunch by using diodes in the transistor feedback loop. But when I switch this second stage of diodes in, I lose the audio signal. I can get a little of it to come through if I turn down the volume pot, which seems odd to me. I've tripled checked the connections on the breadboard, I've replaced the diodes, and I've even removed the switch to hardwire them in. None of that worked, so I'm hoping someone here can help.

I've attached the end of the schematic, and that part on the breadboard. I appreciate it! Thanks.

[antonis]

Hi & Welcome..

postlmg.cc seems to not work (at least for my browser) so I can't see clearly your breadbord arrangement..

P.S.
Your issue appears when having BOTH clipping configurations On..??

[drainyoo]

Hi, thanks! I fixed the images in the post.

Yes, it's not working when both clipping stages are on. The first stage is always on, the second can be switched in to add more clipping.

[antonis]

Try a 1k or so resistor in series with clipping configuration..

[drainyoo]

Ok, tried a 1k in a few locations: before and after the switch, after the diodes, and in serial with the cap and the volume pot. None of it really worked. With the resistor as part of the clipping section, I was able to get some audio when changing the volume pot down to 20k, but it audio faded in after a few seconds, and it wasn't clipping at all. The fading in audio also happens when I turn the switch off. There's also a pop when I flip the switch. Maybe I need another cap somewhere?

[lykwydchykyn]

Your circuit *should* work, so my guess is that either one of your diodes is bad, or else your cap is bad and not blocking DC.

[drainyoo]

Ok, tomorrow I'll swap out the components and see if that fixes it. Thanks.

[antonis]

With bad cap, soft clipping shouldn't work also..

@drainyoo: Could we have a schematic of complete circuit..??

[GibsonGM]

Schematic and a pic of the 'as-built' would probably be easiest. It sounds to me like a build error...

[drainyoo]

Sure, here's the full schematic and build. I added a trim pot so I can make adjustments for biasing the transistor.

[antonis]

Something happens with your posted pics..

Let's try to recover them..

[drainyoo]

Something happens with your posted pics..

What ya mean? Are the images not showing for you?

[antonis]

Can't see no OUT (or IN) on clipping configuration upper side (row 19)..

[drainyoo]

Can't see no OUT (or IN) on clipping configuration upper side (row 19)..

Not sure I understand. The green and red wires on the left of the photo are the switch. The red wire is the out of the switch, and the diodes are going to ground. What do you mean by out? The signal out is the top left of the photo.

[antonis]

OK.. 
(my bad..)

Check your diodes health with DMM diode test mode..
(open in one direction and about 500mV, give or take, in the opposite direction..)

[drainyoo]

Ok, I will check the diodes again, but I swamped all three out for new ones, so doubt it's bad diodes. I haven't replaced the cap yet, so will try that next.

[antonis]

Try to reverse either clipping configuration polarity..

P.S.
Simultaneous soft and hard clipping isn't recommended, but let it be..

[drainyoo]

Simultaneous soft and hard clipping isn't recommended, but let it be..

Why is that?

[antonis]

Simultaneous soft and hard clipping isn't recommended, but let it be..

Why is that?

Due to almost equal clipping thresholds..
(for identical diodes..)

You may consider transistor's Base  "virual ground" (almost), so when both clipping configurations are activated, Collector "sees" half the clipping load (it's double loaded..)

P.S.
I might confused you, so think of two parallel clipping configurations and no feedback one..

[drainyoo]

Simultaneous soft and hard clipping isn't recommended, but let it be..

Why is that?

Due to almost equal clipping thresholds..
(for identical diodes..)

I'm actually thinking of using different diodes for the second stage. Also, because the clipping type is different, wouldn't that make it more of a distortion when the second stage is on? That's my idea with this design. The first stage is just a soft overdrive, then you can switch the second stage to get more of a distortion.